Expression of p21 in non small cell lung cancer relationship with PCNA.

The first cyclin dependent kinase inhibitor to be discovered was the p21 cdk interacting protein (a.k.a., WAF1, Cip1, CAP20, Sdi1, mda6). p21 expression may or may not be dependent on p53. This pathway also inhibits DNA replication by merit of p21's interaction with PCNA, but it has also been shown that this same inhibitory interaction with p21 does not affect PCNA DNA repair abilities. We assessed the immunohistochemical expression of p21 protein in 60 curative surgical resected non small cell lung cancers relating it to the expression of PCNA to clarify the contribution of the p21/PCNA pathway to the development of NSCLC. We did not find any relationship between PCNA and p21 expression. This last result may indicate that the mechanism by which PCNA controls the DNA repair is the most important activity of this protein during lung cancer progression and development, compared to its contribution to cell proliferation. In fact, this last event is strongly counteracted by p21 expression, which in this last case works as an inhibitor of PCNA expression. In conclusion this study highlighted the important role of the p21/PCNA pathway in lung carcinogenesis, pointing out the contribution of PCNA to the response to lung aggression and not only it's role as a proliferation index. Therefore, these results offer a background to further study to evaluate potential novel therapeutic approaches to lung cancer treatment.