Molecular characterization of DEFCAP: A novel apoptosis protein implicated in cancer and inflammation.

Abstract

Apoptosis (or programmed cell death) is the organized series of intracellular events that lead to a cell's demise. The families of proteins controlling these intracellular events have been conserved throughout evolution as seen by the examination and comparison of these proteins from lower organisms such as the nematode <italic>C. elegans</italic> to those of higher eukaryotes. The identification and characterization of proteins involved in these intracellular events are key to understanding the balance between cell survival, proliferation, and apoptosis---processes that have ramifications for normal tissue homeostasis throughout the lifespan of an organism as well as in the pathogenesis and progression of diseases such as cancer. Here we report the deduced amino acid sequences and characterization of DEFCAP-L and DEFCAP-S (D&barbelow;eath E&barbelow;ffector F&barbelow;ilament forming C&barbelow;ed-4-like A&barbelow;poptosis P&barbelow;rotein), two isoforms for a novel member of the mammalian Ced-4 family of proteins. The NH₂-terminal region of DEFCAP consists of a pyrin-like motif (PLM)/pyrin domain (PD), a proline-rich sequence (PR), followed by a highly conserved NBD, a multiple LRR containing domain, and a COOH-terminal CARD. <italic> In vitro</italic> studies suggest that DEFCAP's LRR/CARD domains are critical for the induction of apoptosis and that anti-apoptotic molecules (Bcl-2, Bcl-xL, and DN Caspase-9) can block this event. <italic>In vitro</italic> coimmunoprecipitation studies suggest that DEFCAP is capable of associating with caspase-2 and -9. In order to gain a better understanding of DEFCAP's function and to identify DEFCAP protein-protein interactions, we performed a yeast two-hybrid assay using DEFCAP's PD/PLM domain and identified multiple binding partners including an uncharacterized novel protein designated NDBP-1 (NH₂-terminal DEFCAP Binding Protein-1) and NDBP-2 (Jab1). Although at present the physiological significance of these protein interactions remains unknown, these results give important insight into the potential signaling pathways in which DEFCAP may be involved.