Of the 20 most significantly ethanol-regulated genes, 5 encoded heat-shock proteins (HSPs; Table S1). Additionally, nearly half of all Drosophila Hsp genes (9 of 21) showed significantly increased expression (p < 0.05) following ethanol exposure (Fig. S1). Three of the 4 most strongly regulated Hsp genes belonged to the Hsp70 family that function as molecular chaperones, and regulate diverse biological and cellular processes including apoptosis, immunity, and thermotolerance (Gong and Golic, 2006). As is the case with stressors such as heat, ethanol induced expression of Hsp70 family members to remarkably high expression levels, including a 50-fold induction for Hsp70Ab. Interestingly it was previously reported that heat shock can induce ethanol tolerance, and genetic analyses uncovered both stress-dependent and stress-independent ethanol tolerance pathways (Scholz et al., 2005). HSPs may therefore play an important role in one of these tolerance pathways.
