[Role of p53/p21 signal transduction pathway in the malignant transformation of human embryonic lung fibroblasts induced by quartz].

OBJECTIVE:To observe the expression of p53 protein and investigate the roles of p53 in the expressions and interactions of p21, cyclin D1 and cyclin dependent kinase 4(CDK4) proteins in malignant transformation of human embryonic lung fibroblasts(T-HELF) induced by quartz. METHODS:The cytosolic protein and nuclear protein of both HELF and T-HELF cells were extracted by the separation technique of cytoplasm and nuclei. The distribution and expression of p53, phosphorylated p53 and p21 proteins were detected by Western blot. Based on the RNA interference technique, p53 siRNA was transfected into T-HELF cells to observe the protein expression and change of p53, phosphorylated p53, p21, cyclin D1 and CDK4, while the control group was conducted by transfecting the CMV-neo blank vector into the plasmid. The expression levels of p21, cyclin D1 and CDK4 protein complex in HELF and T-HELF cells were detected by immunoprecipitation. After adding 20 μmol/L of p53 chemical inhibitor pifithrin-α(PFT-α) and 2 μg of p53 siRNA into T-HELF cells respectively, the effect of p53 protein inhibition on p21, cyclin D1 and CDK4 protein complex was also observed. RESULTS:Quartz stimulation of HELF caused a significant increase in the expression of p53 and phosphorylated p53 protein in the nucleus(P<0. 05). The protein expression of p53 in the nucleus of T-HELF was significantly lower than that of HELF(P<0. 05). After transfection of p53 siRNA, the expression of p53 protein was decreased and the expression of p21 and cyclin D1 protein was increased compared with the control group(P<0. 05), while the change of expression in CDK4 was not observed(P>0. 05). Additionally, the result of immunoprecipitation showed that the inhibition of p53 expression could down-regulate the expression level of the binding complex between p21 and cyclin D1 protein(P<0. 05). However, this effect on p21-CDK4 and cyclin D1-CDK4 protein complex was not observed(P>0. 05). CONCLUSION:By regulating the expression and protein-protein interaction between p21 and cyclin D1, p53 would participate in quartz-induced malignant transformation.