ABSTRACT
Homo sapiens longevity assurance homologue 2 (LASS2) is a novel gene isolated from a human liver cDNA library by our laboratory, and it is a human homologue of the yeast longevity assurance gene LAG1 (Saccharomyces cerevisiae longevity assurance gene). According to our previous results, LASS2 could interact with subunit c of vacuolar type H(+)-ATPase (V-ATPase), and the overexpression of LASS2 could inhibit the cell growth of a human hepatocellular carcinoma (HCC) cell line, SMMC-7721. In order to understand the role of the interaction between LASS2 and V-ATPase in HCC cell growth, we transiently transfected plasmid pCMV-HA2-LASS2 into HCCLM3, a HCC cell line without the significant expression of endogenous LASS2. The pH-sensitive fluorescence probes, BCECF and BCECF-AM, were used to measure the intracellular and extracellular H(+) concentrations of HCCLM3 cells respectively. The effect of LASS2 gene on apoptosis was evaluated with Annexin-V/FITC and propidium iodide (PI) by flow cytometry. Western blot was used to detect cytochrome c (Cyt c) in the cytosol and mitochondria, as well as pro-caspase-3 in cytosol. The results showed that the cell growth of LASS2-transfected HCCLM3 cells was significantly inhibited compared with that of the mock control. LASS2 transfection increased intracellular H(+) concentration of HCCLM3 cells, while decreased extracellular H(+) concentration. Moreover, LASS2 transfection significantly enhanced the apoptosis of HCCLM3 cells. In LASS2-transfected cells, the amounts of Cyt c increased in the cytosol, while decreased in the mitochondria. Meanwhile, the expression of pro-caspase-3 in the cytosolic extracts was decreased. These results implicate that LASS2 gene might increase intracellular H(+) of HCC cells via the interaction with V-ATPase, thereby inducing cell apoptosis through mitochondrial pathway.
Subject(s)
Humans , Apoptosis , Carcinoma, Hepatocellular , Pathology , Caspase 3 , Metabolism , Cell Line, Tumor , Cell Proliferation , Liver Neoplasms , Pathology , Membrane Proteins , Metabolism , RNA, Small Interfering , Sphingosine N-Acyltransferase , Metabolism , Transfection , Tumor Suppressor Proteins , Metabolism , Vacuolar Proton-Translocating ATPases , MetabolismABSTRACT
<p><b>BACKGROUND</b>Our previous study confirmed that oligodendrogliomas had higher frequency of chromosome 1p/19q deletion. In order to improve the diagnostic criteria and to predict the prognosis of oligodendroglioma patients, the status of chromosome 1p/19q deletion, the methylation of O(6)-methylguanine-DNA methyltransferase (MGMT), and the expression of p53 protein were evaluated and investigated in relation to patients' outcomes.</p><p><b>METHODS</b>Methylation of MGMT in 73 cases was analyzed by nested methylation-specific PCR (MSP). The levels of MGMT and p53 protein were tested with immunohistochemistry. Pearson's chi-square test and Fisher's exact test were used. Multivariate and Kaplan-Meier analysis were performed to determine patients' outcomes.</p><p><b>RESULTS</b>Both oligodendrogliomas and astrocytic gliomas exhibited frequent methylation of MGMT. However, the results of MSP did not completely correspond to that of the immunohistochemical staining for MGMT. The expression of p53 protein was more frequently observed in patients without a 1p or 19q deletion in anaplastic oligodendrogliomas (P = 0.032, 0.025). In low-grade oligodendrogliomas, methylation of MGMT was more frequent in patients with 1p/19q deletion than in patients with 1p/19q intact (P = 0.038). Patients with oligodendrogliomas with 1p/19q loss of heterozygosity and p53-negative showed a longer progression-free survival.</p><p><b>CONCLUSION</b>Detection of chromosome 1p/19q status combined with p53 protein immunohistochemistry might be beneficial to improve the pathological diagnosis and to determine the prognosis of patients with oligodendrogliomas.</p>