Ratio of Expression of p16INK4a to p14ARF Correlates with the Progression of Non-small Cell Lung Cancer

The CDKN2 gene is located on the short arm of chromosome 9p and encodes two unrelated proteins, p16^INK4a and p14^ARF, through the use of independent first exons and shared exons 2 and 3. p16^INK4a is a cyclin‐dependent kinase inhibitor, whereas p14^ARF regulates the cell cycle through a p53 and MDM2–dependent pathway. We have examined the expression of p16^INK4a and p14^ARF using competitive RT‐PCR in 60 non‐small cell lung cancers (NSCLCs) and matching normal lung tissues. The intensities of bands for p16^INK4a and p14^ARF were nearly equal or the intensity of the p16^INK4a band slightly exceeded that of p14^ARF in the normal lung tissues (n=60). In 38 tumors the intensity of the p16^INK4a band was similar to or slightly weaker than that of p14^ARF. In 6 tumors the intensity of the p16^INK4a band was weaker than that of p14^ARF. In 15 tumors the intensity of the p14^ARF band was very strong and the p16^INK4a band was barely visible. In only one tumor was the intensity of the p16^INK4a band very strong, while the band of p14^ARF was barely visible. The ratio of the intensity of p16^INK4a to p14^ARF had an interesting correlation with the tumor's clinicopathological characteristics. The p stage II‐IV tumors had significantly lower p16^INK4a to p14^ARF ratios than the p stage I tumors (P=0.036). The T2–4 tumors had significantly lower p16^INK4a to p14^ARF ratios than the T1 tumors (P=0.005). The N1–3 tumors had significantly lower p16^INK4a to p14^ARF ratios than the NO tumors (P=0.014). Our results suggest that the ratio of expression of p16^INK4a to p14^ARFtends to decrease during the progression of NSCLC.