Glutamine increases autophagy under Basal and stressed conditions in intestinal epithelial cells.
OBJECTIVE
Glutamine plays a protective role in intestinal cells during physiologic stress; however, the protection mechanisms are not fully understood. Autophagy functions in bulk degradation of cellular components, but has been recognized recently as an important mechanism for cell survival under conditions of stress. We therefore sought to see if glutamine's actions involve the induction of autophagy in intestinal cells and, if so, the mechanisms that underlie this action.


METHODS
Formation of microtubule-associated protein light chain 3 (LC3)-phospholipid conjugates (LC3-II) in rat intestinal epithelial IEC-18 cells and human colonic epithelial Caco-2(BBE) cells was determined by Western blotting and localized by confocal microscopy. Activation of mammalian target of rapamycin (mTOR) pathway, mitogen-activated protein (MAP) kinases, caspase-3, and poly (ADP-ribose) polymerase were monitored by Western blotting.


RESULTS
Glutamine increased LC3-II as well as the number of autophagosomes. Glutamine-induced LC3-II formation was paralleled by inactivation of mTOR and p38 MAP kinase pathways, and inhibition of mTOR and p38 MAP kinase allowed LC3-II induction in glutamine-deprived cells. Under glutamine starvation, LC3-II recovery after heat stress or the increase under oxidative stress was blunted significantly. Glutamine depletion increased caspase-3 and poly (ADP-ribose) polymerase activity after heat stress, which was inhibited by treatment with inhibitors of mTOR and p38 MAP kinase.


CONCLUSIONS
Glutamine induces autophagy under basal and stressed conditions, and prevents apoptosis under heat stress through its regulation of the mTOR and p38 MAP kinase pathways. We propose that glutamine contributes to cell survival during physiologic stress by induction of autophagy.
Sakiyama
Toshio
T
Martin Boyer Laboratories, University of Chicago IBD Research Center, Chicago, Illinois, USA.
Musch
Mark W
MW
Ropeleski
Mark J
MJ
Tsubouchi
Hirohito
H
Chang
Eugene B
EB
D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D001343:Autophagy / Q000187:drug effects* / Q000502:physiology; D018938:Caco-2 Cells; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D003106:Colon / Q000166:cytology; D005973:Glutamine / Q000494:pharmacology* / Q000502:physiology*; D006801:Humans; D007413:Intestinal Mucosa / Q000166:cytology / Q000187:drug effects*; D000076222:Mechanistic Target of Rapamycin Complex 1; D046912:Multiprotein Complexes; D011506:Proteins; D051381:Rats; D013312:Stress, Physiological / Q000502:physiology*; D058570:TOR Serine-Threonine Kinases; D014157:Transcription Factors / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
C519510:Crtc1 protein, rat; D046912:Multiprotein Complexes; D011506:Proteins; D014157:Transcription Factors; D005973:Glutamine; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases; D048051:p38 Mitogen-Activated Protein Kinases