Chromosome separation and exit from mitosis in budding yeast: dependence on growth revealed by cAMP-mediated inhibition.

Cell cycle progression of somatic cells depends on net mass accumulation. In Saccharomyces cerevisiae the cAMP-dependent kinases (PKAs) promote cytoplasmic growth and modulate the growth-regulated mechanism triggering the begin of DNA synthesis. By altering the cAMP signal in budding yeast cells we show here that mitotic events can also depend on growth. In fact, the hyperactivation of PKAs permanently inhibited both anaphase and exit from mitosis when cell growth was repressed. In S. cerevisiae the anaphase promoting complex (APC) triggers entry into anaphase by mediating the degradation of Pds1p. The cAMP pathway activation was lethal together with a partial impairment of the Cdc16p APC subunit, causing a preanaphase arrest, and conversely low PKA activity suppressed the lethality of cdc16-1 cells. Deregulated PKAs partially prevented the decrease of Pds1p intracellular levels concomitantly with the anaphase inhibition, and the PKA-dependent preanaphase arrest could be suppressed in pds1(-) cells. Thus, the cAMP pathway and APC functionally interact in S. cerevisiae and Pds1p is required for the cAMP-mediated inhibition of chromosome separation. Exit from mitosis requires APC, Cdc15p, and the polo-like Cdc5p kinase. PKA hyperactivation and a cdc15 mutation were synthetically lethal and brought to a telophase arrest. Finally, a low cAMP signal allowed cell division at a small cell size and suppressed the lethality of cdc15-2 or cdc5-1 cells. We propose that mitosis progression and the M/G1 phase transition specifically depend on cell growth through a mechanism modulated by PKAs and interacting with the APC/CDC15/CDC5 mitotic system. A possible functional antagonism between PKAs and the mitosis promoting factor is also discussed.