TMSG-1 was a tumor metastasis-related gene identified using mRNA differential dis-play, whose expression level was lower in cancer cell lines with higher metastatic potential and in tumor tissue with metastasis. TMSG-1 was transfected to prostate cancer cell line (PC-3M-1E8) with high metastatic potential to observe the effects of increased expression of TMSG-1 on V-ATPase activity, intracellular pH and cell apoptosis. Subcellular localization of the encoded pro-tein of TMSG-1 was determined by using GFP. Results showed that there were no differences of V-ATPase activity among parental PC-3M-1E8 cell line, pcDNA3 transfectant and anti-TMSG-1 transfectant, whereas the V-ATPase activity was significantly higher in TMSG-1 transfectant than that in parental PC-3M-1E8 cell line, pcDNA3 transfectant and Anti-TMSG-1 transfectant (p<0.001). Intracellular pH (pHi) was detected by using the pH-dependent fluorescence probe BECEF. Re-sults showed the pHi was significantly increased in TMSG-1 transfectant. Cell apoptosis assay demonstrated cell apoptosis was significantly higher in -1 transfectant (p<0.01) and BCL2 expres-sion was down regulated. Subcellular localization of TMSG-1 protein showed TMSG-1 was a transmembrane protein, which predicted TMSG-1 protein was located in cytoplasm system, such as endoplasmic reticulum and mitochondrial. These results indicated TMSG-1 up regulation in prostate cancer cell line could promote V-ATPase activity, increase pHi and cell apoptosis, and inhibit the expression of BCL2. TMSG-1 was a tumor metastasis-related gene identified using mRNA differential dis-play, whose expression level was lower in cancer cell lines with higher metastatic potential and in tumor tissue with metastasis. TMSG-1 was transfected to prostate cancer cell line (PC -3M-1E8) with high metastatic potential to observe the effects of increased expression of TMSG-1 on V-ATPase activity, intracellular localization of the and cellular apoptosis. Subcellular localization of the encoded pro-tein of TMSG-1 was determined by using GFP. Results showed that there were no differences of V-ATPase activity among parental PC-3M-1E8 cell line, pcDNA3 transfectant and anti-TMSG-1 transfectant, whereas the V-ATPase activity was significantly higher in TMSG-1 transfectant than that in parental PC-3M-1E8 cell line, pcDNA3 transfectant and Anti-TMSG-1 transfectant (p <0.001). Intracellular pH (pHi) was detected by using the pH- dependent fluorescence probe BECEF. Re sults showed the pHi was significantly increased in TMSG-1 trans Subcellular localization of TMSG-1 protein showed TMSG-1 was a transmembrane protein, which predicted TMSG-1 (p <0.01) and BCL2 expres-sion was down regulated These results indicate that TMSG-1 upregulation in prostate cancer cell line could promote V-ATPase activity, increase pHi and cell apoptosis, and inhibit the expression of BCL2.