Smooth muscle myosin light chain kinase expression  in cardiac and skeletal muscle

The purpose of this study was to characterize myosin light chain kinase (MLCK) expression in cardiac and skeletal muscle. The only classic MLCK detected in cardiac tissue, purified cardiac myocytes, and in a cardiac myocyte cell line (AT1) was identical to the 130-kDa smooth muscle MLCK (smMLCK). A complex pattern of MLCK expression was observed during differentiation of skeletal muscle in which the 220-kDa-long or “nonmuscle” form of MLCK is expressed in undifferentiated myoblasts. Subsequently, during myoblast differentiation, expression of the 220-kDa MLCK declines and expression of this form is replaced by the 130-kDa smMLCK and a skeletal muscle-specific isoform, skMLCK in adult skeletal muscle. These results demonstrate that the skMLCK is the only tissue-specific MLCK, being expressed in adult skeletal muscle but not in cardiac, smooth, or nonmuscle tissues. In contrast, the 130-kDa smMLCK is ubiquitous in all adult tissues, including skeletal and cardiac muscle, demonstrating that, although the 130-kDa smMLCK is expressed at highest levels in smooth muscle tissues, it is not a smooth muscle-specific protein.

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Abstract 1102: Cardiac-Specific Myosin Light Chain Kinase (MLCK), a Third Member of MLCK Family, Potentiates Sarcomere Formation and Cardiac Contraction

Circulation ◽

10.1161/circ.116.suppl_16.ii_221-a ◽

2007 ◽

Vol 116 (suppl_16) ◽

Author(s):

Jason Y Chan ◽

Morihiko Takeda ◽

Laura E Briggs ◽

Jonathan T Lu ◽

Nobuo Horikoshi ◽

...

Keyword(s):

Heart Failure ◽

Skeletal Muscle ◽

Smooth Muscle ◽

Cardiac Hypertrophy ◽

Light Chain ◽

Myosin Light Chain Kinase ◽

Myosin Light Chain ◽

Contractile Function ◽

Severe Heart Failure ◽

Cardiac Contraction

Background: Two myosin light chain kinase (MLCK) proteins, skeletal (encoded by mylk2 gene) and smooth muscle MLCK (encoded by mylk1 gene) have been shown to be expressed in mammals. Human mylk2 has been mapped as a disease locus for familial cardiac hypertrophy (OMIM 606566 ), suggesting that abnormal function of skeletal MLCK stimulates cardiac hypertrophy. While phosphorylation of the putative substrate of skeletal MLCK, myosin light chain 2 (MLC2), is recognized as a key regulator of cardiac contraction, the abundance of skeletal MLCK in the heart is controversial, suggesting the existence of an additional MLCK that is preferentially expressed in cardiac muscle. Methods and Results: We characterized a new kinase named cardiac MLCK that is encoded by a gene homologous to mylk1 and 2 and is specifically expressed in the heart in both atrium and ventricle. Expression of cardiac MLCK was highly regulated by the cardiac homeobox transcription factor, Nkx2.5, in neonatal cardiomyocytes. The overall structure of cardiac MLCK protein is conserved with skeletal and smooth muscle MLCK including putative catalytic and adjacent Ca2+/calmodulin binding domains at the carboxyl-terminus. The amino-terminus is unique without significant homology to other known proteins. Cardiac MLCK phosphorylated MLC2v with a catalytic value of Km=4.3 micro M (Lineweaver-Burk analysis) indicating high affinity of cardiac MLCK to MLC2v, similar to the affinity of skeletal muscle MLCK to skeletal muscle MLC2 and smooth muscle MLCK to smooth muscle MLC2. Adenoviral-mediated overexpression of cardiac MLCK and knockdown of cardiac MLCK using RNAi in cultured cardiomyocytes revealed that cardiac MLCK regulates MLC2v phosphorylation, sarcomere organization and cardiac myocyte contraction. Expression of cardiac MLCK protein was significantly decreased in severe heart failure in vivo (post-myocardial infarction heart failure mouse model). Conclusion: Cardiac MLCK is a new key regulator of cardiac contraction and sarcomere organization. Reduction of cardiac MLCK function leading to decreased phosphorylation of MLC2v may contribute to compromised contractile function in the failing heart.

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Molecular characterization of rat skeletal muscle myosin light chain kinase

AJP Cell Physiology ◽

10.1152/ajpcell.1989.256.2.c399 ◽

1989 ◽

Vol 256 (2) ◽

pp. C399-C404 ◽

Cited By ~ 9

Author(s):

B. P. Herring ◽

M. H. Nunnally ◽

P. J. Gallagher ◽

J. T. Stull

Keyword(s):

Skeletal Muscle ◽

Light Chain ◽

Myosin Light Chain Kinase ◽

Skeletal Muscles ◽

Myosin Light Chain ◽

Cardiac Tissue ◽

Rat Skeletal Muscle ◽

Skeletal Muscle Myosin ◽

Slow Twitch ◽

Muscle Myosin

A 1.85-kilobase (kb) cDNA has been isolated that encodes the catalytic and calmodulin binding domains of rat skeletal muscle myosin light chain kinase. The cDNA hybridized to a 3.3-kb RNA present in fast- and slow-twitch skeletal muscles. The reported enzymatic activity (3-fold greater in fast- than slow-twitch skeletal muscles) reflects the relative abundance of this RNA in the two types of skeletal muscle. No hybridization of the cDNA was detected to RNA isolated from smooth or nonmuscle tissues. The clone cross hybridized to a 2.2-kb RNA present in cardiac tissue. Ribonuclease protection analysis of skeletal and cardiac muscle RNA revealed major differences in the two hybridizing RNAs. Thus rat skeletal muscle contains a single myosin light chain kinase isoform, which is distinct from the cardiac, smooth, and nonmuscle forms.

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