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Nephritogenic ochratoxin A interferes with hormonal signalling in immortalized human kidney epithelial cells
A Benesic1, S Mildenberger, M Gekle
1Physiologisches Institut der Universität Würzburg, Germany.
Abstract:
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+.
Insights
Ochratoxin A (OTA) disrupts kidney cell calcium and cAMP balance at low nanomolar levels, causing oscillations and altering proliferation. Higher concentrations reduce cell viability independently of calcium.
Area of Science:
- Toxicology
- Cell Biology
- Renal Physiology
Background:
- Ochratoxin A (OTA) is a fungal metabolite with nephrotoxic and carcinogenic properties.
- OTA affects renal epithelial cell function and growth.
- Cellular calcium (Ca2+) homeostasis is crucial for cell function.
Purpose of the Study:
- To investigate the role of Ca2+ homeostasis in OTA's effects on human kidney epithelial cells.
- To examine OTA's impact on cell proliferation, viability, and interaction with growth factors.
- To elucidate the mechanisms underlying OTA-induced changes in cellular Ca2+.
Main Methods:
- Immortalized human kidney epithelial (IHKE-1) cells were used.
- Measurements included intracellular calcium ([Ca2+]i) oscillations, cell proliferation, viability, and cAMP levels.
- Effects of OTA were studied alone and in combination with epidermal growth factor (EGF) and angiotensin II (Ang II).
- Pharmacological inhibitors (SKF 96365, H-89) and thapsigargin were employed.
Main Results:
- Low nanomolar OTA (<0.1 nmol/l) induced reversible [Ca2+]i oscillations dependent on extracellular Ca2+, phospholipase C, and Ca2+-channels.
- OTA potentiated EGF- and Ang II-induced cell proliferation and [Ca2+]i changes at 0.1-1 nmol/l.
- OTA stimulated thapsigargin-sensitive Ca2+-ATPase and increased Ca2+ store filling.
- Cell viability decreased only at higher OTA concentrations (>10 nmol/l) and was Ca2+-independent.
- OTA increased cellular cAMP content, and this was inhibited by H-89.
Conclusions:
- OTA impairs cellular Ca2+ and cAMP homeostasis at low nanomolar concentrations, leading to [Ca2+]i oscillations.
- OTA interferes with hormonal signaling pathways (EGF, Ang II), affecting Ca2+ homeostasis and cell proliferation.
- High-dose OTA reduces cell viability through a Ca2+-independent mechanism.