A novel homocysteine-responsive gene, smap8, modulates mitogenesis in rat vascular smooth muscle cells.
We isolated the cDNA of a gene, designated smooth muscle-associated protein 8 (smap8), during a search for new genes expressed in human aortic smooth muscle cells. The full-length smap8 cDNA is 3241 bp long and contains an open reading frame of 1113 bp encoding an approximately 45 kDa soluble protein identical to NDRG4 protein. Smap8 mRNA was expressed predominantly in the brain and heart, and moderately in vascular smooth muscle cells. Expression of smap8 mRNA was induced within 3-12 h by treatment with 10 mm homocysteine in rat aortic smooth muscle cells (A10 cells). Expression of exogenous smap8 markedly reduced both the proliferation and migration rates of rat A10 cells, however, PDGF-induced proliferation was significantly enhanced in smap8-expressed cells compared with mock-transfected cells. To ascertain the involvement of smap8 in mitogenesis, we tested the effects of stimulation of smap8, MEK1/2 or ERK1/2, which is known as a proliferation relating intermediate, by various growth factors and cytokines. PDGF was the most prominent in promoting phosphorylation of the smap8 protein. PDGF-dependent phosphorylation of smap8 was induced prior to ERK1/2 activation, and was repressed by staurosporine, a general inhibitor of serine/threonine kinases. Furthermore, activation of both MEK1/2 and ERK1/2 was markedly enhanced in these cells. Smap8 might therefore regulate the potentiation of ERK1/2 signalling induced by PDGF treatment. Our results imply that smap8 is involved in the regulation of mitogenic signalling in vascular smooth muscle cells, possibly in response to a homocysteine-induced injury.
Nishimoto
Shinichi
S
Department of Molecular and Cellular Biology, Medicinal Research Laboratories, Taisho Pharmaceutical Co. Ltd, Yoshino-cho, Saitama-shi, Japan.
Tawara
Junko
J
Toyoda
Hitoshi
H
Kitamura
Kunihiro
K
Komurasaki
Toshi
T
D000595:Amino Acid Sequence; D000818:Animals; D015152:Blotting, Northern; D002455:Cell Division; D002460:Cell Line; D002465:Cell Movement; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000378:metabolism; D004331:Drosophila melanogaster / Q000378:metabolism; D005786:Gene Expression Regulation; D006710:Homocysteine / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000737:chemistry* / Q000502:physiology*; D009130:Muscle, Smooth / Q000166:cytology; D009131:Muscle, Smooth, Vascular / Q000166:cytology*; D009419:Nerve Tissue Proteins; D010455:Peptides / Q000737:chemistry; D010766:Phosphorylation; D010982:Platelet-Derived Growth Factor / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D013997:Time Factors; D014018:Tissue Distribution; D014162:Transfection
D018076:DNA, Complementary; D009124:Muscle Proteins; C431705:NDRG4 protein, human; C486613:Ndrg4 protein, rat; D009419:Nerve Tissue Proteins; D010455:Peptides; D010982:Platelet-Derived Growth Factor; D012333:RNA, Messenger; D006710:Homocysteine; D012313:RNA; C482128:MAP2K2 protein, human; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; C482125:MAP2K1 protein, human; D020929:Mitogen-Activated Protein Kinase Kinases