Aim:To characterize the molecular mechanisms of nitrofen-induced pulmonaryhypoplasia.Methods:After administration of nitrofen to cultured type Ⅱ A549pneumocytes,cell proliferation and DNA synthesis were investigated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide colorimetry,colony forma-tion assay,flow cytometry and[~3H]-thymidine incorporation assay.Apoptosiswas measured by terminal transferase-mediated dUTP nick-end-labeling,acridineorange-ethidium bromide staining and flow cytometry.Expression of proliferatingcell nuclear antigen (PCNA) and apoptosis-related genes was assayed byimmunofluorescence,RT-PCR and Western blot.Results:Nitrofen inhibited thecell proliferation of A549 cells in a dose-and time-dependent manner,accompa-nied by downregulation of PCNA.As a result,the DNA synthesis of nitrofen-treated A549 cells decreased,while cell cycle was arrested at G_0/G_1 phase.Moreover,nitrofen induced apoptosis of A549 cells,which was not abolished by Z-Val-Ala-Asp(OCH_3)-fluoromethylketone.In addition,nitrofen decreased the expressionof Bcl-x_L,but not of Bcl-2,Bax,and Bak,resulting in a loss of mitochondrialmembrane potential and the nuclear translocation of apoptosis-inducing factor(AIF).Meanwhile,nitrofen strongly activated the p38 mitogen-activated proteinkinase (p38-MAPK).Pretreatment of cells with SB203580 (5 μmol/L) blockednitrofen-induced phosphorylation of p38-MAPK and abolished nitrofen-inducedAIF translocation and apoptosis in A549 cells.Conclusion:Nitrofen suppressesthe proliferation of cultured type Ⅱ pneumocytes accompanied by thedownregulation of PCNA,and induces mitochondria-mediated apoptosis involv-ing the activation of p38-MAPK. Aim: To characterize the molecular mechanisms of nitrofen-induced pulmonary hypoplasia. Methods: After administration of nitrofen to cultured type II A549 pneumocytes, cell proliferation and DNA synthesis were investigated by 3- (4,5-dimethylthiazol-2-yl) -diphenyl tetrazolium bromide colorimetry, colony forma- tion assay, flow cytometry and [~ 3H] -thymidine incorporation assay. Apoptosis was measured by terminal transferase-mediated dUTP nick-end-labeling, acridine orange-ethidium bromide staining and flow cytometry. Expression of proliferating cells Nuclear antigen (PCNA) and apoptosis-related genes was assayed by immunofluorescence, RT-PCR and Western blot. Results: Nitrofen inhibited the cell proliferation of A549 cells in a dose-and time-dependent manner, accompained by downregulation of PCNA. As a result, the DNA synthesis of nitrofen-treated A549 cells decreased, while cell cycle was arrested at G_0 / G_1 phase. Coreover, nitrofen induced apoptosis of A549 cells, which was not abolished by Z-Val-Ala-Asp H_3) -fluoromethylketone.In addition, nitrofen decreased the expression of Bcl-x_L, but not of Bcl-2, Bax, and Bak, resulting in a loss of mitochondrial membrane potential and the nuclear translocation of apoptosis-inducing factor (AIF) nitrofen strongly activated the p38 mitogen-activated proteinkinase (p38-MAPK). Retreatment of cells with SB203580 (5 μmol / L) blocked nitrofen-induced phosphorylation of p38-MAPK and abolished nitrofen-induced AIF translocation and apoptosis in A549 cells. Confluence: Nitrofen suppressesthe proliferation of cultured type II pneumocytes accompanied by the downregulation of PCNA, and induces mitochondria-mediated apoptosis involv-ing the activation of p38-MAPK.