Characterization and differential expression of human vascular smooth muscle myosin light chain 2 isoform in nonmuscle cells

Biochemistry. 1989 May 2;28(9):4027-35. doi: 10.1021/bi00435a059.


The 20-kDa regulatory myosin light chain (MLC), also known as MLC-2, plays an important role in the regulation of both smooth muscle and nonmuscle cell contractile activity. Phosphorylation of MLC-2 by the enzyme MLC kinase increases the actin-activated myosin ATPase activity and thereby regulates the contractile activity. We have isolated and characterized an MLC-2 cDNA corresponding to the human vascular smooth muscle MLC-2 isoform from a cDNA library derived from umbilical artery RNA. The translation of the in vitro synthesized mRNA, corresponding to the cDNA insert, in a rabbit reticulocyte lysate results in the synthesis of a 20,000-dalton protein that is immunoreactive with antibodies raised against purified chicken gizzard MLC-2. The derived amino acid sequence of the putative human smooth muscle MLC-2 shows only three amino acid differences when compared to chicken gizzard MLC-2. However, comparison with the human cardiac isoform reveals only 48% homology. Blot hybridizations and S1 nuclease analysis indicate that the human smooth muscle MLC-2 isoform is expressed restrictively in smooth muscle tissues such as colon and uterus and in some, but not all, nonmuscle cell lines. Previously reported MLC-2 cDNA from rat aortic smooth muscle cells in culture is ubiquitously expressed in all muscle and nonmuscle cells, and it was suggested that both smooth muscle and nonmuscle MLC-2 proteins are identical and are probably encoded by the same gene. In contrast, the human smooth muscle MLC-2 cDNA that we have characterized from an intact smooth muscle tissue is not expressed in skeletal and cardiac muscles and also in a number of nonmuscle cells.(ABSTRACT TRUNCATED AT 250 WORDS)

MeSH terms

  • Adenosine Triphosphatases / biosynthesis
  • Adenosine Triphosphatases / genetics*
  • Amino Acid Sequence
  • Base Sequence
  • Cell Line
  • Cloning, Molecular
  • Colon / enzymology
  • DNA / genetics*
  • Electrophoresis, Gel, Two-Dimensional
  • Female
  • Humans
  • Isoenzymes / biosynthesis
  • Isoenzymes / genetics*
  • Molecular Sequence Data
  • Molecular Weight
  • Muscle, Smooth / enzymology*
  • Muscle, Smooth, Vascular / enzymology*
  • Myosin Subfragments
  • Myosins / biosynthesis
  • Myosins / genetics*
  • Nucleic Acid Hybridization
  • Peptide Fragments / biosynthesis
  • Peptide Fragments / genetics*
  • Pregnancy
  • Protein Biosynthesis
  • Restriction Mapping
  • Transcription, Genetic
  • Umbilical Arteries / enzymology
  • Uterus / enzymology


  • Isoenzymes
  • Myosin Subfragments
  • Peptide Fragments
  • DNA
  • Adenosine Triphosphatases
  • Myosins

Associated data

  • GENBANK/J02854