Salt-inducible kinases (SIKs) regulate TGFβ-mediated transcriptional and apoptotic responses
AbstractThe signalling pathways initiated by members of the transforming growth factor-{beta} (TGF{beta}) family of cytokines control many metazoan cellular processes, including proliferation and differentiation, epithelial-mesenchymal transition (EMT), and apoptosis. TGF{beta} signalling is therefore strictly regulated to ensure appropriate context-dependent physiological responses. In an attempt to identify novel regulatory components of the TGF{beta} signalling pathway, we performed a pharmacological screen using a cell line engineered to report the endogenous transcription of the TGF{beta}-responsive target gene PAI-1. The screen revealed that small-molecular inhibitors of salt-inducible kinases (SIKs) attenuate TGF{beta}-mediated transcription of PAI-1 without affecting receptor-mediated SMAD phosphorylation, SMAD complex formation or nuclear translocation. We provide evidence that genetic inactivation of SIK isoforms also attenuates TGF{beta}-dependent transcriptional responses. Pharmacological inhibition of SIKs using multiple small-molecule inhibitors potentiated apoptotic cell death induced by TGF{beta} stimulation. Our data therefore provides evidence for a novel function of SIKs in modulating TGF{beta}-mediated transcriptional and cellular responses.