Repair of alkali-labile sites within the mitochondrial DNA of RINr 38 cells after exposure to the nitrosourea streptozotocin

Abstract

Studies were initiated to investigate whether mechanisms exist within mitochondria to repair damage incurred by mitochondrial DNA after exposure to alkylating toxins. A clonal isolate from a rat insulinoma cell line was utilized to measure the formation and repair of alkali-labile sites within the mitochondrial genome after exposure to the alkylating antibiotic streptozotocin. Alkali-labile sites were formed in mitochondrial DNA in a dose-dependent fashion. Eight hours after exposure to the toxin, 55% of the lesions were removed. The level of repair increased to 70% after 24 h. In comparison, only 46% of N7-methylguanines were removed across the entire cellular genome. These studies demonstrate that streptozotocin causes appreciable mitochondrial DNA damage in a dose-dependent manner and provide the first evidence that a repair mechanism for alkali-labile sites is present within the mitochondrion.