Abstract: OBJECTIVE: To study the apoptotic effect and regulation of 1，4-benzoquinone(PBQ) on human embryonic lung fibroblast (HELF)， cells. METHODS：MTT assay was used to detect the relative growth rate (RGR)，cell cycle was determined by single-stained assay with PI and apoptosis was determined by double-stained assay with Annexin-Ⅴand PI using flow cytometry. Bax，Bcl-2，p53 mRNA levels were determined with real-time PCR. RESULTS：The RGRs of HELF cells exposed to different PBQ concentrations after 24 h decreased (P < 0.05)，cell cycle distribution was changed at 40 and 60 μmol/L after 24 h (P <0.05). The RGRs of HELF cells exposed to 40 μmol/L PBQ after different times decreased (P <0.05)，the rates of G0/G1 phase increased with time (P < 0.05). Apoptosis was induced with PBQ higher than 20μmol/L，and increased with PBQ concentration (P < 0.05). The relative expression levels of Bax，Bcl-2，p53 increased with concentration after exposure for 24 h (P < 0.05). The relative expression levels of Bax and p53 exposed at 40μmol/L increased with time (P < 0.05)，while bcl-2 decreased with time (P < 0.05)，with Bax/Bcl-2 ratio increased with time (P < 0.05). CONCLUSION：PBQ was able to change cell cycle distribution of HELF cells，and induce apoptosis，with dose-response and time-response effects. The up-regulation of mRNA expression level of p53 and the elevated Bax/Bcl-2 ratio may be the mechanisms for apoptosis of HELF cells after PBQ exposure.

Key words: 4-benzoquinone, HELF cell, cell apoptosis, Bax/Bcl-2, p53