GLUCOCORTICOIDS REGULATE GLUTAMINASE GENE-EXPRESSION IN HUMAN INTESTINAL EPITHELIAL-CELLS

Glutamine is essential for intestinal metabolism and function, but its circulating and luminal availability to the mucosa may be diminished during critical illness. We hypothesized that glucocorticoids, which a re produced in increased amounts during critical illness, accelerate m ucosal glutamine metabolism. We studied intestinal glutamine utilizati on by examining the regulation of glutaminase in vitro, the enterocyte 's principal enzyme of glutamine metabolism. Differentiated confluent human enterocytic cells (Caco-2 cells) were incubated with dexamethaso ne. Glutaminase activity was assayed and mRNA was extracted. Glutamina se transcripts were labeled with a P-32-labeled glutaminase cDNA probe , quantitated by phosphoimaging, and normalized to beta-actin. Dose- a nd time-response studies were performed. Dexamethasone-treated cells w ere also incubated with actinomycin D and cycloheximide. Dexamethasone (DEX) increased mucosal glutaminase activity by 45%, with maximal res ponse at 12 hr. This increase was dose-dependent and was significant a t doses of 1 and 10 mu M. The dexamethasone-mediated increase in gluta minase activity was associated with a 40% increase in glutaminase mRNA . The DEX-induced increase in glutaminase activity was inhibited by ac tinomycin D and cycloheximide, indicating the requirement for de novo RNA and protein synthesis. Glucocorticoids stimulate glutamine metabol ism in these human enterocytic cells by increasing the activity of glu taminase, a response that is preceded by an increase in gene transcrip tion. This glucocorticoid-mediated increase in glutaminase activity ma y be a mechanism by which gut glutamine metabolism is maintained durin g critical illness when blood glutamine levels are diminished and food intake is often interrupted. (C) 1994 Academic Press, Inc.