STAT5a Activation Mediates the Epithelial to Mesenchymal Transition Induced by Oncogenic RhoA.

Abstract

The involvement of Rho GTPases in signal transduction pathways leading to transcription activation is one of the major roles of this family of GTPases. Thus, the identification of transcription factors regulated by Rho GTPases and the understanding of the mechanisms of their activation and its biological outcome are of great interest. Here, we provide evidence that Rho GTPases modulate Stat5a, a transcription factor of the family of signal transducers and activators of transcription. RhoA triggers tyrosine phosphorylation (Y696) of Stat5a via a JAK2-dependent mechanism and promotes DNA-binding activity of Stat5a. Tyrosine phosphorylation of Stat5a is also stimulated physiologically by lysophosphatidic acid (LPA) in a Rho-dependent manner. Simultaneously, RhoA reduces serine phosphorylation of Stat5a at both serine residues S726 and S780, resulting in a further increase of activity as defined by mutagenesis experiments. Furthermore, serine dephosphorylation of Stat5a by RhoA does not take place by down-modulation of either JNK1, MEK1, or p38 MAP kinases, as determined by transfection experiments or chemical inhibition of both MEK1, p38, and JNK serine kinases. Thus, RhoA regulates Stat5a via tyrosine phosphorylation and via a yet to be determined novel down-modulating pathway that involves serine dephosphorylation. Finally, we provide evidence for a role of Stat5a in RhoA-induced epithelial-to-mesenchymal transition with concomitant increase in vimentin expression, E-cadherin down-regulation, and cell motility

Suppression of Activation of Signal Transducer and Activator of Transcription-5B Signaling in the Vessel Wall Reduces Balloon Injury-Induced Neointima Formation

“…T4 polynucleotide kinase was obtained from Promega (Madison, WI). [␥ 32 P]ATP (3000 Ci/mmol), [ 14 C]chloramphenicol (59 mCi/mmol), and protein-A-Sepharose (CL-4B) were from Amersham Biosciences (Piscataway, NJ). Thymidine [methyl-…”

“…The 1ϫ pSp1GLECAT contains STAT-5-responsive sequence of the human Sp2.1 promoter and thereby drives the CAT reporter gene expression. 32 Cells were then quiesced and treated with and without PDGF-BB (20 ng/ml) for the indicated times, and cell extracts were prepared. In the case of testing the role of STAT-5B, cells were transduced first with the control Ad-GFP or Ad-dnSTAT-5B virus followed by transfection with pSp1GLECAT plasmid DNA.…”

“…Together, these results indicate that PDGF-BB stimulates STAT-5B in VSMCs. To find whether the increased tyrosine phosphorylation of STAT-5B leads to its transcriptional transactivation capacity, nuclear extracts were prepared from various times of PDGF-BB (20 ng/ml)-treated and untreated VSMCs, and an equal amount of nuclear protein from control and each treatment was analyzed for STAT-5 DNA-binding activity using its 32 P-labeled consensus double-stranded oligonucleotides as a probe. PDGF-BB induced STAT-5-DNA binding activity compared with control ( Figure 1C).…”

The interaction between KDR and interleukin-3 receptor (IL-3R) beta common modulates tumor neovascularization

“…This downmodulation might take place via the inactivation of specific kinases responsible for STAT5A serine phosphorylation, modulation of either their half-life or expression, or the activation of a specific phosphatase. Nevertheless, as shown for oncogenic RhoA (Benitah et al, 2003) and glucocorticoid-stimulated cells (Groner et al, 2000), serine phosphorylation of STAT5A plays an inhibitory rather than stimulatory role among signals generated by the activation of IL-3R bc. This possibility is sustained by the following observations: (i) serine phosphorylation of STAT5A was constitutively present in H-END cells under normal serum condition; (ii) tyrosine phosphorylation and serine dephosphorylation of STAT5A occurred in response to IL-3; and as above reported (iii) tyrosine phosphorylation and serine dephosphorylation of STAT5A could not be detected in cells expressing the inactive IL-3R bc.…”

“…The role of STAT tyrosine phosphorylation in regulating VEGF- (Korpelainen et al, 1999;Bartoli et al, 2000) and IL-3-mediated signals (Mui et al, 1995(Mui et al, , 1996Reddy et al, 2000) has been investigated. More recently, a secondary regulatory mechanism independent of tyrosine phosphorylation has been described for several STAT proteins that involves serine phosphorylation (Yamashita et al, 1998;Decker and Kovarik, 2000;Benitah et al, 2003).…”