SIK phosphorylates and degrades Par3 to mediate tight junction disassembly during epithelial-mesenchymal transition
2011 (English)Manuscript (preprint) (Other academic)
Transforming growth factor β (TGFβ) is a multifunctional cytokine involved in homeostasis and disease during embryonic and adult life. TGFβ alters epithelial cell differentiation by inducing epithelial-mesenchymal transition (EMT), which involves disassembly of the epithelial adherens and tight junctions and downregulation of several junctional constituents.The mechanism by which TGFβ controls tight junction disassembly is poorly understood. We found that one of the newly identified gene targets of TGFβ, encodes for the serine/threonine kinase SIK (salt-inducible kinase), and controls tight junction assembly by this cytokine. We then identified a new phosphorylation substrate for SIK, the polarity complex protein Par3, which is an important regulator of tight junction assembly. SIK associates with Par3, phosphorylates serine 885 within the atypical protein kinase C-binding domain of Par3, and causes degradation of Par3. Mutation of serine 885 to alanine renders Par3 resistant to degradation induced by SIK. This mechanism is functionally important because both SIK and Par3 participate in the downregulation of tight junctions during EMT initiated by TGFβ signaling. Furthermore, we verified high level SIK expression in several different advanced and invasive human cancers. Notably, high SIK expression correlated with high level TGFβ/Smad signaling activity and with low or undetectable expression of Par3 in human breast cancers. Our model suggests that as the TGFβ signal progresses, SIK gets engaged in a concerted action that lowers signaling by its own receptor and initiates disassembly of the tight junction by acting directly on the polarity complex protein Par3.
Place, publisher, year, edition, pages
2011. , 230 p.
EMT, Par3, Signal transduction, SIK, TGFβ
IdentifiersURN: urn:nbn:se:uu:diva-152266OAI: oai:DiVA.org:uu-152266DiVA: diva2:413164