Abstract
Members of the Bcl‐2 family of proteins play important roles in the regulation of cell death by apoptosis. The yeast Two‐Hybrid system was utilized to identify a protein that interacts with the anti‐apoptotic protein Bcl‐2, designated BMRP. This protein corresponds to a previously known mitochondrial ribosomal protein (MRPL41). Binding experiments confirmed the interaction of BMRP to Bcl‐2 in mammalian cells. Subcellular fractionation by differential centrifugation studies showed that both Bcl‐2 and BMRP are localized to the same fractions (fractions that are rich in mitochondria). Northern blot analysis revealed a major bmrp mRNA band of approximately 0.8 kb in several human tissues. Additionally, a larger 2.2 kb mRNA species was also observed in some tissues. Western blot analysis showed that endogenous BMRP runs as a band of 16–17 kDa in SDS–PAGE. Overexpression of BMRP induced cell death in primary embryonic fibroblasts and NIH/3T3 cells. Transfection of BMRP showed similar effects to those observed by overexpression of the pro‐apoptotic proteins Bax or Bad. BMRP‐stimulated cell death was counteracted by co‐expression of Bcl‐2. The baculoviral caspase inhibitor p35 also protected cells from BMRP‐induced cell death. These findings suggest that BMRP is a mitochondrial ribosomal protein involved in the regulation of cell death by apoptosis, probably affecting pathways mediated by Bcl‐2 and caspases. © 2004 Wiley‐Liss, Inc.