MLCK

Myosin light chain kinase (MLCK) is a Ca²⁺/calmodulin-dependent serine/threonine kinase that phosphorylates myosin regulatory light chains and thereby controls actomyosin contraction in smooth muscle and nonmuscle cells^[1][2]. Mechanistically, MLCK functions as a central regulator of cytoskeletal dynamics, coupling intracellular calcium signaling to myosin activation, cell contractility, barrier regulation, migration, and tissue permeability^[1][3]. Through phosphorylation-dependent control of actomyosin interactions, MLCK contributes to vascular tone, airway contraction, gastrointestinal motility, and endothelial barrier function, linking its activity to multiple physiological and pathological processes^[1][2]. In disease contexts, altered MLCK expression or activity has been reported in inflammatory lung injury, asthma, cardiovascular disorders, inflammatory bowel disease, pancreatitis, and cancer, supporting its relevance as a disease-associated signaling node and experimental target^[1]. Compared with smooth muscle MLCK (smMLCK), which primarily mediates contractile responses in smooth muscle tissues, nonmuscle MLCK (nmMLCK) has distinct functions in endothelial permeability, leukocyte transmigration, inflammatory responses, and cytoskeletal remodeling, highlighting isoform-specific biological roles^[3][4]. This distinction is particularly important for experimental models investigating vascular inflammation and barrier dysfunction, where nmMLCK deficiency or inhibition can attenuate myosin light chain phosphorylation and reduce pathological permeability responses^[3][4]. For experimental applications, the small-molecule inhibitors ML-7 and ML-9 are widely used to suppress MLCK activity; ML-7 acts as a reversible ATP-competitive inhibitor with submicromolar potency against smooth muscle MLCK and is frequently employed to investigate MLCK-dependent signaling pathways and contractile mechanisms^[6].