cis-acting DNA elements regulating expression of the liver pyruvate kinase gene in hepatocytes and hepatoma cells. Evidence for tissue-specific activators and extinguisher

Abstract

To identify the DNA sequences that cis-regulate the expression of the rat liver pyruvate kinase (L-PK) genes, a series of constructs in which the chloramphenicol acetyltransferase reporter genes is driven by various deleted fragments of the 3200 base pairs (bp) upstream of the L-PK gene cap site have been assayed for transient expression after introduction into hepatoma HepG2 cells, rat hepatocytes in primary culture, fibroblast LTK- cells, myogenic C2C12 cells, and CHO cells. Four distinct regulatory domains have been characterized. A proximal promoter region containing a binding site for the hepatocyte nuclear factor 1 (HNF1) which is sufficient to confer liver specificity, even in the presence of a ubiquitous enhancer. A distal promoter region (-96 to -283 bp) containing binding sites for the liver-specific factor A1 (LFA1), the ubiquitous nuclear factor 1 (NF1), the major late transcriptional factor (MLTF), and so far unidentified proteins binding to the L5-PK region which is essential to maximally activate expression of the construct in HepG2 cells. An extinguisher region, located between positions -2082 and -1170 bp, which decreases efficiency of the L-PK promoter in HepG2 cells, but not in hepatocytes in primary culture. Finally, a far upstream region (-2900 to -2500 bp) which seems to correspond to a liver-specific DNase I hypersensitive site and which behaves in HepG2 cells as an activating sequence efficient in the absence of the extinguisher.