Elevated ceramide is downstream of altered calcium homeostasis in low serum-induced apoptosis.
Two immortalized cell lines, sup (+) and sup (-), derived from mutagenized Syrian hamster embryo cells, were used to study the relationship and temporal order between calcium and ceramide signals during apoptosis. The early preneoplastic cells, termed sup (+), suppress tumorigenicity when hybridized with tumor cells, whereas later-stage sup (-) cells do not. In reduced serum conditions, sup (+) cells cease proliferating and undergo apoptosis; in contrast, sup (-) cells continue slow growth and undergo necrosis. In sup (+) cells, decreased endoplasmic reticulum (ER) calcium occurs 4 h after low serum treatment and precedes apoptosis. Significant elevations in ceramide are observed 16 h after reduced serum treatment of sup (+) cells but are not found in sup (-) cells. Inhibiting ER calcium depletion in low serum-treated sup (+) cells by treating with high levels of calcium prevents both ceramide generation and apoptosis. Conversely, inducing ER calcium depletion in sup (-) cells by treating with low serum plus thapsigargin results in elevated ceramide levels and apoptosis. Furthermore, C(6)-ceramide treatment induced apoptosis of sup (-) cells in low serum, a condition that does not normally cause apoptosis. C(6)-ceramide treatment did not induce apoptosis in either sup (+) or sup (-) cells in 10% serum but did cause G(2)/M arrest. These studies show that ceramide production is downstream of ER calcium release.
Jayadev
S
S
Laboratory of Molecular Carcinogenesis, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709, USA.
Barrett
J C
JC
Murphy
E
E
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D001769:Blood; D020013:Calcium Signaling / Q000502:physiology*; D002453:Cell Cycle / Q000187:drug effects; D002478:Cells, Cultured / Q000187:drug effects; D002518:Ceramides / Q000494:pharmacology / Q000502:physiology*; D006224:Cricetinae; D003470:Culture Media / Q000494:pharmacology*; D004075:Diglycerides / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008647:Mesocricetus; D015398:Signal Transduction / Q000502:physiology*; D019284:Thapsigargin / Q000494:pharmacology
D002518:Ceramides; D003470:Culture Media; D004075:Diglycerides; D004791:Enzyme Inhibitors; C101954:N-caproylsphingosine; D019284:Thapsigargin