Molecular and Cellular Pharmacology of a Calcium/ Calmodulin-Dependent Protein Kinase II (CaM Kinase II) Inhibitor, KN-62, and Proposal of CaM Kinase Phosphorylation Cascades

Abstract

Publisher Summary It is known that Ca 2+ is an important intracellular second messenger. Ca 2+ binds to a variety of proteins and alters their functions. Calmodulin (CaM) is a ubiquitous Ca 2+ -binding protein and the Ca 2+ /CaM complex interacts with target proteins, resulting in their functional changes. In this respect, it is believed that the family of Ca 2+ /CaM-dependent protein kinases (CaM kinases) is important for Ca 2+ -mediated protein phosphorylation. The prototype of this family is smooth muscle myosin light-chain kinase (MLCK), which phosphorylates myosin regulatory light chain in a Ca 2+ /CaM-dependent manner resulting in the activation of actomyosin ATPase required for muscle fiber contraction. The multifunctional CaM kinases have different tissue distributions and substrate specificities, suggesting that each of the enzymes is involved in different types of Ca 2+ -mediated processes. Researchers have succeeded in synthesizing the potent, specific inhibitor of CaM kinase II, KN-62 (1-[ N,O -bis(5-isoquinolinesulfonyl)- N -methyl- l -tyrosyl)-4-phenylpiperazine). CaM kinase II is distributed in a wide range of tissues, but the brain contains the highest amount. This chapter reviews previous studies with KN-62 and propose the involvement of CaM kinase II in various aspects of cell function. Researchers have succeeded in synthesizing W-7, a naphthalenesulfonamide derivative, which can inhibit a protein activator-stimulated cyclic nucleotide phosphodiesterase (PDE). When the naphthalene ring was replaced by an isoquinoline ring in the derivatives with a shorter alkyl chain, the isoquinolinesulfonamide derivatives were no longer CaM antagonists but potent protein kinase inhibitors. KN-62 was proposed to be a specific inhibitor of CaM kinase II because the compound could selectively inhibit the enzyme among a limited number of protein kinases such as PKA, PKC, and smooth muscle MLCK. Research findings suggest that KN-62 occupies the Ca 2+ /CaM binding domain of CaM kinase II, thereby inhibits its Ca 2+ /CaM-dependent activation.