Loss of TGF-β-mediated growth suppression is a major contributor to the development of cancers,best exemplified by loss-offunction mutations in genes encoding components of the TGF-βsignaling pathway in colorectal a...Loss of TGF-β-mediated growth suppression is a major contributor to the development of cancers,best exemplified by loss-offunction mutations in genes encoding components of the TGF-βsignaling pathway in colorectal and pancreatic cancers.Alternatively,gain-of-function oncogene mutations can also disrupt antiproliferative TGF-βsignaling.However,the molecular mechanisms underlying oncogene-induced modulation of TGF-βsignaling have not been extensively investigated.Here,we show that the oncogenic BCR-ABL1 of chronic myelogenous leukemia(CML)and the cellular ABL1 tyrosine kinases phosphorylate and inactivate Smad4 to block antiproliferative TGF-βsignaling.Mechanistically,phosphorylation of Smad4 at Tyr195,Tyr301,and Tyr322 in the linker region interferes with its binding to the transcription co-activator p300/CBP,thereby blocking the ability of Smad4 to activate the expression of cyclin-dependent kinase(CDK)inhibitors and induce cell cycle arrest.In contrast,the inhibition of BCR-ABL1 kinase with Imatinib prevented Smad4 tyrosine phosphorylation and re-sensitized CML cells to TGF-β-induced antiproliferative and pro-apoptotic responses.Furthermore,expression of phosphorylation-site-mutated Y195F/Y301F/Y322F mutant of Smad4 in Smad4-null CML cells enhanced antiproliferative responses to TGF-β,whereas the phosphorylation-mimicking Y195E/Y301E/Y322E mutant interfered with TGF-βsignaling and enhanced the in vivo growth of CML cells.These findings demonstrate the direct role of BCR-ABL1 tyrosine kinase in suppressing TGF-βsignaling in CML and explain how Imatinib-targeted therapy restored beneficial TGF-βanti-growth responses.展开更多
基金grants from NSFC(U21A20356,31730057,and 91540205)and ZNSF(LD21C070001)the Fundamental Research Funds for the Central Universities.L.W.was supported by a short-term predoctoral fellowship from the Graduate School of Zhejiang University for studying abroad.
文摘Loss of TGF-β-mediated growth suppression is a major contributor to the development of cancers,best exemplified by loss-offunction mutations in genes encoding components of the TGF-βsignaling pathway in colorectal and pancreatic cancers.Alternatively,gain-of-function oncogene mutations can also disrupt antiproliferative TGF-βsignaling.However,the molecular mechanisms underlying oncogene-induced modulation of TGF-βsignaling have not been extensively investigated.Here,we show that the oncogenic BCR-ABL1 of chronic myelogenous leukemia(CML)and the cellular ABL1 tyrosine kinases phosphorylate and inactivate Smad4 to block antiproliferative TGF-βsignaling.Mechanistically,phosphorylation of Smad4 at Tyr195,Tyr301,and Tyr322 in the linker region interferes with its binding to the transcription co-activator p300/CBP,thereby blocking the ability of Smad4 to activate the expression of cyclin-dependent kinase(CDK)inhibitors and induce cell cycle arrest.In contrast,the inhibition of BCR-ABL1 kinase with Imatinib prevented Smad4 tyrosine phosphorylation and re-sensitized CML cells to TGF-β-induced antiproliferative and pro-apoptotic responses.Furthermore,expression of phosphorylation-site-mutated Y195F/Y301F/Y322F mutant of Smad4 in Smad4-null CML cells enhanced antiproliferative responses to TGF-β,whereas the phosphorylation-mimicking Y195E/Y301E/Y322E mutant interfered with TGF-βsignaling and enhanced the in vivo growth of CML cells.These findings demonstrate the direct role of BCR-ABL1 tyrosine kinase in suppressing TGF-βsignaling in CML and explain how Imatinib-targeted therapy restored beneficial TGF-βanti-growth responses.
