Gene expression profiling demonstrates that TGF-β1 signals exclusively through receptor complexes involving Alk5 and identifies targets of TGF-β signaling

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Abstract
Transforming growth factor-β1 (TGF-β) regulates cellular functions like proliferation, differentiation, and apoptosis. On the cell surface, TGF-β binds to receptor complexes consisting of TGF-β receptor type II (TβRII) and activin-like kinase receptor-5 (Alk5), and the downstream signaling is transduced by Smad and MAPK proteins. Recent data have shown that alternative receptor combinations aside from the classical pairing of TβRII/Alk5 can be relevant for TGF-β signaling. We have screened for alternative receptors for TGF-β and also for gene targets of TGF-β signaling, by performing functional assays and microarray analysis in murine embryonic fibroblast (MEF) cell lines lacking Alk5. Data from TGF-β-stimulated Alk5−/− cells show them to be completely unaffected by TGF-β. Additionally, 465 downstream targets of Alk5 signaling were identified when comparing Alk5−/− or TGF-β-stimulated Alk5+/+ MEFs with unstimulated Alk5+/+ cells. Our results demonstrate that, in MEFs, TGF-β signals exclusively through complexes involving Alk5, and give insight to its downstream effector genes.