OBJECTIVETo study the influence of Benzo (a) pyrene on cell cycle distribution of quiescent diploid human embryonic lung fibroblast (HELF) cells.

METHODSHELF cells were synchronized at G0 phase of cell cycle by 0.5% serum starvation for 48 hours and identified by flow cytometry (FCM). Cells were treated with 20 micromol/L benzo (a) pyrene for 4 h and detected for the changes of cell cycle distribution 0 h, 24 h, 48 h after treatment respectively. HELF cells were treated with 0, 5, 10, 20 micromol/L Benzo (a) pyrene for 24 h and detected for cell cycle regulators p53, p21 and p16 expression changes using Western Blotting method. On the other hand, the dynamic changes of these regulators were also been detected within 24 h after 20 micromol/L Benzo (a) pyrene treated for 4h.

RESULTS0.5% Serum starvation for 48 hours could effectively synchronize HELF at G0 stage and G0 reached 78%. Well-modulated control cells entered into cell cycle to synthesize DNA and cells at S phase reached 43.9% 24 h after serum re-stimulate, while 20 micromol/L B (a) P treated cells were arrested in G1 stage. Control cells entered into the G1 stage of next cell cycle another 24 h later, B (a) P treated cells recovered from G1 arrest, 26.5% of which reached S phase, having a delay of almost 24 h compared with controls. After a series of B (a) P concentrations acting for 24 h, we found that P53 and P21 expression increased dramatically. On the other hand, P53 and P21 increased 4 h after treatment, P53 recovered to normal level after 12 h while P21 kept increasing in 24 h. P16 initially decreased and became normal at 24 h.

CONCLUSIONB (a) P induced quiescent HELF cells undergoing a reversible G1 arrest related with p53-p21 pathway.