Differential Regulation of Albumin Gene Expression by Heparin-Binding Epidermal Growth Factor-Like Growth Factor in &alpha;-Fetoprotein-Producing and -Nonproducing Human Hepatoma Cells

ABSTRACTGALGT2(alsoB4GALNT2) encodes a glycosyltransferase that is normally confined to the neuromuscular and myotendinous junction in adult skeletal muscle.GALGT2overexpression in muscle can inhibit muscular dystrophy in mouse models of the disease by inducing the overexpression of surrogate muscle proteins, including utrophin, agrin, laminins, and integrins. Despite its well-documented biological properties, little is known about the endogenous regulation of muscleGALGT2expression. Here, we demonstrate that epidermal growth factor receptor (EGFR) ligands can activate the humanGALGT2promoter. Overexpression of one such ligand, soluble heparin-binding EGF-like growth factor (sHB-EGF), also stimulated mouse muscleGalgt2gene expression and expression ofGALGT2-inducible surrogate muscle genes. Deletion analysis of theGALGT2promoter identified a 45-bp region containing a TFAP4-binding site that was required for sHB-EGF activation. sHB-EGF increased TFAP4 binding to this site in muscle cells and increased endogenousTfap4gene expression. sHB-EGF also increased muscle EGFR protein expression and activated EGFR-Akt signaling. sHB-EGF expression was concentrated at the neuromuscular junction, andHbegfdeletion reducedGalgt2-dependent synaptic glycosylation.Hbegfdeletion also mimickedGalgt2-dependent neuromuscular and muscular dystrophy phenotypes. These data demonstrate that sHB-EGF is an endogenous regulator of muscleGalgt2gene expression and can mimicGalgt2-dependent muscle phenotypes.

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Rapid phosphorylation of Ets-2 accompanies mitogen-activated protein kinase activation and the induction of heparin-binding epidermal growth factor gene expression by oncogenic Raf-1.

Molecular and Cellular Biology ◽

10.1128/mcb.17.5.2401 ◽

1997 ◽

Vol 17 (5) ◽

pp. 2401-2412 ◽

Cited By ~ 107

Author(s):

S A McCarthy ◽

D Chen ◽

B S Yang ◽

J J Garcia Ramirez ◽

H Cherwinski ◽

...

Keyword(s):

Gene Expression ◽

Growth Factor ◽

Epidermal Growth Factor ◽

Map Kinase ◽

Gene Transcription ◽

Map Kinases ◽

Heparin Binding ◽

Promoter Activation ◽

Mitogen Activated Protein ◽

Epidermal Growth

Heparin-binding epidermal growth factor (HB-EGF) gene transcription is rapidly activated in NIH 3T3 cells transformed by oncogenic Ras and Raf and mediates the autocrine activation of the c-Jun N-terminal kinases (JNKs) observed in these cells. A 1.7-kb fragment of the promoter of the murine HB-EGF gene linked to a luciferase reporter was strongly induced following activation of deltaRaf-1:ER, a conditionally active form of oncogenic human Raf-1. Promoter activation by deltaRaf-1:ER required a composite AP-1/Ets transcription factor binding site located between bp -974 and -988 upstream of the translation initiation site. In vivo genomic footprinting indicated that the basal level of occupancy of this composite AP-1/Ets element increased following deltaRaf-1:ER activation. Cotransfection of Ets-2 and p44 mitogen-activated protein (MAP) kinase expression vectors strongly potentiated HB-EGF promoter activation in response to deltaRaf-1:ER. Potentiated activation required both p44 MAP kinase catalytic activity and threonine 72 in the Pointed domain of Ets-2. Biochemical assays demonstrated the ability of the p42 and p44 MAP kinases to phosphorylate Ets-2 on threonine 72. Importantly, in intact cells, the kinetics of phosphorylation of Ets-2 on this residue closely mirror the activation of the p42 and p44 MAP kinases and the observed onset of HB-EGF gene transcription following deltaRaf-1:ER activation. These data firmly establish Ets-2 as a direct target of the Raf-MEK-MAP kinase signaling pathway and strongly implicate Ets-2 in the regulation of HB-EGF gene expression.

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