| Research Abstract |
Cell cycle inhibitors, p21^<cip1> and p16^<INK4> mediate growth arrest by inhibiting the action of G1 cyclin-dependent kinases (cdks). We produced adenovirus vectors containing coding sequences of the p21^<cip1> (Ax1CAp21) and p16^<INK4> gene (Ax1CAp16), and investigated wether gene transfer of p21^<cip1> and p16^<INK4> inhibit serum-induced hypertrophy of neonatal rat cardiomyocytes in vitro. Northern blot analysis revealed that endogenous p21 mRNA was up-regulated by the stimulation with 10% fetal calf serum (FCS), but p16 mRNA was not in cardiomyocytes. Ax1CAp21 (50 pfu per cell) and Ax1CAp16 (50 pfu per cell) caused significant inhibition of muscle specific gene, (genetic markers of cardiomyocyte hypertrophy), expressions induced by 10% FCS.Ax1CAp21 and Ax1CAp16 also inhibited serum-induced increases of cell surface area, as well as [^3H] leucine incorporation. However, the number of BrdU-positive myocyte was less than 5% of total myocytes whether of not treated with FCS,and did not alter by infection with Ax1CAp21 or Ax1CAp16. Further, antisense oligonucleotides against cyclin D1, one of major G1 cyclins, as well as overexpression of unphosphorylated retinoblastoma tumor suppresser gene (Rb) product overexpressed by adenovirus vector inhibited serum-induced cardiomyocyte hypertrophy. The results of our present study indicate that G1 cdk inhibitors inhibit hypertrophy of cardiomyocytes, and that the cdk4-cyclin D1 complex and its target protein Rb may, at least, mediate their inhibitory action.
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