Volume 17, Number 1,
Issue of January 1, 1997
pp. 227-240
Copyright ©1997 Society for Neuroscience
Growth Factor-Induced Transcription of GluR1 Increases Functional
AMPA Receptor Density in Glial Progenitor Cells
Received July 12, 1996; revised Oct. 15, 1996; accepted Oct. 22, 1996.
Li-Jin Chew,
Mark W. Fleck,
Paul Wright,
Steven E. Scherer,
Mark L. Mayer, and
Vittorio Gallo
Laboratory of Cellular and Molecular Neurophysiology, National
Institute of Child Health and Human Development, National Institutes of
Health, Bethesda, Maryland 20892
We analyzed the effects of two growth factors that regulate
oligodendrocyte progenitor (O-2A) development on the expression of
glutamate receptor (GluR) subunits in cortical O-2A cells. In the
absence of growth factors, GluR1 was the AMPA subunit mRNA expressed at
the lowest relative level. Basic fibroblast growth factor (bFGF) caused
an increase in GluR1 and GluR3 steady-state mRNA levels.
Platelet-derived growth factor (PDGF) did not modify the mRNA levels
for any of the AMPA subunits but selectively potentiated the effects of
bFGF on GluR1 mRNA (4.5-fold increase). The kainate-preferring subunits
GluR7, KA1, and KA2 mRNAs were increased by bFGF, but these effects
were not modified by cotreatment with PDGF. Nuclear run-on assays
demonstrated that PDGF+bFGF selectively increased the rate of GluR1
gene transcription (2.5-fold over control). Western blot analysis
showed that GluR1 protein levels were increased selectively (sixfold
over control) by PDGF+bFGF. Functional expression was assessed by rapid
application of AMPA to cultured cells. AMPA receptor current densities
(pA/pF) were increased nearly fivefold in cells treated with PDGF+bFGF,
as compared with untreated cells. Further, AMPA receptor channels in
cells treated with PDGF+bFGF were more sensitive to voltage-dependent
block by intracellular polyamines, as expected from the robust and
selective enhancement of GluR1 expression. Our combined molecular and
electrophysiological findings indicate that AMPA receptor function can
be regulated by growth factor-induced changes in the rate of gene
transcription.
Key words:
platelet-derived growth factor;
basic fibroblast growth
factor;
oligodendrocytes;
gene transcription;
glutamate-gated channels;
rectification