Stimulation of MAP kinase signaling by arsenite and UVA. HaCaT cells were treated with 3 μM arsenite (As) or 10kJ/m2 UVA. Dually treated samples were pre-incubated with 3 μM arsenite (As) for 24 hrs and then exposed to UVA. EGF was used as a positive control for MAP kinase activation. Total protein was collected 2 hrs post exposure and 20 μg resolved via a 8-12% SDS-PAGE gradient gel and the indicated proteins were analyzed, transferred to nitrocellulose membrane, immunoreacted with the appropriate antibodies and detected by ECL (A) Blots shown are representative of at least 3 independent experiments. Densitometric analysis of immunoblotting was performed (B). Blots were quantified with a Digital Science Image Station on a Kodak 440CF Imager equipped with ID Image Analysis software. Each bar is the mean of at least 3 independent experiments and the error bars indicate ± S.D. * = significantly different from untreated controls (NT), p<0.05; # = significantly different from singly treated samples, p<0.05.