[Show abstract][Hide abstract] ABSTRACT: 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 approximately 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.
No preview · Article · Jul 2008 · Oncology Reports
[Show abstract][Hide abstract] ABSTRACT: Apoptosis executed by the mammalian caspase family plays a fundamental role in cellular homeostasis. Deregulation of this process is associated with several human diseases. The multimerization of ligand-induced death receptors results in the recruitment of the death inducing signaling complex and autocatalytic activation of initiator caspases, including caspase-8 and -10. However, it is still unclear how initiator caspases trigger and control the early apoptotic signaling pathways, partly because the downstream proteolytic cleavage targets of the initiator caspases are not completely known. Although it is known that a number of proteins are cleaved by various members of the caspase family, the identification of specific cleavage substrates of the initiator caspases 8 and 10, has been hindered by a lack of systematic and broadly applicable strategies for substrate identification. In the present study we constructed a mouse cDNA library and used it to perform a systematic, genome-wide screen for novel in vitro substrates of caspase-8 and -10. From this, we successfully identified six putative caspase substrates, including five novel proteins (ABCF1, AKAP1, CPE, DOPEY1 and GOPC1) that may be targeted specifically by the initiator caspases 8 and 10 during the early stages of apoptosis. These findings may provide useful information for elucidating the apoptotic signaling pathways downstream of the death receptors.
No preview · Article · Apr 2008 · International Journal of Molecular Medicine