Effects of stomatin protein expression on proliferation and apoptosis of lung cancer cells

Abstract

Objective: To investigate the effect of stomatin protein expression on the proliferation and apoptosis of lung cancer cells. Methods: The expressions of stomatin mRNA in human bronchial epithelial cells (HBE) and lung cancer cells (H520, A549, 95D, H460, Glc-82, 973 and H1299) were detected by Real-time PCR. Immunohistochemistry (IHC) was used to detect stomatin protein expression in 4 lung cancer tissue microarrays with 259 cases of lung cancer and adjacent normal tissues. After knocking down the expression of stomatin in A549 cells, the proliferation was detected by 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT) assay, the apoptosis was detected by flow cytometry, the expression levels of total protein kinase B (AKT) and phosphorylated AKT at Ser473 were detected by Western blot. BALB/c nude mice were used to detect the tumorigenic ability of stomatin downregulated A549 cells (3 mice) and control cells (3 mice), and the protein expressions of stomatin, Ki67 and CD31 in tumor tissues were detected by IHC. Results: The M (range) of stomatin mRNA expression level in H520, A549, 95D, H460, Glc-82, 973, H1299 and HBE cells were 2.71 (2.66), 3.55 (3.16), 0.26 (0.22), 2.08 (1.98), 0.87 (0.35), 1.72 (2.53), 1.10 (1.82) and 0.01 (0.02), respectively. The mRNA expression levels of stomatin in H520, A549 and H460 cells were higher than that of HBE cells (all P<0.05), whereas there was no statistical difference among 95D, Glc-82, 973, H1299 and HBE cells (all P>0.05). IHC of lung tissue microarrays showed that the positive rate of stomatin expression in human lung cancer tissues was 34.7% (90/259), which was significantly higher than that in adjacent normal tissues [1.9% (5/259)] (P<0.05). In stomatin positive lung cancer tissues, the M (IQR) of tumor size for lower stomatin expression tissues (67 cases) was [41.22 (2 761.50) cm], which was smaller than that of higher stomatin expression tissues [(23 cases, 57.98(1 333.50) cm) (P<0.05). After knocking down stomatin expression, the fourth day absorbance value of stomatin-downregulated A549 cells was 0.55±0.07, which was lower than that of control cells (0.79±0.16) (P=0.012). The proportion of early apoptotic cells of stomatin-downregulated A549 cells [8.83 (53.00)] was higher than that of control cells [4.17 (25.00)] (P=0.026). The Ser473 phosphorylated AKT protein expression level in stomatin-downregulated A549 cells was 0.68±0.16, which was decreased compared with control cells (1.16±0.39) (P<0.05). The M (IQR) of total AKT expression level in stomatin-downregulated A549 cells was 4.25 (17.00), without statistically significant difference from control cells [4.75 (19.00)] (P>0.05). After inoculation of stomatin-downregulated A549 cells in nude mice for 43 days, the tumor volume was (37.93±3.12) mm(3), which was significantly smaller than that of the control group [(454.04±32.39) mm(3)] (P<0.001). And the expression levels of stomatin, nuclear proliferation antigen Ki67, and platelet-endothelial cell adhesion molecule CD31 were 1.78±0.69, 5.19±3.84, and 10.77±1.67, respectively, which were all decreased compared with control group (17.52±8.76, 54.14±41.02, and 19.72±6.97, respectively) (all P<0.05). Conclusion: Stomatin promotes lung cancer cell proliferation and inhibits cell early apoptosis by regulating AKT signaling pathway.