Activation of Stat3 preassembled with platelet-derived growth factor β receptors requires Src kinase activity

Abstract

Members of the STAT family of transcriptional regulators modulate the expression of a variety of gene products that promote cell proliferation, survival and transformation. Although initially identi®ed as mediators of cytokine signaling, the STAT proteins are also activated by, and thus may contribute to the actions of, polypeptide growth factors. To de®ne the mechanism by which these factors activate STATs, we examined the process of Stat3 activation in Balb/c-3T3 ®broblasts treated with platelet-derived growth factor (PDGF). As STATs are activated by tyrosine phosphorylation, and as PDGF receptors are ligand-activated tyrosine kinases, we considered the possibility that Stat3 interacts with and is phosphorylated by PDGF receptors. We ®nd that Stat3 associates with PDGF b receptors in both the presence and, surprisingly, the absence of PDGF. Moreover, Stat3 was phosphorylated on tyrosine in PDGF b receptor immunoprecipitates of PDGF-treated but not untreated cells. Although required, receptor activation was insucient for Stat3 activation. When added to cells in combination with a pharmacologic agent (PD180970) that speci®cally inhibits the activity of Src family tyrosine kinases, PDGF did not activate Stat3 as monitored by electrophoretic mobility shift assay. PD180970 did not aect MAPK activation by PDGF or the JAK-dependent activation of Stat3 by interleukin-6. The necessity of Src activity for Stat3 activation by PDGF was further evidenced by data showing the presence of Src in complexes containing both Stat3 and PDGF b receptors in PDGF-treated cells. These results suggest a novel mechanism of STAT activation in which inactive Stat3 pre-assembles with inactive PDGF receptors, and in response to ligand binding and in a manner dependent on Src kinase activity, is rapidly phosphorylated and activated. Additional data demonstrate that Src kinase activity is also required for PDGF stimulation of DNA synthesis in density-arrested cells.

Curcumin (Diferuloylmethane) Inhibits Constitutive and IL-6-Inducible STAT3 Phosphorylation in Human Multiple Myeloma Cells

“…Several other kinases have been implicated in the phosphorylation of STAT3, including members of the Src family (hck, src), Erb2, anaplastic lymphoma kinase, protein kinase C-␦, c-fes, and epidermal growth factor receptor (41)(42)(43)(44)(45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55). Whether any of these kinases are active in MM cells, and which of these kinases is activated by IL-6, is not fully known.…”

Potential role of signal transducer and activator of transcription (STAT)3 signaling pathway in inflammation, survival, proliferation and invasion of hepatocellular carcinoma

“…STAT proteins are also triggered by receptor tyrosine kinases such as epidermal growth factor-receptor (EGF-R), PDGF-R [69], and colony stimulating factor-1R (CSF-1R) [70], seven transmembrane G-protein-coupled receptors such as angiotensin II receptor [71] and serotonin 5-HT2A receptor [72] and through the T cell receptor complex [73] and the CD40 receptor [74]. EGF, TGFβ, and PDGF receptors are also capable of directly phosphorylating STAT proteins in the absence of JAK activation, leading to the up-regulation of genes that promote cell proliferation, survival, and cell transformation [75][76][77].…”

“…It is widely believed that the ability of PDGFs to induce liver fibrosis and neoplastic cell transformation is closely associated with the transcriptional induction of TGFβ, an essential mediator of fibrogenesis [241,242]. TGFβ and PDGFs act through activation of STAT3 [75,76] leading to the upregulation of genes promoting cell proliferation, survival, and cell transformation [77]. The role of TGFβ and PDGF pathways in the induction of liver fibrosis and cirrhosis, and putative contributing events to the neoplastic transformation of hepatocytes [243][244][245][246] is well established.…”

Anaplastic lymphoma kinase (ALK) activates Stat3 and protects hematopoietic cells from cell death

“…These ®ndings suggest the catalytic domain of ALK, determined by the analysis of the homology with the catalytic domains of known kinases (Morris et al, 1994), is insu cient and it requires additional¯anking regions possibly for the correct tridimensional folding of the protein. Src and src family members play crucial roles in signaling from RTK and are responsible for Stat activation under some circumstances (Wang et al, 2000). To study whether NPM-ALK mediated activation of Stat3 required src, fyn or yes, the src family proteins expressed in ®broblasts, we examined Stat3 phosphorylation in mouse embryonal ®broblasts (MEFs) speci®cally deleted for all three src-related genes (Klingho er et al, 1999).…”