Immunohistochemical [corrected] detection of the alternate INK4a-encoded tumor suppressor protein p14(ARF) in archival human cancers and cell lines using commercial antibodies: correlation with p16(INK4a) expression.

The INK4a locus encodes two structurally unrelated tumor suppressor proteins, p16(INK4a) and p14(ARF). Although the former is one of the most common targets for inactivation in human neoplasia, the frequency of p14(ARF) abrogation is not established. We have developed an immunohistochemical assay that allows the evaluation of p14(ARF) expression in formalin-fixed, paraffin-embedded tissues, using commercially available antibodies. p14(ARF) positive cells showed nuclear/nucleolar staining, which was absent in all cell lines and tumors with homozygous deletions of the INK4a gene. The assay was applied to 34 paraffin-embedded cell buttons, 30 non-small cell lung cancers and 28 pancreatic carcinomas, and the staining results were correlated with p16(INK4a) expression. Loss of p14(ARF) expression was common but less frequent than down-regulation of p16(INK4a) (53% versus 76% of all specimens). The p14(ARF) and p16(INK4a) expression pattern was concordant in 65 of 92 cases (71%). Significantly, 24 cases were p16(INK4a)-/p14(ARF)+, while the opposite staining pattern was observed in three cases, consistent with the notion that the two proteins have nonredundant functions. The immunohistochemical assay described here may facilitate studies on the prevalence and significance of aberrant p14(ARF) expression in human tumors.