Interferon inducers increase O6-alkylguanine-DNA alkyltransferase in the rat liver

We investigated whether treatment with the interferon inducer polyinosinic-polycytidylic acid and other cytokines (interleukin-1, tumor necrosis factor) or the cytokine inducer lipopolysaccharide modified O⁶-alkylguanine-DNA alkyltransferase (AT) in rat liver. AT levels were determined in liver extracts using N-[³H]methyl-N-nitrosourea alkylated calf thymus DNA as substrate and an HPLC procedure to measure O⁶-methylguanine. Doses as low as 0.1 mg/kg i.p. of polyinosinic-polycytidylic acid caused a highly significant increase (P <0.01) in AT levels in the liver, evident either 24 or 48 h after treatment. Lipopolysaccharide at the dose of 80 μg/kg i.p. also induced AT whereas interleukin-1 (60 μg/kg) or tumor necrosis factor (60 μg/kg) were inactive. Treatment with human recombinant interferon alpha A/D caused a highly significant increase in AT levels, thus confirming the hypothesis that interferon was probably responsible for the observed effect. These results suggest a link between the immune response and DNA repair mechanisms.