Abstract: Background and purpose: Stanniocalcin 1 (STC1) has been reported to be up-regulated in various cancer tissues, and related to malignancy degree of cancer. However, the molecular mechanism of STC1 in lung cancer cells is still not clear. This experiment aimed to investigate the effects of STC1 on cell cycle and apoptosis of lung cancer A549 cells. Methods: A549 cells were transfected with validated siRNA for STC1 A549-STC1-siRNA and a negative control vector RNA A549-Vector. The gene and protein expression of cell cycle-related genes, including CyclinA, CyclinB1, CyclinD1, CyclinE, CDK2 and CDK4, as well as apoptosis-inhibiting genes Bcl-2, Bcl-xl and apoptosis-inducing genes Caspase-3, Bax, Bak and Bid, were detected by real-time fluorescent quantitative polymerase chain reaction (RTFQ-PCR) and Western blot. The cell cycle distribution was determined with flow cytometry. Terminal deoxynucleotidyl transferase-mediated nick-end labeling (TUNEL) was used to detect cell apoptosis. Results: After transfection with STC1-siRNA, the gene and protein expression of CyclinA, CyclinB1, CyclinD1, CyclinE, CDK2 and CDK4 decreased significantly in A549 cells (P<0.05). The proportion of cells in G₀/G₁ phase significantly increased, whereas the proportion of cells in S phase and G₂/M phase decreased (P<0.05). The cell cycle was blocked at G₀/G₁ phase. Furthermore, compared with that in A549-Vector, the gene and protein expression of Bcl-2 and Bcl-xl in A549-STC1-siRNA was reduced significantly (P<0.05), while the expression of apoptosis-inducing genes Caspase-3, Bax, Bak and Bid increased obviously (P<0.05). In addition, the percentage of apoptotic cells significantly increased in A549-STC1-siRNA compared with that in A549-Vector detected by TUNEL method. Conclusion: Down-regulation of STC1 by RNAi can block the cell cycle of A549 cells, inhibit cell proliferation, and promote cell apoptosis.

Key words: Stanniocalcin l, RNA interference, Cell cycle, Apoptosis