Tumor necrosis factor-alpha inhibits store-mediated Ca2+ entry in the human hepatocellular carcinoma cell line HepG2.
Tumor necrosis factor-alpha (TNF-alpha) is an important component of the early signaling pathways leading to liver regeneration and proliferation, but it is also responsible for several hepatotoxic effects. We have investigated the effect of TNF-alpha on thapsigargin (TG)-induced store-mediated Ca2+ entry (SMCE) in the human hepatocellular carcinoma cell line HepG2. In these cells, short-term (10 min) exposure to TNF-alpha slightly increased SMCE. In contrast, long-term (12 h) exposure to TNF-alpha significantly reduced SMCE. This effect was reversed by coincubation with atrial natriuretic peptide (ANP), which itself had no effect on SMCE. Cytochalasin D and latrunculin A, inhibitors of actin polymerization, abolished SMCE. Long-term exposure of HepG2 cells to TNF-alpha abolished TG-induced actin polymerization and membrane association of Ras proteins. When TNF-alpha was added in combination with ANP, these effects were reduced. These findings suggest that in HepG2 cells, TNF-alpha inhibits SMCE by affecting reorganization of the actin cytoskeleton, probably by interfering with the activation of Ras proteins, and that ANP protects against these inhibitory effects of TNF-alpha.
Rosado
J A
JA
Department of Physiology, University of Cambridge, Cambridge CB2 3EG, United Kingdom.
Rosenzweig
I
I
Harding
S
S
Sage
S O
SO
D000199:Actins / Q000378:metabolism; D009320:Atrial Natriuretic Factor / Q000032:analysis / Q000494:pharmacology; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002273:Carcinogens / Q000494:pharmacology; D006528:Carcinoma, Hepatocellular; D002451:Cell Compartmentation / Q000187:drug effects / Q000502:physiology; D015638:Cytochalasin D / Q000494:pharmacology; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D008113:Liver Neoplasms; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D011108:Polymers / Q000378:metabolism; D019284:Thapsigargin / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology; D053778:Thiazolidines; D014407:Tumor Cells, Cultured / Q000737:chemistry / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D018631:ras Proteins / Q000032:analysis
D000199:Actins; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002273:Carcinogens; D019384:Nucleic Acid Synthesis Inhibitors; D011108:Polymers; D013844:Thiazoles; D053778:Thiazolidines; D014409:Tumor Necrosis Factor-alpha; D015638:Cytochalasin D; D019284:Thapsigargin; D009320:Atrial Natriuretic Factor; D018631:ras Proteins; C037067:latrunculin A; D002118:Calcium