Long-term exposure to PM2.5 induces HO-1 expression and nuclear translocation. BEAS-2B cells were cultured in the presence of 100 µg/mL PM2.5 for 3 to 5 weeks, before final passage and re-exposure to 100 µg/mL PM2.5 for the indicated time points (0–24 h). The JNK inhibitor SP600125 (5 µM), the Nrf2 inhibitor IM3829 (5 µM), the Akt inhibitor API-2 (5 µM), or the p38 inhibitor SB203580 (10 µM) were added 1 h prior to the last PM2.5 re-exposure. (a,c–f) Total amounts of HO-1 were detected by immunoblotting in non-fractionated total cell lysates and normalized to GAPDH. (b) Translocated HO-1 was immunodetected in nuclear extracts and normalized to HDAC-2. Cells, cultured in the absence of PM2.5 served as controls (first lane). Inhibition of JNK1/2 or p38 decreased HO-1 expression. Representative blots of three different experiments are shown, except of (b) (n = 2).