Lysophospholipid enhancement of human T cell sensitivity to diphtheria toxin by increased expression of heparin-binding epidermal growth factor

The effects of lysophosphatidic acid (LPA) and sphingosine l-phosphate (S1P ) on T cell expression of heparin-binding epidermal growth factor-like grow th factor (HB-EGF), the diphtheria toxin (DT) receptor, were investigated i n the Tsup-1 cultured line of human CD4(+) 8(+) 3(low) T lymphoblastoma cel ls. Tsup-1 cells bear endothelial differentiation gene (edg)-2 and -4-encod ed G protein-coupled receptors (GPCRs) for LPA and Edg-3 and -5 GPCRs for S 1P. Suppression by DT of Tsup-1 cell protein synthesis was enhanced by LPA and SIP, with lipid structural specificity similar to that required for the ir recognition by Edg receptors. LPA and S1P increased the Tsup-1 cell leve l of immunoreactive HB-EGF, and neutralizing antibodies to HB-EGF inhibited LPA and S1P enhancement of Tsup-1 cell susceptibility to DT. Stabilized tr ansfection of Tsup-1 cells with a combination of plasmids encoding Edg-2 pl us -4 antisense mRNA suppressed the levels of Edg-2 and -4, but not Edg-3 a nd -5, in Western blots and reduced in parallel the increments in HB-EGF an d susceptibility to DT evoked by LPA but not S1P. Similar transfection with Edg-3 plus -5 antisense plasmids suppressed Tsup-1 cell levels of immunore active Edg-3 and -5, but not Edg-2 or -4, and concurrently reduced S1P-, bu t not LPA-, induced Tsup-1 cell increases in both HB-EGF and susceptibility to DT. Edg GPCR-mediated LPA and SIP enhancement of T cell sensitivity to DT, thus, may be attributable to increased expression of the DT receptor HB -EGF.