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The Journal of Immunology, Vol 157, Issue 6 2282-2290, Copyright © 1996 by American Association of Immunologists

ARTICLES

Characterization of the human C6 promoter: requirement of the CCAAT enhancer binding protein binding site for C6 gene promoter activity

S Gonzalez and C Lopez-Larrea
Immunology Service, Central Hospital of Asturias, Oviedo, Spain.

The sixth complement component (C6) is a late-acting complement protein that participates in the assembly of the membrane attack complex. C6 and most of the complement proteins are mainly synthesized in the liver. However, the human hepatoma-derived cell line Hep-G2, which produces the majority of complement proteins, synthesizes traces of C6. Here, we have isolated and characterized the human C6 promoter. Approximately 1 kb of C6 upstream sequence is shown to be sufficient to achieve tissue-specific expression of a luciferase reporter gene in two hepatic (Hep-G2 and Hep-3B) and two extrahepatic cell lines (fibroblast M1 and HeLa) in a manner similar to endogenous C6. There are wide differences in C6 mRNA expression among the four cell lines, whereas Hep-3B expresses high levels of C6, Hep-G2 and M1 poorly synthesize C6, and HeLa completely lacks C6 expression. Deletional and mutational analysis demonstrates that a C/EBP (CCAAT/enhancer binding protein) site located at -67 is required for C6 expression in Hep-3B cells, but it has little effect in M1 and Hep-G2 cells. Electrophoretic mobility shift assays show that this sequence binds to a C/EBP alpha using Hep- 3B nuclear extract, but a negligible activity is detected using a Hep- G2 extract. To further investigate whether C/EBP alpha is the limiting factor for C6 expression, we have transfected a C/EBP alpha expression vector into Hep-G2 and Ml cells. C/EBP alpha expression vector dramatically trans-activates the luciferase reporter gene controlled by the C6 promoter, and it partially restores C6 mRNA expression in Hep-G2 cells.


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A. Lopez-Soto, A. Quinones-Lombrana, R. Lopez-Arbesu, C. Lopez-Larrea, and S. Gonzalez
Transcriptional Regulation of ULBP1, a Human Ligand of the NKG2D Receptor
J. Biol. Chem., October 13, 2006; 281(41): 30419 - 30430.
[Abstract] [Full Text] [PDF]


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