Induction of tumor necrosis factor alpha in human neuronal cells by extracellular human T-cell lymphotropic virus type 1 Tax(1)

To examine the role of human T-lymphotropic virus type 1 (HTLV-I) Tax(1) in the development of neurological disease, we studied the effects of extracellular Tax(1) on gene expression in NT2-N cells, postmitotic cells that share morphologic, phenotypic, and functional features with mature human primary neurons, Treatment with soluble HTLV-1 Tax(1) resulted in the induction of tumor necrosis factor alpha (TNF-alpha) gene expression, as detected by reverse-transcribed PCR and by enzyme-linked immunosorbent assay, TNF-alpha induction was completely blocked by clearance,vith anti-Tax(1) monoclonal antibodies, Furthermore, cells treated with either a mock bacterial extract or with lipopolysaccharide produced no detectable TNF-alpha, Synthesis of TNF-alpha in response to soluble Tax(1) occurred in a dose-dependent fashion between 0.25 and 75 nM and peaked within 6 h of treatment, Interestingly, culturing NT2-N cells in the presence of soluble Tax(1) for as little as 5 min was sufficient to result in TNF-alpha production, indicating that the induction of TNF-alpha in NT2-N does not require Tax(1) to be continually present in the culture medium, Treatment of the undifferentiated parental embryonal carcinoma cell line NT2 with soluble Tax(1) did not result in TNF-alpha synthesis, suggesting that differentiation-dependent, neuron-specific factors may be required, These results provide the first experimental evidence that neuronal cells are sensitive to HTLV-1 Tax(1) as an extracellular cytokine, with a potential role in the pathology of HTLV-1-associated/tropical spastic paraparesis.