Human FasL gene is a target of β-catenin/T-cell factor pathway and complex FasL haplotypes alter promoter functions.
FasL expression on human immune cells and cancer cells plays important roles in immune homeostasis and in cancer development. Our previous study suggests that polymorphisms in the FasL promoter can significantly affect the gene expression in human cells. In addition to the functional FasL SNP -844C>T (rs763110), three other SNPs (SNP -756A>G or rs2021837, SNP -478A>T or rs41309790, and SNP -205 C>G or rs74124371) exist in the proximal FasL promoter. In the current study, we established three major FasL hyplotypes in humans. Interestingly, a transcription motif search revealed that the FasL promoter possessed two consensus T-cell factor (TCF/LEF1) binding elements (TBEs), which is either polymorphic (SNP -205C>G) or close to the functional SNP -844C>T. Subsequently, we demonstrate that both FasL TBEs formed complexes with the TCF-4 and β-catenin transcription factors in vitro and in vivo. Co-transfection of LEF-1 and β-catenin transcription factors significantly increased FasL promoter activities, suggesting that FasL is a target gene of the β-catenin/T-cell factor pathway. More importantly, we found that the rare allele (-205G) of the polymorphic FasL TBE (SNP -205C>G) failed to bind the TCF-4 transcription factor and that SNP -205 C>G significantly affected the promoter activity. Furthermore, promoter reporter assays revealed that FasL SNP haplotypes influenced promoter activities in human colon cancer cells and in human T cells. Finally, β-catenin knockdown significantly decreased the FasL expression in human SW480 colon cancer cells. Collectively, our data suggest that β-catenin may be involved in FasL gene regulation and that FasL expression is influenced by FasL SNP haplotypes, which may have significant implications in immune response and tumorigenesis.
Department of Veterinary and Biomedical Sciences, University of Minnesota, St. Paul, Minnesota, United States of America. jmwu@umn.edu
Jianming
J
Wu
Maureen H
MH
Richards
Jinhai
J
Huang
Lena
L
Al-Harthi
Xiulong
X
Xu
Rui
R
Lin
Fenglong
F
Xie
Andrew W
AW
Gibson
Jeffrey C
JC
Edberg
Robert P
RP
Kimberly
D001483:Base Sequence; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / Q000378:metabolism*; D001665:Binding Sites; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms / Q000235:genetics / Q000378:metabolism; D053222:Fas Ligand Protein / Q000235:genetics* / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D055785:Gene Knockdown Techniques; D006239:Haplotypes / Q000235:genetics*; D006801:Humans; D051821:Lymphoid Enhancer-Binding Factor 1 / Q000378:metabolism; D008969:Molecular Sequence Data; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000378:metabolism; D000073940:Transcription Factor 4; D014157:Transcription Factors / Q000378:metabolism*; D015854:Up-Regulation / Q000235:genetics; D051176:beta Catenin / Q000378:metabolism*
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; C505661:FASLG protein, human; D053222:Fas Ligand Protein; D051821:Lymphoid Enhancer-Binding Factor 1; C532096:TCF4 protein, human; D000073940:Transcription Factor 4; D014157:Transcription Factors; D051176:beta Catenin