The Rho-Regulated ROCK Kinases in Cancer

The Rho-associated protein kinases ROCK I and ROCK II are central effectors for the RhoA, B, and C small molecular weight GTP-binding proteins, and promote actin-filament stabilization as well as actin-myosin contractility. The effects of ROCK on actin filaments initiate changes in cytoskeletal structure and organization that are critical for many physiological and pathological processes. ROCK has been functionally associated with cell cycle control and proliferation, survival and apoptosis, as well as cell motility and migration. Interestingly, regulation of each of these biological process may be significantly altered in tumor cells, resulting in the promotion of cancer progression. Extensive clinical and preclinical investigations provide evidence supportive of a role for ROCK in multiple aspects of cancer, and pharmacological ROCK inhibitors have been developed as potential anticancer chemotherapeutic agents. This chapter reviews the structure and function of ROCK I and ROCK II, with a particular focus on their potential roles in cancer.Grant R Wickman, Michael S. Samuel, Pamela A Lochhead, and Michael F Olso

A chaperone-dependent GSK3 beta transitional intermediate mediates activation-loop autophosphorylation

Glycogen synthase kinase 3 (GSK3), a key component of the insulin and wnt signaling pathways, is unusual, as it is constitutively active and is inhibited in response to upstream signals. Kinase activity is thought to be increased by intramolecular phosphorylation of a tyrosine in the activation loop (Y216 in GSK3 beta), whose timing and mechanism is undefined. We show that GSK3 beta autophosphorylates Y216 as a chaperone-dependent transitional intermediate possessing intramolecular tyrosine kinase activity and displaying different sensitivity to small-molecule inhibitors compared to mature GSK3 beta. After autophosphorylation, mature GSK3 beta is then an intermolecular serine/threonine kinase no longer requiring a chaperone. This shows that autoactivating kinases have adopted different molecular mechanisms for autophosphorylation; and for kinases such as GSK3, inhibitors that affect only the transitional intermediate would be missed in conventional drug screens

dDYRK2: a novel dual-specificity tyrosine-phosphorylation-regulated kinase in Drosophila

Dual-specificity tyrosine-phosphorylation-regulated kinases (DYRKs) are an emerging family of protein kinases that have been identified in all eukaryotic organisms examined to date. DYRK family members are involved in regulating key developmental and cellular processes such as neurogenesis, cell proliferation, cytokinesis and cellular differentiation. Two distinct subgroups exist, nuclear and cytosolic. In Drosophila, the founding family member minibrain, whose human orthologue maps to the Down syndrome critical region, belongs to the nuclear subclass and affects post-embryonic neurogenesis. In the present paper, we report the isolation of dDYRK2, a cytosolic DYRK and the putative product of the smell-impaired smi35A gene. This is the second such kinase described in Drosophila, but the first to be characterized at the molecular and biochemical level. dDYRK2 is an 81 kDa dual-specificity kinase that autophosphorylates on tyrosine and serine/threonine residues, but appears to phosphorylate exogenous substrates only on serine/threonine residues. It contains a YXY motif in the activation loop of the kinase domain in the same location as the TXY motif in mitogen-activated protein kinases. dDYRK2 is tyrosine-phosphorylated in vivo, and mutational analysis reveals that the activation loop tyrosines are phosphorylated and are essential for kinase activity. Finally, dDYRK2 is active at all stages of fly development, with elevated levels observed during embryogenesis and pupation