Protein inhibitor of activated STAT y (PIASy) in androgen receptor signaling and prostate cancer

The goal of these studies is to characterize the function of PIASy in androgen receptor signaling and prostate cancer. The effects of the PIAS proteins on androgen receptor (AR) signaling is described. PIAS1, PIAS3, and PIASy are widely expressed in human tissues including testis and prostate. In addition, PIAS proteins are found in the nuclear fraction of prostate cancer cells. Reporter studies show that PIAS1 and PIAS3 activate, while PIASy inhibits, androgen signaling. PIASy interacts with the AR DNA-binding domain (DBD), but does not affect the DNA-binding activity of AR DBD dimers. Inspection of the coding sequence for PIASy identifies an LXXLL that is required for PIASy to inhibit AR signaling. These results suggest a role for PIAS proteins in regulating the transcriptional activity of AR.; We next characterized the activity of PIASy in Stat1 signaling. PIASy interacts with activated Stat1and represses Stat1-mediated signaling. PIASy does not inhibit the DNA-binding activity of Stat1. Rather, a ternary complex is observed which contains PIASy, activated Stat1, and a Stat1-response element. Lastly, we show that the LXXLL motif in PIASy is required for repression of Stat1 similar to the requirement for this motif in AR inhibition.; Subsequent studies were performed to better define the mechanism of PIASy-mediated AR repression. We confirm that PIASy directly interacts with AR and demonstrate that the Ring-finger like domain mediates the PIASy-AR interaction. We identify two distinct repression domains in PIASy named RD1 and RD2. We show that RD1, but not RD2, is required for PIASy-mediated AR repression. We show that PIASy physically interacts with HDAC2, suggesting a role for PIASy in the function of HDAC containing repressor complexes. PIAS family members, including PIASy, have been shown to promote the sumoylation of many target proteins and sumoylation acceptor sites have been mapped in AR. We show that mutations that abolish the Sumo-ligase activity of PIASy and sumoylation acceptor sites in AR do not affect the ability of PIASy to inhibit AR signaling. Our data suggests that sumoylation is not directly involved in the repression of AR by PIASy.