Sp1 is the major fasl gene activator in abnormal CD4(-)CD8(-)B220(+) T cells of lpr and gld mice

The abnormal CD4(-)CD8(-)TCR alpha beta (+)B220(+) double-negative (DN) T c ells that accumulate in lpr and gld mice are refractory to TCR cross-linkin g and IL-2 stimulation, yet they have an activated phenotype and express a high level of fast mRNA. Specific binding sites for Spl, NFAT, Egr, and NF- kappaB have been identified in the promoter region of the fasl gene. To det ermine the critical factor for fast gene activation, fasl promoter reporter and mutant constructs were transiently transfected into the abnormal DN T cells. The data demonstrate that the Spl binding site is the major response element that regulates fast promoter activity. Moreover, the abnormal DN T cells contain in their nuclei a high level of Spl, a low level of NFAT and NF-RB, and a very low level of Egr. Ectopic expression of Egr-3 but not Sp l protein in the abnormal DN T cells enhanced fast promoter activity, sugge sting that the Egr but not Spl was limiting for fast gene activation. Compa rison between the abnormal DN T cells and the Sertoli TM4 cells showed a st rong correlation between Spl expression and fast mRNA level and FasL functi on. Our study has identified Spl as the major transcription factor responsi ble for fast gene activation in the abnormal DN T cells that are defective in signal transduction through TCR and IL-2R, thereby, implicating a novel regulatory pathway for fast gene activation during the physiological develo pment and elimination of the abnormal DN T cells.