The activity of p53 as a tumor suppressor primarily depends on its ability to transactivate specific target genes in response to genotoxic and other potentially mutagenic stresses. Several histone acetyl transferases (HATs), including p300, CBP, PCAF and GCN5 have been implicated in the activation of p53-dependent transcription of the cyclin-dependent kinase (cdk) inhibitor p21 as well as other target genes. Here we show that PCAF, but not CBP or p300, is a critical regulator of p53-dependent p21 expression in response to multiple p53-activating stresses. PCAF was required for the transcriptional activation of p21 in response to exogenous p53 in p53-null cells, nutlin-3, DNA damaging agents and p14ARF expression, suggesting a broad requirement for PCAF in p53 signaling to p21 after stress. Importantly, cells lacking PCAF failed to undergo cell cycle arrest in response to nutlin-3 treatment or p14ARF expression, consistent with a physiologically important role for PCAF in this p53 function. Surprisingly, the role for PCAF in induction of p21 was independent of p53 lysine 320 acetylation, a previously suggested target of PCAF-mediated acetylation. Though p21 promoter occupancy by p53 was not altered by PCAF knockdown, activation of p21 transcription required an intact PCAF HAT domain, and induction of chromatin marks acetyl-H3K9 and acetyl-H3K14 at the p21 promoter by p53 was dependent upon physiologic levels of PCAF. Together, our experiments indicate that PCAF is required for stress-responsive histone 3 acetylation at the p21 promoter, p53-directed transcription of p21 and the resultant growth arrest.
ARF; DNA damage; PCAF; histone acetylation; p21; p53
Cyclin dependent kinases (cdks) regulate cell cycle progression and transcription. We report here that the transcriptional co-activator PCAF directly interacts with cdk2. This interaction is mainly produced during S and G2/M phases of the cell cycle. As a consequence of this association, PCAF inhibits the activity of cyclin/cdk2 complexes. This effect is specific for cdk2 because PCAF does not inhibit either cyclin D3/cdk6 or cyclin B/cdk1 activities. The inhibition is neither competitive with ATP, nor with the substrate histone H1 suggesting that somehow PCAF disturbs cyclin/cdk2 complexes. We also demonstrate that overexpression of PCAF in the cells inhibits cdk2 activity and arrests cell cycle progression at S and G2/M. This blockade is dependent on cdk2 because it is rescued by the simultaneous overexpression of this kinase. Moreover, we also observed that PCAF acetylates cdk2 at lysine 33. As this lysine is essential for the interaction with ATP, acetylation of this residue inhibits cdk2 activity. Thus, we report here that PCAF inhibits cyclin/cdk2 activity by two different mechanisms: (i) by somehow affecting cyclin/cdk2 interaction and (ii) by acetylating K33 at the catalytic pocket of cdk2. These findings identify a previously unknown mechanism that regulates cdk2 activity.
The generally accepted paradigm of transcription by regulated recruitment defines sequence-specific transcription factors and coactivators as separate categories that are distinguished by their abilities to bind DNA autonomously. The C2H2 zinc finger protein Zac1, with an established role in canonical DNA binding, also acts as a coactivator. Commensurate with this function, p73, which is related to p53, is here shown to recruit Zac1, together with the coactivators p300 and PCAF, to the p21Cip1 promoter during the differentiation of embryonic stem cells into neurons. In the absence of autonomous DNA binding, Zac1's zinc fingers stabilize the association of PCAF with p300, suggesting its scaffolding function. Furthermore, Zac1 regulates the affinities of PCAF substrates as well as the catalytic activities of PCAF to induce a selective switch in favor of histone H4 acetylation and thereby the efficient transcription of p21Cip1. These results are consistent with an authentic coactivator function of Zac1's C2H2 zinc finger DNA-binding domain and suggest coactivation by sequence-specific transcription factors as a new facet of transcriptional control.
β-Catenin plays an important role in development and tumorigenesis. However, the effect of a key acetyltransferase p300/CBP-associated factor (PCAF) on β-catenin signaling is largely unknown. In this study, we found PCAF could increase the β-catenin transcriptional activity, induce its nuclear translocation, and up-regulate its protein level by inhibiting its ubiquitination and improving its stability. Further studies showed that PCAF directly binds to and acetylates β-catenin. The key ubiquitination sites Lys-19 and Lys-49 of β-catenin were shown as the critical residues for PCAF-induced acetylation and stabilization. Knockdown of PCAF in colon cancer cells markedly reduced the protein level, transcriptional activity, and acetylation level of β-catenin; promoted cell differentiation; inhibited cell migration; and repressed xenografted tumorigenesis and tumor growth in nude mice. All these data demonstrate that PCAF acetylates β-catenin and regulates its stability, and they raise the prospect that therapies targeting PCAF may be of clinical use in β-catenin–driven diseases, such as colon cancer.
Nuclear myosin 1c (NM1) mediates RNA polymerase I (pol I) transcription activation and cell cycle progression by facilitating PCAF-mediated H3K9 acetylation, but the molecular mechanism by which NM1 is regulated remains unclear. Here, we report that at early G1 the glycogen synthase kinase (GSK) 3β phosphorylates and stabilizes NM1, allowing for NM1 association with the chromatin. Genomic analysis by ChIP-Seq showed that this mechanism occurs on the rDNA as active GSK3β selectively occupies the gene. ChIP assays and transmission electron microscopy in GSK3β−/− mouse embryonic fibroblasts indicated that at G1 rRNA synthesis is suppressed due to decreased H3K9 acetylation leading to a chromatin state incompatible with transcription. We found that GSK3β directly phosphorylates the endogenous NM1 on a single serine residue (Ser-1020) located within the NM1 C-terminus. In G1 this phosphorylation event stabilizes NM1 and prevents NM1 polyubiquitination by the E3 ligase UBR5 and proteasome-mediated degradation. We conclude that GSK3β-mediated phosphorylation of NM1 is required for pol I transcription activation.
Nuclear actin and myosin are essential regulators of gene expression. At the exit of mitosis, nuclear myosin 1c (NM1) mediates RNA polymerase I (pol I) transcription activation and cell cycle progression by modulating assembly of the chromatin remodeling complex WICH with the subunits WSTF and SNF2h and, crucially, facilitating H3K9 acetylation by the histone acetyl transferase PCAF. The molecular mechanism by which NM1 is regulated remains however unknown. Here, we conducted a genome-wide screen and demonstrate that GSK3β is selectively coupled to the rDNA transcription unit. In embryonic fibroblasts lacking GSK3β there is a significant drop in rRNA synthesis levels and the rDNA is devoid of actin, NM1 and SNF2h. Concomitantly with a transcriptional block we reveal decreased levels of histone H3 acetylation by the histone acetyl transferase PCAF. At G1, transcriptional repression in the GSK3β knockout mouse embryonic fibroblasts, leads to NM1 ubiquitination by the E3 ligase UBR5 and proteasome-mediated degradation. We conclude that GSK3β suppresses NM1 degradation through the ubiquitin-proteasome system, facilitates NM1 association with the rDNA chromatin and transcription activation at G1. We therefore propose a novel and fundamental role for GSK3β as essential regulator of rRNA synthesis and cell cycle progression.
The transcriptional co-activators CBP/p300 and PCAF participate in transcriptional activation by many factors. We have shown that both CBP/p300 and PCAF stimulate the transcriptional activation by KLF13, a member of the KLF/Sp1 family, either individually or cooperatively. Here we further investigated how CBP and PCAF acetylation regulate KLF13 activity, and how these two co-activators functionally interplay in the regulation of KLF13 activity. We found that CBP and PCAF acetylated KLF13 at specific lysine residues in the zinc finger domain of KLF13. The acetylation by CBP, however, resulted in disruption of KLF13 DNA binding. Although the acetyltransferase activity of CBP is not required for stimulating the DNA binding activity of all of the transcription factors that we have examined, the disruption of factor DNA binding by CBP acetylation is factor-specific. We further showed that PCAF and CBP act synergistically and antagonistically to regulate KLF13 DNA binding depending on the status of acetylation. PCAF blocked CBP acetylation and disruption of KLF13 DNA binding. Conversely, acetylation of KLF13 by CBP prevented PCAF stimulation of KLF13 DNA binding. PCAF blocked CBP disruption of KLF13 DNA binding by preventing CBP acetylation of KLF13. These results demonstrate that acetylation by CBP has distinct effects on transcription factor DNA binding, and that CBP and PCAF regulate each other functionally in their regulation of transcription factor DNA binding.
CBP/p300; PCAF; KLF13; acetylation; regulation of DNA-binding
KLF8 regulates target genes by recruiting the p300 and PCAF co-activators via glutamines (Q) 118 and 248, the CtBP co-repressor to 86PVDLS90 or SUMO to lysine (K) 67. Here we examined how these interactions coordinate to regulate KLF8 transactivity. Mass spectrometry and immunoprecipitations determined that p300 and/or PCAF promoted KLF8 acetylation at K67, K93, and K95 and this acetylation was abolished in lysine-to-arginine (R) mutants. Treatment with HDAC inhibitors or expression of co-activators inhibited sumoylation at K67. K93R or K95R mutation exerted high levels of sumoylation while the acetylation mimetic mutations K93Q and K95Q blocked the sumoylation. Interestingly, CtBP promoted sumoylation at K67 of wild-type but not AVALF mutant KLF8, and KLF8 interaction with CtBP was inhibited by treatment with the HDAC inhibitors, ectopic expression of the co-activators, or K93Q or K95Q mutation. Promoter reporter assays showed that CtBP inhibited KLF8 transactivity which was rescued by PCAF or p300 expresson. Finally, KLF8-mediated cyclin D1 protein expression and cell cycle progression were significantly decreased in the K93R and K95R but increased in the K93Q, K95Q, K67R or K67Q mutant. Taken together, these results identified a novel mechanism by which co-activators promote KLF8 transactivity by competing with SUMO for K67 modification and by acetylating K93 and K95 to inhibit CtBP-induced K67 sumoylation.
Krüppel-like factor 8 (KLF8); histone acetyltransferase (HAT); small ubiquitin modifier (SUMO); p300; p300/CBP associated factor (PCAF); histone deacetylase (HDAC); C-terminal binding protein (CtBP); acetylation and sumoylation
The class II transactivator (CIITA), the master regulator of the tissue-specific and interferon gamma-inducible expression of major histocompatibility complex class II genes, synergizes with the histone acetylase coactivator CBP to activate gene transcription. Here we demonstrate that in addition to CBP, PCAF binds to CIITA both in vivo and in vitro and enhances CIITA-dependent transcriptional activation of class II promoters. Accordingly, E1A mutants defective for PCAF or CBP interaction show reduced ability in suppressing CIITA activity. Interestingly, CBP and PCAF acetylate CIITA at lysine residues within a nuclear localization signal. We show that CIITA is shuttling between the nucleus and cytoplasm. The shuttling behavior and activity of the protein are regulated by acetylation: overexpression of PCAF or inhibition of cellular deacetylases by trichostatin A increases the nuclear accumulation of CIITA in a manner determined by the presence of the acetylation target lysines. Furthermore, mutagenesis of the acetylated residues reduces the transactivation ability of CIITA. These results support a novel function for acetylation, i.e., to regulate gene expression by stimulating the nuclear accumulation of an activator.
The Hedgehog (Hh) signaling regulates tissue development, and its aberrant activation is a leading cause of malignancies, including medulloblastoma (Mb). Hh-dependent tumorigenesis often occurs in synergy with other mechanisms, such as loss of p53, the master regulator of the DNA damage response. To date, little is known about mechanisms connecting DNA-damaging events to morphogen-dependent processes. Here, we show that genotoxic stress triggers a cascade of signals, culminating with inhibition of the activity of Gli1, the final transcriptional effector of Hh signaling. This inhibition is dependent on the p53-mediated elevation of the acetyltransferase p300/CBP-associated factor (PCAF). Notably, we identify PCAF as a novel E3 ubiquitin ligase of Gli1. Indeed PCAF, but not a mutant with a deletion of its ubiquitination domain, represses Hh signaling in response to DNA damage by promoting Gli1 ubiquitination and its proteasome-dependent degradation. Restoring Gli1 levels rescues the growth arrest and apoptosis effect triggered by genotoxic drugs. Consistently, DNA-damaging agents fail to inhibit Gli1 activity in the absence of either p53 or PCAF. Finally, Mb samples from p53-null mice display low levels of PCAF and upregulation of Gli1 in vivo, suggesting PCAF as potential therapeutic target in Hh-dependent tumors. Together, our data define a mechanism of inactivation of a morphogenic signaling in response to genotoxic stress and unveil a p53/PCAF/Gli1 circuitry centered on PCAF that limits Gli1-enhanced mitogenic and prosurvival response.
Hedgehog signaling; ubiquitylation; PCAF; p53; medulloblastoma
The NAD+-dependent histone deacetylase hSirT1 regulates cell survival and stress responses by inhibiting p53-, NF-κB-, and E2F1-dependent transcription. Here we show that the hSirT1/PCAF interaction controls the E2F1/p73 apoptotic pathway. hSirT1 represses E2F1-dependent P1p73 promoter activity in untreated cells and inhibits its activation in response to DNA damage. hSirT1, PCAF, and E2F1 are corecruited in vivo on theP1p73 promoter. hSirT1 deacetylates PCAF in vitro and modulates PCAF acetylation in vivo. In cells exposed to apoptotic DNA damage, nuclear NAD+ levels decrease and inactivate hSirT1 without altering the hSirT1 interaction with PCAF and hSirT1 binding to the P1p73 promoter. The reactivation of hSirT1 by pyruvate that increases the [NAD+]/[NADH] ratio completely abolished the DNA damage-induced activation of TAp73 expression, thus linking the modulation of chromatin-bound hSirT1 deacetylase activity by the intracellular redox state with P1p73 promoter activity. The release of PCAF from hSirT1 repression favors the assembly of transcriptionally active PCAF/E2F1 complexes onto the P1p73 promoter and p53-independent apoptosis. Our results identify hSirT1 and PCAF as potential targets to modulate tumor cell survival and chemoresistance irrespective of p53 status.
Malignant pleural mesothelioma (MPM) is a devastating disease with an overall poor prognosis. Despite the recent advances in targeted molecular therapies, there is a clear and urgent need for the identification of novel mesothelioma targets for the development of highly efficacious therapeutics.
In this study, we report that the expression of Sphingosine Kinase 1 (SphK1) protein was preferentially elevated in MPM tumor tissues (49 epithelioid and 13 sarcomatoid) compared to normal tissue (n = 13). In addition, we also observed significantly elevated levels of SphK1 and SphK2 mRNA and SphK1 protein expression in MPM cell lines such as H2691, H513 and H2461 compared to the non-malignant mesothelial Met5 cells. The underlying mechanism appears to be mediated by SphK1 induced upregulation of select gene transcription programs such as that of CBP/p300 and PCAF, two histone acetyl transferases (HAT), and the down regulation of cell cycle dependent kinase inhibitor genes such as p27Kip1 and p21Cip1. In addition, using immunoprecipitates of anti-acetylated histone antibody from SphK inhibitor, SphK-I2 treated Met5A and H2691 cell lysates, we also showed activation of other cell proliferation related genes, such as Top2A (DNA replication), AKB (chromosome remodeling and mitotic spindle formation), and suppression of p21 CIP1 and p27KIP1. The CDK2, HAT1 and MYST2 were, however, unaffected in the above study. Using SphK inhibitor and specific siRNA targeting either SphK1 or SphK2, we also unequivocally established that SphK1, but not SphK2, promotes H2691 mesothelioma cell proliferation. Using a multi-walled carbon nanotubes induced peritoneal mesothelioma mouse model, we showed that the SphK1−/− null mice exhibited significantly less inflammation and granulamatous nodules compared to their wild type counterparts.
The lipid kinase SphK1 plays a positive and essential role in the growth and development of malignant mesothelioma and is therefore a likely therapeutic target.
p300/CBP-associated factor (PCAF) is a coactivator of the tumor suppressor, p53. PCAF participates in p53's transactivation of target genes through acetylation of both bound p53 and histones within p53 target promoters. Using microarrays, we discovered that PCAF itself is induced by p53 in a panel of breast tumor cell lines. Two p53 mutant breast tumor cell lines, BT-549 and UACC-1179, were chosen for further study of PCAF induction by wild-type p53. PCAF induction following adenoviral transduction of p53 expression was confirmed with real-time polymerase chain reaction in a time course experiment. Chromatin immunoprecipitation experiments then showed that PCAF induction was associated with increased p53 binding to the PCAF promoter, which contains p53 consensus-binding sites. PCAF induction by p53 activity was further demonstrated in wild-type p53 MCF10A cells when PCAF expression was induced following activation of endogenous wild-type p53 with doxorubicin in a dose- and time-dependent manner. Furthermore, the doxorubicin-induced increase in PCAF expression was blocked by pretreatment of the MCF10A cells with siRNA (small interfering RNA) targeted against p53 mRNA. Taken together, the results show that PCAF expression can be induced by wild-type p53.
Microarray; p53; PCAF; p300/CBP-associated factor; acetyltransferase; ChIP, chromatin immunoprecipitation; PCAF, p300/CBP-associated factor; RT-PCR, reverse transcription-polymerase chain reaction; siRNA, small interfering RNA; GFP, green fluorescent protein
Epithelial to mesenchymal transition (EMT) not only occurs during embryonic development and in response to injury, but is an important element in cancer progression. EMT and its reverse process, mesenchymal to epithelial transition (MET) is controlled by a network of transcriptional regulators and can be influenced by posttranscriptional and posttranslational modifications. EMT/MET involves many effectors that can activate and repress these transitions, often yielding a spectrum of cell phenotypes. Recent studies have shown that the miR-200 family and the transcriptional suppressor ZEB1 are important contributors to EMT. Our previous data showed that forced expression of SPRR2a was a powerful inducer of EMT and supports the findings by others that SPRR gene members are highly upregulated during epithelial remodeling in a variety of organs. Here, using SPRR2a cells, we characterize the role of acetyltransferases on the microRNA-200c/141 promoter and their effect on the epithelial/mesenchymal status of the cells. We show that the deacetylase inhibitor TSA as well as P300 and PCAF can cause a shift towards epithelial characteristics in HUCCT-1-SPRR2a cells. We demonstrate that both P300 and PCAF act as cofactors for ZEB1, forming a P300/PCAF/ZEB1 complex on the miR200c/141 promoter. This binding results in lysine acetylation of ZEB1 and a release of ZEB1 suppression on miR-200c/141 transcription. Furthermore, disruption of P300 and PCAF interactions dramatically down regulates miR-200c/141 promoter activity, indicating a PCAF/P300 cooperative function in regulating the transcriptional suppressor/activator role of ZEB1. These data demonstrate a novel mechanism of miRNA regulation in mediating cell phenotype.
The p300, CBP, and pCAF lysine acetyltransferase (KAT) proteins have been reported to physically interact with bovine (BPV) and human (HPV) papillomavirus E2 proteins. While overexpression of these KAT proteins enhances E2-dependent transcription, the mechanism has not been determined. Using RNA interference (RNAi) to deplete these factors, we demonstrated that E2 transcriptional activity requires physiological levels of p300, CBP, and pCAF. Each protein appears to have a unique function in E2-dependent transcription, since overexpression of one KAT failed to compensate for RNAi knockdown of another KAT. Using an in vitro acetylation assay, we identified highly conserved lysines that are targeted by p300 for acetylation. The conservative changes of lysines at positions 111 and 112 to arginine were of particular interest. The K111R and the K111R/K112R mutants showed reduced transcriptional activity that was not responsive to p300 overexpression, while the K112R mutant retained activity. p300 and CBP were detected at the viral promoter; however, pCAF was not. We propose a model by which E2 transcriptional activity is controlled by p300-mediated acetylation of lysine 111. This model represents a novel mechanism regulating papillomavirus gene expression.
The p53 tumour suppressor is involved in several crucial cellular functions including cell cycle arrest and apoptosis. p53 stabilisation occurs under hypoxic and DNA damage conditions. However, only in the latter scenario is stabilised p53 capable of inducing the expression of its pro-apoptotic targets. Here we present evidence that under hypoxia mimicking conditions p53 acetylation is reduced to a greater extent at K320 site targeted by PCAF than at K382 site targeted by p300/CBP. The limited amounts of acetylated p53 at K320 are preferentially recruited to the promoter of the p21WAF-1/CIP-1 gene, which appears to be unaffected by hypoxia, but are not recruited to the BID promoter and hence p53 is incapable of up-regulating pro-apoptotic BID in hypoxic conditions. Since the K320 p53 acetylation is the site predominantly affected in hypoxia the PCAF HAT activity is the key regulator of the cellular fate modulated by p53 under these conditions. In addition, we provide evidence that PCAF acetylates HIF-1α in hypoxic conditions and that the acetylated HIF-1α is recruited to a particular subset of its targets. In conclusion, PCAF regulates the balance between cell cycle arrest and apoptosis in hypoxia by modulating the activity and protein stability of both p53 and HIF-1α.
transcription; p53; Hypoxia Inducible Factor; PCAF; apoptosis
The promoters of poised rRNA genes (rDNA) are marked by both euchromatic and heterochromatic histone modifications and are associated with two transcription factors, UBF and SL1 that nucleate transcription complex formation. Active rRNA genes contain only euchromatic histone modifications and are loaded with all components of transcriptional initiation complex including RNA polymerase I. Coupled with histone acetylation and RNA polymerase I targeting, poised promoters can be converted to active ones by ATP-dependent chromatin remodeling factor CSB for initiation of rDNA transcription. However, it is not clear how dynamic histone modifications induce the assembly of polymerase I transcription initiation complex to active promoters during such conversion. Here we show that a complex consisting of CSB, RNA polymerase I and histone acetyltransferase PCAF is present at the rDNA promoters in active state. CSB is required for the association of PCAF with rDNA, which induces acetylation of histone H4 and histone H3K9. Overexpression of CSB promotes the association of PCAF with rDNA. Knockdown of PCAF leads to decreased levels of H4ac and H3K9ac at rDNA promoters, prevents the association of RNA polymerase I and inhibits pre-rRNA synthesis. The results demonstrate that CSB recruits PCAF to rDNA, which allows histone acetylation that is required for the assembly of polymerase I transcription initiation complex during the transition from poised to active state of rRNA genes, suggesting that CSB and PCAF play cooperative roles to establish the active state of rRNA genes by histone acetylation.
The Sp1/KLF family of factors regulates diverse cellular processes, including growth and development. Fetal Krüppel-like factor (FKLF2) is a new member of this family. In this study, we characterized the coactivators involved in FKLF2 transcriptional activation. Our results show that both CBP/p300 and p300/CBP-associated factor (PCAF) enhance FKLF2 transcriptional activity. We demonstrate that the acetyltransferase activity of PCAF but not that of CBP/p300 is required for stimulating FKLF2 transcription activity. We further show that p300 and PCAF act cooperatively in stimulating FKLF2 transcriptional activation. FKLF2 interacts with both CBP and PCAF through specific domains, and CBP and PCAF acetylate FKLF2. Both CBP/p300 and PCAF stimulate FKLF2 DNA binding activity. The integrity of the acetyltransferase domain of PCAF but not that of CBP/p300 is required for stimulating FKLF2 DNA binding activity. These results demonstrate that CBP/p300 and PCAF stimulate FKLF2 transcriptional activity at least by enhancing its DNA binding. The acetyltransferase activities of CBP/p300 and PCAF play a distinct role in stimulating FKLF2 transcription and DNA binding.
Therapeutic arteriogenesis, i.e., expansive remodeling of pre-existing collaterals, using single-action factor therapies has not been as successful as anticipated. Modulation of factors that act as a master switch for relevant gene programs may prove more effective. Transcriptional co-activator P300/CBP-associated factor (PCAF) has histone acetylating activity and promotes transcription of multiple inflammatory genes. Because arteriogenesis is an inflammation-driven process, we hypothesized that PCAF acts as multifactorial regulator of arteriogenesis.
Approach and Results
After induction of hind limb ischemia, blood flow recovery was impaired in both PCAF−/− mice and healthy wild type mice treated with the pharmacological PCAF inhibitor Garcinol, demonstrating an important role for PCAF in arteriogenesis. PCAF deficiency reduced the in vitro inflammatory response in leukocytes and vascular cells involved in arteriogenesis. In vivo gene expression profiling revealed that PCAF deficiency results in differential expression of 3505 genes during arteriogenesis and, more specifically, in impaired induction of multiple pro-inflammatory genes. Additionally, recruitment from the bone marrow of inflammatory cells, in particular “pro-inflammatory” Ly6Chi monocytes, was severely impaired in PCAF−/− mice.
These findings indicate that PCAF acts as master switch in the inflammatory processes required for effective arteriogenesis.
arteriogenesis; inflammation; monocyte subtypes; PCAF
Aberrant cellular responses to pro-inflammatory cytokines, such as TNF-α, are pathogenic features in most chronic inflammatory diseases. A variety of extracellular and intracellular feedback pathways have evolved to prevent an inappropriate cellular reaction to these pro-inflammatory cytokines. Here, we report that TNF-α treatment of human and mouse cholangiocytes and hepatocytes downregulated expression of p300/CBP-associated factor (PCAF), a co-activator and an acetyltransferase that promotes histone acetylation and gene transcription. Of these upregulated microRNAs (miRNAs) in TNF-α-treated cells, miR-181a/b (miR-181a and miR-181b) suppressed translation of PCAF mRNA. Functional manipulation of miR-181a/b caused reciprocal alterations in PCAF protein expression in cultured cholangiocytes and hepatocytes. Inhibition of miR-181a/b function with anti-miRs blocked TNF-α-induced suppression of PCAF expression. Promoter recruitment of PCAF was shown to be associated with TNF-α-induced transcription of inflammatory genes. Intriguingly, pretreatment of cells with TNF-α inhibited transcription of inflammatory genes in response to subsequent TNF-α stimulation. Overexpression of PCAF or inhibition of miR-181a/b function with anti-miRs attenuated the inhibitory effects of TNF-α pretreatment on epithelial inflammatory response to subsequent TNF-α stimulation. Downregulation of PCAF and the inhibitory effects of TNF-α pretreatment on liver epithelial inflammatory response were further confirmed in a mouse model of TNF-α intraperitoneal injection. These data suggest that PCAF is a target for miR-181a/b, and downregulation of PCAF by TNF-α provides negative feedback regulation to inflammatory reactions in liver epithelial cells, a process that may be relevant to the epigenetic fine-tuning of epithelial inflammatory processes in general.
miRNAs; PCAF; Negative feedback; Epithelial cells; Inflammation; TNF-α
High mobility group (HMG) A1 proteins are subject to a number of post-translational modifications, which may regulate their function in gene transcription and other cellular processes. We examined, by using mass spectrometry, the acetylation of HMGA1a and HMGA1b proteins induced by histone acetyltransferases p300 and PCAF in vitro and in PC-3 human prostate cancer cells in vivo. It turned out that five lysine residues in HMGA1a, i.e., Lys-14, Lys-64, Lys-66, Lys-70, and Lys-73, could be acetylated by both p300 and PCAF. We further quantified the level of acetylation by analyzing, with LC-MS/MS, the proteolytic peptides of the in-vitro or in-vivo acetylated HMGA1 proteins where the unmodified lysine residues were chemically derivatized with a perdeuterated acetyl group. Quantification results revealed that p300 and PCAF exhibited different site preferences for the acetylation; the preference of p300 acetylation followed the order of Lys-64~Lys-70 > Lys-66 > Lys-14~Lys73, whereas the selectivity of PCAF acetylation followed the sequence of Lys-70~Lys-73 > Lys-64~Lys-66 > Lys-14. HMGA1b was acetylated in a very similar fashion as HMGA1a. We also demonstrated that C-terminal phosphorylation of HMGA1 proteins did not affect the in-vitro acetylation of the two proteins by either p300 or PCAF. Moreover, we examined the acetylation of lysine residues in HMGA1a and HMGA1b isolated from PC-3 human prostate cancer cells. Our results showed that all the above five lysine residues were also acetylated in vivo, with Lys-64, Lys-66 and Lys-70 in HMGA1a exhibiting higher levels of acetylation than Lys-14 and Lys-73.
Tumor-derived mutant forms of p53 compromise its DNA binding, transcriptional, and growth regulatory activity in a manner that is dependent upon the cell-type and the type of mutation. Given the high frequency of p53 mutations in human tumors, reactivation of the p53 pathway has been widely proposed as beneficial for cancer therapy. In support of this possibility p53 mutants possess a certain degree of conformational flexibility that allows for re-induction of function by a number of structurally different artificial compounds or by short peptides. This raises the question of whether physiological pathways for p53 mutant reactivation also exist and can be exploited therapeutically. The activity of wild-type p53 is modulated by various acetyl-transferases and deacetylases, but whether acetylation influences signaling by p53 mutant is still unknown. Here, we show that the PCAF acetyl-transferase is down-regulated in tumors harboring p53 mutants, where its re-expression leads to p53 acetylation and to cell death. Furthermore, acetylation restores the DNA-binding ability of p53 mutants in vitro and expression of PCAF, or treatment with deacetylase inhibitors, promotes their binding to p53-regulated promoters and transcriptional activity in vivo. These data suggest that PCAF-mediated acetylation rescues activity of at least a set of p53 mutations. Therefore, we propose that dis-regulation of PCAF activity is a pre-requisite for p53 mutant loss of function and for the oncogenic potential acquired by neoplastic cells expressing these proteins. Our findings offer a new rationale for therapeutic targeting of PCAF activity in tumors harboring oncogenic versions of p53.
The cortactin oncoprotein is frequently overexpressed in head and neck squamous cell carcinoma (HNSCC), often due to amplification of the encoding gene (CTTN). While cortactin overexpression enhances invasive potential, recent research indicates that it also promotes cell proliferation, but how cortactin regulates the cell cycle machinery is unclear. In this article we report that stable short hairpin RNA-mediated cortactin knockdown in the 11q13-amplified cell line FaDu led to increased expression of the Cip/Kip cyclin-dependent kinase inhibitors (CDKIs) p21WAF1/Cip1, p27Kip1, and p57Kip2 and inhibition of S-phase entry. These effects were associated with increased binding of p21WAF1/Cip1 and p27Kip1 to cyclin D1- and E1-containing complexes and decreased retinoblastoma protein phosphorylation. Cortactin regulated expression of p21WAF1/Cip1 and p27Kip1 at the transcriptional and posttranscriptional levels, respectively. The direct roles of p21WAF1/Cip1, p27Kip1, and p57Kip2 downstream of cortactin were confirmed by the transient knockdown of each CDKI by specific small interfering RNAs, which led to partial rescue of cell cycle progression. Interestingly, FaDu cells with reduced cortactin levels also exhibited a significant diminution in RhoA expression and activity, together with decreased expression of Skp2, a critical component of the SCF ubiquitin ligase that targets p27Kip1 and p57Kip2 for degradation. Transient knockdown of RhoA in FaDu cells decreased expression of Skp2, enhanced the level of Cip/Kip CDKIs, and attenuated S-phase entry. These findings identify a novel mechanism for regulation of proliferation in 11q13-amplified HNSCC cells, in which overexpressed cortactin acts via RhoA to decrease expression of Cip/Kip CDKIs, and highlight Skp2 as a downstream effector for RhoA in this process.
Transcription factors of the interferon regulatory factor (IRF) family bind to the type I interferon (IFN)-responsive element (ISRE) and activate transcription from IFN-inducible genes. To identify cofactors that associate with IRF proteins, DNA affinity binding assays were performed with nuclear extracts prepared from tissue culture cells. The results demonstrated that the endogenous IRFs bound to the ISRE are complexed with the histone acetylases, PCAF, GCN5, and p300/CREB binding protein and that histone acetylase activities are accumulated on the IRF-ISRE complexes. By testing recombinant proteins, we show that PCAF directly binds to some but not all members of the IRF family through distinct domains of the two proteins. This interaction was functionally significant, since transfection of PCAF strongly enhanced IRF-1- and IRF-2-dependent promoter activities. Further studies showed that expression of PCAF and other histone acetylases was markedly induced in U937 cells upon phorbol ester treatment, which led to increased recruitment of PCAF to the IRF-ISRE complexes. Coinciding with the induction of histone acetylases, phorbol ester markedly enhanced IFN-α-stimulated gene expression in U937 cells. Supporting the role for PCAF in conferring IFN responsiveness, transfection of PCAF into U937 cells led to a large increase in IFN-α-inducible promoter activity. These results demonstrate that PCAF is a phorbol ester-inducible coactivator of the IRF proteins which contributes to the establishment of type I IFN responsiveness.
The adenovirus E1B 55-kDa protein binds to cellular tumor suppressor p53 and inactivates its transcriptional transactivation function. p53 transactivation activity is dependent upon its ability to bind to specific DNA sequences near the promoters of its target genes. It was shown recently that p53 is acetylated by transcriptional coactivators p300, CREB bidning protein (CBP), and PCAF and that acetylation of p53 by these proteins enhances p53 sequence-specific DNA binding. Here we show that the E1B 55-kDa protein specifically inhibits p53 acetylation by PCAF in vivo and in vitro, while acetylation of histones and PCAF autoacetylation is not affected. Furthermore, the DNA-binding activity of p53 is diminished in cells expressing the E1B 55-kDa protein. PCAF binds to the E1B 55-kDa protein and to a region near the C terminus of p53 encompassing Lys-320, the specific PCAF acetylation site. We further show that the E1B 55-kDa protein interferes with the physical interaction between PCAF and p53, suggesting that the E1B 55-kDa protein inhibits PCAF acetylase function on p53 by preventing enzyme-substrate interaction. These results underscore the importance of p53 acetylation for its function and suggest that inhibition of p53 acetylation by viral oncoproteins prevent its activation, thereby contributing to viral transformation.
Androgen receptor (AR) signalling is critical to the initiation and progression of prostate cancer (PCa). Transcriptional activity of AR involves chromatin recruitment of co-activators, including the p300/CBP-associated factor (PCAF). Distinct miRNA expression profiles have been identified in PCa cells during the development and progression of the disease. Whether miRNAs regulate PCAF expression in PCa cells to regulate AR transcriptional activity is still unclear.
Expression of PCAF was investigated in several PCa cell lines by qRT-PCR, Western blot, and immunocytochemistry. The effects of PCAF expression on AR-regulated transcriptional activity and cell growth in PCa cells were determined by chromatin immunoprecipitation, reporter gene construct analysis, and MTS assay. Targeting of PCAF by miR-17-5p was evaluated using the luciferase reporter assay.
PCAF was upregulated in several PCa cell lines. Upregulation of PCAF promoted AR transcriptional activation and cell growth in cultured PCa cells. Expression of PCAF in PCa cells was associated with the downregulation of miR-17-5p. Targeting of the 3’-untranslated region of PCAF mRNA by miR-17-5p caused translational suppression and RNA degradation, and, consequently, modulation of AR transcriptional activity in PCa cells.
PCAF is upregulated in cultured PCa cells, and upregulation of PCAF is associated with the downregulation of miR-17-5p. Targeting of PCAF by miR-17-5p modulates AR transcriptional activity and cell growth in cultured PCa cells.