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1.  Synthesis and Structure-Activity Relationships of Benzothienothiazepinone Inhibitors of Protein Kinase D 
ACS medicinal chemistry letters  2011;2(2):154-159.
Protein kinase D (PKD) is a member of a novel family of serine/threonine kinases that regulate fundamental cellular processes. PKD is implicated in the pathogenesis of several diseases, including cancer. Progress in understanding the biological functions and therapeutic potential of PKD has been hampered by the lack of specific inhibitors. The benzoxoloazepinolone CID755673 was recently identified as the first potent and selective PKD inhibitor. The study of structure-activity relationships (SAR) of this lead structure led to further improvements in PKD1 potency. We describe herein the synthesis and biological evaluation of novel benzothienothiazepinone analogs. We achieved a ten-fold increase in the in vitro PKD1 inhibitory potency for the second generation lead kb-NB142-70 and accomplished a transition to an almost equally potent novel pyrimidine scaffold, while maintaining excellent target selectivity. These promising results will guide the design of pharmacological tools to dissect PKD function and pave the way for the development of potential anti-cancer agents.
PMCID: PMC3100199  PMID: 21617763
Protein kinase D; small molecule inhibitor; benzothienothiazepinone; pyrimidines; CID755673
2.  Design, Synthesis, and Biological Evaluation of PKD Inhibitors 
Pharmaceutics  2011;3(2):186-228.
Protein kinase D (PKD) belongs to a family of serine/threonine kinases that play an important role in basic cellular processes and are implicated in the pathogenesis of several diseases. Progress in our understanding of the biological functions of PKD has been limited due to the lack of a PKD-specific inhibitor. The benzoxoloazepinolone CID755673 was recently reported as the first potent and kinase-selective inhibitor for this enzyme. For structure-activity analysis purposes, a series of analogs was prepared and their in vitro inhibitory potency evaluated.
PMCID: PMC3261798  PMID: 22267986
protein kinase D; small molecule inhibitor; benzothienothiazepinone; pyrimidines; CID755673; thiazepinothiophenopyrimidinone
3.  Design, Synthesis, and Biological Evaluation of PKD Inhibitors 
Pharmaceutics  2011;3(2):186-228.
Protein kinase D (PKD) belongs to a family of serine/threonine kinases that play an important role in basic cellular processes and are implicated in the pathogenesis of several diseases. Progress in our understanding of the biological functions of PKD has been limited due to the lack of a PKD-specific inhibitor. The benzoxoloazepinolone CID755673 was recently reported as the first potent and kinase-selective inhibitor for this enzyme. For structure-activity analysis purposes, a series of analogs was prepared and their in vitro inhibitory potency evaluated.
PMCID: PMC3261798  PMID: 22267986
protein kinase D; small molecule inhibitor; benzothienothiazepinone; pyrimidines; CID755673; thiazepinothiophenopyrimidinone
4.  CID755673 enhances mitogenic signaling by phorbol esters, bombesin and EGF through a protein kinase D-independent pathway 
Recently, CID755673 was reported to act as a highly selective inhibitor of protein kinase D (PKD). In the course of experiments using CID755673, we noticed that it exerted unexpected stimulatory effects on [3H]thymidine incorporation and cell cycle progression in Swiss 3T3 cells stimulated by bombesin, a Gq-coupled receptor agonist, phorbol 12,13-dibutyrate (PDBu), a biologically active tumor promoting phorbol ester and epidermal growth factor (EGF). These stimulatory effects could be dissociated from the inhibitory effect of CID755673 on PKD activity, since enhancement of DNA synthesis was still evident in cells with severely down-regulated PKD1 after transfection of siRNA targeting PKD1. A major point raised by our study is that CID755673 can not be considered a specific inhibitor of PKD and it should be used with great caution in experiments attempting to elucidate the role of PKD family members in cellular regulation, particularly cell cycle progression from G1/Go to S phase.
PMCID: PMC2812606  PMID: 19896460
Swiss 3T3 cells; PDGF; PKD knock down; cell cycle; DNA synthesis
5.  A Targeted Library Screen Reveals a New Inhibitor Scaffold for Protein Kinase D 
PLoS ONE  2012;7(9):e44653.
Protein kinase D (PKD) has emerged as a potential therapeutic target in multiple pathological conditions, including cancer and heart diseases. Potent and selective small molecule inhibitors of PKD are valuable for dissecting PKD-mediated cellular signaling pathways and for therapeutic application. In this study, we evaluated a targeted library of 235 small organic kinase inhibitors for PKD1 inhibitory activity at a single concentration. Twenty-eight PKD inhibitory chemotypes were identified and six exhibited excellent PKD1 selectivity. Five of the six lead structures share a common scaffold, with compound 139 being the most potent and selective for PKD vs PKC and CAMK. Compound 139 was an ATP-competitive PKD1 inhibitor with a low double-digit nanomolar potency and was also cell-active. Kinase profiling analysis identified this class of small molecules as pan-PKD inhibitors, confirmed their selectivity again PKC and CAMK, and demonstrated an overall favorable selectivity profile that could be further enhanced through structural modification. Furthermore, using a PKD homology model based on similar protein kinase structures, docking modes for compound 139 were explored and compared to literature examples of PKD inhibition. Modeling of these compounds at the ATP-binding site of PKD was used to rationalize its high potency and provide the foundation for future further optimization. Accordingly, using biochemical screening of a small number of privileged scaffolds and computational modeling, we have identified a new core structure for highly potent PKD inhibition with promising selectivity against closely related kinases. These lead structures represent an excellent starting point for the further optimization and the design of selective and therapeutically effective small molecule inhibitors of PKD.
PMCID: PMC3445516  PMID: 23028574
6.  Protein Kinase D Regulates Cell Death Pathways in Experimental Pancreatitis 
Inflammation and acinar cell necrosis are two major pathological responses of acute pancreatitis, a serious disorder with no current therapies directed to its molecular pathogenesis. Serine/threonine protein kinase D family, which includes PKD/PKD1, PKD2, and PKD3, has been increasingly implicated in the regulation of multiple physiological and pathophysiological effects. We recently reported that PKD/PKD1, the predominant PKD isoform expressed in rat pancreatic acinar cells, mediates early events of pancreatitis including NF-κB activation and inappropriate intracellular digestive enzyme activation. In current studies, we investigated the role and mechanisms of PKD/PKD1 in the regulation of necrosis in pancreatic acinar cells by using two novel small molecule PKD inhibitors CID755673 and CRT0066101 and molecular approaches in in vitro and in vivo experimental models of acute pancreatitis. Our results demonstrated that both CID755673 and CRT0066101 are PKD-specific inhibitors and that PKD/PKD1 inhibition by either the chemical inhibitors or specific PKD/PKD1 siRNAs attenuated necrosis while promoting apoptosis induced by pathological doses of cholecystokinin-octapeptide (CCK) in pancreatic acinar cells. Conversely, up-regulation of PKD expression in pancreatic acinar cells increased necrosis and decreased apoptosis. We further showed that PKD/PKD1 regulated several key cell death signals including inhibitors of apoptotic proteins, caspases, receptor-interacting protein kinase 1 to promote necrosis. PKD/PKD1 inhibition by CID755673 significantly ameliorated necrosis and severity of pancreatitis in an in vivo experimental model of acute pancreatitis. Thus, our studies indicate that PKD/PKD1 is a key mediator of necrosis in acute pancreatitis and that PKD/PKD1 may represent a potential therapeutic target in acute pancreatitis.
PMCID: PMC3313474  PMID: 22470346
pancreatic acinar cells; CCK; CID755673; CRT0066101; apoptosis; necrosis
7.  Protein Kinase Inhibitors CK59 and CID755673 Alter Primary Human NK Cell Effector Functions 
Natural killer (NK) cells are part of the innate immune response and play a crucial role in the defense against tumors and virus-infected cells. Their effector functions include the specific killing of target cells, as well as the modulation of other immune cells by cytokine release. Kinases constitute a relevant part in signaling, are prime targets in drug research and the protein kinase inhibitor Dasatinib is already used for immune-modulatory therapies. In this study, we tested the effects of the kinase inhibitors CK59 and CID755673. These inhibitors are directed against calmodulin kinase II (CaMKII; CK59) and PKD family kinases (CID755673) that were previously suggested as novel components of NK activation pathways. Here, we use a multi-parameter, FACS-based assay to validate the influence of CK59 and CID755673 on the effector functions of primary NK cells. Treatment with CK59 and CID755673 indeed resulted in a significant dose-dependent reduction of NK cell degranulation markers and cytokine release in freshly isolated Peripheral blood mononuclear cell populations from healthy blood donors. These results underline the importance of CaMKII for NK cell signaling and suggest protein kinase D2 as a novel signaling component in NK cell activation. Notably, kinase inhibition studies on pure NK cell populations indicate significant donor variations.
PMCID: PMC3600540  PMID: 23508354
NK cells; immune modulation; signaling pathways; PKD; CaMKII; effector function; Fyn; CID755673
8.  Discovery of Diverse Small Molecule Chemotypes with Cell-Based PKD1 Inhibitory Activity 
PLoS ONE  2011;6(10):e25134.
Protein kinase D (PKD) is a novel family of serine/threonine kinases regulated by diacylglycerol, which is involved in multiple cellular processes and various pathological conditions. The limited number of cell-active, selective inhibitors has historically restricted biochemical and pharmacological studies of PKD. We now markedly expand the PKD1 inhibitory chemotype inventory with eleven additional novel small molecule PKD1 inhibitors derived from our high throughput screening campaigns. The in vitro IC50s for these eleven compounds ranged in potency from 0.4 to 6.1 µM with all of the evaluated compounds being competitive with ATP. Three of the inhibitors (CID 1893668, (1Z)-1-(3-ethyl-5-methoxy-1,3-benzothiazol-2-ylidene)propan-2-one; CID 2011756, 5-(3-chlorophenyl)-N-[4-(morpholin-4-ylmethyl)phenyl]furan-2-carboxamide; CID 5389142, (6Z)-6-[4-(3-aminopropylamino)-6-methyl-1H-pyrimidin-2-ylidene]cyclohexa-2,4-dien-1-one) inhibited phorbol ester-induced endogenous PKD1 activation in LNCaP prostate cancer cells in a concentration-dependent manner. The specificity of these compounds for PKD1 inhibitory activity was supported by kinase assay counter screens as well as by bioinformatics searches. Moreover, computational analyses of these novel cell-active PKD1 inhibitors indicated that they were structurally distinct from the previously described cell-active PKD1 inhibitors while computational docking of the new cell-active compounds in a highly conserved ATP-binding cleft suggests opportunities for structural modification. In summary, we have discovered novel PKD1 inhibitors with in vitro and cell-based inhibitory activity, thus successfully expanding the structural diversity of small molecule inhibitors available for this important pharmacological target.
PMCID: PMC3187749  PMID: 21998636
9.  Protein Kinase D isoforms – New targets for therapy in invasive Breast Cancers? 
Expert review of anticancer therapy  2013;13(8):10.1586/14737140.2013.816460.
The Protein Kinase D (PKD) family of serine/threonine kinases consists of three members-PKD1, PKD2, and PKD3. While PKD1 in many cancers has been identified as a suppressor of the invasive phenotype, the two other PKD subtypes, PKD2 and PKD3, have been attributed oncogenic functions. In invasive Breast Cancer cells PKD1 expression is downregulated by methylation of the PRKD1 promoter. On the other hand, PKD2 and PKD3 are not silenced, and drive proliferation, invasion, and mediate chemoresistance. Two strategies emerge to utilize this knowledge for novel treatment opportunities. First, pan PKD inhibitors could be developed and used for these aggressive cancers. An alternative approach to obtain similar effects would be to induce the re-expression of PKD1.
PMCID: PMC3856925  PMID: 23944680
Protein Kinase D; PKD; isoforms; breast cancer; therapy
10.  New Pyrazolopyrimidine Inhibitors of Protein Kinase D as Potent Anticancer Agents for Prostate Cancer Cells 
PLoS ONE  2013;8(9):e75601.
The emergence of protein kinase D (PKD) as a potential therapeutic target for several diseases including cancer has triggered the search for potent, selective, and cell-permeable small molecule inhibitors. In this study, we describe the identification, in vitro characterization, structure-activity analysis, and biological evaluation of a novel PKD inhibitory scaffold exemplified by 1-naphthyl PP1 (1-NA-PP1). 1-NA-PP1 and IKK-16 were identified as pan-PKD inhibitors in a small-scale targeted kinase inhibitor library assay. Both screening hits inhibited PKD isoforms at about 100 nM and were ATP-competitive inhibitors. Analysis of several related kinases indicated that 1-NA-PP1 was highly selective for PKD as compared to IKK-16. SAR analysis showed that 1-NA-PP1 was considerably more potent and showed distinct substituent effects at the pyrazolopyrimidine core. 1-NA-PP1 was cell-active, and potently blocked prostate cancer cell proliferation by inducing G2/M arrest. It also potently blocked the migration and invasion of prostate cancer cells, demonstrating promising anticancer activities on multiple fronts. Overexpression of PKD1 or PKD3 almost completely reversed the growth arrest and the inhibition of tumor cell invasion caused by 1-NA-PP1, indicating that its anti-proliferative and anti-invasive activities were mediated through the inhibition of PKD. Interestingly, a 12-fold increase in sensitivity to 1-NA-PP1 could be achieved by engineering a gatekeeper mutation in the active site of PKD1, suggesting that 1-NA-PP1 could be paired with the analog-sensitive PKD1M659G for dissecting PKD-specific functions and signaling pathways in various biological systems.
PMCID: PMC3781056  PMID: 24086585
11.  Inducible silencing of protein kinase D3 inhibits secretion of tumor-promoting factors in prostate cancer 
Molecular Cancer Therapeutics  2012;11(7):1389-1399.
Protein kinase D acts as a major mediator of several signaling pathways related to cancer development. Aberrant PKD expression and activity have been demonstrated in multiple cancers, and novel PKD inhibitors show promising anti-cancer activities. Despite these advances, the mechanisms through which PKD contributes to the pathogenesis of cancer remain unknown. Here, we establish a novel role for PKD3, the least studied member of the PKD family, in the regulation of prostate cancer cell growth and motility through modulation of secreted tumor-promoting factors. Using both a stable inducible knockdown cell model and a transient knockdown system employing multiple siRNAs, we demonstrate that silencing of endogenous PKD3 significantly reduces prostate cancer cell proliferation, migration, and invasion. Additionally, conditioned medium from PKD3 knockdown cells exhibits less migratory potential compared to that from control cells. Further analysis indicated that depletion of PKD3 blocks secretion of multiple key tumor-promoting factors including MMP-9, IL-6, IL-8, and GROα, but does not alter mRNA transcript levels for these factors, implying impairment of the secretory pathway. More significantly, inducible depletion of PKD3 in a subcutaneous xenograft model suppresses tumor growth and decreases levels of intratumoral GROα in mice. These data validate PKD3 as a promising therapeutic target in prostate cancer and shed light on the role of secreted tumor-promoting factors in prostate cancer progression.
PMCID: PMC3392457  PMID: 22532599
Protein kinase D; prostate cancer; cytokines; secretion; inducible knockdown
12.  In vitro Cytotoxicity, Pharmacokinetics, Tissue Distribution, and Metabolism of Small-Molecule Protein Kinase D Inhibitors, kb-NB142-70 and kb-NB165-09, in Mice bearing Human Cancer Xenografts 
Protein kinase D (PKD) mediates diverse biological responses including cell growth and survival. Therefore, PKD inhibitors may have therapeutic potential. We evaluated the in vitro cytotoxicity of two PKD inhibitors, kb-NB142-70 and its methoxy analog, kb-NB165-09, and examined their in vivo efficacy and pharmacokinetics.
The in vitro cytotoxicities of kb-NB142-70 and kb-NB165-09 were evaluated by MTT assay against PC-3, androgen independent prostate cancer cells, and CFPAC-1 and PANC-1, pancreatic cancer cells. Efficacy studies were conducted in mice bearing either PC-3 or CPFAC-1 xenografts. Tumor-bearing mice were euthanized between 5 and 1440 min after iv dosing, and plasma and tissue concentrations were measured by HPLC-UV. Metabolites were characterized by LC-MS/MS.
kb-NB142-70 and kb-NB165-09 inhibited cellular growth in the low-mid μM range. The compounds were inactive when administered to tumor-bearing mice. In mice treated with kb-NB142-70, the plasma Cmax was 36.9 nmol/mL and the PC-3 tumor Cmax was 11.8 nmol/g. In mice dosed with kb-NB165-09, the plasma Cmax was 61.9 nmol/mL while the PANC-1 tumor Cmax was 8.0 nmol/g. The plasma half-lives of kb-NB142-70 and kb-NB165-09 were 6 and 14 min, respectively. Both compounds underwent oxidation and glucuronidation.
kb-NB142-70 and kb-NB165-09 were rapidly metabolized, and concentrations in tumor were lower than those required for in vitro cytotoxicity. Replacement of the phenolic hydroxyl group with a methoxy group increased the plasma half-life of kb-NB165-09 2.3-fold over that of kb-NB142-70. Rapid metabolism in mice suggests that next-generation compounds will require further structural modifications to increase potency and/or metabolic stability.
PMCID: PMC3557573  PMID: 23108699
Protein Kinase D (PKD) inhibitors; pharmacokinetics; prostate cancer; pancreatic cancer; kb-NB142-70; kb-NB165-09
13.  Protein kinase D as a potential new target for cancer therapy 
Biochimica et biophysica acta  2010;1806(2):183-192.
Protein kinase D is a novel family of serine/threonine kinases and diacylglycerol receptors that belongs to the calcium/calmodulin-dependent kinase superfamily. Evidence has established that specific PKD isoforms are dysregulated in several cancer types, and PKD involvement has been documented in a variety of cellular processes important to cancer development, including cell growth, apoptosis, motility, and angiogenesis. In light of this, there has been a recent surge in the development of novel chemical inhibitors of PKD. This review focuses on the potential of PKD as a chemotherapeutic target in cancer treatment and highlights important recent advances in the development of PKD inhibitors.
PMCID: PMC2947595  PMID: 20580776
Protein kinase D; cancer; small molecule inhibitors
14.  Protein Kinase D Protects Against Oxidative Stress-Induced Intestinal Epithelial Cell Injury via Rho/ROK/PKC-δ Pathway Activation 
Protein kinase D (PKD) is a novel protein serine kinase which has recently been implicated in diverse cellular functions, including apoptosis and cell proliferation. The purpose of our present study was: (i) to define the activation of PKD in intestinal epithelial cells treated with hydrogen peroxide (H2O2), an agent which induces oxidative stress, and (ii) to delineate the upstream signaling mechanisms mediating the activation of PKD. We found that the activation of PKD is induced by H2O2 in both a dose- and time-dependent fashion. PKD phosphorylation was attenuated by rottlerin, a selective protein kinase C (PKC)-δ inhibitor, and small interfering RNA (siRNA) directed against PKC-δ, suggesting the regulation of PKD activity by upstream PKC-δ. Activation of PKD was also blocked by a Rho kinase (ROK) specific inhibitor, Y27632, as well as C3, a Rho protein inhibitor, demonstrating that the Rho/ROK pathway also mediates PKD activity in intestinal cells. In addition, H2O2-induced PKC-δ phosphorylation was inhibited by C3 treatment, further suggesting that PKC-δ is downstream of Rho/ROK. Interestingly, H2O2-induced intestinal cell apoptosis was enhanced by PKD siRNA. Taken together, these results clearly demonstrate that oxidative stress induces PKD activation in intestinal epithelial cells, and this activation is regulated by upstream PKC-δ and Rho/ROK pathways. Importantly, our findings suggest that PKD activation protects intestinal epithelial cells from oxidative stress-induced apoptosis. These findings have potential clinical implications to intestinal injury associated with oxidative stress (e.g., necrotizing enterocolitis in infants).
PMCID: PMC2613753  PMID: 16421204
Intestinal epithelial injury; oxidative stress; PKD; PKC-δ; Rho/ROK
15.  Multiple Protein Kinases Determine the Phosphorylated State of the Small Heat Shock Protein, HSP27, in SH-SY5Y Neuroblastoma Cells 
Neuropharmacology  2011;61(1-2):12-24.
In SH-SY5Y human neuroblastoma cells, the cholinergic agonist, carbachol, stimulates phosphorylation of the small heat shock protein 27 (HSP27). Carbachol increases phosphorylation of both Ser-82 and Ser-78 while the phorbol ester, phorbol-12, 13-dibutyrate (PDB) affects only Ser-82. Muscarinic receptor activation by carbachol was confirmed by sensitivity of Ser-82 phosphorylation to hyoscyamine with no effect of nicotine or bradykinin. This response to carbachol is partially reduced by inhibition of protein kinase C (PKC) with GF 109203X and p38 mitogen-activated protein kinase (MAPK) with SB 203580. In contrast, phosphorylation produced by PDB is completely reversed by GF 109203X or CID 755673, an inhibitor of PKD. Inhibition of phosphatidylinositol 3-kinase or Akt with LY 294002 or Akti-1/2 stimulates HSP27 phosphorylation while rapamycin, which inhibits mTORC1, does not. The stimulatory effect of Akti-1/2 is reversed by SB 203580 and correlates with increased p38 MAPK phosphorylation. SH-SY5Y cells differentiated with a low concentration of PDB and basic fibroblast growth factor to a more neuronal phenotype retain carbachol-, PDB- and Akti-1/2-responsive HSP27 phosphorylation. Immunofluorescence microscopy confirms increased HSP27 phosphorylation in response to carbachol or PDB. At cell margins, PDB causes f-actin to reorganize forming lamellipodial structures from which phospho-HSP27 is segregated. The resultant phenotypic change in cell morphology is dependent upon PKC, but not PKD, activity. The major conclusion from this study is that the phosphorylated state of HSP27 in SH-SY5Y cells results from integrated signaling involving PKC, p38 MAPK and Akt.
PMCID: PMC3105189  PMID: 21338617
16.  A Novel Small Molecule Inhibitor of Protein Kinase D Blocks Pancreatic Cancer Growth In Vivo 
Protein kinase D (PKD) is a novel family (PKD1, PKD2, and PKD3) of serine-threonine kinases with diverse biologic functions including cell proliferation and growth. Pancreatic cancer (PaCa) is a devastating disease with few therapeutic options. We showed earlier that PKD signaling pathways promote mitogenesis in multiple PaCa cell lines. However, nothing is known about targeting biologic functions of PKD family in PaCa. Our PKD inhibitor discovery program yielded CRT0066101, which specifically blocks activation of PKD family.
The aim of this study was to determine the effects of CRT0066101 in PaCa, both in vitro and in vivo.
Methods and Results:
Immunohistochemical analysis showed that activated PKD1 (pS916-PKD1) is significantly upregulated in PaCa as compared with normal ducts (91% vs. 22%; P < .001). We also showed that PKD1 and PKD2 are over-expressed in multiple PaCa cell lines including Panc-1. Using Panc-1 as a model system, we demonstrated that CRT0066101 blocked proliferation and BrdU incorporation with an IC50 of 1 μM, and also blocked PKD1-dependent NF-κB activation using luciferase reporter assays. CRT0066101 given orally (80 mg/kg/d) for 4 weeks significantly abrogated growth in a subcutaneous Panc-1 xenograft model (n=8; P < .01). The expression of activated PKD1 (pS916-PKD1) in the treated tumor explants was significantly inhibited (P < .05), with peak plasma CRT0066101 concentration (12 μM) achieved within 6 hours of oral administration. Further, CRT0066101 given orally (80 mg/kg/d) for 21 days in an orthotopic model potently blocked Panc-1 tumor growth (n=7; P < .01). CRT0066101 significantly reduced Ki-67+ proliferation index (P < .01), increased apoptosis (measured by in situ TUNEL assay) of PaCa tumors (P < .05), and potently abrogated expression of NF-κB-regulated multiple proliferative and pro-survival proteins, including cyclin D1, survivin, Bcl-2, Bcl-xL, activated PKD1 (pS916-PKD1), and activated PKD2 (pS876-PKD2).
These results demonstrate for the first time that the PKD-specific small molecule inhibitor CRT0066101 blocks PaCa growth both in vitro and in vivo. Thus, PKD is a novel therapeutic target in PaCa.
PMCID: PMC3047024
17.  β-Catenin Mediates Alteration in Cell Proliferation, Motility and Invasion of Prostate Cancer Cells by Differential Expression of E-Cadherin and Protein Kinase D1 
Journal of cellular biochemistry  2008;104(1):82-95.
We have previously demonstrated that Protein Kinase D1 (PKD1) interacts with E-cadherin and is associated with altered cell aggregation and motility in prostate cancer (PC). Because both PKD1 and E-cadherin are known to be dysregulated in PC, in this study we investigated the functional consequences of combined dysregulation of PKD1 and E-cadherin using a panel of human PC cell lines. Gainand loss of function studies were carried out by either transfecting PC cells with full-length E-cadherin and/or PKD1 cDNA or by protein silencing by siRNAs, respectively. We studied major malignant phenotypic characteristics including cell proliferation, motility, and invasion at the cellular level, which were corroborated with appropriate changes in representative molecular markers. Down regulation or ectopic expression of either E-cadherin or PKD1 significantly increased or decreased cell proliferation, motility, and invasion, respectively, and combined down regulation cumulatively influenced the effects. Loss of PKD1 or E-cadherin expression was associated with increased expression of the pro-survival molecular markers survivin, β-catenin, cyclin-D, and c-myc, whereas overexpression of PKD1 and/or E-cadherin resulted in an increase of caspases. The inhibitory effect of PKD1 and E-cadherin on cell proliferation was rescued by coexpression with β-catenin, suggesting that β-catenin mediates the effect of proliferation by PKD1 and E-cadherin. This study establishes the functional significance of combined dysregulation of PKD1 and E-cadherin in PC and that their effect on cell growth is mediated by β-catenin.
PMCID: PMC2928064  PMID: 17979146
proliferation; β-catenin; adhesion; E-cadherin; PKD1
18.  Protein Kinase Cδ mediates the activation of Protein Kinase D2 in Platelets 
Biochemical pharmacology  2011;82(7):720-727.
Protein Kinase D (PKD) is a subfamily of serine/threonine specific family of kinases, comprised of PKD1, PKD2 and PKD3 (PKCμ, PKD2 and PKCν in humans). It is known that PKCs activate PKD, but the relative expression of isoforms of PKD or the specific PKC isoform/s responsible for its activation in platelets is not known. This study is aimed at investigating the pathway involved in activation of PKD in platelets. We show that PKD2 is the major isoform of PKD that is expressed in human as well as murine platelets but not PKD1 or PKD3. PKD2 activation induced by AYPGKF was abolished with a Gq inhibitor YM-254890, but was not affected by Y-27632, a RhoA/p160ROCK inhibitor, indicating that PKD2 activation is Gq-, but not G12/13-mediated Rho-kinase dependent. Calcium-mediated signals are also required for activation of PKD2 as dimethyl BAPTA inhibited its phosphorylation. GF109203X, a pan PKC inhibitor abolished PKD2 phosphorylation but Go6976, a classical PKC inhibitor had no effect suggesting that novel PKC isoforms are involved in PKD2 activation. Importantly, Rottlerin, a non-selective PKCδ inhibitor, inhibited AYPGKF-induced PKD2 activation in human platelets. Similarly, AYPGKF- and Convulxin-induced PKD2 phosphorylation was dramatically inhibited in PKCδ-deficient platelets, but not in PKCθ– or PKCε–deficient murine platelets compared to that of wild type platelets. Hence, we conclude that PKD2 is a common signaling target downstream of various agonist receptors in platelets and Gq-mediated signals along with calcium and novel PKC isoforms, in particular, PKCδ activate PKD2 in platelets.
PMCID: PMC3156373  PMID: 21736870
Protein kinase C; Calcium; Protein kinase D; Protease activated receptor; Platelet; Gq
19.  Protein kinase D1 (PKD1) influences androgen receptor (AR) function in prostate cancer cells 
Protein kinase D1 (PKD1), founding member of PKD protein family, is down-regulated in advanced prostate cancer (PCa). We demonstrate that PKD1 and androgen receptor (AR) are present as a protein complex in PCa cells. PKD1 is associated with a transcriptional complex which contains AR and promoter sequence of the Prostate Specific Antigen (PSA) gene. Ectopic expression of wild type PKD1 and the kinase dead mutant PKD1 (K628W) attenuated the ligand-dependent transcriptional activation of AR in prostate cancer cells and yeast cells indicating that PKD1 can affect AR transcription activity, whereas knocking down PKD1 enhanced the ligand-dependent transcriptional activation of AR. Co-expression of kinase dead mutant with AR significantly inhibited androgen-mediated cell proliferation in both LNCaP and DU145 PC cells. Our data demonstrate for the first time that PKD1 can influence AR function in PCa cells.
PMCID: PMC2925514  PMID: 18602367
Protein kinase D1; Androgen receptor; Interaction; Prostate cancer
20.  Protein Kinase D regulates several aspects of development in Drosophila melanogaster 
Protein Kinase D (PKD) is an effector of diacylglycerol-regulated signaling pathways. Three isoforms are known in mammals that have been linked to diverse cellular functions including regulation of cell proliferation, differentiation, motility and secretory transport from the trans-Golgi network to the plasma membrane. In Drosophila, there is a single PKD orthologue, whose broad expression implicates a more general role in development.
We have employed tissue specific overexpression of various PKD variants as well as tissue specific RNAi, in order to investigate the function of the PKD gene in Drosophila. Apart from a wild type (WT), a kinase dead (kd) and constitutively active (SE) Drosophila PKD variant, we also analyzed two human isoforms hPKD2 and hPKD3 for their capacity to substitute PKD activity in the fly. Overexpression of either WT or kd-PKD variants affected primarily wing vein development. However, overexpression of SE-PKD and PKD RNAi was deleterious. We observed tissue loss, wing defects and degeneration of the retina. The latter phenotype conforms to a role of PKD in the regulation of cytoskeletal dynamics. Strongest phenotypes were larval to pupal lethality. RNAi induced phenotypes could be rescued by a concurrent overexpression of Drosophila wild type PKD or either human isoform hPKD2 and hPKD3.
Our data confirm the hypothesis that Drosophila PKD is a multifunctional kinase involved in diverse processes such as regulation of the cytoskeleton, cell proliferation and death as well as differentiation of various fly tissues.
PMCID: PMC1933421  PMID: 17592635
21.  A novel small molecule inhibitor of protein kinase D blocks pancreatic cancer growth in vitro and in vivo 
Molecular cancer therapeutics  2010;9(5):1136-1146.
Protein kinase D (PKD) family members are increasingly implicated in multiple normal and abnormal biological functions, including signaling pathways that promote mitogenesis in pancreatic cancer (PaCa). However, nothing is known about the effects of targeting PKD in PaCa. Our PKD-inhibitor discovery program identified CRT0066101 as a specific inhibitor of all PKD isoforms. The aim of our study was to determine the effects of CRT0066101 in PaCa. Initially, we showed that autophosphorylated PKD1 and PKD2 (activated PKD1/2) are significantly upregulated in PaCa and that PKD1/2 are expressed in multiple PaCa cell-lines. Using Panc-1 as a model system, we demonstrated that CRT0066101 reduced BrdU incorporation, increased apoptosis, blocked neurotensin (NT)-induced PKD1/2 activation, reduced NT-induced PKD-mediated Hsp27 phosphorylation, attenuated PKD1-mediated NF-κB activation, and abrogated expression of NF-κB-dependent-dependent proliferative and pro-survival proteins. We showed that CRT0066101 given orally (80 mg/kg/day) for 28 days significantly abrogated PaCa growth in Panc-1 subcutaneous xenograft model. Activated PKD1/2 expression in the treated tumor-explants was significantly inhibited with peak tumor concentration (12 µM) of CRT0066101 achieved within 2 h after oral administration. Further, we showed that CRT0066101 given orally (80 mg/kg/day) for 21 days in Panc-1 orthotopic model potently blocked tumor growth in vivo. CRT0066101 significantly reduced Ki-67+ proliferation index (p< 0.01), increased TUNEL+ apoptotic cells (p<0.05), and abrogated expression of NF-κB-dependent proteins including cyclin D1, survivin, and cIAP-1. Our results demonstrate for the first time that a PKD-specific small molecule inhibitor CRT0066101 blocks PaCa growth in vivo and show that PKD is a novel therapeutic target in PaCa.
PMCID: PMC2905628  PMID: 20442301
protein kinase D; small molecule inhibitor; pancreatic cancer; tumor xenografts
22.  Characterization of the biological effects of a novel protein kinase D inhibitor in endothelial cells 
Biochemical Journal  2010;429(Pt 3):565-572.
VEGF (vascular endothelial growth factor) plays an essential role in angiogenesis during development and in disease largely mediated by signalling events initiated by binding of VEGF to its receptor, VEGFR2 (VEGF receptor 2)/KDR (kinase insert domain receptor). Recent studies indicate that VEGF activates PKD (protein kinase D) in endothelial cells to regulate a variety of cellular functions, including signalling events, proliferation, migration and angiogenesis. To better understand the role of PKD in VEGF-mediated endothelial function, we characterized the effects of a novel pyrazine benzamide PKD inhibitor CRT5 in HUVECs (human umbilical vein endothelial cells). The activity of the isoforms PKD1 and PKD2 were blocked by this inhibitor as indicated by reduced phosphorylation, at Ser916 and Ser876 respectively, after VEGF stimulation. The VEGF-induced phosphorylation of three PKD substrates, histone deacetylase 5, CREB (cAMP-response-element-binding protein) and HSP27 (heat-shock protein 27) at Ser82, was also inhibited by CRT5. In contrast, CRT6, an inactive analogue of CRT5, had no effect on PKD or HSP27 Ser82 phosphorylation. Furthermore, phosphorylation of HSP27 at Ser78, which occurs solely via the p38 MAPK (mitogen-activated protein kinase) pathway, was also unaffected by CRT5. In vitro kinase assays show that CRT5 did not significantly inhibit several PKC isoforms expressed in endothelial cells. CRT5 also decreased VEGF-induced endothelial migration, proliferation and tubulogenesis, similar to effects seen when the cells were transfected with PKD siRNA (small interfering RNA). CRT5, a novel specific PKD inhibitor, will greatly facilitate the study of the role of PKD signalling mechanisms in angiogenesis.
PMCID: PMC2907712  PMID: 20497126
angiogenesis; CRT5 inhibitor; endothelium; protein kinase C (PKC); protein kinase D (PKD); vascular endothelial growth factor (VEGF); CREB, cAMP-response-element-binding protein; DAG, diacylglycerol; EBM, endothelial basal medium; EGF, epidermal growth factor; ERK, extracellular-signal-regulated kinase; FBS, fetal bovine serum; HDAC, histone deacetylase; HSP27, heat-shock protein 27; HUVEC, human umbilical vein endothelial cell; IMAP, immobilized metal-ion-affinity-based fluorescence polarization; MAPK, mitogen-activated protein kinase; MAKAPK2, MAPK-activated protein kinase 2; MTT, 3-(4,5-dimethylthiaziazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide; PKC, protein kinase C; PKD, protein kinase D; siRNA, small interfering RNA; VEGF, vascular endothelial growth factor
23.  Differential PKC-dependent and -independent PKD activation by G protein α subunits of the Gq family: selective stimulation of PKD Ser748 autophosphorylation by Gαq 
Cellular Signalling  2011;24(4):914-921.
Protein kinase D (PKD) is activated within cells by stimulation of multiple G protein coupled receptors (GPCR). Earlier studies demonstrated a role for PKC to mediate rapid activation loop phosphorylation-dependent PKD activation. Subsequently, a novel PKC-independent pathway in response to Gαq-coupled GPCR stimulation was identified. Here, we examined further the specificity and PKC-dependence of PKD activation using COS-7 cells cotransfected with different Gq-family Gα and stimulated with aluminum fluoride (AlF4−). PKD activation was measured by kinase assays, and Western blot analysis of activation loop sites Ser744, a prominent and rapid PKC transphosphorylation site, and Ser748, a site autophosphorylated in the absence of PKC signaling. Treatment with AlF4− potently induced PKD activation and Ser744 and Ser748 phosphorylation, in the presence of cotransfected Gαq, Gα11, Gα14 or Gα15. These treatments achieved PKD activation loop phosphorylation similar to the maximal levels obtained by stimulation with the phorbol ester, PDBu. Preincubation with the PKC inhibitor GF1 potently blocked Gα11-, Gα14-, and Gα15-mediated enhancement of Ser748 phosphorylation induced by AlF4−, and largely abolished Ser744 phosphorylation. In contrast, Ser748 phosphorylation was almost completely intact, and Ser744 phosphorylation was significantly activated in cells cotransfected with Gαq. Importantly, the differential Ser748 phosphorylation was also promoted by treatment of Swiss 3T3 cells with Pasteurella multocida toxin, a selective activator of Gαq but not Gα11. Taken together, our results suggest that Gαq, but not the closely related Gα11, promotes PKD activation in response to GPCR ligands in a unique manner leading to PKD autophosphorylation at Ser748.
PMCID: PMC3286641  PMID: 22227248
24.  Protein Kinase D1 Inhibits Cell Proliferation through Matrix Metalloproteinase (MMP) -2 and -9 Secretion in Prostate Cancer 
Cancer research  2010;70(5):2095-2104.
We and others previously demonstrated that Protein Kinase D1 (PKD1) is down regulated in several cancers including prostate, interacts with E-cadherin, a major cell adhesion epithelial protein and causes increased cell aggregation and decreased motility of prostate cancer cells. In this study, we demonstrate that PKD1 complexes with β3-integrin resulting in activation of Mek-Erk pathway, which causes increased production of MMP-2 and -9, that is associated with shedding of soluble 80 kDa E-cadherin extracellular domain. Interestingly, decreased cell proliferation following PKD1 transfection was rescued by MMP-2 and MMP-9 inhibitors and augmented by recombinant MMP-2 and MMP-9 proteins, suggesting an anti-proliferative role for MMPs in prostate cancer. Translational studies by in silico analysis of publicly available DNA microarray data sets demonstrate a significant direct correlation between PKD1 and MMP-2 expression in human prostate tissues. The study demonstrates a novel mechanism for anti-proliferative effects of PKD1, a protein of emerging translational interest in several human cancers, through increased production of MMP-2 and -9 in cancer cells.
PMCID: PMC3197700  PMID: 20160036
PKD1; E-cadherin shedding; MMP-2; MMP-9; Prostate Cancer; Protein Kinase
25.  Overexpression of Wild-Type PKD2 Leads to Increased Proliferation and Invasion of BON Endocrine Cells* 
Carcinoid tumors are rare neuroendocrine tumors with a predilection for the gastrointestinal tract. Protein kinase D (PKD), a novel serine/threonine protein kinase, has been implicated in the regulation of transport processes in certain cell types. We have reported an important role for PKD in stimulated peptide secretion from a human (BON) carcinoid cell line; however, the role of PKD isoforms, including PKD2, in the proliferation and invasion of carcinoid tumors remains unclear. In the present study, we found that overexpression of PKD2 by stable transfection of BON cells with PKD2-wild type (PKD2WT) significantly increased proliferation and invasion compared to cells transfected with PKD2-kinase dead (PKD2KD) or pcDNA3 (control). Similarly, inhibition of PKD2 activity with small interfering RNA (siRNA) significantly decreased proliferation and invasion compared to cells transfected with non-targeting control (NTC) siRNA. These data support an important role for PKD2 in carcinoid tumor progression. Targeted inhibition of the PKD family may prove to be a novel treatment option for patients with carcinoid tumors.
PMCID: PMC2430871  PMID: 16899224
protein kinase D2 (PKD2); carcinoid; BON cell line; small interfering RNA (siRNA); neuroendocrine

Results 1-25 (683517)