ten Hoeve Johanna, de Jesus Ibarra-Sanchez Maria, Fu Yubin, Zhu Wei, Tremblay Michel, David Michael, Shuai Ke
Department of Medicine, University of California-Los Angeles, Los Angeles, California 90095, USA.
Mol Cell Biol. 2002 Aug;22(16):5662-8. doi: 10.1128/MCB.22.16.5662-5668.2002.
Upon interferon (IFN) stimulation, Stat1 becomes tyrosine phosphorylated and translocates into the nucleus, where it binds to DNA to activate transcription. The activity of Stat1 is dependent on tyrosine phosphorylation, and its inactivation in the nucleus is accomplished by a previously unknown protein tyrosine phosphatase (PTP). We have now purified a Stat1 PTP activity from HeLa cell nuclear extract and identified it as TC45, the nuclear isoform of the T-cell PTP (TC-PTP). TC45 can dephosphorylate Stat1 both in vitro and in vivo. Nuclear extracts lacking TC45 fail to dephosphorylate Stat1. Furthermore, the dephosphorylation of IFN-induced tyrosine-phosphorylated Stat1 is defective in TC-PTP-null mouse embryonic fibroblasts (MEFs) and primary thymocytes. Reconstitution of TC-PTP-null MEFs with TC45, but not the endoplasmic reticulum (ER)-associated isoform TC48, rescues the defect in Stat1 dephosphorylation. The dephosphorylation of Stat3, but not Stat5 or Stat6, is also affected in TC-PTP-null cells. Our results identify TC45 as a PTP responsible for the dephosphorylation of Stat1 in the nucleus.
在干扰素（IFN）刺激下，Stat1发生酪氨酸磷酸化并转位进入细胞核，在细胞核中它与DNA结合以激活转录。Stat1的活性依赖于酪氨酸磷酸化，其在细胞核中的失活是由一种先前未知的蛋白酪氨酸磷酸酶（PTP）完成的。我们现在已经从HeLa细胞核提取物中纯化出一种Stat1 PTP活性，并将其鉴定为TC45，即T细胞PTP（TC-PTP）的核异构体。TC45在体外和体内均可使Stat1去磷酸化。缺乏TC45的核提取物无法使Stat1去磷酸化。此外，在缺乏TC-PTP的小鼠胚胎成纤维细胞（MEF）和原代胸腺细胞中，IFN诱导的酪氨酸磷酸化Stat1的去磷酸化存在缺陷。用TC45而非内质网（ER）相关异构体TC48重建缺乏TC-PTP的MEF可挽救Stat1去磷酸化的缺陷。在缺乏TC-PTP的细胞中，Stat3的去磷酸化也受到影响，但Stat5或Stat6不受影响。我们的结果表明TC45是一种负责细胞核中Stat1去磷酸化的PTP。
