Functional analysis of membrane TNF-α on activated T cells

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The membrane tumor necrosis factor-α (TNF-α) is known to serve as a precursor of the soluble form of TNF-α. Although it has been reported the biological functions of the membrane TNF-α as a ligand, the reverse (outside-to-inside) signal transmitted through membrane TNF-α is poorly understood. We here report a novel function mediated by outside-to-inside signal via membrane TNF-α. Activation by anti-TNF-α antibody (Ab) against membrane TNF-α on HTLV-I-infected T cell line, MT-2, or PHA-activated normal human CD4+ T cells resulted in the induction of an adhesion molecule, E-selectin (CD62E), on the cells with the peak of 12 to 24 h, which was completely disappeared at 45 h. When wild-type or mutant membrane TNF-α (R78T/S79T) resistant to proteolytical cleavage was introduced into Jurkat or HeLa cells, E-selectin was induced by the treatment with anti-TNF-α Ab with the similar kinetics. Northern blot analysis and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis showed that the membrane TNF-α-mediated E-selectin expression was upregulated at the level of transcription. These results not only confirmed our previous findings of reverse signaling through membrane TNF-α, but also presented for the first time that E-selectin was inducible in cell types different from endothelial cells. It is strongly suggested that membrane TNF-α is a novel proinflammatory cell surface molecule that transmit bipolar signals in local inflammation.