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1 Department of Medicine, University of Toronto, Toronto, and 2 Department of Medicine, McMaster University, Hamilton, Ontario M5G 2C4, Canada
Expression of glutamine:fructose-6-phosphate amidotransferase
(GFAT), the rate-limiting enzyme for glucose entry into the hexosamine
pathway, is transcriptionally regulated. Immunohistochemical studies of
human kidney biopsies demonstrate increased GFAT expression in diabetic
glomeruli, but the mechanism responsible for this overexpression is
unknown. Given the role of ANG II in diabetic kidney disease, we chose
to study the effect of ANG II on GFAT promoter activity in mesangial
cells (MC). Exposure of MC to ANG II (10
7 M) increased
GFAT promoter activity (2.5-fold), mRNA (3-fold), and protein
(1.6-fold). ANG II-mediated GFAT promoter activation was inhibited by
the ANG II type I receptor antagonist candesartan (10
8 M)
but was unaffected by the ANG II type II receptor antagonist PD-123319
(10
8 M). The intracellular calcium chelator
1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid
(10
6 M), protein kinase C (PKC) inhibitors
bisindoylmaleimide-4 (10
6 M) and calphostin C
(10
7 M), protein tyrosine kinase (PTK) inhibitor
genistein (10
4 M), Src family kinase inhibitor PP2
(2.5 × 10
7 M), p42/44 mitogen-activated protein
kinase (MAPK) inhibitor PD-98059 (10
5 M), and the
epidermal growth factor (EGF) inhibitor AG-1478 all attenuated GFAT
promoter activation by ANG II. We conclude that the GFAT promoter is
activated by ANG II via the AT1 receptor. Promoter
activation is calcium dependent and PKC dependent but also involves PTK
signaling pathways including Src, the EGF receptor, and p42/44 MAPK.
angiotensin II; signaling; glomerulus; mesangial cells; glutamine:fructose-6-phosphate amidotransferase
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