Outside-to-inside signal through the membrane TNF-alpha induces E-selectin(CD62E) expression on activated human CD4(+) T cells

The membrane TNF-alpha is known to serve as a precursor of the soluble form of TNF-alpha. Although it has been reported the biological functions of th e membrane TNF-alpha as a ligand, the outside-to-inside (reverse) signal tr ansmitted through membrane TNF-alpha is poorly understood. Here we report a novel function mediated by outside-to-inside signal via membrane TNF-alpha into the cells expressing membrane TNF-alpha. Activation by anti-TNF-alpha Ab against membrane TNF-alpha on human T cell leukemia virus (HTLV) I-infe cted T cell line, MT-2, or PHA-activated normal human CD4(+) T cells result ed in the induction of an adhesion molecule, E-selectin (CD62E), on the cel ls with the peak of 12-24 h, which completely disappeared by 48 h. When wil d-type or mutant membrane TNF-alpha (R78T/S79T) resistant to proteolytic cl eavage was introduced into Jurkat or HeLa cells, E-selectin was induced by the treatment with anti-TNF-alpha Ab with the similar kinetics. Membrane TN F-alpha -expressing Jurkat cells also up-regulated E-selectin when brought into cell-to-cell contact with TNF receptor-expressing HeLa cells. Northern blot analysis and RT-PCR analysis showed that the membrane TNF-alpha -medi ated E-selectin expression was up-regulated at the level of transcription. These results not only confirmed our previous findings of reverse signaling through membrane TNF-alpha, but also presented evidence that E-selectin wa s inducible in cell types different from endothelial cells, It is strongly suggested that membrane TNF-alpha is a novel proinflammatory cell surface m olecule that transmits bipolar signals in local inflammation.