Abstract
gC1qR is an ubiquitously expressed cell protein that interacts with the globular heads of C1q (gC1q) and many other ligands. In this study, the 7.8-kilobase pair (kb) human gC1qR/p32 (C1qBP) gene was cloned and found to consist of 6 exons and 5 introns. Analysis of a 1.3-kb DNA fragment at the 5'-flanking region of this gene revealed the presence of multiple TATA, CCAAT, and Sp1 binding sites. Luciferase reporter assays performed in different human cell lines demonstrated that the reporter gene was ubiquitously driven by this 1.3-kb fragment. Subsequent 5' and 3' deletion of this fragment confined promoter elements to within 400 base pairs (bp) upstream of the translational start site. Because the removal of the 8-bp consensus TATATATA at -399 to -406 and CCAAT at -410 to -414 did not significantly affect the transcription efficiency of the promoter, GC-rich sequences between this TATA box and the translation start site may be very important for the promoter activity of the C1qBP gene. One of seven GC-rich sequences in this region binds specifically to PANC-1 nuclear extracts, and the transcription factor Sp1 was shown to bind to this GC-rich sequence by the supershift assay. Primer extension analysis mapped three major transcription start regions. The farthest transcription start site is 49 bp upstream of the ATG translation initiation codon and is in close proximity of the specific SP1 binding site.
Highlights
GC1qR is a biologically important, widely distributed, multiligand-binding and multifunctional protein [1]
Numerous reports have claimed that gC1qR and its homologue could be isolated or identified in various cellular compartments, including plasma membrane, cytoplasm, mitochondria and nucleus. gC1qR isolated from the plasma membrane was originally characterized as a high affinity C1q-binding protein [2], and later many reports showed that gC1qR could interact with several proteins of the intrinsic coagulation/bradykinin-forming cascade, including high molecular weight kininogen [3], Factor XII [4], fibrinogen [5], and multimeric vitronectin [6]
Exon 6 in the human C1qBP gene is about 100 bp larger in than the mouse gene because of a longer 3Ј-untranslated region defined by the polyadenylation sites
Summary
GC1qR is a biologically important, widely distributed, multiligand-binding and multifunctional protein [1]. GC1qR isolated from the plasma membrane was originally characterized as a high affinity C1q-binding protein [2], and later many reports showed that gC1qR could interact with several proteins of the intrinsic coagulation/bradykinin-forming cascade, including high molecular weight kininogen [3], Factor XII [4], fibrinogen [5], and multimeric vitronectin [6]. The findings of Dedio et al [14] do not exclude the possibility that gC1qR, like many other proteins, could be exported from the mitochrondria by an unknown mechanism [15] This possibility is supported by a recent report showing that anti-gC1qR monoclonal antibody can reverse the antiproliferation effects of hepatitis virus C core antigen on activated T cells [16]. The transcription start site and its promoter elements were mapped and characterized
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