Cyclin-dependent kinase 11 isoforms (CDK11) are members of the p34(edc2) superfamily. They have been shown to play a role in RNA processing and apoptosis. In the present study, we investigate whether CDK11 interacts with 14-3-3 proteins. Our study shows that the putative 14-3-3 binding site (113-RHRSHS-118) within the N-terminal domain of CDK11(p110) is functional. Endogenous CDK11(p110) binds directly to 14-3-3 proteins and phosphorylation of the serine 118 within the RHRSHS motif seems to be required for the binding. Besides, CDK11(p110) is capable of interacting with several different isofortns of 14-3-3 proteins both in vitro and in vivo. The interaction of 14-3-3 gamma with CDK11(p110) occurs throughout the entire cell cycle and reaches maximum at the G2/M phase. Interestingly. 14-3-3 gamma shows strong interaction with N-terminal portion of caspase-cleaved CDK11(p110) (CDK11(p60)) product at 48 h after Fas treatment. which correlates with the maximal cleavage level of CDK11(p110) and the maximum activation level of CDK11(p110) kinase activity during apoptosis. Collectively, these results suggest that CDK11 kinases could be regulated by interaction with 14-3-3 proteins during cell cycle and apoptosis. (c) 2005 Elsevier Inc. All rights reserved.