Metabolic mechanism of retinoic acid in glioma cells and its impact on cell proliferation

AIM: To investigate the mechanism for regulating the synthesis and metabolism of retinoic acid in glioma cell line SWO-Z2 and its effect on cell proliferation. METHODS: The siRNA targeting to human KLF9 mRNA was transfected into SWO-Z2 cells. The silencing efficiency was detected by real-time PCR and Western blotting. After silencing of KLF9 , the protein level of ALDH1A1 was detected by Western blotting. CCK-8 colorimetric assay was used to screen the optimal concentration of retinoic acid, and the strongest inhibitory effect of retinoic acid from 3 types of chemicals,13- cis -retinoic acid (13- cis RA),9- cis -retinoic acid (9- cis RA)and all- trans retinoic acid (ATRA), on SWO-Z2 cell growth was selected. Western blotting was also applied to explore the expression levels of cyclin D1, Bcl-2, cleaved PARP and GFAP in SWO-Z2 cells with the treatment of ATRA for 72 h. Simultaneously, the mRNA levels of retinoic acid receptors (RARs) in SWO-Z2 cells were determined by real-time PCR. RESULTS: siRNA-KLF9 knocked-down the expression of KLF9 and down-regulated the expression of aldehyde dehydrogenase 1 family member A1 (ALDH1A1) at mRNA and protein levels (P<0.05). Among the 3 retinoic acid drugs, ATRA was the most effective in inhibiting the proliferation of SWO-Z2 cells. After treated with ATRA on SWO-Z2 cells for 72 h, the expression of cleaved PARP was increased, Bcl-2 and cyclin D1 were decreased, and GFAP didn't change. The mRNA level of RARs in SWO-Z2 cells was very low. CONCLUSION: KLF9 positively regulates the expression of ALDH1A1 gene to increase the synthesis of retinoic acid. ATRA inhibits proliferation but does not induce differentiation of SWO-Z2 cells, which might result from lack of retinoic acid receptors in human glioma cells.