Mitogen-induced up-regulation of non-smooth muscle isoform of alpha-tropomyosin in rat aortic smooth muscle cells

Correlation between the expression of the alpha-tropomyosin isoforms and ce ll growth was investigated in rat aortic smooth muscle cells. The levels of exon 1a, exons 1a + 2a (smooth muscle type) and exons 1a + 2b (non-smooth muscle type) were determined by reverse transcription-polymerase chain reac tion (RT-PCR). When the cells were cultured, the level of exons 1a + 2b tra nsiently increased while reaching a maximum at 3-5 days. When the serum-dep rived confluent cells were stimulated with 3-20% serum for 1.5 h, the level of exons 1a + 2b increased by about twofold. The 1-(5-isoquinolinesulphony l)-2-methylpiperazine (H-7) but not 2-[1-(3-dimethylaminopropyl)-1H-indol-3 -yl]-3-(1H-indol-3-yl)-maleimide (GF 109203X) inhibited this up-regulation. Phorbol-12, 13-dibutyrate (PDB) mimicked the effect of serum. The DNA synt hesis as determined by the incorporation of 5-bromo-2'-deoxy-uridine (BrdU) was not enhanced by the 1.5 h stimulation with serum or phorbol ester. The up-regulation of non-smooth muscle isoform of cr-tropomyosin occurred duri ng G(0)/G(1) transition before entering S phase. Protein phosphorylation is suggested to be involved in the up-regulation. However, the responsible ki nase(s) remain to be elucidated. (C) 2000 Elsevier Science B.V. All rights reserved.