Cell cycle dependent gene expression in quiescent stimulated and asynchronously cycling arterial smooth muscle cells in culture

Abstract

The expression of a set of cell cycle dependent (CCD) genes (c-fos, c-myc, ornithine decarboxylase (ODC), and thymidine kinase (TK)) was comparatively studied in cultured arterial smooth muscle cells (SMC) during exit from quiescence and exponential proliferation. These genes, which were not expressed in quiescent SMC, were chronologically induced after serum stimulation. c-fos mRNA were rapidly and transiently expressed very early in the G₁ phase; c-myc and ODC peaked a few hours after serum stimulation and then remained at an intermediary level throughout the first cell cycle; TK mRNA and activity then appeared at the G₁/S boundary and peak in G₂/M phases. Except for c-fos, the other genes were also expressed in asynchronously cycling SMC (ACSMC); their expression was studied in elutriated subpopulations representative of cell cycle progression. c-fos mRNA were undetectable in any sorted subpopulations, even in the pure early G₁ population. Despite a slight increase as the cell cycle advanced, c-myc and ODC genes were expressed throughout the ACSMC cell cycle. A faint TK activity was found in G₁ subpopulations and increased in populations enriched in other phases; in contrast, TK mRNA remained highly expressed in all elutriated subpopulations. This study demonstrates significant modulations in CCD gene expression between quiescent stimulated and asynchronously cycling SMC in culture. This suggests that the events occurring during the emergence of SMC from quiescence are probably different from those in the G₁ phase of ACSMC.