Cloning and Functional Characterization of Ptpcd2 as a Novel Cell Cycle Related Protein Tyrosine Phosphatase that Regulates Mitotic Exit

Faithful transmission of genetic information depends on accurate chromosome segregation as cells exit frommitosis, and errors in chromosomal segregation are catastrophic and may lead to aneuploidy which is the hallmarkof cancer. In eukaryotes, an elaborate molecular control system ensures proper orchestration of events at mitoticexit. Phosphorylation of specific tyrosyl residues is a major control mechanism for cellular proliferation and theactivities of protein tyrosine kinases and phosphatases must be integrated. Although mitotic kinases are wellcharacterized, phosphatases involved in mitosis remain largely elusive. Here we identify a novel variant of mouseprotein tyrosine phosphatase containing domain 1 (Ptpcd1), that we named Ptpcd2. Ptpcd1 is a Cdc14 relatedcentrosomal phosphatase. Our newly identified Ptpcd2 shared a significant homology to yeast Cdc14p (34.1%)and other Cdc14 family of phosphatases. By subcellular fractionation Ptpcd2 was found to be enriched in thecytoplasm and nuclear pellets with catalytic phosphatase activity. By means of immunofluorescence, Ptpcd2 wasspatiotemporally regulated in a cell cycle dependent manner with cytoplasmic abundance during mitosis, followedby nuclear localization during interphase. Overexpression of Ptpcd2 induced mitotic exit with decreased levels ofsome mitotic markers. Moreover, Ptpcd2 failed to colocalize with the centrosomal marker γ-tubulin, suggestingit as a non-centrosomal protein. Taken together, Ptpcd2 phosphatase appears a non-centrosomal variant ofPtpcd1 with probable mitotic functions. The identification of this new phosphatase suggests the existence of aninteracting phosphatase network that controls mammalian mitosis and provides new drug targets for anticancermodalities.