title: Smooth muscle type isoform of 20 kDa myosin light chain is expressed in monocyte/macrophage cell lineage.
abstract: Myosin light chain genes of human hematopoietic cells have not been fully characterized. We previously reported the cloning of the full-length cDNAs of 20 kDa regulatory myosin light chain (MLC-2), named as MLC-2A, from Meg-01, a human megakaryoblastic leukemia cell line (J. Smooth Muscle Res. 37: 25-38, 2001). We now cloned another MLC-2 isoforms from human platelets and U937, a human monocytic leukemia cell line, named as MLC-2B and MLC-2C, respectively. Both MLC-2A and MLC-2B consisted of three exons, which were situated on gene loci 18p1.3. Analysis of the gene structure indicated that MLC-2A and MLC-2B utilized different exons. MLC-2C also consisted of three exons, which was situated on gene loci 20p12. Amino acid sequence of MLC-2C was, of interest, apparently almost the same as that of MLC-2 from chicken gizzard smooth muscle LC20-A (one amino acid's difference) and human vascular smooth muscle LC-20 (two amino acids' difference). All three protein kinase C phosphorylation residues (Ser-1, Ser-2, Thr-9) and both myosin light chain kinase phosporylation residues (Thr-18, Ser-19) are conserved in these three isoforms. The MLC-2A and MLC-2B mRNA were expressed constitutively in all of the human hematopoietic cell lines examined and their expression levels were almost the same. On the other hand, MLC-2C mRNA was expressed in untreated monocytic cell lines (U937 and A-THP-1) and HL-60 differentiated into monocyte/macrophage cell lineage by TPA treatment. These results indicate that smooth muscle type isoform, MLC-2C is the inducible isoform, and might play a crucial role in monocyte/macrophage cell lineage.
authors.affiliation: Department of Hematology, Internal Medicine, Kitasato University School of Medicine, Sagamihara-shi, Kanagawa 228-8555, Japan. mahigash@med.kitasato-u.ac.jp
authors.forename: Masaaki
authors.initials: M
authors.lastname: Higashihara
authors.forename: Mariko
authors.initials: M
authors.lastname: Watanabe
authors.forename: Shigeki
authors.initials: S
authors.lastname: Usuda
authors.forename: Kouji
authors.initials: K
authors.lastname: Miyazaki
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D024722:Cardiac Myosins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D002645:Chickens; D005091:Exons; D006801:Humans; D008264:Macrophages / Q000166:cytology / Q000378:metabolism* / Q000473:pathology; D008969:Molecular Sequence Data; D009000:Monocytes / Q000166:cytology / Q000378:metabolism* / Q000473:pathology; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D018994:Myosin Light Chains / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism
chemical_list: D018994:Myosin Light Chains; D020033:Protein Isoforms; D012333:RNA, Messenger; C107184:myosin light chain 2; D024722:Cardiac Myosins