Human mesothelial cells (LP9/TERT-1) were exposed to low andhigh (15 and 75 μm2/cm2 dish) equal surface area concentrations of crocidolite asbestos, nonfibrous talc, fine titanium dioxide (TiO2), or glass beads for 8 or 24 hours. RNA was then isolated for Affymetrix microarrays, GeneSifter analysis and QRT-PCR. Gene changes by asbestos were concentration- and time-dependent. At low nontoxic concentrations, asbestos caused significant changes in mRNA expression of 29 genes at 8 hoursandof 205 genes at 24 hours, whereas changes in mRNA levels of 236 genes occurred in cells exposed to high concentrations of asbestos for 8 hours. Human primary pleural mesothelial cells also showed the same patterns of increased gene expression by asbestos. Nonfibrous talc at low concentrations in LP9/TERT-1 mesothelial cells caused increased expression of 1 gene Activating Transcription Factor 3 (ATF3) at 8 hours and no changes at 24 hours, whereas expression levels of 30 genes were elevated at 8 hours at high talc concentrations. Fine TiO2 or glass beads caused no changes in gene expression. In human ovarian epithelial (IOSE) cells, asbestos at high concentrations elevated expression of two genes (NR4A2, MIP2) at 8 hours and 16 genes at 24 hours that were distinct from those elevated in mesothelial cells. Since ATF3 was the most highly expressed gene by asbestos, its functional importance in cytokine production by LP9/TERT-1 cells was assessed using siRNA approaches. Results reveal that ATF3 modulates production of in-flammatory cytokines (IL-1β, IL-13, G-CSF) and growth factors (VEGF and PDGF-BB) in human mesothelial cells.