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Ligation of the WC1 Receptor Induces T Cell Growth Arrest Through Fumonisin B1-Sensitive Increases in Cellular Ceramide¹

Paul A. Kirkham^2,*, Haru-Hisa Takamatsu^*, Eric W.-F. Lam and R. M. E. Parkhouse^*

^* Department of Immunology, Institute for Animal Health, Pirbright, Surrey, United Kingdom; and Ludwig Institute for Cancer Research and Section of Virology and Cell Biology, Imperial College School of Medicine at St. Mary’s Hospital, London, United Kingdom

Ceramide is a powerful regulator of cell fate, inducing either apoptosis or growth arrest. We have previously shown that an Ab to the T cell-specific orphan receptor, WC1, is able to induce growth arrest in proliferating IL-2-dependent T cells. We now show that this WC1-mediated growth arrest is associated with an increase in cellular ceramide, in the absence of any measurable changes in acidic/neutral sphingomyelinase activity. Moreover, cell-permeable analogues of ceramide also mimicked WC1-induced growth arrest along with an associated decrease in pocket protein expression and phosphorylation status. An important role for ceramide in WC1-induced growth arrest was confirmed by demonstrating that the specific ceramide synthase inhibitor fumonisin B1 blocked WC1-induced growth arrest and the 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 proposed that ligation of WC1 leads to an accumulation in cellular ceramide through activation of ceramide synthase. This in turn results in a decreased overall expression of the pocket proteins pRb and p107, their hypophosphorylation, and an eventual growth arrest of the T cell. To our knowledge, these results demonstrate for the first time that cell surface receptor-mediated ceramide synthase activation can affect cell fate through increases in cellular ceramide and provide further evidence that the orphan receptor WC1 regulates T cell biology through a novel signaling pathway.