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1.  PTPL1/FAP-1 Negatively Regulates TRIP6 Function in Lysophosphatidic Acid-induced Cell Migration*,S 
The Journal of biological chemistry  2007;282(33):24381-24387.
The LIM domain-containing TRIP6 (Thyroid Hormone Receptor-interacting Protein 6) is a focal adhesion molecule known to regulate lysophosphatidic acid (LPA)-induced cell migration through interaction with the LPA2 receptor. LPA stimulation targets TRIP6 to the focal adhesion complexes and promotes c-Src-dependent phosphorylation of TRIP6 at Tyr-55, which creates a docking site for the Crk Src homology 2 domain, thereby promoting LPA-induced morphological changes and cell migration. Here we further demonstrate that a switch from c-Src-mediated phosphorylation to PTPL1/Fas-associated phosphatase-1-dependent dephosphorylation serves as an inhibitory feedback control mechanism of TRIP6 function in LPA-induced cell migration. PTPL1 dephosphorylates phosphotyrosine 55 of TRIP6 in vitro and inhibits LPA-induced tyrosine phosphorylation of TRIP6 in cells. This negative regulation requires a direct protein-protein interaction between these two molecules and the phosphatase activity of PTPL1. In contrast to c-Src, PTPL1 prevents TRIP6 turnover at the sites of adhesions. As a result, LPA-induced association of TRIP6 with Crk and the function of TRIP6 to promote LPA-induced morphological changes and cell migration are inhibited by PTPL1. Together, these results reveal a novel mechanism by which PTPL1 phosphatase plays a counteracting role in regulating TRIP6 function in LPA-induced cell migration.
PMCID: PMC3923842  PMID: 17591779
2.  TRIP6 Enhances Lysophosphatidic Acid-induced Cell Migration by Interacting with the Lysophosphatidic Acid 2 Receptor* 
The Journal of biological chemistry  2003;279(11):10459-10468.
Lysophosphatidic acid (LPA) induces actin rearrangement, focal adhesion assembly, and cell migration through the activation of small G protein Rho and its downstream effectors. These diverse cellular responses are mediated by its associated G protein-coupled receptors. However, the mechanisms and specificity by which these LPA receptors mediate LPA actions are still poorly understood. Here we show that LPA stimulation promotes the interaction of the LPA2 receptor with a focal adhesion molecule, TRIP6 (thyroid receptor interacting protein 6)/ZRP-1 (zyxin-related protein 1). TRIP6 directly binds to the carboxyl-terminal tail of the LPA2 receptor through its LIM domains. LPA-dependent recruitment of TRIP6 to the plasma membrane promotes its targeting to focal adhesions and co-localization with actin stress fibers. In addition, TRIP6 associates with the components of focal complexes including paxillin, focal adhesion kinase, c-Src, and p130cas in an agonist-dependent manner. Overexpression of TRIP6 augments LPA-induced cell migration; in contrast, suppression of endogenous TRIP6 expression by a TRIP6-specific small interfering RNA reduces it in SKOV3 ovarian cancer cells. Strikingly, the association with TRIP6 is specific to the LPA2 receptor but not LPA1 or LPA3 receptor, indicating a specific role for TRIP6 in regulating LPA2 receptor-mediated signaling. Taken together, our results suggest that TRIP6 functions at a point of convergence between the activated LPA2 receptor and downstream signals involved in cell adhesion and migration.
PMCID: PMC3904432  PMID: 14688263
3.  TRIP6 Regulates p27KIP1 To Promote Tumorigenesis 
Molecular and Cellular Biology  2013;33(7):1394-1409.
TRIP6 is an adaptor protein that regulates cell motility and antiapoptotic signaling. Although it has been implicated in tumorigenesis, the underlying mechanism remains largely unknown. Here we provide evidence that TRIP6 promotes tumorigenesis by serving as a bridge to promote the recruitment of p27KIP1 to AKT in the cytosol. TRIP6 regulates the membrane translocation and activation of AKT and facilitates AKT-mediated recognition and phosphorylation of p27KIP1 specifically at T157, thereby promoting the cytosolic mislocalization of p27KIP1. This is required for p27KIP1 to enhance lysophosphatidic acid (LPA)-induced ovarian cancer cell migration. TRIP6 also promotes serum-induced reduction of nuclear p27KIP1 expression levels through Skp2-dependent and -independent mechanisms. Consequently, knockdown of TRIP6 in glioblastoma or ovarian cancer xenografts restores nuclear p27KIP1 expression and impairs tumor proliferation. As TRIP6 is upregulated in gliomas and its levels correlate with poor clinical outcomes in a dose-dependent manner, it may represent a novel prognostic marker and therapeutic target in gliomas.
PMCID: PMC3624266  PMID: 23339869
4.  Epithelial-mesenchyme transition induced by TNF-α requires NF-κB-mediated transcriptional upregulation of Twist1 
Cancer Research  2012;72(5):1290-1300.
Pro-inflammatory cytokines produced in the tumor microenvironment facilitate tumor development and metastatic progression. In particular, TNF-α promotes cancer invasion and angiogenesis associated with epithelial-mesenchyme transition (EMT), however, the mechanisms underlying its induction of EMT in cancer cells remain unclear. Here we show that EMT and cancer stemness properties induced by chronic treatment with TNFα̣ are mediated by the upregulation of the transcriptional repressor Twist1. Exposure to TNF-α rapidly induced Twist1 mRNA and protein expression in normal breast epithelial and breast cancer cells. Both IKK-β and NF-κB p65 were required for TNF-α-induced expression of Twist1, suggesting the involvement of canonical NF-κB signaling. In support of this likelihood, we defined a functional NF-κB binding site in the Twist1 promoter and overexpression of p65 was sufficient to induce transcriptional upregulation of Twist1 along with EMT in mammary epithelial cells. Conversely, suppressing Twist1 expression abrogated p65-induced cell migration, invasion, EMT and stemness properties, establishing that Twist1 is required for NF-κB to induce these aggressive phenotypes in breast cancer cells. Taken together, our results establish a signaling axis through which the tumor microenvironment elicits Twist1 expression to promote cancer metastasis. We suggest that targeting NF-κB-mediated Twist1 upregulation may offer an effective a therapeutic strategy for breast cancer treatment.
PMCID: PMC3350107  PMID: 22253230
5.  The Lysophosphatidic Acid 2 Receptor Mediates Down-regulation of Siva-1 to Promote Cell Survival*χ 
The Journal of biological chemistry  2007;282(52):37759-37769.
Lysophosphatidic acid (LPA) promotes cell survival through the activation of G protein-coupled LPA receptors. However, whether different LPA receptors activate distinct anti-apoptotic signaling pathways is not yet clear. Here we report a novel mechanism by which the LPA2 receptor targets the proapoptotic Siva-1 protein for LPA-dependent degradation, thereby attenuating Siva-1 function in DNA damage response. The carboxyl-terminal tail of the LPA2 receptor, but not LPA1 or LPA3 receptor, specifically associates with the carboxyl cysteine-rich domain of Siva-1. Prolonged LPA stimulation promotes the association of Siva-1 with the LPA2 receptor and targets both proteins for ubiquitination and degradation. As a result, adriamycin-induced Siva-1 protein stabilization is attenuated by LPA in an LPA2-dependent manner, and the function of Siva-1 in promoting DNA damage-induced apoptosis is inhibited by LPA pretreatment. Consistent with this result, inhibition of the LPA2 receptor expression increases Siva-1 protein levels and augments adriamycin-induced caspase-3 cleavage and apoptosis. Together, these findings reveal a critical and specific role for the LPA2 receptor through which LPA directly inactivates a critical component of the death machinery to promote cell survival.
PMCID: PMC3496872  PMID: 17965021
6.  The Adaptor Protein TRIP6 Antagonizes Fas-Induced Apoptosis but Promotes Its Effect on Cell Migration ▿  
Molecular and Cellular Biology  2010;30(23):5582-5596.
The Fas/CD95 receptor mediates apoptosis but is also capable of triggering nonapoptotic signals. However, the mechanisms that selectively regulate these opposing effects are not yet fully understood. Here we demonstrate that the activation of Fas or stimulation with lysophosphatidic acid (LPA) induces cytoskeletal reorganization, leading to the association of Fas with actin stress fibers and the adaptor protein TRIP6. TRIP6 binds to the cytoplasmic juxtamembrane domain of Fas and interferes with the recruitment of FADD to Fas. Furthermore, through physical interactions with NF-κB p65, TRIP6 regulates nuclear translocation and the activation of NF-κB upon Fas activation or LPA stimulation. As a result, TRIP6 antagonizes Fas-induced apoptosis and further enhances the antiapoptotic effect of LPA in cells that express high levels of TRIP6. On the other hand, TRIP6 promotes Fas-mediated cell migration in apoptosis-resistant glioma cells. This effect is regulated via the Src-dependent phosphorylation of TRIP6 at Tyr-55. As TRIP6 is overexpressed in glioblastomas, this may have a significant impact on enhanced NF-κB activity, resistance to apoptosis, and Fas-mediated cell invasion in glioblastomas.
PMCID: PMC2976429  PMID: 20876301
7.  A New Microsphere-Based Immunoassay for Measuring the Activity of Transcription Factors 
There are several traditional and well-developed methods for analyzing the activity of transcription factors, such as EMSA, enzyme-linked immunosorbent assay, and reporter gene activity assays. All of these methods have their own distinct disadvantages, but none can analyze the changes in transcription factors in the few cells that are cultured in the wells of 96-well titer plates. Thus, a new microsphere-based immunoassay to measure the activity of transcription factors (MIA-TF) was developed. In MIA-TF, NeutrAvidin-labeled microspheres were used as the solid phase to capture biotin-labeled double-strand DNA fragments which contain certain transcription factor binding elements. The activity of transcription factors was detected by immunoassay using a transcription factor-specific antibody to monitor the binding with the DNA probe. Next, analysis was performed by flow cytometry. The targets hypoxia-inducible factor-1α (HIF-1α) and nuclear factor-kappa B (NF-κB) were applied and detected in this MIA-TF method; the results that we obtained demonstrated that this method could be used to monitor the changes of NF-κB or HIF within 50 or 100 ng of nuclear extract. Furthermore, MIA-TF could detect the changes in NF-κB or HIF in cells that were cultured in wells of a 96-well plate without purification of the nuclear protein, an important consideration for applying this method to high-throughput assays in the future. The development of MIA-TF would support further progress in clinical analysis and drug screening systems. Overall, MIA-TF is a method with high potential to detect the activity of transcription factors.
PMCID: PMC3055901  PMID: 21406071
transcription factor; microsphere-based immunoassay; NF-κB; HIF-1
8.  Regulation of the LPA2 Receptor Signaling through the Carboxyl-Terminal Tail-Mediated Protein-Protein Interactions 
Biochimica et biophysica acta  2008;1781(9):558-562.
While it is well known that lysophosphatidic acid (LPA) mediates diverse physiological and pathophysiological responses through the activation of G protein-coupled LPA receptors, the specificity and molecular mechanisms by which different LPA receptors mediate these biological responses remain largely unknown. Recent identification of several PDZ proteins and zinc finger proteins that interact with the carboxyl-terminal tail of the LPA2 receptor provides a considerable progress towards the understanding of the mechanisms how the LPA2 receptor specifically mediates LPA signaling pathways. These findings have led to the proposal that there are at least two distinct protein interaction motifs present in the carboxyl terminus of the LPA2 receptor. Together, these data provide a new concept that the efficiency and specificity of the LPA2 receptor-mediated signal transduction can be achieved through the cross-regulation between the classical G protein-activated signaling cascades and the interacting partner-mediated signaling pathways.
PMCID: PMC2574565  PMID: 18501721
LPA; LPA2 receptor; PDZ; LIM; zinc finger; protein-protein interactions
9.  c-Src-Mediated Phosphorylation of TRIP6 Regulates Its Function in Lysophosphatidic Acid-Induced Cell Migration†  
Molecular and Cellular Biology  2005;25(14):5859-5868.
TRIP6 (thyroid receptor-interacting protein 6), also known as ZRP-1 (zyxin-related protein 1), is a member of the zyxin family that has been implicated in cell motility. Previously we have shown that TRIP6 binds to the LPA2 receptor and associates with several components of focal complexes in an agonist-dependent manner and, thus, enhances lysophosphatidic acid (LPA)-induced cell migration. Here we further report that the function of TRIP6 in LPA signaling is regulated by c-Src-mediated phosphorylation of TRIP6 at the Tyr-55 residue. LPA stimulation induces tyrosine phosphorylation of endogenous TRIP6 in NIH 3T3 cells and c-Src-expressing fibroblasts, which is virtually eliminated in Src-null fibroblasts. Strikingly, both phosphotyrosine-55 and proline-58 residues of TRIP6 are required for Crk binding in vitro and in cells. Mutation of Tyr-55 to Phe does not alter the ability of TRIP6 to localize at focal adhesions or associate with actin. However, it abolishes the association of TRIP6 with Crk and p130cas in cells and significantly reduces the function of TRIP6 to promote LPA-induced ERK activation. Ultimately, these signaling events control TRIP6 function in promoting LPA-induced morphological changes and cell migration.
PMCID: PMC1168818  PMID: 15988003

Results 1-9 (9)