LACK OF CELL-SURFACE FAS APO-1 EXPRESSION IN PULMONARY ADENOCARCINOMAS/

The Fas receptor and ligand initiate an apoptotic pathway. Alterations in this pathway within tumor cells can result in escape from apoptosi s and immune surveillance, We evaluated Fas protein expression in 42 p rimary pulmonary adenocarcinomas, and Fas expression and function in t he lung adenocarcinoma cell lines A549 and A427, Immunohistochemical a nalysis demonstrated Fas protein expression in 47.6% of the tumors; ho wever, Fas-positive tumors demonstrated cytoplasmic staining without c ell surface expression, Northern blot analysis indicated that levels o f Fas mRNA were similar in Fas protein-positive humors to levels In no rmal lung tissue, but were reduced in Fas protein-negative tumors, Sol uble form Fas was not detected in the majority of these tumors either bg RT-PCR or Western blot analysis, Cell surface Fas protein expressio n was minimal in A549 and A427 cell lines as determined by flow cytome try. Both cell lines demonstrated Fas mRNA expression by Northern blot analysis and abundant protein expression by Western blot analysis, Tr ansfection of the Fas cDNA derived from A549 cells induced surface Fas protein in COS cells; however, stable transfection of a native Fas cD NA into A549 cells failed to induce surface Fas protein expression, Pa rental A549 cells and A549 cells transfected with a Fas expression vec tor were resistant to Fas-mediated apoptosis, Transgenic expression of a FLAG-tagged Fas cDNA in A549 cells, with visualization of the Fas-F LAG protein using confocal microscopy, demonstrated that the Fas-FLAG protein was retained within cytoplasmic portions of the cell and was n ot translocated to the cell surface, These findings suggest that the F as protein is reduced or not present on the cell surface in the primar y lung tumors and is sequestered within A549 tumorigenic lung cells, a nd these alterations directly affect the cells resistance to Fas-media ted apoptosis.