Kazansky A V, Kabotyanski E B, Wyszomierski S L, Mancini M A, Rosen J M
Department of Cell Biology, Baylor College of Medicine, Houston, Texas 77030-3498, USA.
J Biol Chem. 1999 Aug 6;274(32):22484-92. doi: 10.1074/jbc.274.32.22484.
In this study, DNA binding and tyrosine phosphorylation of STAT5A and STAT5B were compared with their subcellular localization determined using indirect immunofluorescence microscopy. Following prolactin activation, both STAT5A and STAT5B were rapidly translocated into the nucleus and displayed a detergent-resistant, punctate nuclear staining pattern. Similar to prolactin induction, src activation resulted in tyrosine phosphorylation and DNA binding of both STAT5A and STAT5B. However, nuclear translocation of only STAT5B but not STAT5A was observed. This selective nuclear translocation appears to be mediated via the carboxyl-terminal sequences in STAT5B. Furthermore, overexpression of a dominant negative kinase-inactive mutant of JAK2 prevented prolactin-induced tyrosine phosphorylation and nuclear translocation of STAT5A and STAT5B but did not block src kinase activation and nuclear translocation of STAT5B. In co-transfection assays, prolactin-mediated activation but not src kinase-mediated activation of STAT5B resulted in the induction of a beta-casein promoter-driven reporter construct. These results suggest that STAT5 activation by src may occur by a mechanism distinct from that employed in cytokine activation of the JAK/STAT pathway, resulting in the selective nuclear translocation of STAT5B.
在本研究中，将STAT5A和STAT5B的DNA结合及酪氨酸磷酸化与其通过间接免疫荧光显微镜确定的亚细胞定位进行了比较。催乳素激活后，STAT5A和STAT5B均迅速转位至细胞核，并呈现出耐去污剂的点状核染色模式。与催乳素诱导相似，src激活导致STAT5A和STAT5B的酪氨酸磷酸化及DNA结合。然而，仅观察到STAT5B而非STAT5A的核转位。这种选择性核转位似乎是通过STAT5B中的羧基末端序列介导的。此外，JAK2的显性负性激酶失活突变体的过表达可阻止催乳素诱导的STAT5A和STAT5B的酪氨酸磷酸化及核转位，但不阻断src激酶激活及STAT5B的核转位。在共转染实验中，催乳素介导的STAT5B激活而非src激酶介导的激活导致了β-酪蛋白启动子驱动的报告基因构建体的诱导。这些结果表明，src对STAT5的激活可能通过一种不同于JAK/STAT途径细胞因子激活所采用的机制发生，导致STAT5B的选择性核转位。
