Akt modulates Raf1 signalling and malignant characteristics in human non‐small cell lung cancer

The majority of human non‐small cell lung cancers (NSCLCs) harbor aberrations upstream or downstream of GTPase Ras and the lipid kinase PI3K. Recent advances indicate that components of these signalling pathways have much more complex interactions than previously appreciated. We examined relationships between Raf1 and Akt, two major proteins downstream of Ras and PI3K, and their impacts on malignant characteristics in NSCLC, such as vascular endothelial growth factor (VEGF) and matrix metalloproteinase (MMP) expression. Akt activation (phosphorylation at Thr‐308 and Ser473), Akt‐mediated phosphorylation of Raf1, Akt‐Raf1 association, and expression of VEGF and MMPs were studied by Western blotting, immunoprecipitation and immunofluorescence in NSCLC. Akt phosphorylation at Thr‐308 and/or Ser473 was detected in 92% of cases; tumors showed higher levels of Akt phosphorylation than adjacent normal tissue. Furthermore, Akt was found to associate with and phosphorylate Raf1, alter MEK/ERK activation and induce VEGF and MMP expression in adenocarcinoma, but not in squamous carcinoma. These findings, combined with our previous work on cell lines, indicate that Akt modulates Raf1 function and malignant characteristics in NSCLC. Such information will be important in refining therapeutic strategies in lung cancer. Research support: Penn State College of Medicine, Department of Pathology.