PREFERENTIAL EFFECTS OF THE CHEMOTHERAPEUTIC DNA CROSS-LINKING AGENT MITOMYCIN-C ON INDUCIBLE GENE-EXPRESSION IN-VIVO

The immediate effects of a single dose of the chemotherapeutic DNA cro sslinking agent, mitomycin C (MMC), on the expression of several const itutive and drug-inducible genes were examined in a simple in vivo sys tem, the 14 day chick embryo. We observed no effect of MMC on the stea dy-state mRNA expression of the constitutively expressed beta-actin, t ransferrin, or albumin genes. In contrast, MMC treatment significantly altered both the basal and drug-inducible mRNA expression of two glut ethimide-inducible genes, 5-aminolevulinic acid (ALA) synthase and cyt ochrome P450 CYP2H1. The basal expression of these genes was transient ly but significantly increased over a 24 hr period following a single dose of MMC. Conversely, MMC significantly suppressed the glutethimide -inducible expression of these genes when administered 1 to 24 hr prio r to the inducing drug. The effects of MMC on both basal and drug-indu cible ALA synthase and CYP2H1 mRNA expression were principally a resul t of changes in the transcription rates of these genes. In contrast, M MC treatment had little or no effect on glutethimide-induced expressio n of ALA synthase or CYP2H1 when administered 1 hr after the inducing drug, suggesting that a very early event in the induction process repr esents the target for these MMC effects. Covalent binding studies demo nstrated that the effects of MMC on gene expression were closely corre lated temporally with formation of [H-3]-porfiromycin-DNA adducts. The se results support the hypothesis that genotoxic chemicals specificall y target their effects to inducible genes in vivo. (C) 1995 Wiley-Liss , Inc.