title: Crosstalk between Raf/MEK/ERK and PI3K/AKT in suppression of Bax conformational change by Grp75 under glucose deprivation conditions.
abstract: During glucose deprivation (GD)-induced cellular stress, the molecular chaperone glucose-regulated protein 75 (Grp75)/Mortalin/PBP74/mtHSP70 (hereafter termed "Grp75") plays an important role in the suppression of apoptosis by inhibiting the Bax conformational change that delays the release of cytochrome c. The molecular pathways by which it carries out these functions are still unclear. We hypothesize that the anti-apoptotic effect by the overexpression of Grp75 was through the signal of AKT activated by classic phosphoinositide 3-kinase (PI3K) and also involved PI3K-independent pathways. Using the PC12 cell GD model, we demonstrated a novel mechanism of Grp75 activating AKT, which may be PI3K independent and associated with Raf/MEK (mitogen-activated protein kinase/ERK kinase)/ERK signaling. The PI3K inhibitor LY294002 did not influence the activation of AKT by the Grp75 overexpression under GD; however, the MEK inhibitor U0126 dramatically inhibited AKT phosphorylation in the same assay. In addition to the PI3K/AKT signal pathway, Grp75 overexpression also inhibited the Bax conformational change through the Raf/MEK/ERK signal pathway. In conclusion, Grp75 overexpression in activating AKT can be PI3K independent and associated with Raf/MEK/ERK signaling under GD. At the same time, PI3K may also crosstalk with Raf-1, in which the prosurvival signal of PI3K maintains the expression of Raf-1. The activated AKT and extracellular signal-regulated protein kinases 1 and 2 by Grp75 inhibited the Bax conformational change and subsequent apoptosis.
authors.affiliation: Department of Cellular and Genetic Medicine, Shanghai Medical College, Fudan University, Shanghai 200032, China.
authors.forename: Ling
authors.initials: L
authors.lastname: Yang
authors.forename: Weiwei
authors.initials: W
authors.lastname: Guo
authors.forename: Qunling
authors.initials: Q
authors.lastname: Zhang
authors.forename: Hongyan
authors.initials: H
authors.lastname: Li
authors.forename: Xiaoyu
authors.initials: X
authors.lastname: Liu
authors.forename: Yunlong
authors.initials: Y
authors.lastname: Yang
authors.forename: Ji
authors.initials: J
authors.lastname: Zuo
authors.forename: Wen
authors.initials: W
authors.lastname: Liu
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002070:Butadienes / Q000494:pharmacology; D002867:Chromones / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D020935:MAP Kinase Signaling System; D008565:Membrane Proteins / Q000378:metabolism*; D009025:Morpholines / Q000494:pharmacology; D009570:Nitriles / Q000494:pharmacology; D016716:PC12 Cells; D058539:Phosphatidylinositol 3-Kinase / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D011487:Protein Conformation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D051381:Rats; D051028:bcl-2-Associated X Protein / Q000737:chemistry* / Q000378:metabolism*
chemical_list: C494828:Bax protein, rat; D002070:Butadienes; D002867:Chromones; D004791:Enzyme Inhibitors; D018840:HSP70 Heat-Shock Proteins; D008565:Membrane Proteins; D009025:Morpholines; D009570:Nitriles; D000081082:Phosphoinositide-3 Kinase Inhibitors; C113580:U 0126; D051028:bcl-2-Associated X Protein; C018551:glucose-regulated proteins; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D058539:Phosphatidylinositol 3-Kinase; D051057:Proto-Oncogene Proteins c-akt