Background: Attenuated endogenous protein levels of cyclin-dependent kinase 2 associated protein 1 (p12(CDK2AP1)) and its active homodimer p25(CDK2AP1) were found in myxofibrosarcoma-derived cell lines. Clinical and biological significances of this putative tumor suppressor in myxofibrosarcoma were studied.
Methods: 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 p12(CDK2AP1) was interpretable in 102 primary myxofibrosarcomas and correlated with clinicopathological variables, CDK2, Ki-67 and active CASP3 protein levels, and disease-specific survival.
Results: Exogenous expression of p12(CDK2AP1) 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 p12(CDK2AP1) 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, p12(CDK2AP1) down-regulation was predictive of worse disease-specific survival in univariate (p = 0.003) and multivariate (p = 0.004) analyses.
Conclusions: Through down-regulation of CDK2, high p12(CDK2AP1) level induced cell cycle arrest and the mitochondrial-dependent apoptotic pathway. Low p12(CDK2AP1) level represents a poor prognostic factor in patients with myxofibrosarcoma.