Investigation of Novel Human CED-4 Homolog NAC-X in Apoptosis Regulation of Breast Cancer

Proteins containing a Caspase-Associated Recruitment Domain (CARD) have previously been shown to serve as key regulators of tumor cell survival as well as regulators of other cellular processes, such as cytokine production. Interleukin-l beta (IL-1B) is a cytokine which has been found to be expressed in breast cancer cells and may be associated with more aggressive and invasive breast tumors. Through a bioinformatics approach, we identified a novel CARD protein which also contained a nucleotide binding domain (NACHT) and a region of leucine-rich repeats (LRR). Here we report the cloning and functional characterization of CLAN (CARD, LRR, And NACHT-containing protein) - CLAN was found to be expressed in several breast cancer cell lines as well as in monocytes by RT-PCR. Co- immunoprecipitation studies revealed that the CARD of CLAN associated with the CARD of several other proteins including caspase-l, Nod2, and NAC. When assayed using an IL-1B ELISA, CLAN was found to induce the activation of caspase-l. Through its interactions with other CARD-containing proteins, CLAN may regulate the survival of breast cancer cells and could be utilized as a novel anti-tumor target or diagnostic/prognostic biomarker.