Disease relevance of MYLK

• These data strongly implicate MYLK genetic variants to confer increased risk of sepsis and sepsis-associated ALI [1].
• When added to contracting solution at the peak of a contracture, anti-MLCK Fab elicited a relaxation that was complete in about 120 minutes despite the presence of Ca2+ [2].
• To localize the actin- and myosin-binding activities in the MLCK molecule and to examine their possible role in regulating the actin-myosin interaction, we expressed various fragments of cDNA encoding MLCK in Escherichia coli as recombinant proteins [3].
• Genetic variants in MYLK are significantly associated with both asthma and sepsis in populations of African ancestry [4].

High impact information on MYLK

• Ca2+ sensitivity of smooth muscle and nonmuscle myosin II reflects the ratio of activities of myosin light-chain kinase (MLCK) to myosin light-chain phosphatase (MLCP) and is a major, regulated determinant of numerous cellular processes [5].
• These data indicate that MLCK is a target for PAKs and that PAKs may regulate cytoskeletal dynamics by decreasing MLCK activity and MLC phosphorylation [6].
• MLCK activity and MLC phosphorylation were decreased, and cell spreading was inhibited in baby hamster kidney-21 and HeLa cells expressing constitutively active PAK1 [6].
• F-actin was decorated with a peptide containing the NH2-terminal 147 residues of MLCK (MLCK-147) that binds to F-actin with high affinity [7].
• It is widely accepted that actin filaments and the conventional double-headed myosin interact to generate force for many types of nonmuscle cell motility, and that this interaction occurs when the myosin regulatory light chain (MLC) is phosphorylated by MLC kinase (MLCK) together with calmodulin and Ca(2+) [8].

Biological context of MYLK

• A genomic region encompassing a cluster of olfactory receptor genes and a myosin light chain kinase (MYLK) gene is duplicated on human chromosome regions 3q13-q21 and 3p13 [9].
• Here, we present the localization of the MYLK gene in a >5-Mb region of the chromosome 3q21 integrated map [10].
• The 3p13 site contains a MYLK pseudogene (MYLKP) associated with a cluster of OR pseudogenes and therefore could have arisen from the duplication of a large region in 3q13-->q21 [10].
• Post-translational modifications to MLCK down-regulate enzyme activity, suppressing RLC phosphorylation, myosin II activation, and tension development [11].
• In contrast, localization of the long MLCK to the cleavage furrow in dividing cells requires the five DXRXXL motifs as well as additional amino acid sequences present in the NH(2)-terminal extension [12].

Anatomical context of MYLK

• Phosphorylation of myosin II regulatory light chains (RLC) by Ca(2+)/calmodulin-dependent myosin light chain kinase (MLCK) is a critical step in the initiation of smooth muscle and non-muscle cell contraction [11].
• In interphase cells, localization of the long MLCK to stress fibers is mediated by five DXRXXL motifs, which span the junction of the NH(2)-terminal extension and the short MLCK [12].
• These data suggest that the novel 214-kD kinase, the only MLCK isoform found in endothelium, may be preferentially expressed in this nonmuscle tissue [13].
• The phosphorylation of myosin light chains by myosin light chain kinase (MLCK) is a key event in agonist-mediated endothelial cell gap formation and vascular permeability [14].
• Monitoring of MLCK expression in different cell types with antibodies generated against a unique human EC MLCK N-terminal sequence revealed a high level of expression of the 214-kD enzyme in endothelium, minimal level of expression in smooth muscle, and no expression in skeletal muscle [13].

Associations of MYLK with chemical compounds

• Post-integrin occupancy signaling through MAPK and MLCK after alpha(IIb)beta(3) cross-linking may explain in part the increased adhesive properties of the Pro(33) variant of integrin beta(3) [15].
• PAK2 catalyzes MLCK phosphorylation on serine residues 439 and 991 [11].
• The influence of Rho-dependent kinase (ROCK) and myosin light chain kinase (MLCK) were studied by using specific kinase inhibitors (Y-27632, HA-1077, H-1152, and ML-7) [16].
• Immunoprecipitation with NH2-specific antisera revealed a 214 kD high molecular weight MLCK in bovine and human endothelium which exhibits MLC phosphorylation properties [14].
• The determination of the human KRP amino acid sequence through cDNA sequence analysis and its comparison to the exon/intron organization of the human KRP gene revealed an alternative splice pattern at the start of KRP exon 2, resulting in the insertion of a single glutamic acid in the middle of the protein [17].

Regulatory relationships of MYLK

• Although ERK1/2 can activate MLCK, its inhibition had no impact on EPEC disruption of the tight junction barrier [18].
• TNF-alpha-induced increase in MLCK promoter activity was mediated by NF-kappaB activation [19].

Other interactions of MYLK

• Cdc42-activated placenta and recombinant, constitutively active PAK2 phosphorylate MLCK in vitro with a stoichiometry of 1.71 +/- 0 [11].
• Previous studies from our laboratory suggested that the TNF-alpha-induced increase in intestinal TJ permeability was mediated by an increase in myosin light chain kinase (MLCK) protein expression [20].
• Phosphorylation of myosin regulatory light chain may be mediated directly and indirectly by several kinases including myosin light chain kinase (MLCK) and kinases activated by small GTP-binding proteins [21].

Analytical, diagnostic and therapeutic context of MYLK

• Furthermore, compared with platelets and cells expressing the Leu(33) isoform, the Pro(33) variant showed greater alpha-granule release, clot retraction, and adhesion to fibrinogen under shear stress, and these functional differences were abolished by MLCK and MAPK kinase inhibition [15].
• Immunofluorescence studies reveal rapid, Rac-dependent translocation of cortactin to the expanded cortical actin band following S1P challenge, where colocalization with EC MLCK occurs within 5 min [22].
• Sequence analysis also identified, however, a 5' stretch of novel sequence (amino acids #1-922) which is not contained in the open reading frame of mammalian SM MLCK, and is only 58% homologous to the avian fibroblast MLCK sequence [14].
• The chromosomal localization of the gene for human MLCK is shown to be at 3qcen-q21, as determined by PCR and Southern blotting using two somatic cell hybrid panels [23].
• We examined MLCK activation quantitatively with a fluorescent biosensor MLCK where Ca(2+)-dependent increases in kinase activity were coincident with decreases in fluorescence resonance energy transfer (FRET) in vitro [24].

References