Akt-1 mediates survival of chondrocytes from endoplasmic reticulum-induced stress.
The unfolded protein response (UPR) is an evolutionary conserved adaptive mechanism that permits cells to react and adjust to conditions of endoplasmic reticulum (ER) stress. In addition to UPR, phosphatidylinositol 3-kinase (PI3K)/Akt and extracellular signal regulated kinase (ERK) signaling pathways protect a variety of cells from ER stress. The goal of the present study was to assess the susceptibility of chondrocytes to ER stress and to determine the signaling pathways involved in their survival. We found that low concentration of thapsigargin (10 nM) reduced the viability of a chondrocyte cell line (N1511 cells) and that these cells were approximately 100 fold more susceptible to thapsigargin-induced stress than fibroblasts. Interestingly, in thapsigargin and tunicamycin-stressed chondrocytes induction of the proapoptotic transcription factor CHOP preceded that of the anti-apoptotic BiP by 12 h. Although both of these agents caused sustained Akt and ERK phosphorylation; inhibition of Akt phosphorylation sensitized chondrocytes to ER stress, while blocking ERK signaling by U0126 had no effect. We found that Akt-1, but not Akt-2 or Akt-3, is predominantly expressed in N1511 chondrocytes. Furthermore, siRNA-mediated knockdown of Akt-1 sensitized chondrocytes to ER stress, which was associated with increased capsase-3 activity and decreased Bcl(XL) expression. These data suggest that under condition of ER stress, multiple signaling processes regulate chondrocyte's survival-death decisions. Thus, rapid upregulation of CHOP likely contributes to chondrocyte death, while Akt-1-mediated inactivation of caspase 3 and induction of BclXL promotes survival.
Price
Jeremy
J
Department of Pathology, University of Pennsylvania School of Dental Medicine, Philadelphia, Pennsylvania 19104, USA.
Zaidi
Asifa K
AK
Bohensky
Jolene
J
Srinivas
Vickram
V
Shapiro
Irving M
IM
Ali
Hydar
H
D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000378:metabolism; D002070:Butadienes / Q000494:pharmacology; D053148:Caspase 3 / Q000378:metabolism; D002460:Cell Line; D002470:Cell Survival; D019902:Chondrocytes / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology; D002867:Chromones / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000201:enzymology*; D000091342:Endoplasmic Reticulum Chaperone BiP; D004791:Enzyme Inhibitors / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism; D051379:Mice; D009025:Morpholines / Q000494:pharmacology; D009570:Nitriles / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013312:Stress, Physiological; D019284:Thapsigargin / Q000494:pharmacology; D013997:Time Factors; D051742:Transcription Factor CHOP / Q000378:metabolism; D014415:Tunicamycin / Q000494:pharmacology; D056811:Unfolded Protein Response; D051020:bcl-X Protein / Q000378:metabolism
D055396:Bone Morphogenetic Protein 2; D002070:Butadienes; D053148:Caspase 3; D002867:Chromones; D000091342:Endoplasmic Reticulum Chaperone BiP; D004791:Enzyme Inhibitors; D048049:Extracellular Signal-Regulated MAP Kinases; D006360:Heat-Shock Proteins; D009025:Morpholines; D009570:Nitriles; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D019284:Thapsigargin; D051742:Transcription Factor CHOP; D014415:Tunicamycin; D051020:bcl-X Protein; C494812:Bcl2l1 protein, mouse; C497250:Ddit3 protein, mouse; C113580:U 0126; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C514862:Akt1 protein, mouse; C494922:Akt2 protein, mouse; C491753:Akt3 protein, mouse; C505409:Casp3 protein, mouse