Ly-6A-Induced Growth Inhibition and Cell death in a Transformed CD4+ T cell line: Role of Tumor Necrosis Factor-α (TNF-α)
Engaging the Ly-6A protein, an inhibitory signaling protein, on CD4+ T cell lines triggers apoptosis. Signaling through Ly-6A activates cell-intrinsic apoptotic cell death pathway as indicated by release of cytochrome C, activation of caspase 3 and 9. In addition Ly-6A induces cytokine production and growth inhibition. The mechanism underlying simultaneous distinct cellular responses has remained unknown. To examine the relatedness of distinct responses generated by engaging Ly-6A, we have quantified the secretion of TNF, TGF{beta} and a related protein GDF10, the three pro-apoptotic, growth inhibitory and tumor suppressive cytokines. While low levels of TGF{beta} and GDF10 were detected after engaging Ly-6A, the production of TNF- was elevated in cell cultures stimulated the Ly-6A protein. Blocking the biological activity of TNF resulted in reduced apoptosis induced by engaging Ly-6A. In contrast, growth inhibition/apoptosis in response to antigen receptor complex stimulation was not observed. Engaging the antigen receptor through activating the epsilon ({varepsilon}) chain of CD3 generated high levels of TGF-{beta} and GDF10 while decreasing TNF. These results suggest that the TNF- cytokine contributes to the Ly-6A-induced growth inhibitory and pro-apoptotic response in CD4+ T cells and provides mechanistic explanation of the observed biologically distinct responses initiated after engaging Ly-6A protein. These findings aid in understanding the inhibitory signaling initiated by Ly-6A protein, especially in the context of its potential immune checkpoint inhibitory role in T cells.