Iyer Janaki, Reich Nancy C
Dept. of Molecular Genetics and Microbiology, Stony Brook University, Stony Brook, NY 11794, USA.
FASEB J. 2008 Feb;22(2):391-400. doi: 10.1096/fj.07-8965com. Epub 2007 Sep 10.
Signal transducer and activator of transcription 5a (STAT5a) is a critical transcription factor for a number of physiological processes including hematopoiesis and mammary gland development. Cytokines such as growth hormone, prolactin, erythropoietin, and interleukin-2 stimulate the activation of STAT5a by tyrosine phosphorylation. Tyrosine phosphorylation confers a conformational change and the ability to bind specific target DNA. To execute its function as a signaling molecule and transcription factor, accurate cellular localization of STAT5a is essential. This study explores the nuclear trafficking of STAT5a both before phosphorylation and after tyrosine phosphorylation. With the use of live cell imaging we demonstrate the continuous shuttling of STAT5a in and out of the nucleus. Evaluation of a series of mutations and deletions identifies a region within the coiled coil domain of STAT5a that is critical for nuclear import of both unphosphorylated and tyrosine-phosphorylated forms. The mechanism that regulates transport of STAT5a through nuclear pore complexes into the nucleus is therefore independent of tyrosine phosphorylation. However, after tyrosine phosphorylation, STAT5a accumulates in the nucleus because of its retention by DNA binding. These findings should provide a foundation for further studies that involve targeting the activity of STAT5a.
信号转导与转录激活因子5a(STAT5a)是多种生理过程(包括造血和乳腺发育)中的关键转录因子。生长激素、催乳素、促红细胞生成素和白细胞介素-2等细胞因子通过酪氨酸磷酸化刺激STAT5a的激活。酪氨酸磷酸化导致构象变化并赋予其结合特定靶DNA的能力。为了执行其作为信号分子和转录因子的功能,STAT5a在细胞内的准确定位至关重要。本研究探讨了STAT5a在磷酸化之前和酪氨酸磷酸化之后的核运输情况。通过使用活细胞成像技术,我们证明了STAT5a在细胞核内外持续穿梭。对一系列突变和缺失的评估确定了STAT5a卷曲螺旋结构域内的一个区域,该区域对于未磷酸化和酪氨酸磷酸化形式的核输入都至关重要。因此,调节STAT5a通过核孔复合体进入细胞核的机制与酪氨酸磷酸化无关。然而,酪氨酸磷酸化后,STAT5a由于与DNA结合而滞留在细胞核中。这些发现应为进一步研究靶向STAT5a的活性提供基础。