[Effect of down-regulation of growth arrest and DNA damage inducible protein 45β on PC9 lung adenocarcinoma cells].

OBJECTIVE:To explore the effect of down-regulation of growth arrest and DNA damage inducible protein 45β (GADD45β) on the PC9 lung adenocarcinoma cells.
 Methods: GADD45β gene siRNA sequence was designed and synthesized, which was transfected into PC9 lung adenocarcinoma cells through lentivirus transfection. Quantitative real-time PCR (qRT-PCR) and Western blot are used to examine the mRNA and protein levels of GADD45β in PC9 cells before and after the transfection. Annexin V-allophycocyanin (APC) double-staining flow cytometry was used to detect the apoptosis level after the transfection. The intracellular DNA content after transfection was detected by flow cytometry. The percentage of the cells at each period of cell cycle was calculated, and the effect of RNA interference on the cell growth were analyzed. The effects of RNA interference on the tumor-formation ability of cells were tested by counting the number of clones. MTT assay was used to test the half maximal inhibitory concentration (IC50) of PC9 cells for gefitinib. 
 Results: The 5'-AAATCCACTTCACGCTCAT-3' sequence was identified as the effective sequence for GADD45β gene RNA interference. The mRNA and protein expression levels of GADD45β were markedly decreased (both P<0.05) at 48 h after transfection of GADD45β-siRNA, which resulted in the increased apoptosis rate (P<0.05), decreased tumor clone number (P<0.05) and increased percentage of PC9 cell at the S stage and G2/M stage (P<0.05). The IC50 for gefitinib was decreased obviously (P<0.05).
 Conclusion: Down-regulation of GADD45β can reduce the colony-forming ability of PC9 cells, promote the cell apoptosis, and enhance the sensitivity of PC9 cells to gefitinib.