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AJP - Cell Physiology, Vol 270, Issue 3 C825-C831, Copyright © 1996 by American Physiological Society
ARTICLES |
B. Gowda, M. Sar, X. Mu, J. Cidlowski and T. Welbourne
Department of Physiology, Louisiana State University Medical Center,Shreveport 71130, USA.
The effect of glucocorticoid receptor on glutaminase gene expression and related glutamine metabolism was studied in proximal tubule-like LCC-PK1-F+ cells. These cells express functional glucocorticoid receptors as demonstrated by immunoreactivity with antiglucocorticoid receptor antibody, specific ligand binding, and a 14-fold increase in chloramphenicol acetyltransferase (CAT) reporter gene activity after exposure to dexamethasone (10(-6)M). Dexamethasone exposure for 18 h increased glutaminase mRNA and activity by 32 and 42%, respectively (both P< 0.05, paired t-test), associated with a small (9%) but significant increase in glutamine utilization (P<0.05). In an effort to elicit a greater response, endogenous glucocorticoid receptors were supplemented by transfecting cells with a plasmid, pMAMGR, expressing the rat glucocorticoid receptor gene. Transfected cells expressed a 39-fold increase in CAT activity with dexamethasone treatment, confirming a higher level of functional receptors, but glutaminase mRNA and activity were now decreased by 34 and 32%, respectively, associated with a 15% fall in glutamine utilization after 18-h exposure to dexamethasone. This biphasic response in glutaminase gene expression was mirrored by glucocorticoid receptor mRNA that increased 41% after dexamethasone in LLC-PK(1)-F+ cells, but decreased 63% after transfection (both P<0.05). These findings are consonant with glucocorticoid receptor gene modulation of glutaminase gene expression and glutamine utilization.
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