Specific allelic loss of p16INK4A tumor suppressor gene after weeks of iron-mediated oxidative damage during rat renal carcinogenesis

Oxidative tissue damage has been shown to be associated with carcinogenesis. In human cancers p16(INK4A) is one of the most frequently mutated tumor suppressor genes. The present study used the ferric nitrilotriacetate (Fe-NTA)-induced rat renal carcinogenesis model to determine whether oxidative damage can cause specific allelic loss of p16(INK4A). By the use of fluorescent in situ hybridization in combination with imprint cytology at single-cell resolution, we found that the number of renal tubular cells with aneuploidy (I or 3 signals) at the p16(INK4A) locus was significantly and specifically increased (1 week, 37.2 +/- 2.3%; 3 weeks, 37.8 +/- 1.3% vs control, 22.5 +/- 1.9%; mean SE +/- 5 N = 8; P < 0.001 and P < 0.0001, respectively) after repeated intraperitoneal administration of 5 to 10 mg of iron/kg in the form of Fe-NTA for 3 weeks. No increase in aneuploidy was observed at the loci of either the p53 or vhl tumor suppressor gene. Furthermore, the increase in the cells with 3 signals was followed by a continuous increase in those with 1 signal. Therefore, the p16(INK4A) locus is specifically vulnerable to oxidative damage, leading to its allelic loss within weeks, presumably due to a deficiency in the replication of both the alleles.