P38MAP kinase, but not phosphoinositol-3 kinase, signal downstream of glutamine-mediated fibronectin-integrin signaling after intestinal injury

BACKGROUND Glutamine appears to mediate protection against gut injury via multiple pathways. These include fibronectin-integrin, PI3-K/MAPK pathways, and activation of heat shock protein (HSP) response. We hypothesize there may be a relationship between these pathways mediating glutamine's protection in intestinal epithelial-6 cells after heat stress. We assessed whether p38MAPK and PI3-K/Akt signaling are involved in glutamine's cytoprotective mechanism and the role they play in glutamine-mediated protection in conjunction with fibronectin-integrin osmosignaling after hyperthermia. METHODS Intestinal epithelial cells were treated for 15 min with glutamine, with/without the fibronectin-integrin interaction inhibitor GRGDSP, inactive control peptide GRGESP, p38MAPK inhibitor SB203580, or PI3-K/Akt inhibitor LY294002 under basal (37°C) and stressed (43°C or 44°C) conditions. Cell survival was measured via MTS assay 24 h post-heat stress (44°C × 50 min). Total p38MAPK, [T(P)180/Y(P)182]p38MAPK, total Akt, [S(P)473]Akt, HSP70, FN, and caspase-3 levels were determined via Western blot after non-lethal HS (43°C × 50 min). Additionally, HSP70 levels were assessed via Western blot and ELISA. RESULTS We were able to show that GRGDSP and LY294002 attenuated glutamine's protective effect. However, SB203580 increased cell survival after heat stress. LY294002 attenuated glutamine-mediated increases in fibronectin and in HSP70 expression after hyperthermia. GRGDSP increased glutamine-mediated attenuations in p38MAPK phosphorylation, but had no effect on glutamine-mediated augmentations in Akt phosphorylation. CONCLUSIONS These data suggest that glutamine is protective after heat stress by activating PI3-K/Akt signaling preventing fibronectin-integrin expression and increasing HSP70 expression. Furthermore, dephosphorylation of p38MAPK after heat stress plays an important role in glutamine-mediated cellular protection. However, p38MAPK, but not PI3-K/Akt, signals downstream of glutamine-mediated fibronectin-integrin signaling after hyperthermia.