Structural alterations of the FAS gene in cutaneous T-cell lymphoma (CTCL)

FAS (TNF receptor superfamily member 6, also known as CD95) plays a major role in T-cell apoptosis and is often dysregulated in CTCL. We searched for structural alterations of the FAS gene with the potential to affect its function. Although several heterozygous FAS promoter single nucleotide polymorphisms (SNPs) were detected, the only homozygous one was the −671 GG SNP present in 24/80 CTCL cases (30%). This SNP maps to an interferon response element activated by STAT-1. EMSA and supershift EMSA showed decreased CTCL nuclear protein/STAT-1 binding to oligonucleotides bearing this SNP. Luciferase reporters showed significantly less interferon-alfa responsive expression by FAS promoter constructs containing this SNP in multiple CTCL lines. Finally, FAS was upregulated by interferon-alfa in wildtype CTCL cells but not those bearing the −671 GG SNP. These findings indicate that many CTCL patients harbor the homozygous FAS promoter −671 GG SNP capable of blunting its response to interferon. This may have implications for CTCL pathogenesis, racial incidence and the response of patients to interferon-alfa therapy. In contrast, functionally significant mutations in FAS coding sequences were detected uncommonly. Among CTCL lines with the potential to serve as models of FAS regulation, FAS-high MyLa had both FAS alleles, FAS-low HH was FAS-hemizygous and FAS-negative SeAx was FAS-null.

Research highlights
► Homozygous FAS promoter −671 GG SNP is present in 30% of Caucasian CTCL cases.
► The −671 GG SNP results in decreased STAT-1 binding to the FAS promoter.
► The −671 GG SNP blocks FAS protein up-regulation in response to interferon.
► Functionally significant mutations in FAS coding sequences were detected uncommonly.
► CTCL cell lines MyLa, HH and SeAx had both, one and no FAS alleles, respectively.