Pathogenetic and biologic significance of TP14ARF alterations in nonsmall cell lung carcinoma

Abstract

The INK4a/ ARF locus on human chromosome band 9p21 carries two tumor suppressor genes, TP14 ARF and TP16 INK4a, and both are frequently inactivated in nonsmall cell lung carcinoma (NSCLC). TP14 ARF and TP16 INK4a play important roles in the TP53 and RB tumor suppressor pathways, respectively. To elucidate the genetic and epigenetic status of the TP14 ARF and TP16 INK4 a genes in NSCLC, we comprehensively analyzed mutations, homozygous deletions, methylations in the CpG regions, and expression of the TP14 ARF and TP16 INK4a genes in 31 NSCLC cell lines. TP16 INK4a (84%) was inactivated more frequently than TP14 ARF (55%). Moreover, p16 INK4a was inactivated in all 17 cell lines with TP14 ARF inactivation. Three cell lines with base substitutions in exon 2 resulted in missense mutations of TP16 INK4a but silent mutations of TP14 ARF. There was a case of mutation in exon 1α unique to TP16 INK4a, but not a mutation in exon 1β unique to TP14 ARF. The TP16 INK4a gene was methylated in 6 cell lines, but the TP14 ARF gene was not methylated in any cell line. Unlike a mutually exclusive relationship for inactivation between TP16 INK4a and RB, TP14 ARF and TP53 did not show such a relationship ( P = 0.61, Fisher exact test). Thus, the present results indicate the TP16 INK4a gene to be the primary target of INK4a/ ARF locus alterations. Transient TP14 ARF expression induced G1 arrest in the cells with wild-type TP53, but not in the cells with mutated TP53. Thus, the pathogenetic and biologic significance of TP14 ARF inactivation is different between NSCLC cells with wild-type TP53 and those with mutated TP53.