Death-signal-induced relocalization of cyclin-dependent kinase 11 to mitochondria

Fas receptor-Fas ligand interaction appears to be important in carcinogenesis, tumour outgrowth and metastasis. Emerging evidence suggests that CDK11 (cyclin-dependent kinase 11) plays a role in apoptosis and melanoma development. Here, we show that CDK11(p110) protein kinase was cleaved after induction of apoptosis by Fas. The N-terminal portion of CDK11(p110), CDK11(p160), was translocated from the nucleus to the mitochondria. The targeting of CDK11(p60) to mitochondria occurred as early as 12 h after treatment. Overexpression of EGFP (enhanced green fluorescent protein)-tagged CDK11(p60) could partially break down the mitochondrial membrane potential, induce cytochrome c release and promote apoptosis. Reduction of endogenous CDK11(p60) protein levels with siRNA (small interfering RNA) resulted in the suppression of both cytochrome c release and apoptosis. In addition, subcellular fractionation studies of Fas-mediated apoptosis demonstrated that CDK11(p60) was associated with the mitochondrial import motor, mitochondrial heat shock protein 70. Taken together, our data suggest that CDK11(p60) can contribute to apoptosis by direct signalling at the mitochondria, thereby amplifying Fas-induced apoptosis in melanoma cells.