Micronuclei formation with chromosome breaks and gene amplification causedby Vpr, an accessory gene of human immunodeficiency virus

Vpr, an accessory gene of human immunodeficiency virus, induces cell cycle abnormality by accumulating cells at the G(2)-M phase. We reported recently that Vpr caused both micronuclei formation and aneuploidy. Here, we show t hat Vpr also induced chromosome breaks and gene amplification. Expression o f Vpr induced more than 10-fold increase of colonies resistant to N-(phosph onacetyl)-L-aspartate, an inhibitor of pyrimidine de novo synthesis. Fluore scence in situ hybridization analysis detected that 4 of 10 N-(phosphonacet yl)-L-aspartate resistant clones studied had intrachromosomal amplification of carbamyl-phosphate synthetase/aspartate transcarbamoylase/dihydroorotas e gene. Another single clone had dicentrics, Data suggested that the Vpr-in duced chromosome breaks leading to gene amplification, followed by bridge-b reakage-fusion cycle, were one of the possible mechanisms of Vpr-induced ge nomic instability.