Cdc14-dependent dephosphorylation of Inn1 contributes to Inn1-Cyk3 complex formation

In Saccharomyces cerevisiae the Cdc14 phosphatase plays a well-established role in reverting phosphorylation events on substrates of the mitotic cyclin-dependent kinase (M-Cdk1), thereby promoting mitotic exit and downregulation of M-Cdk1 activity. Cdc14 localizes at the site of cell cleavage after M-Cdk1 inactivation, suggesting that Cdc14 may perform a crucial, yet ill-defined, role during cytokinesis. Here, we identified Inn1, as a novel direct substrate of both M-Cdk1 and Cdc14. Cdc14 colocalizes with Inn1 at the cell division site and interacts with the C-terminal proline-rich domain of Inn1 that mediates its binding to the SH3-domain-containing proteins Hof1 and Cyk3. We show that phosphorylation of Inn1 by Cdk1 partially perturbs the interaction of Inn1 with Cyk3 thereby reducing the levels of Cyk3 at the cell division site. We propose that Cdc14 counteracts Cdk1 phosphorylation of Inn1 to facilitate Inn1-Cyk3 complex formation and so promote cytokinesis.