TY - JOUR
T1 - Transforming growth factor β activates Smad2 in the absence of receptor endocytosis
AU - Lu, Zhongxian
AU - Murray, James T.
AU - Luo, Wenjie
AU - Li, Hongling
AU - Wu, Xiaoping
AU - Xu, Huaxi
AU - Backer, Jonathan M.
AU - Chen, Ye Guang
PY - 2002/8/16
Y1 - 2002/8/16
N2 - Like many other cell surface receptors, transforming growth factor β (TGF-β) receptors are internalized upon ligand stimulation. Given that the signaling-facilitating molecules Smad anchor for receptor activation (SARA) and Hrs are mainly localized in early endosomes, it was unclear whether receptor internalization is required for Smad2 activation. Using reversible biotin labeling, we directly monitored internalization of the TGF-β type I receptor. Our data indicate that TGF-β type I receptor is endocytosed via a clathrin-dependent mechanism and is effectively blocked by depletion of intracellular potassium or by expression of a mutant dynamin (K44A). However, blockage of receptor endocytosis by these two means has no effect on TGF-β-mediated Smad2 activation. Furthermore, TGF-β-induced Smad2 activation was unaffected by inhibition of hVPS34 activity with wortmannin or inhibitory anti-hVPS34 antibodies. Finally, we demonstrated that Smad2 interacted with cell surface receptors and that a SARA binding-deficient Smad2 mutant was phosphorylated by the receptors. Thus, our findings suggest that receptor endocytosis is dispersible for TGF-β-mediated activation of Smad2 and that this activation can be mediated by both SARA-dependent and -independent mechanisms.
AB - Like many other cell surface receptors, transforming growth factor β (TGF-β) receptors are internalized upon ligand stimulation. Given that the signaling-facilitating molecules Smad anchor for receptor activation (SARA) and Hrs are mainly localized in early endosomes, it was unclear whether receptor internalization is required for Smad2 activation. Using reversible biotin labeling, we directly monitored internalization of the TGF-β type I receptor. Our data indicate that TGF-β type I receptor is endocytosed via a clathrin-dependent mechanism and is effectively blocked by depletion of intracellular potassium or by expression of a mutant dynamin (K44A). However, blockage of receptor endocytosis by these two means has no effect on TGF-β-mediated Smad2 activation. Furthermore, TGF-β-induced Smad2 activation was unaffected by inhibition of hVPS34 activity with wortmannin or inhibitory anti-hVPS34 antibodies. Finally, we demonstrated that Smad2 interacted with cell surface receptors and that a SARA binding-deficient Smad2 mutant was phosphorylated by the receptors. Thus, our findings suggest that receptor endocytosis is dispersible for TGF-β-mediated activation of Smad2 and that this activation can be mediated by both SARA-dependent and -independent mechanisms.
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U2 - 10.1074/jbc.M203495200
DO - 10.1074/jbc.M203495200
M3 - Article
C2 - 12034739
AN - SCOPUS:0037119489
SN - 0021-9258
VL - 277
SP - 29363
EP - 29368
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 33
ER -