A Negative Feedback Control of Transforming Growth Factor-β Signaling by Glycogen Synthase Kinase 3-mediated Smad3 Linker Phosphorylation at Ser-204

Abstract

Through the action of its membrane-bound type I receptor, transforming growth factor-␤ (TGF-␤) elicits a wide range of cellular responses that regulate cell proliferation, differentiation, and apoptosis. Many of these signaling responses are mediated by Smad proteins. As such, controlling Smad activity is crucial for proper signaling by TGF-␤ and its related factors. Here, we show that TGF-␤ induces phosphorylation at three sites in the Smad3 linker region in addition to the two C-terminal residues, and glycogen synthase kinase 3 is responsible for phosphorylation at one of these sites, namely Ser-204. Alanine substitution at Ser-204 and/or the neighboring Ser-208, the priming site for glycogen synthase kinase 3 in vivo activity, strengthened the affinity of Smad3 to CREBbinding protein, suggesting that linker phosphorylation may be part of a negative feedback loop that modulates Smad3 transcriptional activity. Thus, our findings reveal a novel aspect of the Smad3 signaling mechanism that controls the final amplitude of cellular responses to TGF-␤.

A retinoic acid–dependent network in the foregut controls formation of the mouse lung primordium

“…Indeed, endogenous Gsk3b can act as a negative regulator of Tgfβ signaling (30). Thus, RA appears to be critical in the foregut in controlling at least 3 major pathways, Tgfβ, Wnt, and Fgf, to allow proper formation of the lung primordium.…”

Definition of Smad3 Phosphorylation Events That Affect Malignant and Metastatic Behaviors in Breast Cancer Cells

“…Interestingly, Smad linker phosphorylation has been associated with more aggressive disease in certain cancer and fibrosis models (18). Previous reports showed that mutation of the Smad3 linker phosphorylation sites increased the ability of Smad3 to activate TGFb target genes as well as growth-inhibitory function (13,14) and EMT (21) based on cell culture studies. However, currently, it is not clear what functional roles the Smad3 Ctail and linker phosphorylation play in tumorigenesis and metastasis.…”

“…The Smad3 linker region containing four serine/threonine phosphorylation sites at Thr179, Ser204, Ser208, and Ser213 (10)(11)(12)(13)(14)(15)(16)(17)(18) can be phosphorylated by several kinases, such as the MAPK family and cyclin-dependent kinase (CDK) family (10)(11)(12)(13)(15)(16)(17)(18)(19)(20). These residues except Ser213 are subject to phosphorylation in response to TGFb (11,12,14). Although phosphorylation of Smad3 C-tail SXS motifs by the TGFb type I receptor is required for the linker phosphorylation, the receptor itself does not phosphorylate the linker region (13).…”

TGF-β signal shifting between tumor suppression and fibro-carcinogenesis in human chronic liver diseases

“…The linker domain undergoes regulatory phosphorylation by mitogen-activated protein kinase (MAPK) pathways including extracellular signal-regulated kinase, c-Jun N-terminal kinase (JNK), p38 MAPK, and cyclin-dependent kinase (CDK) as well as glycogen synthase kinase 3-b (Fig. 1a, middle) [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37].…”