Cyclin A is required in S phase in normal epithelial cells.

We have investigated cyclin A expression in a primary culture of normal rat hepatocytes and during rat liver regeneration after partial hepatectomy. In both cases, cyclin A mRNA and protein accumulate as the cells enter S phase. To investigate the potential implication of cyclin A accumulation at S phase, we microinjected anti-sense DNA constructs for cyclin A, resulting in effective inhibition of S phase entry. These effects were specific for cyclin A since anti-sense cyclin B construct had no similar effects. These results therefore, obtained in normal epithelial cells, indicate that cyclin A is involved in S phase and thus should not be only considered as a mitotic cyclin.