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[Effects of p53 in benzo (a) pyrene induced p21 and E2F-1 expression and cell cycle changes].

OBJECTIVE
To investigate the roles of p53 in cell cycle changes on human embryo lung fibroblasts (HELF) induced by benzo(a) pyrene[ B(a) P], and relationships between p53 and p21, E2F-1.


METHODS
Cells transfected with p53 siRNA plasmid (p53-H) and CMV vector (HELF/CMV) were cultured with serum-free R/MINI-1640 for 48 hours, then treated with 2 micromol/L B(a)P for 24 hours. Flow cytometry assay was used for detecting the cell cycle alteration after being exposed to B(a)P. Changes of p53 and p21 expressions were checked using Western blot assay, and the cytoplasmic and nuclear extraction was used to observe the subcellular localizations of p53 and p21. The immunofluorescence assay was used to check changes of E2F-1 expression and the distribution of E2F-1 in nuclear and cytoplasm after exposed to B (a)P. p53siRNA plasmid and the chemical inhibitor of p53 [pifithrin-alpha (PFT)] were used to observe effects of p53 in B(a)P induced cell cycle changes and the relationships of p53 and p21, E2F-1.


RESULTS
After 2 micromol/L B(a)P exposure, the ratio of G1 phase cells (71 +/- 5)% was decreased to (39 +/- 4)% (P < 0.05). p53, p21 and E2F-1 expressions were increased significantly, and over expressed proteins were mostly located in nuclear after B(a)P treatment. When p53 expression was inhibited by p53 siRNA or PFT, the decreases of G1 phase in response to B(a)P treatment still existed, and over expression of p21 induced by B(a)P was attenuated, especially in nuclear, but E2F-1 over expression was not changed significantly.


CONCLUSION
B(a)P could induce cell cycle changes through p53 independent pathways. And p53 could regulate p21 expression positively, but not E2F-1.