Nephritogenic ochratoxin A interferes with hormonal signalling in immortalized human kidney epithelial cells.
The ubiquitous nephritogenic and carcinogenic fungal metabolite ochratoxin A (OTA) affects function and growth of renal epithelial cells. We studied the possible contribution of changes in cellular Ca2+ homeostasis to the effects of nanomolar concentrations of OTA on immortalized human kidney epithelial (IHKE-1) cells. The effects of OTA on cellular calcium homeostasis ([Ca2+]i), cell proliferation and viability and its interaction with angiotensin II (Ang II) and epidermal growth factor (EGF) were investigated. OTA potentiated EGF- and Ang II-induced cell proliferation Ca2+ dependently at OTA concentrations of 0.1 or 1 nmol/l. A decrease in cell viability could be observed only after 24 h exposure, with threshold concentrations greater than 10 nmol/l. This reduction of cell viability was independent of Ca2+. Within seconds, OTA evoked reversible and concentration-dependent [Ca2+]i oscillations with a threshold concentration of < or =0.1 nmol/l. These oscillations were abolished by removal of extracellular Ca2+, by the Ca(2+)-channel blocker SKF 96365 and by inhibition of phospholipase C. OTA also stimulated thapsigargin-sensitive Ca(2+)-ATPase activity and increased the filling state of thapsigargin-sensitive Ca(2+)-stores. Exposure to OTA concentration dependently increased cellular adenosine 3',5'-cyclic monophosphate (cAMP) content. In addition, OTA-induced changes of [Ca2+]i were reduced significantly by the protein kinase A inhibitor H-89. Finally, 0.1 or 1 nmol/l OTA potentiated the effects of Ang II and EGF on cellular Ca2+ homeostasis. We conclude that OTA may impair cellular Ca2+ and cAMP homeostasis already at low nanomolar concentrations, resulting in concentration-dependent [Ca2+]i oscillations. OTA interferes also with hormonal Ca2+ signalling, thereby leading to altered cell proliferation. The reduction of cell viability at higher OTA concentrations seems not to depend on Ca2+.
Benesic
A
A
Physiologisches Institut der Universität Würzburg, Germany.
Mildenberger
S
S
Gekle
M
M
D000804:Angiotensin II / Q000502:physiology; D002118:Calcium / Q000378:metabolism / Q000502:physiology; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002452:Cell Count / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D000242:Cyclic AMP / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000201:enzymology; D004815:Epidermal Growth Factor / Q000502:physiology; D004847:Epithelial Cells / Q000187:drug effects / Q000502:physiology*; D006706:Homeostasis / Q000187:drug effects; D006728:Hormones / Q000502:physiology*; D006801:Humans; D007668:Kidney / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008345:Manganese / Q000378:metabolism; D009183:Mycotoxins / Q000633:toxicity*; D009393:Nephritis / Q000139:chemically induced*; D009793:Ochratoxins / Q000633:toxicity*; D015398:Signal Transduction / Q000187:drug effects*
D006728:Hormones; D009183:Mycotoxins; D009793:Ochratoxins; D000804:Angiotensin II; C025589:ochratoxin A; D008345:Manganese; D004815:Epidermal Growth Factor; D000242:Cyclic AMP; D007770:L-Lactate Dehydrogenase; D000252:Calcium-Transporting ATPases; D002118:Calcium