A-Kinase-Anchoring Protein 95 Functions as a Potential Carrier for the Nuclear Translocation of Active Caspase 3 through an Enzyme-Substrate-Like Association

Abstract

Caspase-mediated proteolysis is a critical and central element of the apoptotic process, and caspase 3, one of the effector caspases, is proposed to play essential roles in the nuclear morphological changes of apoptotic cells. Although many substrates for caspase 3 localize in the nucleus and caspase 3 translocates from the cytoplasm to the nuclei after activation in apoptotic cells, the molecular mechanisms of nuclear translocation of active caspase 3 have been unclear. Recently, we suggested that a substrate-like protein(s) served as a carrier to transport caspase 3 from the cytoplasm into the nucleus. In the present study, we identified A-kinase-anchoring protein 95 (AKAP95) as a caspase 3-binding protein. Small interfering RNA-mediated depletion of AKAP95 reduced apoptotic nuclear morphological changes, suggesting that AKAP95 is involved in the process of apoptotic nuclear morphological changes. The association of AKAP95 with active caspase 3 was analogous to an enzyme-substrate interaction. Furthermore, overexpression of AKAP95 with nuclear localization sequence mutations inhibited nuclear morphological changes in apoptotic cells. These results indicate that AKAP95 is a potential carrier protein for active caspase 3 from the cytoplasm into the nuclei in apoptotic cells.

ACKNOWLEDGMENTS

We thank Joel D. Leverson and Han-Kuei Huang for critical reading of the manuscript, Vishva M. Dixit for the pcDNA3/Yama plasmid, Kjetil Tasken for the human AKAP95 cDNA, John D. Scott for the anti-AKAP95 serum, and Jun-ichi Miyazaki for the pUC-CAGGS plasmid.

This study was supported in part by Grants-in-aid for Scientific Research on Priority Areas from the Ministry of Education, Science, Sports, and Culture of Japan (to S.K.) and by Public Health Service grants CA82683 and CA14195 from the National Cancer Institute (to T.H.). T.H. is a Frank and Else Schilling American Cancer Society Professor.