Lack of TNFα expression protects anaplastic lymphoma kinase-positive T-cell lymphoma (ALK+ TCL) cells from apoptosis

Here we report that T-cell lymphomas characterized by the expression of anaplastic lymphoma kinase (ALK+ TCL) fail to express the TNFα and frequently display DNA methylation of the TNFα gene promoter. While only a subset of the ALK+ TCL-derived cell lines showed a high degree of the promoter methylation, all 6 showed low to nondetectable expression of the TNFα mRNA, and none expressed the TNFα protein. All 14 ALK+ TCL tissue samples examined displayed some degree of the TNFα promoter methylation, which was the most prominent in the distal portion of the the promoter. Treatment with a DNA methyltransferase inhibitor, 5′-aza-2′-deoxy-cytidine (5-ADC), reversed the promoter methylation and led to the expression of TNFα mRNA and protein. Furthermore, in vitro DNA methylation of the promoter impaired its transcriptional activity in the luciferase reporter assay. This impairment was seen even if only either distal or proximal portion were methylated, with methylation of the former exerting a more profound inhibitory effect. Notably, the ALK+ TCL cell lines uniformly expressed the type 1 TNFα receptor (TNF-R1) protein known to transduce the TNFα-induced pro-apoptotic signals. Moreover, exogeneous TNFα inhibited growth of the ALK+ TCL cell lines in a dose-dependent manner and induced activation of the members of the cell apoptotic pathway: Caspase 8 and caspase 3. These findings provide additional rationale for the therapeutic inhibition of DNA methyltransferases in ALK+ TCL. They also suggest that treatment with TNFα may be highly effective in this type of lymphoma.