Genetic alterations of INK4a/ARF locus and p53 in human hepatocellular carcinoma

The INK4a/ARF locus encodes p14^ARF and p16^INK4a, that function to arrest the cell cycle through the p53 and RB pathways, respectively. Genetic alterations of p14ARF and their relationship with p16^INK4a or p53 inactivation have not been characterized in hepatocellular carcinoma (HCC). We examined 40 pairs of HCCs/noncancerous liver tissues for homozygous deletions (HD), methylation and mutations of the INK4a/ARF locus and for mutations of p53, and analyzed their clinicopathological correlation. p16^INK4a, p53 and p14^ARF were inactivated in 62.5% (25 out of 40), 42.5% (17 out of 40) and 20% (8 out of 40) of HCCs, respectively. Inactivation of p14^ARF was always associated with the concomitant inactivation of p16^INK4a and occurred more frequently in hepatitis C virus (HCV)-associated HCC (p=0.042). Inactivation of p16^INK4a occurred more frequently in older patients (p=0.0027). The predominant mechanism of inactivation of p14^ARF was homozygous deletion (7 out of 8), while that of p16^INK4a was methylation (21 out of 25). Although statistically insignificant, genetic alterations of p14^ARF tended to occur in tumors with wild-type p53. Genetic alterations of the INK4a/ARF locus could occur in small HCCs. In contrast, p53 mutations occurred more frequently in advanced HCCs (p=0.041). Inactivation of either p14^ARF/p53 or p16^INK4a occurred in 80% (32 out of 40) and concomitant disruption of both pathways occurred in 40% (16 out of 40) of HCCs, respectively. These results suggest that p14^ARF, p16^INK4a and p53 are differentially disrupted through distinct molecular mechanisms at different stages in HCC and that p14^ARF and p53 appear to function in the same tumor suppression pathway in HCC.