Mark3: Proteins and Enzymes

MARK3 is a dual-specificity protein kinase that controls entry into mitosis by dephosphorylating Cdc2 on both threonine 14 and tyrosine 15. MARK3 is phosphorylated on serine 216 throughout interphase but not during mitosis. Serine 216 phosphorylation mediates the binding of 14-3-3 protein to MARK3, and MARK3/14-3-3 complexes are present throughout interphase but not during mitosis (1). Kinase suppressor of Ras (KSR) is a conserved component of the Ras pathway that interacts directly with MEK and MAPK. It has been shown that KSR1 translocates from the cytoplasm to the cell surface in response to growth factor treatment and that this process is regulated by MARK3 (2). MARK3 seems to be a positive regulator of the beta-catenin pathway and an inhibitor of the JNK pathway. These findings show that MARK3, a regulator of polarity, is also a modulator of Wnt-beta-catenin signalling, indicating a link between two important developmental pathways (3).