Fas/Apo-1 (CD95) receptor lacking the intracytoplasmic signaling domain protects tumor cells from Fas-mediated apoptosis

Fas/Apo-1 (CD95) is an apoptosis-signaling cell surface receptor belonging to the TNF receptor family. Tumor cells resistant to Fas-mediated apoptosis have been described, but to date, the mechanisms responsible for this resistance are not well understood. We found that a series of apoptosis-resistant clones from human HUT78 lymphoma cells express a splicing variant coding for a truncated Fas molecule that lacks the intracellular death-signaling domain. The mutation responsible for the FasExo8Del expression was identified as a deletion-insertion in the intron 7/exon 8 region of the Fas gene. Moreover this mutation affects the phenotype in a dominant negative fashion, i.e., even in the presence of the normal receptor.