The Fas (Apo-1/CD95)/
Fas ligand (L) system is involved in cell death signaling, and has been suggested to be important for the regulation of germ cell apoptosis in the testis. Mutations of the Fas gene may result in accumulation of germ cells and thus might contribute to testicular
carcinogenesis. The open reading frame of Fas
cDNA was examined in 24 cases of testicular
germ cell tumors (TGCTs), comprised of 19 pure histological type (15
seminomas, 3
embryonal carcinomas, 1
immature teratoma) and 5 mixed-type
tumors. Mutations of the Fas gene were found in nine (37.5%) of these cases. Each lesion with a homogeneous histological picture was selectively microdissected using a
laser capture microdissection method: samples consisted of 18 lesions from
seminomas, 7
embryonal carcinomas, 4
immature teratomas, 2
choriocarcinomas, and 1 from a
yolk sac tumor. Microdissected genomic
DNA was examined to determine which mutations were derived from which kind of histological lesion. Eleven mutations were detected in 10 TGCT lesions from nine cases, but none were found in benign lesions. All were point mutations, and eight missense mutations occurred in exon 9 encoding the core
protein of the death domain essential for apoptotic signal transduction. Three were silent mutations. Mutations were found in the
seminoma (27.8%) and
embryonal carcinoma lesions (62.5%), but none were found in the one
yolk sac tumor, two
choriocarcinomas, or four
immature teratoma lesions. Each
seminoma and
embryonal carcinoma lesion found in the same case had a different type of Fas mutation from the others. Mouse
T-cell lymphoma cells transfected with missense mutated genes were resistant to apoptosis induced by anti-Fas antibody, indicating these to be loss-of-function mutations. These findings suggested a role of Fas gene mutations in the pathogenesis of TGCTs.