Vanadium induces VL30 retrotransposition at an unusually high level: a possible carcinogenesis mechanism.

Abstract Carcinogenesis by vanadium is thought to occur through induction of DNA-double-strand breaks (DSBs) but its mechanism is not fully understood. We investigated the effect of vanadium on induction of viral-like 30 element (VL30) retrotransposition using a NIH3T3 cell-retrotransposition assay based on a recombinant VL30/EGFP element. Incubation of assay cells with vanadyl sulphate (VOSO 4 ) induced retrotransposition frequency in a dose and time-dependent manner, measured by fluorescence-activated cell scanning (FACS) and retrotransposition events were confirmed by UV microscopy and PCR analysis. Among vanadium salts with different valence tested, vanadyl (4+) ions were the most potent retrotransposition inducers. VOSO 4 , at 50 μM induced retrotranspositions at an unusually high frequency of up to 0.185 events per cell per generation. VOSO 4 , acting at the transcription level, strongly induced VL30 and endogenous reverse transcriptase (enRT) transcripts with maxima at 50 μM and 100 μM of 22 and 18-fold, respectively. VOSO 4 -induced retrotransposition frequency was inhibited by 42% with efavirenz, an inhibitor of enRTs, while paraquat, a DNA-DSBs inducer, had no effect. Furthermore, it was completely abolished with deferoxamine, a metal chelator, while reduced by 75% with N -acetyl-cysteine, a general antioxidant. Remarkably, H 2 O 2 reproduced inducible retrotransposition linking for the first time oxidative stress to induction of retrotransposition. We propose that VOSO 4 -induced VL30 retrotransposition through H 2 O 2 generation may be an alternative mutagenic, DNA-DSBs independent, mechanism leading to carcinogenesis.