CDK2AP1

Abstract: Previous reports support the role of cyclin-dependent kinase 2-associated protein 1 (CDK2AP1) as a tumor suppressor that functions as a key player in cell cycle regulation. Although the misadjustment of CDK2AP1 has been revealed in several types of human malignancies, the functional role of CDK2AP1 in human glioma remains unknown. The present study was undertaken to investigate the effects of CDK2AP1 knockdown by RNA interference (RNAi) on glioma cell growth and tumorigenesis. We employed lentivirus-mediated RNAi to down-regulate CDK2AP1 expression in U251 and U373 cells. Knockdown of CDK2AP1 resulted in a significant reduction in U251 and U373 cell proliferation, as determined by MTT and colony formation assays. Cell cycle analysis showed CDK2AP1 silencing caused U251 cells arrest in G0/G1 phase, especially in the sub-G1 phase representing apoptotic cells. In vivo tumorigenesis was assessed using xenograft formation and CDK2AP1 depletion remarkably inhibited glioma growth and tumorigenesis. Taken together, these results suggest that CDK2AP1 siRNA may have an anti-tumorigenic effect on human glioma.

Abstract: Attenuated endogenous protein levels of cyclin-dependent kinase 2 associated protein 1 (p12CDK2AP1) and its active homodimer p25CDK2AP1 were found in myxofibrosarcoma-derived cell lines. Clinical and biological significances of this putative tumor suppressor in myxofibrosarcoma were studied. Plasmids carrying the CDK2AP1 gene and small hairpin RNA interference (shRNAi) targeting CDK2AP1 were transfected into NMFH-1 and/or OH931 cells to evaluate the effects on the CDK2, active caspase 3 (CASP3), cleaved-CASP8 and -CASP9 levels, cell cycle regulation, and/or apoptotic responses. Immunostaining of p12CDK2AP1 was interpretable in 102 primary myxofibrosarcomas and correlated with clinicopathological variables, CDK2, Ki-67 and active CASP3 protein levels, and disease-specific survival. Exogenous expression of p12CDK2AP1 in NMFH-1 and OH931 cells significantly induced G0/G1 cell cycle arrest and down-regulated CDK2 protein level. In NMFH-1 cells, these aspects were reversed by shRNAi targeting CDK2AP1 gene. Increased active CASP3 and cleaved-CASP9, but not -CASP8, were detected after CDK2AP1 overexpression, suggesting the cellular apoptosis were induced through the mitochondrial pathway. Immunostains of p12CDK2AP1 were aberrantly decreased in 56.9 % of cases; positively and negatively correlated with protein levels of CDK2 (p = 0.023), Ki-67 (p = 0.001) and active CASP3 (p < 0.001), respectively. Following by high histological grades, p12CDK2AP1 down-regulation was predictive of worse disease-specific survival in univariate (p = 0.003) and multivariate (p = 0.004) analyses. Through down-regulation of CDK2, high p12CDK2AP1 level induced cell cycle arrest and the mitochondrial-dependent apoptotic pathway. Low p12CDK2AP1 level represents a poor prognostic factor in patients with myxofibrosarcoma.