Signal Transduction Pathways Regulated by Prolactin and Src Result in Different Conformations of Activated Stat5b

Abstract

Stat5 is activated by a broad spectrum of cytokines, as well as non-receptor tyrosine kinases, such as Src. In this study, the DNA binding properties of the two closely related Stat5 proteins, Stat5a and Stat5b, induced either by prolactin (Prl) or by Src were analyzed by electrophoretic mobility shift assays using several different Stat5 binding sites. Src-induced Stat5b-DNA binding complexes consistently displayed a slightly faster mobility than those induced by Prl, as well as differences in their ability to be supershifted by anti-Stat5 antibodies. IP-Westerns performed using specific antibodies directed at the N and C termini of Stat5b suggested that depending on the activating stimulus, Stat5b exhibited different conformations, which influenced antibody accessibility at its C terminus. These conformational differences may in part be due to differential effects of Prl

c-Src tyrosine kinase co-associates with and phosphorylates signal transducer and activator of transcription 5b which mediates the proliferation of normal human B lymphocytes

“…Indeed, c-Src may be an initial player that then activates a second factor by tyrosine phophorylation, and it is this second factor that then acts to increase proliferation. Several reports have demonstrated an essential role for c-Src kinase in mediating constitutive STAT5b activation in many human cancer cells [24,25,[35][36][37]. In general, c-Src serves as an intermediate between tumorigenic protein-tyrosine kinases and STAT activation.…”

STAT3- and DNA methyltransferase 1-mediated epigenetic silencing of SHP-1 tyrosine phosphatase tumor suppressor gene in malignant T lymphocytes

“…4A and 5B) to but also induce marked DNA methylation of the SHP-1 promoter (Figs. 2 and 7) is due to additional posttranscriptional modification(s) of the STAT protein that might change its conformation (25), expression of a corepressor that enhances STAT3 binding to the promoter, mutation(s) of the STAT3 gene, or other reasons remains to be determined.…”

Hypoxia activates the cyclin D1 promoter via the Jak2/STAT5b pathway in breast cancer cells

“…STAT5 has been shown to mediate the transcriptional regulation of cyclin D1, thereby contributing to cytokine-and prolactin-dependent growth of hematopoietic and breast cancer cells, respectively (Matsumura et al, 1999;Schroeder et al, 2002). The cyclin D1 promoter contains binding sites for a number of transcription factors other than STAT5, whose activity may be modulated either directly or indirectly by Src kinase (Lee et al, 1999;Kabotyanski and Rosen, 2003). STAT5 may participate in hypoxia-induced cell growth through transcriptional regulation of cyclin D1, which plays a key role in both G1 progression and G1/S transition in the cell cycle.…”