Protein Inhibitor Of Activated STAT Research Articles

PIAS3 Interacts with ATF1 and Regulates the Human Ferritin H Gene through an Antioxidant-responsive Element

Gene transcription is coordinately regulated by the balance between activation and repression mechanisms in response to various external stimuli. Ferritin, composed of H and L subunits, is the major intracellular iron storage protein involved in iron homeostasis. We previously identified an enhancer, termed antioxidant-responsive element (ARE), in the human ferritin H gene and its respective transcriptional activators including Nrf2 and JunD. Here we found that ATF1 (activating transcription factor 1) is a transcriptional repressor of the ferritin H ARE. Subsequent yeast two-hybrid screening identified PIAS3 (protein inhibitor of activated STAT3) as an ATF1-binding protein. Further investigation of the human ferritin H ARE regulation showed that 1) PIAS3 reversed ATF1-mediated repression of the ferritin H ARE; 2) ATF1 was sumoylated, but PIAS3, a SUMO E3 ligase, did not appear to play a major role in SUMO1-mediated ATF1 sumoylation or ATF1 transcription activating function; 3) PIAS3 decreased ATF1 binding to the ARE; and 4) ATF1 knockdown with siRNA increased ferritin H expression, whereas PIAS3 knockdown decreased basal expression and oxidative stress-mediated induction of ferritin H. These results suggest that PIAS3 antagonizes the repressor function of ATF1, at least in part by blocking its DNA binding, and ultimately activates the ARE. Collectively our results suggest that PIAS3 is a new regulator of ATF1 that regulates the ARE-mediated transcription of the ferritin H gene.

PIAS1 interacts with the KRAB zinc finger protein, ZNF133, via zinc finger motifs and regulates its transcriptional activity

Zinc finger protein 133 (ZNF133) is composed of a Krüppel-associated box (KRAB) domain and 14 contiguous zinc finger motifs. ZNF133 is regarded as a transcriptional repressor because the KRAB domain has potent repressor activity and the zinc finger motifs usually act in binding to DNA. However, we found that the zinc finger motifs of ZNF133 also possessed transcriptional repressor activity. By two-hybrid screening assay, we found that the zinc finger motifs of ZNF133 interacted with protein inhibitor of activated STAT1 (PIAS1). PIAS1 enhanced the transcriptional repression activity of ZNF133 through the zinc finger motifs. This effect of PIAS1 was relieved by an inhibitor of the histone deacetylases (HDACs). These results demonstrate that the transcriptional repressor activity of ZNF133 is regulated by both the KRAB domain and the zinc finger motifs, and that the repressive effect by zinc finger motifs is mediated by PIAS1.

Control of specificity and magnitude of NF-κB and STAT1-mediated gene activation through PIASy and PIAS1 cooperation

NF-kappaB and STATs regulate multiple cellular processes through the transcriptional activation of genes with diversified functions. Although the molecular mechanisms that can turn on/off the overall NF-kappaB/STAT signaling have been extensively studied, how NF-kappaB/STAT-target genes can be differentially regulated is poorly understood. Here we report that PIASy, a member of the PIAS (for protein inhibitor of activated STAT) protein family, is a physiologically important transcriptional repressor of NF-kappaB and STAT1. Piasy deletion in dendritic cells resulted in enhanced expression of a subset of NF-kappaB and STAT1-dependent genes in response to LPS or IFN-gamma treatment, respectively. Consistently, Piasy null mice are hypersensitive to the LPS-induced endotoxic shock. Furthermore, PIASy and PIAS1 display specific as well as redundant effects on the regulation of NF-kappaB/STAT1 signaling. Pias1-/-Piasy-/- embryos died before day 11.5. The disruption of one allele of Pias1 in the Piasy-/- background significantly enhanced the effect of Piasy deletion on the transcriptional induction of NF-kappaB/STAT1-dependent genes, and vice versa. Our results demonstrate that PIASy cooperates with PIAS1 to regulate the specificity and magnitude of NF-kappaB/STAT1-mediated gene activation.

Proinflammatory Stimuli Induce IKKα-Mediated Phosphorylation of PIAS1 to Restrict Inflammation and Immunity

How inflammatory stimuli signal to the nucleus to restrict inflammation is poorly understood. Protein inhibitor of activated STAT1 (PIAS1), a transcriptional regulator that possesses small ubiquitin-related modifier (SUMO) E3 ligase activity, inhibits immune responses by selectively blocking the binding of NF-kappaB and STAT1 to gene promoters. We report here that PIAS1 becomes rapidly phosphorylated on Ser90 residue in response to various inflammatory stimuli. Mutational studies indicate that Ser90 phosphorylation is required for PIAS1 to repress transcription. Upon TNF treatment, wild-type PIAS1, but not the Ser90A mutant, becomes rapidly associated with the promoters of NF-kappaB target genes. Furthermore, IKKalpha, but not IKKbeta, interacts with PIAS1 in vivo and mediates PIAS1 Ser90 phosphorylation, a process that requires the SUMO ligase activity of PIAS1. Our results identify a signaling pathway in which proinflammatory stimuli activate the IKKalpha-mediated sumoylation-dependent phosphorylation of PIAS1 for the immediate repression of inflammatory gene activation.

The Transcriptional Repression Activity of KyoT2 on the Notch/RBP-J Pathway Is Regulated by PIAS1-catalyzed SUMOylation

The LIM domain protein KyoT2 negatively regulates the Notch signaling pathway through interaction with RBP-J, the core element of the Notch signaling pathway in the nucleus. Here we show that PIAS1 (the protein inhibitor of activated STAT1) interacts with KyoT2 directly and attenuates KyoT2-mediated transcriptional repression. We demonstrate that KyoT2 is modified by SUMOylation at two lysine residues, K144 and K171. SUMOylation of the transfected KyoT2 is enhanced by PIAS1 but not hPc2, another KyoT2-interacting protein with SUMO E3 ligase activity, and is repressed by a PIAS1 mutant that is deficient of E3 ligase activity. Using mutants disrupting either or both of the SUMO sites, we show that SUMOylation of KyoT2 does not influence its expression, intracellular localization, or interaction with known partners. However, disruption of the K171 SUMOylation site does reinforce the transcriptional repression activity of KyoT2, suggesting that SUMOylation of this site counters the repression activity of KyoT2. Finally, we show that PIAS1 fails to attenuate the repression activity of the K171R mutant of KyoT2, suggesting that PIAS1 may potentially antagonize the transcriptional repression activity of KyoT2 through catalyzing its SUMOylation at K171. These results suggest that KyoT2 is a substrate of SUMO modification catalyzed by PIAS1, and that SUMOylation may modulate the transcriptional repression effect of KyoT2 on the Notch/RBP-J signaling pathway.

Protein Inhibitor of Activated STAT1 Interacts with and Up-regulates Activities of the Pro-proliferative Transcription Factor Krüppel-like Factor 5

Krüppel-like factor 5 (KLF5) is a zinc finger-containing transcription factor that regulates proliferation of various cell types, including fibroblasts, smooth muscle cells, and intestinal epithelial cells. To identify proteins that interact with KLF5, we performed a yeast two-hybrid screen of a 17-day mouse embryo cDNA library with KLF5 as bait. The screen revealed 21 preys clustered in four groups as follows: proteins mediating gene expression, metabolism, trafficking, and signaling. Among them was protein inhibitor of activated STAT1 (PIAS1), a small ubiquitin-like modifier (SUMO) ligase that regulates transcription factors through SUMOylation or physical interaction. Association between PIAS1 and KLF5 was verified by co-immunoprecipitation. Structural determination showed that the acidic domain of PIAS1 bound to both the amino- and carboxyl-terminal regions of KLF5 and that this interaction was inhibited by the amino terminus of PIAS1. Indirect immunofluorescence demonstrated that PIAS1 and KLF5 co-localized to the nucleus. Furthermore, the PIAS1-KLF5 complex was co-localized with the TATA-binding protein and was enriched in RNA polymerase II foci. Transient transfection of COS-7 cells by PIAS1 and KLF5 significantly increased the steady-state protein levels of each other. Luciferase reporter and chromatin immunoprecipitation assays showed that PIAS1 significantly activated the promoters of KLF5 and PIAS1 and synergistically increased the transcriptional activity of KLF5 in activating the cyclin D1 and Cdc2 promoters. Importantly, PIAS1 increased the ability of KLF5 to enhance cell proliferation in transfected cells. These results indicate that PIAS1 is a functional partner of KLF5 and enhances the ability of KLF5 to promote proliferation.

Regulation of protein tyrosine phosphatase 1B by sumoylation

Protein-tyrosine phosphatase 1B (PTP1B) is an ubiquitously expressed enzyme that negatively regulates growth-factor signalling and cell proliferation by binding to and dephosphorylating key receptor tyrosine kinases, such as the insulin receptor. It is unclear how the activity of PTP1B is regulated. Using a yeast two-hybrid assay, a protein inhibitor of activated STAT1 (PIAS1) was isolated as a PTP1B-interacting protein. Here, we show that PIAS1, which functions as a small ubiquitin-like modifier (SUMO) E3 ligase, associates with PTP1B in mammalian fibroblasts and catalyses sumoylation of PTP1B. Sumoylation of PTP1B reduces its catalytic activity and inhibits the negative effect of PTP1B on insulin receptor signalling and on transformation by the oncogene v-crk. Insulin-stimulated sumoylation of endogenous PTP1B results in a transient downregulation of the enzyme; this event does not occur when the endogenous enzyme is replaced with a sumoylation-resistant mutant of PTP1B. These results suggest that sumoylation, which has been implicated primarily in processes in the nucleus and nuclear pore, also modulates a key enzyme-substrate signalling complex that regulates metabolism and cell proliferation.

Regulation of the SUMO pathway sensitizes differentiating human endometrial stromal cells to progesterone

cAMP is required for differentiation of human endometrial stromal cells (HESCs) into decidual cells in response to progesterone, although the underlying mechanism is not well understood. We now demonstrate that cAMP signaling attenuates ligand-dependent sumoylation of the progesterone receptor (PR) in HESCs. In fact, decidualization is associated with global hyposumoylation and redistribution of small ubiquitin-like modifier (SUMO)-1 conjugates into distinct nuclear foci. This altered pattern of global sumoylation was not attributable to impaired maturation of SUMO-1 precursor or altered expression of E1 (SAE1/SEA2) or E2 (Ubc9) enzymes but coincided with profound changes in the expression of E3 ligases and SUMO-specific proteases. Down-regulation of several members of the protein inhibitors of activated STAT (PIAS) family upon decidualization pointed toward a role of these E3 ligases in PR sumoylation. We demonstrate that PIAS1 interacts with the PR and serves as its E3 SUMO ligase upon activation of the receptor. Furthermore, we show that silencing of PIAS1 not only enhances PR-dependent transcription but also induces expression of prolactin, a decidual marker gene, in progestin-treated HESCs without the need of simultaneous activation of the cAMP pathway. Our findings demonstrate how dynamic changes in the SUMO pathway mediated by cAMP signaling determine the endometrial response to progesterone.

Signalling pathways mediating inflammatory responses in brain ischaemia

Stroke causes neuronal necrosis and generates inflammation. Pro-inflammatory molecules intervene in this process by triggering glial cell activation and leucocyte infiltration to the injured tissue. Cytokines are major mediators of the inflammatory response. Pro-inflammatory and anti-inflammatory cytokines are released in the ischaemic brain. Anti-inflammatory cytokines, such as interleukin-10, promote cell survival, whereas pro-inflammatory cytokines, such as TNFalpha (tumour necrosis factor alpha), can induce cell death. However, deleterious effects of certain cytokines can turn to beneficial actions, depending on particular features such as the concentration, time point and the very intricate network of intracellular signals that become activated and interact. A key player in the intracellular response to cytokines is the JAK (Janus kinase)/STAT (signal transducer and activator of transcription) pathway that induces alterations in the pattern of gene transcription. These changes are associated either with cell death or survival depending, among other things, on the specific proteins involved. STAT1 activation is related to cell death, whereas STAT3 activation is often associated with survival. Yet, it is clear that STAT activation must be tightly controlled, and for this reason the function of JAK/STAT modulators, such as SOCS (suppressors of cytokine signalling) and PIAS (protein inhibitor of activated STAT), and phosphatases is most relevant. Besides local effects in the ischaemic brain, cytokines are released to the circulation and affect the immune system. Unbalanced pro-inflammatory and anti-inflammatory plasma cytokine concentrations favouring an 'anti-inflammatory' state can decrease the immune response. Robust evidence now supports that stroke can induce an immunodepression syndrome, increasing the risk of infection. The contribution of individual cytokines and their intracellular signalling pathways to this response needs to be further investigated.

PIAS3 induction of PRB sumoylation represses PRB transactivation by destabilizing its retention in the nucleus

Progesterone receptor (PR) plays a critical role in cell proliferation and differentiation, and its transcriptional activity is known to be modulated by cofactor proteins. In the present study, we demonstrated that in the presence of progesterone, protein inhibitor of activated STAT-3 (PIAS3) significantly inhibited the PR transcriptional activity and the expression of progesterone-responsive genes. Reduction of endogenous PIAS3 by PIAS3 small-interfering RNA enhanced PR transactivation in a ligand-dependent manner. PIAS3 interacted with PR both in vitro and in vivo and the interaction was enhanced by progesterone. Furthermore, our findings suggested that PIAS3 strongly induced PRB sumoylation at three sites, Lys-7, Lys-388 and Lys-531. In addition, novel roles in PRB nuclear retention and transactivation were identified for these sites. Our data also suggested that PIAS3 was recruited in a largely hormone-dependent manner in response to a progesterone-responsive promoter. Finally, we demonstrated that PIAS3 inhibited the DNA-binding activity of PR and influenced its nuclear export as well as PR transactivation. Taken together, these data strongly suggested that PIAS3 played an important physiological role in PR function.

Phosphorylation-Dependent Control of Pc2 SUMO E3 Ligase Activity by Its Substrate Protein HIPK2

Sumoylation serves to control key cellular functions, but the regulation of SUMO E3 ligase activity is largely unknown. Here we show that the polycomb group protein Pc2 binds to and colocalizes with homeodomain interacting protein kinase 2 (HIPK2) and serves as a SUMO E3 ligase for this kinase. DNA damage-induced HIPK2 directly phosphorylates Pc2 at multiple sites, which in turn controls Pc2 sumoylation and intranuclear localization. Inducible phosphorylation of Pc2 at threonine 495 is required for its ability to increase HIPK2 sumoylation in response to DNA damage, thereby establishing an autoregulatory feedback loop between a SUMO substrate and its cognate E3 ligase. Sumoylation enhances the ability of HIPK2 to mediate transcriptional repression, thus providing a mechanistic link for DNA damage-induced transcriptional silencing.

The Interaction of Piasy with Trim32, an E3-Ubiquitin Ligase Mutated in Limb-girdle Muscular Dystrophy Type 2H, Promotes Piasy Degradation and Regulates UVB-induced Keratinocyte Apoptosis through NFκB

Protein inhibitors of activated STATs (PIAS) family members are ubiquitin-protein isopeptide ligase-small ubiquitin-like modifier ligases for diverse transcription factors. However, the regulation of PIAS protein activity in cells is poorly understood. Previously, we reported that expression of Trim32, a RING domain ubiquitin-protein isopeptide ligase-ubiquitin ligase mutated in human limb-girdle muscular dystrophy type 2H (LGMD2H) and Bardet-Biedl syndrome, is elevated during mouse skin carcinogenesis, protecting keratinocytes from apoptosis induced by UVB and tumor necrosis factor-alpha (TNFalpha). Here we report that Trim32 interacts with Piasy and promotes Piasy ubiquitination and degradation. Ubiquitination of Piasy by Trim32 could be reproduced in vitro using purified components. Their interaction was induced by treatment with UVB/TNFalpha and involved redistribution of Piasy from the nucleus to the cytoplasm, where it accumulated in cytoplasmic granules that colocalized with Trim32. Piasy destabilization and ubiquitination required an intact RING domain in Trim32. The LGMD2H-associated missense point mutation prevented Trim32 binding to Piasy, and human Piasy failed to colocalize with human Trim32 in fibroblasts isolated from an LGMD2H patient. Trim32 expression increased the transcriptional activity of NFkappaB in epidermal keratinocytes, both under basal treatment and after UVB/TNFalpha treatment. Conversely, Piasy inhibited NFkappaB activity under the same conditions and sensitized keratinocytes to apoptosis induced by TNFalpha and UVB. Our results indicate that, by controlling Piasy stability, Trim32 regulates UVB-induced keratinocyte apoptosis through induction of NFkappaB and suggests loss of function of Trim32 in LGMD2H.

The Novel PIAS-like Protein hZimp10 Enhances Smad Transcriptional Activity

Transforming growth factor beta (TGF-beta) plays critical roles in the control of cell proliferation, differentiation, and apoptosis. Smad proteins are substrates of the TGF-beta type I receptor and are responsible for transducing receptor signals to target genes in the nucleus. The PIAS (protein inhibitor of activated STAT) proteins were originally identified as transcriptional co-regulators of the JAK-STAT pathway. Subsequently, cross-talk between the PIAS proteins and other signaling pathways has been shown to be involved in various cellular processes. Importantly, PIAS proteins modulate TGF-beta signaling by regulating the transcriptional activity of Smad3. In this study we tested whether hZimp10, a novel PIAS-like protein, acts as other PIAS proteins to regulate Smad3-mediated transcription. We show that expression of exogenous hZimp10 enhances the transcriptional activity of Smad3, which appears to be Smad4-dependent and responsive to TGF-beta induction. Furthermore, knockdown of endogenous hZimp10 reduced the transcriptional activity of Smad3. A protein-protein interaction between Smad3 and Smad4 with hZimp10 was identified in glutathione S-transferase-pulldown and co-immunoprecipitation assays. The Miz domain of hZimp10 and the MH2 domains of Smad3 and Smad4 were mapped as the regions responsible for binding. Results from immunostaining assays further demonstrated that Smad3, Smad4, and hZimp10 co-localize within cell nuclei. Finally, we demonstrated that Smad3/4-mediated transcription is significantly impaired in response to TGF-beta induction in Zimp10 null (zimp10-/-) embryonic fibroblasts. Taken together, these results provide the first line of evidence to demonstrate a role for Zimp10 in regulating the TGF-beta/Smad signaling pathway.

Interaction of Protein Inhibitor of Activated STAT (PIAS) Proteins with the TATA-binding Protein, TBP

Transcription activators often recruit promoter-targeted assembly of a pre-initiation complex; many repressors antagonize recruitment. These activities can involve direct interactions with proteins in the pre-initiation complex. We used an optimized yeast two-hybrid system to screen mouse pregnancy-associated libraries for proteins that interact with TATA-binding protein (TBP). Screens revealed an interaction between TBP and a single member of the zinc finger family of transcription factors, ZFP523. Two members of the protein inhibitor of activated STAT (PIAS) family, PIAS1 and PIAS3, also interacted with TBP in screens. Endogenous PIAS1 and TBP co-immunoprecipitated from nuclear extracts, suggesting the interaction occurred in vivo. In vitro-translated PIAS1 and TBP co-immunoprecipitated, which indicated that other nuclear proteins were not required for the interaction. Deletion analysis mapped the PIAS-interacting domain of TBP to the conserved TBP(CORE) and the TBP-interacting domain on PIAS1 to a 39-amino acid C-terminal region. Mammals issue seven known PIAS proteins from four pias genes, pias1, pias3, piasx, and piasy, each with different cell type-specific expression patterns; the TBP-interacting domain reported here is the only part of the PIAS C-terminal region shared by all seven PIAS proteins. Direct analyses indicated that PIASx and PIASy also interacted with TBP. Our results suggest that all PIAS proteins might mediate situation-specific regulatory signaling at the TBP interface and that previously unknown levels of complexity could exist in the gene regulatory interplay between TBP, PIAS proteins, ZFP523, and other transcription factors.

S‐adenosylmethionine and betaine correct hepatitis C virus induced inhibition of interferon signaling in vitro†

Hepatitis C virus (HCV) infection is an important cause of chronic liver disease. Standard therapy, pegylated interferon alpha (pegIFNalpha) combined with ribavirin, results in a sustained response rate in approximately half of patients. The cause of treatment failure in the other half of the patients is unknown, but viral interference with IFNalpha signal transduction through the Jak-STAT pathway might be an important factor. We have shown previously that the expression of HCV proteins leads to an impairment of Jak-STAT signaling because of an inhibition of STAT1 methylation. Unmethylated STAT1 is less active because it can be bound and inactivated by its inhibitor, protein inhibitor of activated STAT1 (PIAS1). We show that treating cells with S-adenosyl-L-methionine (AdoMet) and betaine could restore STAT1 methylation and improve IFNalpha signaling. Furthermore, the antiviral effect of IFNalpha in cell culture could be significantly enhanced by the addition of AdoMet and betaine. In conclusion, we propose that the addition of these drugs to the standard therapy of patients with chronic hepatitis C could overcome treatment resistance.

Interactions between PIAS Proteins and SOX9 Result in an Increase in the Cellular Concentrations of SOX9

We have identified PIAS1 (protein inhibitor of activated STAT-1), -3, -xalpha, and -xbeta as SOX9-associated polypeptides using the Gal4-based yeast two-hybrid system and a cDNA library derived from a chondrocytic cell line. These PIAS proteins were shown to interact directly with SOX9 in two-hybrid, co-immunoprecipitation, and electrophoretic mobility shift assays. SOX9 was sumoylated in cotransfection experiments with COS-7 cells using PIAS and SUMO-1 (small ubiquitin-like modifier-1) expression vectors. SOX9 was also sumoylated in vitro by PIAS proteins in the presence of SUMO-1, the SUMO-activating enzyme, and the SUMO-conjugating enzyme. In COS-7 cells, PIAS proteins stimulated the SOX9-dependent transcriptional activity of a Col2a1 promoter-enhancer reporter. This increase in reporter activity was paralleled by an increase in the cellular levels of SOX9. Cotransfection with a SUMO-expressing vector further enhanced the transcriptional activity of this SOX9-dependent Col2a1 reporter in COS-7 cells, and this additional activation was inhibited in the presence of either SUMO-1 mutants or PIAS RING domain mutants or by coexpression of a desumoylation enzyme. Immunofluorescence microscopy of SOX9-transfected COS-7 cells showed that the subnuclear distribution of SOX9 became more diffuse in the presence of PIAS1 and SUMO-1. Our results suggest that, by controlling the cellular concentrations of SOX9, PIAS proteins and sumoylation may be part of a major regulatory system of SOX9 functions.

Regulation of cytokine signaling pathways by PIAS proteins

Cytokines activate multiple signal transduction pathways to regulate gene expression. STATs and NF-kB are two important families of transcription factors activated by cytokines. Abnormal regulation of STAT and NF-kB activities has been associated with human diseases. The protein inhibitor of activated STAT (PIAS) protein family has been proposed to interact with over 60 proteins, many of which are transcription factors involved in the immune system. PIAS proteins regulate transcription through several mechanisms, including blocking the DNA-binding activity of transcription factors, recruiting transcriptional co-repressors and promoting protein sumoylation. This article is to review the role of PIAS proteins in the regulation of STAT and NF-kB signaling pathways.

JAK/STAT signal transduction: Regulators and implication in hematological malignancies

Signal transducers and activators of transcription (STATs) comprise a family of several transcription factors that are activated by a variety of cytokines, hormones and growth factors. STATs are activated through tyrosine phosphorylation, mainly by JAK kinases, which lead to their dimerization, nuclear translocation and regulation of target genes expression. Stringent mechanisms of signal attenuation are essential for insuring appropriate, controlled cellular responses. Among them phosphotyrosine phosphatases (SHPs, CD45, PTP1B/TC-PTP), protein inhibitors of activated STATs (PIAS) and suppressors of cytokine signaling (SOCS) inhibit specific and distinct aspects of cytokine signal transduction. SOCS proteins bind through their SH2 domain to phosphotyrosine residues in either cytokine receptors or JAK and thus can suppress cytokine signaling. Many recent findings indicate that SOCS proteins act, in addition, as adaptors that regulate the turnover of certain substrates by interacting with and activating an E3 ubiquitin ligase. Thus, SOCS proteins act as negative regulators of JAK/STAT pathways and may represent tumour suppressor genes. The discovery of oncogenic partner in this signaling pathway, more especially in diverse hematologic malignancies support a prominent role of deregulated pathways in the pathogenesis of diseases. Fusion proteins implicating the JH1 domain of JAK2 ( TEL- JAK2, BCR- JAK2), leading to deregulated activity of JAK2, have been described as the result of translocation. Somatic point mutation in JH2 domain of JAK2 (JAK2 V617F), leading also to constitutive tyrosine phosphorylation of JAK2 and its downstream effectors was reported in myeloproliferative disorders. Furthermore, silencing of socs- 1 and shp- 1 expression by gene methylation is observed in some cancer cells.

Zimp7 and Zimp10, two novel PIAS-like proteins, function as androgen receptor coregulators

The androgen receptor (AR) plays a critical role in male sexual development and in normal and malignant prostate cell growth and survival. It has been shown that AR transcriptional activation is regulated through interactions with a variety of transcriptional co-regulators. The Protein Inhibitors of Activated STATs (PIAS) are transcriptional co-regulators, and have been shown to modulate AR-mediated transcription. In this brief, we summarize our recent studies on two novel PIAS-like proteins, Zimp7 and Zimp10. Particularly, we address the functional interactions between the AR and these two proteins, and potential mechanisms by which they regulate AR mediated transcription. In addition, we explore potential roles of Zimp10 in transcriptional regulation in vivo using a recent Zimp10 knockout mouse model. Taken together, our findings thus far suggest that Zimp7 and Zimp10 are functionally non-redundant and share unique characteristics that have not been described for the PIAS family. Further investigation into the functional roles of these two PIAS-like proteins may help to better understand prostate cancer progression, and yield possible new targets for therapeutic intervention.

Protein inhibitor of activated STAT3 inhibits adipogenic gene expression

Protein inhibitor of activated STAT3 (PIAS3), a cytokine-induced repressor of signal transducer and activator of transcription 3 (STAT3) and a modulator of a broad array of nuclear proteins, is expressed in white adipose tissue, but its role in adipogenesis is not known. Here, we determined that PIAS3 was constitutively expressed in 3T3-L1 cells at all stages of adipogenesis. However, it translocated from the nucleus to the cytoplasm 4 days after induction of differentiation by isobutylmethylxanthine, dexamethasone, and insulin (MDI). In ob/ ob mice, PIAS3 expression was increased in white adipose tissue depots compared to lean mice and was found in the cytoplasm of adipocytes. Overexpression of PIAS3 in differentiating preadipocytes, which localized primarily to the nucleus, inhibited mRNA level gene expression of adipogenic transcription factors C/EBPα and PPARγ, as well as their downstream target genes aP2 and adiponectin. PIAS3 also inhibited C/EBPα promoter activation mediated specifically by insulin, but not dexamethasone or isobutylmethylxanthine. Taken together, these data suggest that PIAS3 may play an inhibitory role in adipogenesis by modulating insulin-activated transcriptional activation events. Increased PIAS3 expression in adipose tissue may play a role in the metabolic disturbances of obesity.