Serine/threonine-protein kinase SIK1 (Sik1)

Serine/threonine-protein kinase involved in various processes such as cell cycle regulation, gluconeogenesis and lipogenesis regulation, muscle growth and differentiation and tumor suppression. Phosphorylates HDAC4, HDAC5, PPME1, SREBF1, CRTC1/TORC1 and CRTC2/TORC2.

Acts as a tumor suppressor and plays a key role in p53/TP53-dependent anoikis, a sort of apoptosis triggered by cell detachment: required for phosphorylation of p53/TP53 in response to lack of adhesion and can suppress metastasis. Part of a sodium-sensing signaling network, probably by mediating phosphorylation of PPME1: subsequent increases in intracellular sodium, SIK1 is activated by CaMK1 and phosphorylates PPME1 subunit of protein phosphatase 2A (PP2A), leading to dephosphorylation of sodium/potassium-transporting ATPase ATP1A1 and subsequent increase activity of ATP1A1.