Overexpressed Raf-1 and phosphorylated cyclic adenosine 3'-5'-monophosphatate response element-binding protein are early markers for lung adenocarcinoma.

Pulmonary adenocarcinoma (PAC) is the leading type of lung cancer and has a high mortality. The tobacco carcinogen nicotine-derived nitrosamine 4-(N-methyl-N-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) stimulates the proliferation of human PAC cells and small airway epithelial cells through beta-1 adrenorecptor-mediated transactivation of the epidermal growth factor receptor (EGFR). Using the NNK hamster PAC model and human PAC tissue arrays with matched and unmatched normal lung tissues, the authors tested the hypothesis that Raf-1, an effector of the EGFR, and P-CREB, an effector of the beta-adrenoreceptor, are overexpressed in a significant subset of human PACs and are early markers of PAC development. Western blots from respiratory epithelial cells and microadenomas harvested by laser-capture microdissection from hamster lungs accompanied by immunostains were used to monitor the expression levels of Raf-1 and P-CREB after 5 weeks, 10 weeks, and 20 weeks of NNK treatment. Expression levels of these markers in human PAC tissue arrays were assessed by immunostains. Reverse-phase proteomics, Western blot analysis, and immunoprecipitation in immortalized human small-airway epithelial cells and in a human PAC cell line in the presence and absence of dominant-negative Raf were used to determine Raf dependence of extracellular signal-regulated kinase 1 and 2 (ERK1/2) activation in response to NNK or isoproterenol. The data showed a time-dependent increase in the expression of Raf-1 and P-CREB after NNK treatment in small-airway epithelial cells and microadenomas of hamsters. The majority of human lung adenocarcinomas simultaneously overexpressed Raf-1 and P-CREB. Dominant-negative Raf completely abrogated ERK1/2 activation by NNK and isoproterenol. The current results indicated that RAF-1 and P-CREB may contribute to the development of a significant subset of human lung adenocarcinomas and may offer promising targets for early detection and treatment.