Specific proteolysis of the A-kinase-anchoring protein 149 at the Asp582 residue by caspases during apoptosis

A-kinase-anchoring protein 149 (AKAP149) is a member of a structurally diverse, though functionally similar anchoring protein family and is localized to the outer membrane of mitochondria and in the endoplasmic reticulum-nuclear envelope network. AKAP149 plays an important role in controlling the subcellular localization and temporal specificity of protein phosphorylation and mRNA metabolism by tethering kinases and phosphatases, such as protein kinase A and type I protein phosphatase, through its N-terminal protein-binding motifs and mRNAs via its C-terminal RNA-binding motifs. It is well recognized that caspases play a central role in transducing and amplifying the intracellular death signal and that apoptosis is executed as a consequence of caspase-mediated cleavage of multiple cellular substrates. The identification of novel death substrates and elucidation of the consequences of their proteolytic cleavages by caspases are therefore crucial for our understanding of cell death and other biological processes. Herein, we demonstrated that AKAP149 is a direct substrate of active caspase-3, -8 -and -10 in vitro and in vivo. 35S-labeled full-length AKAP149 was completely cleaved in vitro by active caspase-3, -8 and -10 into two fragments of ≈105 and 45 kDa, while caspase-2 cleaved it partially and caspase-1 did not cleave it at all. AKAP149 was also cleaved by caspases during Fas- and staurosporine-induced apoptosis in Jurkat T and HeLa cells, which were blocked by specific inhibitors of caspase-3 and -8. The specific cleavage site for these caspases was mapped in vitro and in vivo to Asp582 at AKAP149, which is located between the protein kinase A regulatory subunit anchoring and KH RNA-binding domains. In addition, HeLa cells transiently overexpressing AKAP149 D582E mutant were resistant to staurosporine-induced HeLa cell apoptosis. Taken together, these data suggest that AKAP149 activity may be deregulated by caspase-dependent proteolysis during apoptotic cell death and may provide useful information for elucidating the apoptosis signaling pathways in detail.