CaMK phosphatase (CaMKP/POPX2/PPM1F) inhibitors suppress the migration of human breast cancer MDA-MB-231 cells with loss of polarized morphology

CaMK phosphatase (CaMKP/POPX2/PPM1F) is a Ser/Thr protein phosphatase that belongs to the PPM family. Accumulating evidence suggests that CaMKP is involved in the pathogenesis of various diseases, including cancer. To clarify the relationship between CaMKP activity and human breast cancer cell motility, we examined the phosphatase activity of CaMKP in cell extracts. CaMKP activity assays of the immunoprecipitates prepared from the cell extract revealed that cells exhibiting higher motility had higher CaMKP activity, with no significant differences in the specific activity being observed. Two CaMKP-specific inhibitors, 1-amino-8-naphthol-4-sulfonic acid (ANS) and 1-amino-8-naphthol-2,4-disulfonic acid (ANDS), inhibited the migration of highly invasive MDA-MB-231 breast cancer cells without significant cytotoxicity, while an inactive analog, naphthionic acid, did not. Furthermore, the cells lost their elongated morphology and assumed a rounded shape following treatment with ANS, whereas they retained their elongated morphology following treatment with naphthionic acid. Consistent with these findings, ANS and ANDS significantly enhanced the phosphorylation level of CaMKI, a cellular substrate of CaMKP, while naphthionic acid did not. The present data suggest that CaMKP could be a novel therapeutic target for cancer metastasis. •Breast cancer cells with higher motility showed higher CaMKP activity.•Two CaMKP-specific inhibitors significantly reduced MDA-MB-231 cell migration.•Treatment with the CaMKP inhibitors showed no significant cytotoxicity.•CaMKP inhibitor treatment caused loss of polarized morphology in MDA-MB-231 cells.•Enhanced phosphorylation of CaMKI was observed after CaMKP inhibitor treatment.