c-Abl is a non-receptor-type tyrosine kinase that plays an important role in cell proliferation, migration, apoptosis, and fibrosis. Furthermore, although c-Abl is involved in transforming growth factor-beta (TGF-beta) signaling, its molecular functions in TGF-beta signaling are not fully understood. Here, we found that c-Abl phosphorylates SKI-interacting protein (SKIP), a nuclear cofactor of the transcription factor Smad3. The cAbl inhibitor imatinib suppressed TGF-beta-induced expression of Smad3 targets as well as SKIP/Smad3 interaction. TGF-beta-stimulation induced tyrosine phosphorylation of SKIP, and this phosphorylation was suppressed by imatinib. Tyr(292), Tyr(43,) and Tyr(433) residues in SKIP were shown to be involved in c-Abl-mediated phosphorylation. Phosphomimetic glutamic acid substitution at Tyr(292) in SKIP enhanced, whereas its phospho-dead phenylalanine substitution attenuated TGF-beta-induced SKIP/Smad3 interaction. Moreover, the phosphomimetic mutant of SKIP augmented transcriptional activity of Smad3. Taken together, these results suggest that c-Abl phosphorylates SKIP mainly at Tyr(292) and promotes SKIP/Smad3 interaction for the full activation of TGF-beta/Smad3 signaling. (C) 2017 Elsevier Inc. All rights reserved.