PLK-1 interacts with RASSF1C and regulates its expression by a phosphorylation dependent mechanism

5197 Polo-like kinase-1 (Plk1) belongs to the polo-like kinase protein family which regulates mitotic progression and its activities was recently showed to be regulated by progressive phosphorylation at Ser137 and Thr210 during the cell cycle. One of its major roles during mitosis is to promote the mitotic spindle formation through direct interaction and phosphorylation of proteins involved in microtubule organization and assembly. Here, we report that Plk1 interacts with the 1C isoform of the RASSF1 protein family. RASSF1C, like RASSF1A, was recently showed to bind to and regulate microtubule stability. Although ectopic expression of the wild-type Plk1 failed to affect the expression of RASSF1C, the dominant active Plk1 mutants (T210D or S137D) significantly downregulated RASSF1C protein level. Meanwhile, a further downregulation of the RASSF1C protein was observed when a double mutant (T210D+S137D) was expressed, suggesting that the effect of Plk1 on RASSF1C depends on the kinase activities of Plk1. Interestingly, while Plk1 can also interact with RASSF1A, expression of either the wild-type or dominant active mutants did not affect the RASSF1A protein level. Taken together, our result demonstrated the microtubule regulator RASSF1C as a novel target of Plk1.