The Function And Interaction Of Protein Inhibitor Of Activated STAT3 (PIAS3) With Progesterone Receptor B

The steroid hormone, progesterone, plays key roles in normal reproductive functions(1) .The physiological effects of progesterone are mediated by interaction of the hormone with specific intracellular progesterone receptors (PRs) ,expressed as two protein forms ,PR-A and PR-B. The progesterone receptors are members of a large family of structurally related gene products known as the nuclear receptor (NR) superfamily, which are ligand-activated nuclear transcription regulators(2). The exactly discrimination of two forms of PR is that PR-B contains an additional 164 N-terminal amino acids in the B upstream segment (BUS)(3).The transcriptional regulation of PR and other nuclear receptors has been linked to protein post-translational covalent modifications,which alters protein structure on protein-protein interactions. This modification contains protein phosphorylation (4) ,acetylation (5), ubiquitylation(6),and sumoylation(7). Sumoylation, involves covalent binding of the SUMO (small ubiquitin-like modifier) protein.. Several important transcription factors, such as GR, androgen receptors (AR), p53, c-Jun, and c-Myb are covalently modified by SUMO-1. Like ubiquitylation, sumoylation uses a battery of activating (El), conjugating (E2), and ligating (E3) enzymes for covalent attachment. Sumoylation modifies their functional properties: subcellular localization, stability, or ability to regulate gene transcription(8).In this study, when we observed the subcellular localization of PRB by the laser scanning confocal microscopy(LSCM), we found that most of PRB located in the cytoplasm with PIAS3 cotransfected in spite of the presence of progesterone,suggested that there may be some functional interaction between PRB and PIAS3. We then successfully set up a luciferase reporter system in 293T cells for analyse PRB transcriptional activity, luciferase assays showed that PIAS3 could repressed PR-dependent transcription in a progesterone-dependent manner.To test whether there is physical interaction between PRB and PIAS3, we constructed two yeast expression vectors for the two protein respectively. By following yeast two-hybrid method, we...