BMC Genomics 2007, 8:99 http://www.biomedcentral.com/1471-2164/8/99 EFfifgeuctreof6serial 5'-deletions of the human HL promoter region on transcriptional activity in HepG2 cells Effect of serial 5'-deletions of the human HL promoter region on transcriptional activity in HepG2 cells. HepG2 cells were transiently transfected with the indicated promoter-reporter constructs. At 48 h post-transfection, transcriptional activity was determined as the firefly over renilla luciferase activity. Data are expressed as percentage of the ratio measured in the hHL-685luc – transfected cells. Data are means ± SD from 4 independent experiments, each performed in quadruplicate. *: P < 0.05; n.s.: not significant. DR4 module (-295 to -265) conserved among human and mouse, in basal transcriptional activity in HepG2 cells. We propose, therefore, that this part of the HL promoter region is involved in modulation of gene transcription under different hormonal or nutritional conditions. We show here that the conserved module B (-80 to -40) plays a dual role in mediating liver-restricted transcription of the HL gene. On the one hand, the module mediates moderate stimulation of minimal promoter activity in liver-derived HepG2 cells, and on the other hand, it medi- ates inhibition of minimal promoter activity in the non- hepatic HeLa cells. Of the potential TFBS identified in module B, the liver-enriched HNF1 is a likely candidate for effecting the liver-specific activation of the HL pro- moter. Other groups have already suggested an important role for the HNF1 binding site [22-24], and in vitro HNF1 binding to this sequence has been demonstrated by gelshift assays [24]. Furthermore, HNF1α knockout mice have 3.4 fold lower HL mRNA levels than control mice [28]. In primary hepatocytes, HL secretion increases with HNF1α gene dosage [28]. However, HL mRNA and HL secretion are not completely lost by HNF1α knockout, indicating that HNF1α is not the only transcription factor determining HL expression in liver. HL secretion was only observed with hepatoma cell lines that express HNF1α or HNF1β mRNA [24], but not all cell lines with detectable HNF1α or -β expression do also secrete HL. In fact, HL secretion correlated with expression of HNF4 rather than with HNF1 mRNA [24]. The HNF4α gene itself is a target Page 9 of 13 (page number not for citation purposes)