COORDINATE MODULATION OF GLUCOCORTICOID RECEPTOR AND GLUTAMINASE GENE-EXPRESSION IN LLC-PK1-F+ CELLS

The effect of glucocorticoid receptor on glutaminase gene expression a nd related glutamine metabolism was studied in proximal tubulelike LLC -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 chloramph enicol acetyltransferase (CAT) reporter gene activity after exposure t o 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 incre ase in glutamine utilization (P < 0.05). In an effort to elicit a grea ter response, endogenous glucocorticoid receptors were supplemented by transfecting cells with a plasmid, pMAMGR, expressing the rat glucoco rticoid receptor gene. Transfected cells expressed a 39-fold increase in CAT activity with dexamethasone treatment, confirming a higher leve l of functional receptors, but glutaminase mRNA and activity were now decreased by 34 and 32%, respectively, associated with a 15% fall in g lutamine utilization after 18-h exposure to dexamethasone. This biphas ic response in glutaminase gene expression was mirrored by glucocortic oid receptor mRNA that increased 41% after dexamethasone in LLC-PK1-F cells, but decreased 63% after transfection (both P < 0.05). These fi ndings are consonant with glucocorticoid receptor gene modulation of g lutaminase gene expression and glutamine utilization.