Accessory elements, flanking DNA sequence, and promoter context play key roles in determining the efficacy of insulin and phorbol ester signaling through the malic enzyme and collagenase-1 AP-1 motifs.

Ayala JE, Streeper RS, Svitek CA, Goldman JK, Oeser JK, O'Brien RM
J Biol Chem. 2002 277 (31): 27935-44

PMID: 12032154 · DOI:10.1074/jbc.M203682200

Insulin stimulates malic enzyme (ME)-chloramphenicol acetyltransferase (CAT) and collagenase-1-CAT fusion gene expression in H4IIE cells through identical activator protein-1 (AP-1) motifs. In contrast, insulin and phorbol esters only stimulate collagenase-1-CAT and not ME-CAT fusion gene expression in HeLa cells. The experiments in this article were designed to explore the molecular basis for this differential cell type- and gene-specific regulation. The results highlight the influence of three variables, namely promoter context, AP-1 flanking sequence, and accessory elements that modulate insulin and phorbol ester signaling through the AP-1 motif. Thus, fusion gene transfection and proteolytic clipping gel retardation assays suggest that the AP-1 flanking sequence affects the conformation of AP-1 binding to the collagenase-1 and ME AP-1 motifs such that it selectively binds the latter in a fully activated state. However, this influence of ME AP-1 flanking sequence is dependent on promoter context. Thus, the ME AP-1 motif will mediate both an insulin and phorbol ester response in HeLa cells when introduced into either the collagenase-1 promoter or a specific heterologous promoter. But even in the context of the collagenase-1 promoter, the effects of both insulin and phorbol esters, mediated through the ME AP-1 motif are dependent on accessory factors.

MeSH Terms (20)

Base Sequence beta-Galactosidase Cell Line Chloramphenicol O-Acetyltransferase Collagenases DNA Primers Gene Expression Regulation, Enzymologic HeLa Cells Humans Insulin Malate Dehydrogenase Mutagenesis Oligodeoxyribonucleotides Phorbol Esters Polymerase Chain Reaction Promoter Regions, Genetic Recombinant Proteins Transcription Factor AP-1 Transcription Factors Transfection

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