Abstract
Abstract Human FGL2 is a T lymphocyte-secreted protein that has been reported to possess prothrombinase activity and can inhibit T cell proliferation and maturation in vitro. In mouse, FGL2 is thought to contribute to the pathogenesis of xenograft and allograft rejection, virally induced hepatocellular injury and cytokine induced fetal loss syndrome. Understanding transcription initiation of the human FGL2 gene can enhance our understanding of the biological function of FGL2. Through Q-PCR & RT-PCR, we found that, HMEC-1 (endothelial cell line) and EBV-transformed B cells can constitutively express FGL2. TNF-α and IL-4 can increase FGL2 expression in HMEC-1 cells. Thus, transcriptional regulation of the human FGL2 promoter was analyzed in HMEC-1 cells under conditions of constitutive expression, and under IL-4 induction. By deletion studies, we found that the region that supports constitutive and IL-4 induced FGL2 transcription is located within the nucleotides -135 to -1 upstream of the translation start site of FGL2. Furthermore, the region within -237 to -135 nucleotides may function as a cis negative regulatory DNA element. Upon IL-4 treatment, FGL2 promoter activity was increased in HMEC-1 cells. This IL-4 responsiveness was abrogated in HMEC-1 cells transiently transfected with human FGL2 promoter that consists of an altered Stat6 binding element located at -87 to -89 relative to ATG start codon. Three loci of single nucleotide polymorphism (SNP) were identified at position -165, -656, and -1285 within the 5’promoter of the FGL2 gene among Taiwanese individuals. In luciferase reporter assays, the variants -656T & -1285T have the same luciferase activity with -656A & -1285A. The -165C genotype has a lower, though not significant different, basal activity than that of the -165T construct.