The Journal of Neuroscience, January 1, 2001, 21(1):18-26
Nerve Growth Factor, But Not Epidermal Growth Factor, Increases
Fra-2 Expression and Alters Fra-2/JunD Binding to AP-1 and CREB
Binding Elements in Pheochromocytoma (PC12) Cells
Valerie
Boss1,
John D.
Roback2,
Andrew N.
Young2,
Linda J.
Roback2,
Daniela M. Vogt
Weisenhorn2,
Rafael
Medina-Flores2, and
Bruce H.
Wainer2
Departments of 1 Pharmacology and
2 Pathology, Emory University School of Medicine, Atlanta,
Georgia 30329
In pheochromocytoma (PC12) cells nerve growth factor (NGF) and
epidermal growth factor (EGF) activate similar receptor tyrosine kinase
signaling pathways but evoke strikingly different biological outcomes:
NGF induces differentiation and EGF acts as a mitogen. A novel approach
was developed for identifying transcription factor activities
associated with NGF-activated, but not EGF-activated, signaling, using
random oligonucleotide clones from a DNA recognition library to isolate
specific DNA binding proteins from PC12 nuclear extracts. A protein
complex from NGF-treated, but not EGF-treated, cells was identified
that exhibits increased mobility and DNA binding activity in gel
mobility shift assays. The binding complex was identified in supershift
assays as Fra-2/JunD. The clones used as probes contain either AP-1 or
cAMP response element binding (CREB) recognition elements. Time course
experiments revealed further differences in NGF and EGF signaling in
PC12 cells. NGF elicits a more delayed and sustained ERK
phosphorylation than EGF, consistent with previous reports. Both growth
factors transiently induce c-fos, but NGF evokes a
greater response than EGF. NGF specifically increases Fra-1 and Fra-2
levels at 4 and 24 hr. The latter is represented in Western blots by
bands in the 40-46 kDa range. NGF, but not EGF, enhances the upper
bands, corresponding to phosphorylated Fra-2. These findings suggest
that prolonged alterations in Fra-2 and subsequent increases in
Fra-2/JunD binding to AP-1 and CREB response elements common among many
gene promoters could serve to trigger broadly an NGF-specific program
of gene expression.
Key words:
nerve growth factor; epidermal growth factor; differentiation; transcription factor; Fra-2; PC-12
Copyright © 2001 Society for Neuroscience 0270-6474/01/21118-09$05.00/0