AbstractApoptosis plays a critical role in cellular homeostasis during development, immune responses, and tumorigenesis. Recent studies have identified a number of genes that control this process. We report here our identification of a novel cell survival-related gene (SRG) from a human expression cDNA library by functional cloning. SRG shows no significant nucleotide sequence homology to any known genes in the Genbank. Our fluorescence in situ hybridization analysis has estimated that SRG is located at 1p36, agreeing with the location at 1p36.22 in the human genome sequence. SRG encodes a putative protein of 172 amino acids, which is mainly located in the perinuclear region. Northern blotting analysis indicates that SRG is highly expressed in many human cancer cell lines although it is low in most tissues except liver and placenta. To investigate the function of SRG in apoptosis, we transfected SRG cDNA into BAF/BO3 and B16/F0 cells and induced apoptosis by cytokine/serum deprivation. We found that SRG-transfected cells are resistant to apoptosis induced by cytokine/serum deprivation. In addition, mice bearing SRG-transfected melanoma had more tumor formation and larger tumor growth. Melanoma transfected with antisense SRG showed significantly less tumor formation and smaller tumor growth. Interestingly, mouse SRG gene was also identified on chromosome 4 and blocking SRG expression with small interfering RNA promoted serum deprivation–induced apoptosis of NIH3T3 cells. Our results show that SRG is a novel cell survival gene that critically controls apoptosis and tumor formation.