Glutamine induces heat shock protein expression via O-glycosylation and phosphorylation of HSF-1 and Sp1.

BACKGROUND: Glutamine (GLN) improves outcome in experimental and clinical states of illness and injury. The authors hypothesized GLN-mediated enhancement of O-glycosylation and subsequent phosphorylation of key transcription factors in the HSP70 pathway would lead to increased HSP70 expression following experimental sepsis.
METHODS: Mice underwent cecal ligation and puncture (CLP)-induced sepsis and were treated with GLN (0.75 g/kg) or a saline placebo 30 minutes after CLP. A separate group of mice was treated with mithramycin, an Sp1 inhibitor. Lung tissue was harvested at 1, 2, 6, and 24 hours after CLP and was analyzed for HSF-1 and Sp1 O-GlcNAc modification, alpha-p-threonine modification, and HSP70.
RESULTS: GLN increased O-GlcNAc modification of HSF-1 and Sp1 at 1 and 2 hours after sepsis (P < .001 vs saline). Samples immunoprecipitated for Sp1 and probed for subsequent phosphorylation showed a significant increase in nuclear alpha-p-threonine-modified Sp1 at 2 and 6 hours after sepsis (P < .001 vs saline). GLN increased phosphorylated nuclear HSF-1 at 1 and 2 hours after CLP (P < .001). Finally, GLN treatment increased HSP70 4-fold (P < .01), but when treated with mithramycin, this increase was attenuated at 2, 6, and 24 hours (P < .001 vs no mithramycin treatment).
CONCLUSIONS: These results indicate that GLN induces HSF-1 and Sp1, which is known to lead to their nuclear translocation. The molecular mechanism of GLN-mediated HSP70 expression appears to be dependent on O-GlcNAc pathway activation and subsequent O-glycosylation and phosphorylation of key transcription factors required for HSP70 induction.