EVIDENCE FOR DISTINCT KINASE-MEDIATED PATHWAYS IN GADD GENE RESPONSES

We have evaluated the role of various protein kinases on the induction of the gadd (growth arrest and DNA damage inducible) genes, using a p anel of protein kinase inhibitors. Our data indicate that three differ ent stress response pathways mediating gadd gene induction are most li kely regulated by different protein kinases or combinations of protein kinases. The protein kinase inhibitor staurosporine and the temperatu re sensitive (ts) p34(cdc2) mutant reduced induction by the alkylating agent methylmethane sulfonate (MMS) of the rodent gadd45 and gadd153 genes. However, staurosporine had no effect of the ionising radiation (IR) induction of the human GADD45. Caffeine and 2-aminopurine, on the other hand, completely blocked this IR induction. Suramin, an antitum or drug that interferes with the interaction of growth factors with th eir receptors, inhibited the UV radiation induction of GADD45 and GADD 153 but had no effect on the MMS and IR pathways. Elevated expression of gadd45 by medium depletion (starvation) was partially reduced by th e addition of either genistein or tyrphostin, two protein tyrosine kin ase inhibitors, while gadd153 was affected by tyrphostin only. Two inh ibitors acting preferentially on cAMP-dependent protein kinase (PKA), -[2-(methylamino)ethyl]-5-isoquinolinesulfonamide, HCl (H8) and protei n kinase inhibitor (PKI), also had a moderate effect on the medium dep letion-induced levels of both gadd genes. Thus, these varied effects o f inhibitors on gadd gene responses point to important differences in the pathways controlling these responses. (C) 1998 Elsevier Science In c.