Phosphorylation of ?Np63? via a novel TGF?/ALK5 signaling mechanism mediates the anti-clonogenic effects of TGF?.

ABSTRACT: Genetic analysis of TP63 implicates ?Np63 isoforms in preservation of replicative capacity and cellular lifespan within adult stem cells. ?Np63? is also an oncogene and survival factor that mediates therapeutic resistance in squamous carcinomas. These diverse activities are the result of genetic and functional interactions between TP63 and an array of morphogenic and morphostatic signals that govern tissue and tumor stasis, mitotic polarity, and cell fate; however the cellular signals that account for specific functions of TP63 are incompletely understood. To address this we sought to identify signaling pathways that regulate expression, stability or activity of ?Np63?. An siRNA-based screen of the human kinome identified the Type 1 TGF? receptor, ALK5, as the kinase required for phosphorylation of ?Np63? at Serine 66/68 (S66/68). This activity is TGF?-dependent and sensitive to either ALK5-directed siRNA or the ALK5 kinase inhibitor A83-01. Mechanistic studies support a model in which ALK5 is proteolytically cleaved at the internal juxtamembrane region resulting in the translocation of the C-terminal ALK5-intracellular kinase domain (ALK5(IKD)). In this study, we demonstrate that ALK5-mediated phosphorylation of ?Np63? is required for the anti-clonogenic effects of TGF? and ectopic expression of ALK5(IKD) mimics these effects. Finally, we present evidence that ultraviolet irradiation-mediated phosphorylation of ?Np63? is sensitive to ALK5 inhibitors. These findings identify a non-canonical TGF?-signaling pathway that mediates the anti-clonogenic effects of TGF? and the effects of cellular stress via ?Np63? phosphorylation.

SUBMITTER: Cherukuri P 

PROVIDER: S-EPMC3500343 | biostudies-literature | 2012

REPOSITORIES: biostudies-literature