Ligation of the WC1 receptor induces gamma delta T cell growth arrest through fumonisin B1-sensitive increases in cellular ceramide

Ceramide is a powerful regulator of cell fate, inducing either apoptosis or growth arrest. We have previously shown that an Ab to the gamma delta T ce ll-specific orphan receptor, WC1, is able to induce growth arrest in prolif erating IL-2-dependent gamma delta T cells, We now show that this WC1-media ted growth arrest is associated with an increase in cellular ceramide, In t he absence of any measurable changes in acidic/neutral sphingomyelinase act ivity. Moreover, cell-permeable analogues of ceramide also mimicked WC1-ind uced growth arrest along with an associated decrease in pocket protein expr ession and phosphorylation status. An important role for ceramide in WC1-in duced growth arrest was confirmed by demonstrating that the specific cerami de synthase inhibitor fumonisin B1 blocked WC1-induced growth arrest and th e associated molecular effects on the pocket proteins. Finally, we observed constitutive expression of both antiapoptotic factors bcl-2 and bcl-X, the former having increased expression upon WC1 stimulation. It is therefore p roposed that ligation of WC1 leads to an accumulation in cellular ceramide through activation of ceramide synthase, This in turn results in a decrease d overall expression of the pocket proteins pRb and p107, their hypophospho rylation, and an eventual growth arrest of the gamma delta T cell. To our k nowledge, these results demonstrate for the first time that cell surface re ceptor-mediated ceramide synthase activation can affect cell fate through i ncreases in cellular ceramide and provide further evidence that the orphan receptor WC1 regulates gamma delta T cell biology through a novel signaling pathway.