We examined the effects of several kinds of protein kinase inhibitors against calcium/phospholipid-dependent protein kinase (PKC) and cAMP-dependent protein kinase (PKA) on heat-induced hsp72 gene expression in a human glioblastoma cell line (T98G) as a source of insight into the type of protein kinase contributing to its gene expression. When the cells were treated with 1-(5-isoquinolinesulphonyl)-2-methylpiperazine [(H7) a potent inhibitor of PKC, PKA, and others], the suppression of heat-induced Hsp72 accumulation was observed. Heat-induced Hsp72 accumulation was also suppressed by staurosporine (a potent inhibitor of PKC and PKA) or calphostin C [(CAL) a potent inhibitor of PKC] at high concentration (10 x IC50) but not at low concentration (1 x IC50). N-(2-(p-Bromocinnamylamino)ethyl]-5-isoquinolinesulphonamide [(H89) a potent inhibitor of PKA] did not affect heat-induced Hsp72 accumulation at either low (1 x IC50) or high concentrations (10 x IC50). Combination treatment with CAL and H89 suppressed the heat-induced Hsp72 accumulation more strongly than did treatment with either inhibitor alone. Furthermore, the heat-induced DNA-binding activation of heat-shock factor (HSF) was suppressed by CAL at high concentration (10 x IC50), and combination treatment with CAL and H89 showed stronger suppression. In the H7 treatment, the clear suppression of HSF activation was observed even at low concentration (1 x IC50). In addition, the cellular content of Hsp72 increased after the treatment of PKC or PKA activator. These results suggest that not only PKC, but also PKA may play an important role in heat-induced hsp72 gene expression.