Expression of apoptosis and proliferation related genes in carcinogenesis of lung squamous cell carcinoma in rats

BACKGROUND & OBJECTIVE: The activation of caspase-3 protein, located the downstream of apoptosis, is the key of cell apoptosis signal conduction. Caspase-3 is the most important performer in accelerating apoptosis in the caspase family. Much progress has been achieved in the study of caspase-3 and human non-small cell lung cancer. This study was designed to investigate the effect of cellular proliferation and apoptosis related genes caspase-3 and proliferating cell nuclear antigen (PCNA), and to seek whether they could be chosen as molecular biology markers for lung cancer. METHODS: 3-Methylcholanthrene (MCA) and diethyinitrosamine (DEN) were used to induce lung squamous cell carcinoma by intra-left lobar-bronchial instillation in 50 Wistar rats. The other 10 rats instilled with iodized oil were regarded as control group. The expression of caspase-3 and PCNA were evaluated by SP immunohistochemistry during carcinogenesis. TUNEL(TDT-mediated dUTP nick end labeling) method was used to examine apoptotic cells. RESULTS: For the rat bronchial epithelium cells in control group, precancerous lesions, and lung squamous cell carcinoma, positive coefficient values of caspase-3 protein were 3.10+/-0.99, 2.25+/-1.13, and 1.38+/-0.95 on average, respectively; the means of PCNA-labeling index (PCNA-LI)were 14.10+/-5.02, 28.13+/-8.72, and 41.88+/-14.24, respectively; the means of apoptotic index(AI) were 0.60+/-0.52, 2.06+/-0.85, and 2.26+/-1.14, respectively.Significant differences in caspase-3 protein expression were observed between bronchial epithelium in control group and lung squamous cell carcinoma (P< 0.01). Caspase-3 expression was showed stronger in precancerous lesions than that in lung cancer (P< 0.05). Low proliferation index and low AI were detected in rat bronchial epithelium region in control group,which were significant differences in precancerous lesions and lung cancer, respectively (P< 0.01). In 34 rats with lung squamous cell carcinoma, there was negative relationship between caspase-3 and PCNA-LI (r=-0.7306, P< 0.01), so did it in AI and PCNA-LI(r=-0.8127,P< 0.01), but there was no relationship between caspase-3 expression and AI(P >0.05). CONCLUSION: Loss of caspase-3 expression may be associated with the development of lung squamous cell carcinoma in Wistar rats, but it is not associated with AI. PCNA-LI is an important marker for malignant progression of lung cancer.