Percentage of induction of apoptosis is calculated accord ing to the following formula % 100. Recombinant EGF and EGFR inhibitor are from Sigma. The speci fic AhR antagonist alpha naphthoflavone or agonist beta naphthoflavone were used for 1 h prior to PM2. 5 e posure and or apoptosis induction. Electron Microscopy Cells were fi ed 1 h by immersion at 4 C in 2. 5% glutar aldehyde and 1% tannic acid in 0. 1 M sodium cacodylate buffer, washed, postfi ed in 2% osmium tetro ide deshy drated before embedding in Epon. Electron microscopy was performed with a transmission electron microscope, at 80 kV on ultrathin sections. Amphiregulin and GM CSF secretion Subconfluent 16HBE cells were e posed to PM2. 5 AW for 4 h or 24 h and supernatants were recovered, centri fuged at 15,000 g for 15 min at 4 C to pellet particles, and then frozen at 80 C until further analysis.

The con centrations of Amphiregulin and GM CSF released were evaluated with an enzyme linked immunosorbent assay kit according to the manufacturers recommendations. AhR gene silencing 16HBE cells were simultaneously seeded at 2 104 cells cm2 either in T25 dishes or in a P24 well plate and incubated under normal cell culture conditions overnight. Then, 10 nM of AhR siRNA or control non silencing siRNA and HiPerFect Transfection Reagent were mi ed separately in medium and the formed comple es were then added drop wise onto the cells, according to the manufacturers recommendations. At 48 h after transfec tion, the cells were subjected to our usual protocol 4 h PM2. 5 pretreatement and or A23187 for addi tional 20 h.

Western Blots Western Blots were performed according to the method previously described and the primary antibodies used were Brefeldin_A mouse monoclonal anti AhR and anti Actin. The secondary antibodies were anti mouse immunoglobulin. Immunoreactive bands were detected by chemiluminescence using a Chemilumi nescent Sensitive HRP Substrate using a FujiFilm LAS 4000 camera system. Statistical analysis All results are presented as the mean standard deviation of three independent e periments. Data were analyzed using one way ANOVA analysis of variance. The Dunnetts test was performed for all multiple com parisons versus control group. Moreover, the Student Newman Keuls test was used for all pairwise compari sons of mean responses among the different treatment groups. Differences between groups were considered significant if the p value was less than 0. 05.