Pdcd4 protein and mRNA level alterations do not correlate in human lung tumors

Pdcd4 (programmed cell death 4) gene is tumor suppressor which expression is frequently down-regulated in tumors, which is considered as a diagnostic and prognostic marker as well as promising target for anti-cancer therapy. Pdcd4 protein is a target for post-translational regulation by phosphorylation marking Pdcd4 for degradation. We questioned if Pdcd4 mRNA decline in human lung tumors is accompanied by proportional depletion of Pdcd4 protein. We found that Pdcd4 protein-to-mRNA ratio varies greatly in human lung cancer cell lines. In squamous cell carcinoma samples where Pdcd4 mRNA suppression was found to be a typical event, Pdcd4 protein level frequently remained unchanged or even up-regulated. Our studies demonstrate that at least in squamous cell carcinoma, alterations in Pdcd4 mRNA and protein levels are not directly linked, and this fact should be taken into consideration when developing Pdcd4-based anti-cancer therapeutic approaches.