Differential expression of Fas ligand in Th1 and Th2 cells is regulated byearly growth response gene and NF-AT family members

Inducible expression of Fas ligand (CD95 ligand) by activated T cells and t he resulting apoptosis of CD95-bearing cells is a critical component of per ipheral T cell homeostasis and cytotoxic effector mechanisms. Transcription al control of the expression of Fas ligand has been attributed to a number of factors, including early growth response gene 2 (Egr2), Egr3, Sp1, and N F-AT, although a direct contribution of NF-AT is controversial. The present study confirms a role for Egr factors and indicates that NF-AT is essentia l for optimal expression of murine Fas ligand through a direct interaction with an NF-AT consensus element. The role of these factors was further defi ned by studying the differential expression of Fas ligand in Th1 and Th2 li nes derived from DO11.10 TCR transgenic mice. EMSA analyses of a composite Egr/NF-AT site showed recruitment of Sp1 to this site in Th2 cells, but not in Th1 cells. Furthermore, gel-shift analyses demonstrated the binding of Egr1, 2, and 3 in Th2 cells and Egr1 and 2, but not Egr3 in Th1 cells at a known Egr site. Northern analysis corroborated the lack of Egr3 in Th1 cell s. Differential usage of these transcription factors by Th1 and Th2 cells s uggests a potential mechanism underlying the differential expression of Fas ligand by distinct T cell lineages.