Negatively regulates the G2-M phase transition, possibly by promoting cyclin B1/CCNB1 and CDK1 proteasomal degradation and thereby preventing their accumulation during interphase. A higher concentration is observed in the cytoplasm compared to the nucleus. Seems to be expressed in prostate and less abundantly in adult brain, fetal liver, and fetal kidney. The B30.2/SPRY domain is required for the negative regulation of cell proliferation. Phosphorylated by PKC and CDK1 (PubMed:20725088). The antiproliferative effect seems to be positively regulated by PKC phosphorylation and negatively by CDK1 phosphorylation (PubMed:20725088).