Dual involvement of caspase-4 in inflammatory and ER stress-induced apoptotic responses in human retinal pigment epithelial cells.
OBJECTIVE
To investigate the functional involvement of caspase-4 in human retinal pigment epithelial (hRPE) cells.


METHODS
Expression and activation of caspase-4 in hRPE cells were measured after stimulation with proinflammatory agents IL-1beta (2 ng/mL), TNF-alpha (20 ng/mL), lipopolysaccharide (1000 ng/mL), interferon-gamma (500 U/mL), or monocyte coculture in the absence or presence of immunomodulating agent cyclosporine (3 or 30 ng/mL), dexamethasone (10 microM), or IL-10 (100 U/mL) and endoplasmic reticulum (ER) stress inducer thapsigargin (25 nM) or tunicamycin (3 or 10 microM). The onset of ER stress was determined by expression of GRP78. The involvement of caspase-4 in inflammation and apoptosis was further examined by treating the cells with caspase-4 inhibitor Z-LEVD-fmk, caspase-1 and -4 inhibitor Z-YVAD-fmk, and pan-caspase inhibitor Z-VAD-fmk.


RESULTS
Caspase-4 mRNA expression and protein activation were induced by all the proinflammatory agents and ER stress inducers tested in this study. Caspase-4 activation was blocked or reduced by dexamethasone and IL-10. Elevated ER stress by proinflammatory agents and ER stress inducers was shown by increased expression of the ER stress marker GRP78. The induced caspase-4 and caspase-3 activities by tunicamycin and the stimulated IL-8 protein expression by IL-1beta were markedly reduced by caspase-4 inhibitor Z-LEVD-fmk. Although caspase-4 inhibitor Z-LEVD-fmk and caspase-1 and -4 inhibitor Z-YVAD-fmk reduced tunicamycin-induced hRPE apoptotic cell death by 59% and 86%, respectively, pan-caspase inhibitor Z-VAD-fmk completely abolished the induced apoptosis.


CONCLUSIONS
Caspase-4 is dually involved in hRPE proinflammatory and proapoptotic responses. Various proinflammatory stimuli and ER stress induce hRPE caspase-4 mRNA synthesis and protein activation. ER stress-induced hRPE cell death is caspase and, in part, caspase-4 dependent.
Bian
Zong-Mei
ZM
Department of Ophthalmology, University of Michigan, Ann Arbor, Michigan 48105, USA.
Elner
Susan G
SG
Elner
Victor M
VM
D017209:Apoptosis; D061945:Caspase Inhibitors; D053471:Caspases, Initiator / Q000502:physiology*; D002469:Cell Separation; D002478:Cells, Cultured; D016207:Cytokines / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000201:enzymology*; D000091342:Endoplasmic Reticulum Chaperone BiP; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D006360:Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D020287:In Situ Nick-End Labeling; D008070:Lipopolysaccharides / Q000494:pharmacology; D018384:Oxidative Stress / Q000187:drug effects*; D012333:RNA, Messenger / Q000378:metabolism; D055213:Retinal Pigment Epithelium / Q000201:enzymology* / Q000473:pathology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019284:Thapsigargin / Q000494:pharmacology; D014415:Tunicamycin / Q000494:pharmacology
D061945:Caspase Inhibitors; D016207:Cytokines; D000091342:Endoplasmic Reticulum Chaperone BiP; D004791:Enzyme Inhibitors; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; D008070:Lipopolysaccharides; D012333:RNA, Messenger; D014415:Tunicamycin; D019284:Thapsigargin; C093516:CASP4 protein, human; D053471:Caspases, Initiator