| Glutamine is considered a non-essential amino acid; however, it becomes conditionally essential under critical illness when body consumption exceeds production. This dissertation examines the role of glutamine in the heat shock (Hsp25)/stress response-an important cellular response for survival. Glutamine, but not glucose or serum, omission dramatically decreases the induction of Hsp25 by heat in both epithelial IEC18 and mesenchymal NIH/3T3 cells. Glutamine promotes the expression of Hsp25 at both protein and mRNA levels in a concentration dependent manner. It appears that glutamine modulates transcription of Hsp25 gene through the activation of HSF1 binding to HSE located within the promoter sequence. The requirement of glutamine in the expression of Hsp25 is shared by a variety of stress stimulating insults such as heat shock, proteasome inhibition, and amino acid analog. However glutamine's effect seems to be specific to the expression of certain inducible heat shock genes for example Hsp25 and Hsp72 but not the constitutive heat shock gene such as Hsc73. The glutamine's effect was also unique since neither arginine, histidine, proline (metabolized as glutamine to 2-oxoglutarate for TCA cycle metabolism), leucine, arginine, nor tyrosine could replace glutamine for heat induction of Hsp25. The lack of effect of these amino acids did not appear to be caused by lack of transport, although some amino acids, importantly including glutamate, were transported poorly by IEC18 cells. By increasing glutamate uptake, glutamate could also promote heat induction of Hsp25. Additionally, a glutaminase inhibitor, 6-diazo-5-oxo-L-norieucine, could inhibit glutamine's effect of heat-induced Hsp25. Glutamine or glutamate conversion to glutathione was apparently not involved as the glutathione synthesis inhibitor, buthionine sulfoximine, did not block glutamine's effect on heat-induction of Hsp25. In summary, the requirement of glutamine underscores an important role of this amino acid to support cell survival under conditions of stress and injury, when depleted, severe injury and tissue destruction could ensue. The glutamine's effect on the heat shock response might contribute to the widely protective roles of glutamine against tissue inflammation and organ complications in critical illness. |
