Rogers Richard S, Horvath Curt M, Matunis Michael J
Johns Hopkins University, Bloomberg School of Public Health, Department of Biochemistry and Molecular Biology, Baltimore, Maryland 21205, USA.
J Biol Chem. 2003 Aug 8;278(32):30091-7. doi: 10.1074/jbc.M301344200. Epub 2003 May 22.
The PIAS (protein inhibitors of activated STAT) family of proteins were first discovered as inhibitors of activated signal transducers and activators of transcription (STATs). More recently these proteins have been shown to function as E3 ligases that promote the SUMO modification of a number of transcription regulators. We have investigated the relationship between the effects of PIAS proteins on STAT1 transcriptional activity and the ability of the PIAS proteins to function as SUMO E3 ligases. We demonstrate that STAT1 is a substrate for SUMO modification and that PIASx-alpha, but not PIAS1, functions as an E3 ligase to promote STAT1 modification. In addition, we have mapped the major site for SUMO modification on STAT1 to lysine 703. This lysine residue is in close proximity to the regulatory tyrosine residue at position 701, whose phosphorylation mediates STAT1 activation in response to cytokine signaling. Mutation of lysine 703 to arginine abolishes SUMO modification of STAT1 both in vitro and in vivo. However, this mutation does not affect the activation of STAT1 or the ability of either PIAS1 or PIASx-alpha to function as an inhibitor of STAT1-mediated transcription activation. Our findings demonstrate that inhibition of STAT1 by PIAS proteins does not require SUMO modification of STAT1 itself. SUMO modification of STAT1 may nonetheless be functionally important given the close proximity between the SUMO modification site and tyrosine 701.
PIAS（活化STAT的蛋白抑制剂）蛋白家族最初被发现是活化的信号转导子和转录激活子（STATs）的抑制剂。最近，这些蛋白已被证明可作为E3连接酶，促进许多转录调节因子的SUMO修饰。我们研究了PIAS蛋白对STAT1转录活性的影响与PIAS蛋白作为SUMO E3连接酶发挥功能的能力之间的关系。我们证明STAT1是SUMO修饰的底物，并且PIASx-α而非PIAS1作为E3连接酶促进STAT1修饰。此外，我们已将STAT1上SUMO修饰的主要位点定位到赖氨酸703。该赖氨酸残基紧邻701位的调节性酪氨酸残基，其磷酸化介导STAT1响应细胞因子信号传导而激活。将赖氨酸703突变为精氨酸会在体外和体内消除STAT1的SUMO修饰。然而，这种突变并不影响STAT1的激活或PIAS1和PIASx-α作为STAT1介导的转录激活抑制剂的功能。我们的研究结果表明，PIAS蛋白对STAT1的抑制作用并不需要STAT1自身的SUMO修饰。鉴于SUMO修饰位点与酪氨酸701之间的紧密相邻关系，STAT1的SUMO修饰在功能上可能仍然很重要。
