Enhanced Binding of HLF/DBP Heterodimers Represents One Mechanism of PAR Protein Transactivation of the Factor VIII and Factor IX Genes

Abstract

The regulatory regions of the genes for coagulation Factors VIII and IX contain binding sites for both liver-enriched and ubiquitous transcriptional regulators. We investigated the role of the liver-enriched protein, hepatic leukemia factor (HLF), in mediating transcriptional regulation of the Factor VIII and IX genes. Using transient transfection assays in HepG2 hepatoma cells, we demonstrated the ability of HLF alone and in synergistic combination with the D-box binding protein (DBP), another proline and acidic-rich (PAR) protein family member, to transactivate these promoters. HLF is capable of binding to multiple sites in both the Factor VIII and Factor IX promoters. At least some of the synergistic activation of the Factor VIII promoter seen with HLF and DBP cotransfection can be attributed to increased binding of HLF-DBP heterodimers to two Factor VIII promoter sites. We have also demonstrated that an E2A-HLF chimera, derived from a t(17;19) translocation in pre-B acute lymphoblastic leukemia (ALL) cells, is capable of mediating expression from the Factor VIII and Factor IX promoters in both hepatoma cells and pre-B ALL cells. These observations indicate that the PAR family of transcription factors plays an important and complex role in regulating expression of the Factor VIII and Factor IX genes, involving the binding of both homodimeric and heterodimeric complexes of HLF and DBP to several sites in the promoters. Finally, these studies reaffirm the potential role of dimeric transcription factor complexes in mediating interactions with specific promoter elements, which, in the case of the Factor VIII promoter, results in dramatically enhanced binding of HLF-DBP heterodimers to two cis-acting sequences. These observations further our understanding of the role played by members of the PAR family of transcription factors in regulating expression of the Factor VIII and Factor IX genes.

The HLF/IL-6/STAT3 feedforward circuit drives hepatic stellate cell activation to promote liver fibrosis

“…Triple deletion of TEF, DBP and HLF in mice led to the impaired detoxification35 and lipid metabolism,36 whereas the specific role of HLF was missing. In addition, HLF was reported to be involved in viral replication23 and factor IX expression24 in HepG2 or Huh7 cancer cells. Nevertheless, the role of HLF in liver fibrosis remains unreported.…”

A PAR domain transcription factor is involved in the expression from a hematopoietic-specific promoter for the human LMO2 gene

“…29,34,35 Because in many cases, such as in K562 and 293 cells as shown here, all 3 family members are present, the possibility exists for a number of different functional complexes. Begbie et al 36 have presented data demonstrating a synergistic effect on the transactivation of the factor VIII and factor IX genes by DBP and HLF. Although our data suggest both HLF and TEF may be functionally active, we have no evidence at this time for a similar synergistic or even additive effect by PAR proteins in the regulation of the LMO2 gene.…”

Liver-Enriched Transcription Factors in Liver Function and Development. Part II: the C/EBPs and D Site-Binding Protein in Cell Cycle Control, Carcinogenesis, Circadian Gene Regulation, Liver Regeneration, Apoptosis, and Liver-Specific Gene Regulation

“…DBP was shown to be able to from heterodimers with other family members of the proline and acidic-rich (PAR) protein family like HLF (Begbie et al, 1999). In transient transfection assays with HepG2 cells, HLF alone and in synergistic combination with the DBP was able to transactivate the promoters of the blood coagulation factors factor VIII and factor IX.…”

“…At least some of the synergistic activation of the factor VIII promoter seen with HLF and DBP cotransfection could be attributed to increased binding of HLF-DBP heterodimers to two factor VIII promoter sites. Several observations indicated that the PAR family of transcription factors plays an important and complex role in regulating expression of the factor VIII and factor IX genes, involving the binding of both homodimeric and heterodimeric complexes of HLF and DBP to several sites in the promoters (Begbie et al, 1999).…”