Myosin Light Chain Kinase Is Central to Smooth Muscle Contraction and Required for Gastrointestinal Motility in Mice

Abstract

Background & Aims-Smooth muscle is essential for maintaining homeostasis for many body functions and provides adaptive responses to stresses imposed by pathological disorders. Identified cell signaling networks have defined many potential mechanisms for initiating smooth muscle contraction with or without myosin regulatory light chain (RLC) phosphorylation by myosin light chain kinase (MLCK). We generate tamoxifen-inducible and smooth muscle-specific MLCK knockout (KO) mice and provide direct loss-of-function evidence that shows the primary importance of MLCK in phasic smooth muscle contractions.

Regulation of 130-kDa Smooth Muscle Myosin Light Chain Kinase Expression by an Intronic CArG Element

“…Deletion of both the 220-and 130-kDa MLCK from smooth muscle tissues has been previously shown to impair contractility, MLC phosphorylation, and gastrointestinal motility in mice (27). The current studies suggest that it is primarily the 130-kDa smMLCK rather than the 220-kDa MLCK that is responsible for regulating contraction in gastrointestinal smooth muscle.…”

“…Global knock-out of the 220-kDa MLCK in mice results in numerous defects in epithelial and endothelial barrier function, suggesting that this isoform has a specific role in regulating these processes (22)(23)(24)(25)(26). Through specific targeting of a portion of the catalytic domain shared by the 220-and 130-kDa MLCKs, it has been possible to determine the combined roles of these kinases in specific tissues and cell types (27). As anticipated, ablation of both MLCK isoforms in smooth muscle cells resulted in impaired contractility and decreased myosin light chain phosphorylation (20,27).…”

“…Through specific targeting of a portion of the catalytic domain shared by the 220-and 130-kDa MLCKs, it has been possible to determine the combined roles of these kinases in specific tissues and cell types (27). As anticipated, ablation of both MLCK isoforms in smooth muscle cells resulted in impaired contractility and decreased myosin light chain phosphorylation (20,27). Surprisingly, deletion of both 220-and 130-kDa smMLCK specifically from endothelial cells had very little effect on vascular permeability, bringing into question the importance of endothelial cell-expressed MLCK in regulating endothelial barrier function (28).…”

Loss of LMOD1 impairs smooth muscle cytocontractility and causes megacystis microcolon intestinal hypoperistalsis syndrome in humans and mice

“…On the other hand, genetic inactivation of Myh11, encoding the major thick filament protein in smooth muscle, leads to megacystis, a decrease in intestinal motility, defective contraction of the bladder, and early postnatal death, all of which are reminiscent of the Lmod1 −/− phenotype and human MMIHS (40). Further, smooth muscle-specific knockout of myosin light chain kinase results in early postnatal demise due to similar phenotypes observed in the Lmod1 and Myh11 knockouts (41). Although human mutations in the latter have not yet been documented, there is a report of a consanguineous family with a nonsense mutation in MYH11 associated with MMIHS (10).…”

Myosin Light Chain Kinase (MLCK) Regulates Cell Migration in a Myosin Regulatory Light Chain Phosphorylation-independent Mechanism

“…We generated smooth muscle-specific MLCK-knock-out mice as previously described (37). Eight-to 12-week-old mice were killed by cervical dislocation.…”