Glutamine metabolism stimulates intestinal cell MAPKs by a cAMP-inhibitable, Raf-independent mechanism.
OBJECTIVE
Infectious diarrhea caused by viruses plus enterotoxigenic bacteria is often more severe than diarrhea induced by either pathogen alone. We postulated that the increased cell adenosine 3',5'-cyclic monophosphate (cAMP) concentration observed during infection by enterotoxigenic organisms retards the intestinal repair process by blocking activation of mitogen-activated protein kinases (MAPKs) in proliferating intestinal cells.


METHODS
We evaluated the effects of glutamine on MAPK activity, thymidine incorporation, and cell number in glutamine-starved and -sufficient rat intestinal crypt cells (IEC-6).


RESULTS
In glutamine-starved cells, 10 mmol/L glutamine in the absence of serum stimulated [(3)H]thymidine incorporation 8-fold. This effect was inhibited by 60% with 8-(4-chlorophenylthio) (8-CPT)-cAMP (100 micromol/L) + isobutyl methylxanthine (100 micromol/L). In cells not starved of glutamine, glutamine stimulated thymidine incorporation by 3-fold, and 8-CPT-cAMP completely blocked the mitogenic effect. Inhibition of proliferation by cAMP persisted for at least 68 hours after cAMP removal. In vitro kinase assays showed that glutamine signaling requires an intact ERK (extracellular signal-related kinase) pathway in unstarved cells. In starved cells, at least one other pathway (JNK) was activated by glutamine, and the mitogenic inhibition by 8-CPT-cAMP was incomplete. Other intestinal fuels (glucose and acetate) were not mitogenic.


CONCLUSIONS
Increased levels of intracellular cAMP inhibit ERKs but only partially reduce glutamine-stimulated proliferation in enterocytes adapted to low glutamine.
Rhoads
J M
JM
Department of Pediatrics, University of North Carolina, Chapel Hill, NC27599-7220, USA.
Argenzio
R A
RA
Chen
W
W
Graves
L M
LM
Licato
L L
LL
Blikslager
A T
AT
Smith
J
J
Gatzy
J
J
Brenner
D A
DA
D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D004247:DNA / Q000096:biosynthesis / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000378:metabolism / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D005973:Glutamine / Q000378:metabolism* / Q000494:pharmacology; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000166:cytology; D020935:MAP Kinase Signaling System / Q000187:drug effects; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010101:Oxygen Consumption / Q000187:drug effects; D013873:Thionucleotides / Q000494:pharmacology; D013936:Thymidine / Q000378:metabolism
D004791:Enzyme Inhibitors; D005419:Flavonoids; D013873:Thionucleotides; D005973:Glutamine; C015929:8-((4-chlorophenyl)thio)cyclic-3',5'-AMP; D004815:Epidermal Growth Factor; D004247:DNA; D000242:Cyclic AMP; D020928:Mitogen-Activated Protein Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D013936:Thymidine