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

The novel PIAS-like protein hZimp10 is a transcriptional co-activator of the p53 tumor suppressor

The tumor suppressor, p53, plays critical roles in the cell cycle progression, DNA repair and apoptosis. The PIAS proteins (protein inhibitor of activated STAT) were originally identified as inhibitors of the JAK-STAT pathway. Subsequently, crosstalk between the PIAS proteins and other signaling pathways has been shown to be involved in various cellular processes. Particularly, previous studies have demonstrated that PIAS proteins regulate p53-mediated transcription through sumoylation. hZimp10, also named zmiz1, is a novel PIAS-like protein and functions as a transcriptional co-activator. We recently identified p53 to be an hZimp10 interacting protein in the yeast two-hybrid screen. The interaction between p53 and hZimp10 was confirmed by GST pull-down and co-immunoprecipitation assays. Co-localization of p53 and hZimp10 proteins was also observed within cell nuclei by immunostaining. Moreover, we show that expression of exogenous hZimp10 enhances the transcriptional activity of p53 and knockdown of endogenous hZimp10 reduces the transcriptional activity of p53. Furthermore, using chromatin immunoprecipitation assays, we demonstrate that hZimp10 binds to p53 on the p21 promoter. Finally, p53-mediated transcription is significantly impaired in Zimp10 null embryonic fibroblasts. Taken together, these results provide the first line of evidence to demonstrate a role for Zimp10 in regulating p53 function

A promoting role of androgen receptor in androgen-sensitive and -insensitive prostate cancer cells

Although the vital role of the androgen receptor (AR) has been well demonstrated in primary prostate cancers, its role in the androgen-insensitive prostate cancers still remains unclear. Here, we used a small hairpin RNA approach to directly assess AR activity in prostate cancer cells. Reduction of AR expression in the two androgen-sensitive prostate cancer cell lines, LNCaP and LAPC4, significantly decreased AR-mediated transcription and cell growth. Intriguingly, in two androgen-insensitive prostate cell lines, LNCaP-C42B4 and CWR22Rv1, knockdown of AR expression showed a more pronounced effect on AR-induced transcription and cell growth than androgen depletion. Using cDNA microarrays, we also compared the transcriptional profiles induced by either androgen depletion or AR knockdown. Although a significant number of transcripts appear to be regulated by both androgen depletion and AR knockdown, we observed a subset of transcripts affected only by androgen depletion but not by AR knockdown, and vice versa. Finally, we demonstrated a direct role for AR in promoting tumor formation and growth in a xenograft model. Taken together, our results elucidate an important role for the AR in androgen-insensitive prostate cancer cells, and suggest that AR can be used as a therapeutic target for androgen-insensitive prostate cancers

Regulation of estrogen receptor function by molecular chaperones

The estrogen receptor (ER) plays a major role in breast cancer progression, and ER+ tumors respond favorably to hormonal manipulation. The selective estrogen receptor modulator (SERM) tamoxifen (Tam) induces remissions in most ER+ patients. However, acquired resistance is often observed. Tam-resistant breast cancer is sensitive to other antiestrogenic compounds, but resistance to these agents has also been described, illustrating a major limitation to antiestrogen therapy. Therefore, we investigated a ligand-independent approach for treating Tam-resistant breast cancer by targeting the molecular chaperone Hsp90. The ER exists in a multi-protein complex containing Hsp90, which regulates the activity and stability of the receptor. Hsp90 regulates the stability of other proteins relevant to breast cancer, including Akt and Raf-1. The benzoquinone ansamycin antibiotic geldanamycin (GA) and its clinically relevant analog, 17-demethoxy-17-allylaminogeldanamycin (17AAG), bind to Hsp90 and induce the degradation of Hsp90 clients. In these studies, we show that GA depletes ER levels in Tam-resistant cell lines, and the Hsp90 clients Akt and Raf-1. Unexpectedly, Tam inhibited GA-induced degradation of the ER, but not Akt and Raf-1. This effect was consistent in vivo, where ER levels were measured in tumor xenografts growing in Tam-supplemented mice. However, Tam-stimulated tumor growth was inhibited by 17AAG, and tumor Akt and Raf-1 levels were downregulated. Immunoprecipitation experiments showed that Tam does not inhibit GA-induced changes in the ER-chaperone complex, suggesting an alternate mechanism for the inhibition of GA-mediatied ER degradation. Through cell fractionation, immunostaining, and chromatin immunoprecipitation experiments, we have found that the mechanism involves prolonged association of the ER with the DNA in the presence of Tam, which leads to nuclear accumulation of the ER and sequestration from the proteasome. Furthermore, inhibition of GA-induced ER degradation was inhibited by another SERM, Raloxifene, indicating that the effect is not Tam-specific. Based on its ability to downregulate critical signaling proteins involved in breast cancer, including the ER, 17AAG may provide a useful alternative for patients that have failed hormonal therapy. Because SERMs inhibit the degradation of ER protein induced by GA, they may compromise the efficacy of GA on ER activity, and combined therapy should be approached with caution

The PIAS-Like Protein Zimp10 Is Essential for Embryonic Viability and Proper Vascular Development▿

Members of the PIAS (for protein inhibitor of activated STAT) family play critical roles in modulating the activity of a variety of transcriptional regulators. Zimp10, a novel PIAS-like protein, is a transcriptional coregulator and may be involved in the modification of chromatin through interactions with the SWI/SNF chromatin-remodeling complexes. Here, we investigate the biological role of Zimp10 in zimp10-deficient mice. Homozygosity for the Zimp10-targeted allele resulted in developmental arrest at approximately embryonic day 10.5. Analysis of knockout embryos revealed severe defects in the reorganization of the yolk sac vascular plexus. No significant abnormality in hematopoietic potential was observed in zimp10 null mice. Microarray and quantified reverse transcription-PCR analyses showed that the expression of the Fos family member Fra-1, which is involved in extraembryonic vascular development, was reduced in yolk sac tissues of zimp10 null embryos. Using fra-1 promoter/reporter constructs, we further demonstrate the regulatory role of Zimp10 on the transcription of Fra-1. This study provides evidence to demonstrate a crucial role for Zimp10 in vasculogenesis