Sp1 is the major fasl gene activator in abnormal CD4(-)CD8(-)B220(+) T cells of lpr and gld mice.
The abnormal CD4(-)CD8(-)TCRalpha beta(+)B220(+) double-negative (DN) T cells that accumulate in lpr and gld mice are refractory to TCR cross-linking and IL-2 stimulation, yet they have an activated phenotype and express a high level of fasl mRNA. Specific binding sites for Sp1, NFAT, Egr, and NF-kappaB have been identified in the promoter region of the fasl gene. To determine the critical factor for fasl gene activation, fasl promoter reporter and mutant constructs were transiently transfected into the abnormal DN T cells. The data demonstrate that the Sp1 binding site is the major response element that regulates fasl promoter activity. Moreover, the abnormal DN T cells contain in their nuclei a high level of Sp1, a low level of NFAT and NF-kappaB, and a very low level of Egr. Ectopic expression of Egr-3 but not Sp1 protein in the abnormal DN T cells enhanced fasl promoter activity, suggesting that the Egr but not Sp1 was limiting for fasl gene activation. Comparison between the abnormal DN T cells and the Sertoli TM4 cells showed a strong correlation between Sp1 expression and fasl mRNA level and FasL function. Our study has identified Sp1 as the major transcription factor responsible for fasl 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 fasl gene activation during the physiological development and elimination of the abnormal DN T cells.
Xiao
S
S
Department of Medicine, Boston University School of Medicine, Boston, USA.
Marshak-Rothstein
A
A
Ju
S T
ST
D000818:Animals; D015704:CD4 Antigens / Q000032:analysis*; D016827:CD8 Antigens / Q000032:analysis*; D002460:Cell Line; D003602:Cytotoxicity, Immunologic; D004268:DNA-Binding Proteins / Q000502:physiology; D051776:Early Growth Response Protein 3; D053222:Fas Ligand Protein; D005786:Gene Expression Regulation; D017493:Leukocyte Common Antigens / Q000032:analysis*; D008562:Membrane Glycoproteins / Q000235:genetics*; D051379:Mice; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000032:analysis; D016329:Sp1 Transcription Factor / Q000502:physiology*; D013601:T-Lymphocytes / Q000378:metabolism*; D014157:Transcription Factors / Q000502:physiology; D015533:Transcriptional Activation
D015704:CD4 Antigens; D016827:CD8 Antigens; D004268:DNA-Binding Proteins; C497369:Egr3 protein, mouse; D053222:Fas Ligand Protein; C505658:Fasl protein, mouse; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D016329:Sp1 Transcription Factor; D014157:Transcription Factors; D051776:Early Growth Response Protein 3; D017493:Leukocyte Common Antigens