Mutation analysis of the FAS and TNFR apoptotic cascade genes in hematological malignancies

The existence of properly functioning apoptotic pathways is of utmost importance in the maintenance of a normal cell count. Several groups have searched for mutations in the FAS receptor, a well-characterized apoptotic protein carrying a death domain, and reported the existence of rare mutations in multiple myeloma, T-acute lymphoblastic leukemia (T-ALL), and adult T-cell leukemia. Our aim was to expand these searches by looking for mutations in the death domains of FAS, FADD, TNFR, TRADD, and RIP, in the promoter region of FAS, and in the protease domain of caspase 10, in a larger variety of hematological malignancies, some of which express an apoptosis-resistant phenotype.

We extracted RNA and DNA samples from 92 hematological malignancies: chronic lymphocytic leukemia (CLL; 31 cases), chronic myelogenous leukemia (CML; 28 cases), essential thrombocythemia (ET; 8 cases), acute lymphocytic leukemia (ALL; 6 cases), acute myeloblastic leukemia (AML; 6 cases), hairy-cell leukemia (HCL; 3 cases), Burkitt's lymphoma (3 cases), polycythemia vera (PV; 3 cases), myelofibrosis (2 cases), and chronic myelomonocytic leukemia (CMML; 2 cases) and performed PCR-SSCP and sequence analysis on these samples.

Five polymorphic patterns were found: three in the death domain of the FAS gene in CML patients, one in the promoter of this gene in a CLL patient, and the fifth in the death domain of the TRADD gene in a CML patient. No mutations, altering amino acids, were found in these genes in any of the aforementioned malignancies.

These observations imply that mutations in the death domains of FAS, FADD, TNFR, TRADD, and RIP and in the protease domain of caspase 10 are not a major cause for failure of apoptosis in hematological malignancies, mainly CML and CLL. Regulatory and epigenetic abnormalities in these apoptotic cascade members and aberrations in other components of all death machinery should be looked for.