Search for the regulatory factor of apoptosis in adult T-cell leukemia (ATL) cells

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1. Anti-Fas monoclonal antibody (mAb) resistant adult T-cell leukemia (ATL) cell line, RS04RS04 RS04 cells did not show apoptosis after treatment with IgM anti-Fas mAb. We found that the lactacystin, which was a specific inhibitor of the proteosome, activated the caspase 8 and induced apoptosis in RS04 cells, indicating that the apoptotic pathway in the cytoplasm in RS04 cells was intact. By sequencing analysis of Fas gene, we found the heterozygous missense mutation with the transition of A to G at exon 2, resulting in substitution of arginine for histidine. The three dimensional molecular modeling of the mutated Fas protein indicated the definitive conformational alteration around the amino acids 52 to 58. It was suggested that the trimerization of Fas molecules was interfered with the mutated Fas, resulting in the impairment of signal transduction of apoptosis by dominant negative mechanism.2. Anti-Fas mAb resistantATL cell line, OMTIn OMT cells, we found the missense point mutation at nucleotide 1132 with the transition of T to C, resulting in the substitution of threonine for isoleucine. This mutation might cause the conformational alteration of death domain and fail to associate with the FADD molecule, which located at right downstream under the Fas molecule.3. ATL cells which barely express membrane FasBecause the Fas gene mutations were detected at the relatively high rate in Fas-resistant ATL cell lines, we investigated the primary ATL cells, which barely expressed membrane Fas and were resistant to IgM anti-Fas mAb. In four of seven cases of patients with ATL, we found Fas gene mutations, three point mutations and a 2 base pair deletion. It was indicated that the various mutations of Fas gene were one of the mechanisms of preventing the apoptosis in ATL cells.