Abstract
Geranylgeranylacetone (GGA), an antiulcer agent, has the ability to induce 70-kDa heat shock protein (HSP70) in various cell types and to protect cells from apoptogenic insults. However, little is known about effects of GGA on other HSP families of molecules. We found that, at concentrations ≥100 μM, GGA caused selective expression of 78-kDa glucose-regulated protein (GRP78), an HSP70 family member inducible by endoplasmic reticulum (ER) stress, without affecting the level of HSP70 in various cell types. Induction of ER stress by GGA was also evidenced by expression of another endogenous marker, CCAAT/enhancer-binding protein-homologous protein (CHOP); decreased activity of ER stress-responsive alkaline phosphatase; and unfolded protein response (UPR), including activation of the activating transcription factor 6 (ATF6) pathway and the inositol-requiring ER-to-nucleus signal kinase 1-X-box-binding protein 1 (IRE1-XBP1) pathway. Incubation of mesangial cells with GGA caused significant apoptosis, which was attenuated by transfection with inhibitors of caspase-12 (i.e., a dominant-negative mutant of caspase-12 and MAGE-3). Dominant-negative suppression of IRE1 or XBP1 significantly attenuated apoptosis without affecting the levels of CHOP and GRP78. Inhibition of c-Jun NH2-terminal kinase, the molecule downstream of IRE1, by 1,9-pyrazoloanthrone (SP600125) did not improve cell survival. Blockade of ATF6 by 4-(2-aminoethyl) benzenesulfonyl fluoride enhanced apoptosis by GGA, and it was correlated with attenuated induction of both GRP78 and CHOP. Overexpression of GRP78 or dominant-negative inhibition of CHOP significantly attenuated GGA-induced apoptosis. These results suggested that GGA triggers both proapoptotic (IRE1-XBP1, ATF6-CHOP) and antiapoptotic (ATF6-GRP78) UPR and thereby coordinates cellular fate even without induction of HSP70.
Footnotes
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This work was supported, in part, by Grants-in-Aid for Scientific Research 16390243, 17651026, and 19651024 from the Ministry of Education, Culture, Sports, Science and Technology, Japan (to M.K.).
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Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
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doi:10.1124/mol.107.039164.
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ABBREVIATIONS: GGA, geranylgeranylacetone; HSP, heat shock protein; ER, endoplasmic reticulum; GRP, glucose-regulated protein; UPR, unfolded protein response; CHOP, CCAAT/enhancer-binding protein-homologous protein; JNK, c-Jun NH2-terminal kinase; PERK, RNA-dependent protein kinase-like ER kinase; ATF6, activating transcription factor 6; IRE1, inositol-requiring ER-to-nucleus signal kinase 1; eIF2α, eukaryotic translation initiation factor 2α; XBP1, X-box-binding protein 1; FBS, fetal bovine serum; AEBSF, 4-(2-aminoethyl) benzenesulfonyl fluoride; DTT, dithiothreitol; SEAP, secreted alkaline phosphatase; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; TUNEL, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling; ES-TRAP, ER stress-responsive alkaline phosphatase; ERAI, ER stress-activated indicator; nt, nucleotide(s); ASK, apoptosis signal-regulating kinase; DN, dominant-negative; TRAF, tumor necrosis factor receptor-associated factor; SP600125, 1,9-pyrazoloanthrone.
- Received June 19, 2007.
- Accepted August 16, 2007.
- The American Society for Pharmacology and Experimental Therapeutics
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