title: The essential role for c-Ski in mediating TGF-beta1-induced bi-directional effects on skin fibroblast proliferation through a feedback loop.
abstract: The bi-directional regulation of TGF-beta1 (transforming growth factor-beta1) on fibroblast proliferation with stimulation at low concentration, but inhibition at high concentration, has important significance during tissue repair. The mechanism has not been defined. c-Ski is a major co-repressor of TGF-beta1/Smad3 signalling; however, the exact role of c-Ski in the bi-directional regulation of fibroblast proliferation remains to be determined. In the present study, we established a dose-effect relationship of bi-directional regulation of TGF-beta1-mediated proliferation in rat skin fibroblasts, and found that c-Ski overexpression promoted fibroblast proliferation by inhibiting Smad3 activity. Importantly, c-Ski expression was decreased at the high concentration of TGF-beta1, but increased at the low concentration of TGF-beta1. This dose-dependent change in TGF-beta1 action did not affect Smad3 phosphorylation or nuclear translocation, but altered Smad3 DNA-binding activity, transcriptional activity and expression of the downstream gene p21 that both increased at the high concentration and decreased at the low concentration. Furthermore, c-Ski overexpression exerted synergistic stimulation with TGF-beta1 at the low concentration, but reversed the inhibitory effect of TGF-beta1 at high concentrations, while knockdown of c-Ski by RNA interference abrogated bi-directional role of TGF-beta1 on fibroblast proliferation. Thus our data reveal a new mechanism for this bi-directional regulation, i.e. c-Ski expression change induced by low or high TGF-beta1 concentration in turn determines the promoting or inhibiting effects of TGF-beta1 on fibroblast proliferation, and suggests an important role of c-Ski that modulates the local availability of TGF-beta1 within the wound repair microenvironment.
authors.affiliation: Molecular Biology Center, State Key Laboratory of Trauma, Burn and Combined Injury, Research Institute of Surgery and Daping Hospital, Third Military Medical University, Chongqing, China.
authors.forename: Xia
authors.initials: X
authors.lastname: Liu
authors.forename: Ping
authors.initials: P
authors.lastname: Li
authors.forename: Ping
authors.initials: P
authors.lastname: Liu
authors.forename: Renping
authors.initials: R
authors.lastname: Xiong
authors.forename: En
authors.initials: E
authors.lastname: Zhang
authors.forename: Xingyun
authors.initials: X
authors.lastname: Chen
authors.forename: Dayong
authors.initials: D
authors.lastname: Gu
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhao
authors.forename: Zhengguo
authors.initials: Z
authors.lastname: Wang
authors.forename: Yuanguo
authors.initials: Y
authors.lastname: Zhou
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D001483:Base Sequence; D049109:Cell Proliferation; D002478:Cells, Cultured; D025461:Feedback, Physiological; D005347:Fibroblasts / Q000378:metabolism*; D008954:Models, Biological; D008969:Molecular Sequence Data; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000737:chemistry / Q000378:metabolism* / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D051900:Smad3 Protein / Q000378:metabolism; D053773:Transforming Growth Factor beta1 / Q000378:metabolism*
chemical_list: D011518:Proto-Oncogene Proteins; C525545:Ski protein, rat; D051900:Smad3 Protein; D053773:Transforming Growth Factor beta1