Biomedical subjects

Claudia Schuster

Publications and source records attributed to Claudia Schuster.

5 recordsLinked to original sources

PubMed2005

Cisplatin-induced apoptosis is enhanced by hypoxia and by inhibition of mitochondria in renal collecting duct cells.

Cisplatin is a widely used chemotherapeutic agent. Here we show that cisplatin induces apoptosis in renal collecting duct-derived cells (MDCK-C7 cells, resembling principal cells) in a dose-dependent manner. Additionally, we studied the role of mitochondria in this process by inhibition of the mitochondrial respiratory chain, the F1F(o)-ATP synthase or by uncoupling. The role of intra- and extracellular pH in apoptosis induction was investigated. Activation of caspase-3 and DNA ladder formation were used to monitor the apoptotic response. When cells were incubated with inhibitors of the mitochondrial respiratory chain or an inhibitor of the ATP-synthase, cisplatin-induced apoptosis was markedly enhanced. Mitochondrial blockade led to enhanced production of lactic acid. Also, anoxia potentiated the cisplatin-induced caspase-3 activation. Neither intra- nor extracellular pH had an influence on caspase-3 activation at low cisplatin concentrations. Acidic conditions (pH 6.8) potentiated the caspase-3 activation when high (100 microM) cisplatin concentrations were used. We demonstrate that intact mitochondria are important to prevent cisplatin-induced apoptosis in MDCK-C7 cells and that acidic conditions can aggravate the toxic effects of cisplatin.

Animals↗

PubMed2004

Inhibition of mitochondria and extracellular acidification enhance achratoxin A-induced apoptosis in renal collecting duct-derived MDCK-C7 cells.

Ochratoxin A (OTA) is a potent nephrotoxin and suspected to be involved in the etiology of Balkan endemic nephropathy. Nanomolar concentrations of this mycotoxin induce apoptosis in renal collecting duct-derived cells (MDCK-C7 cells, resembling principal cells). We studied the role of mitochondria in this process by inhibition of the mitochondrial respiratory chain, the F1FO-ATP synthase or by uncoupling. Also, the role of intra- and extracellular pH in apoptosis induction was investigated. Activation of caspase-3 and DNA ladder formation were used to monitor the apoptotic response. When cells were incubated with inhibitors of the mitochondrial respiratory chain or an inhibitor of the ATP-synthase, OTA-induced apoptosis was enhanced dramatically. Also, mitochondrial uncoupling potentiated the effects of OTA. OTA-induced apoptosis was not dependent on a decrease of the mitochondrial potential. Mitochondrial blockade led to medium acidification due to enhanced production of lactic acid. Artificial extracellular acidification potentiated OTA-induced caspase-3 activation. Artificial extracellular alkalization had no influence on caspase-3 activity. Intracellular pH after 24 hours exposure to inhibitors of mitochondria or acidic or alkaline media did not correlate with caspase-3 activity but correlated with caspase-3 activity when OTA was present: acidic intracellular pH (pHin) was associated with higher caspase-3 activity as compared to alkaline pHin. We conclude that extra- and intracellular pH are important factors in OTA-induced apoptosis in MDCK-C7 cells. The physiologically changing pH conditions in the collecting duct can thus alter or even aggravate the toxic effects of OTA.

Acids↗

PubMed2003

Aldosterone stimulates epidermal growth factor receptor expression.

The steroid hormone aldosterone plays an important role during pathological tissue modifications, similar to cardiovascular or renal fibrosis. The underlying mechanisms for the pathological actions are not understood. Interaction of aldosterone with the epidermal growth factor (EGF) receptor is an attractive hypothesis to explain pathological tissue remodeling elicited by aldosterone, because (i) mineralocorticoids can sensitize cells for EGF, (ii) mineralocorticoid receptor (MR)-antagonists reduce EGFR-mRNA expression, (iii) EGFR itself supports the development of cardiovascular or renal fibrosis, and (iv) signaling elements involved in the pathological action of aldosterone (similar to ERK1/2 or NFkB) are typical downstream modules during EGF signaling. In addition, an interaction of aldosterone and EGF with respect to ERK1/2 activation has been described. Here we show that aldosterone stimulates EGFR expression in renal tissue of adrenalectomized rats and in human renal primary cell cultures. Furthermore, Chinese hamster ovary (CHO) cells normally devoid of EGFR or MR express EGFR after transfection with human MR (CHO-MR cells) but not after transfection with human glucocorticoid receptor (CHO-GR cells). In CHO-MR cells, EGFR-expression is up-regulated by aldosterone and inhibited by spironolactone. CHO-MR cells but not CHO-GR cells respond with ERK1/2 phosphorylation to EGF exposure. The responsiveness to other peptide hormones was virtually not affected. These data suggest that EGFR is an aldosterone-induced protein and is involved in the manifold (patho)biological actions of aldosterone.

Aldosterone↗

PubMed2003

Inhibition of mitochondria prevents cell death in kidney epithelial cells by intra- and extracellular acidification.

BACKGROUND: Nephrotoxic substances like cisplatin or ochratoxin A (OTA) induce cell death in human proximal tubule-derived cells (IHKE cells). Mitochondria play a significant role in apoptosis and loss of their function may influence OTA- or cisplatin-induced apoptosis. Extracellular pH also plays an important role in tumor genesis. Therefore, we investigated the role of mitochondria and intra- and extracellular pH on cell death induction by cisplatin or OTA. METHODS: IHKE cells were incubated in the presence of OTA or cisplatin, together with inhibitors of the mitochondrial metabolism, and the activity of caspase-3 was measured and DNA laddering was monitored. Adenosine triphosphate (ATP) content of the cells, lactate release into the media, and glucose consumption was determined. In addition, media and cells were acidified or alkalized artificially to investigate the effect of intra- and extracellular pH on cell death induction. Cytochrome C was immunodetected in cellular compartments. RESULTS: Inhibition of the mitochondrial function reduced OTA- or cisplatin-induced cell death and led to considerable lactic acid production and extracellular acidification. Intra- and extracellular acidification prevented cells from cell death induced by OTA or cisplatin. No cytochrome C release from mitochondria could be detected during 24 hours of exposure to OTA or cisplatin. CONCLUSION: We conclude that OTA- or cisplatin-induced cell death is dependent on functional and intact, ATP-producing mitochondria and that intra- and extracellular pH is crucial for induction of cell death in IHKE cells.

Acidosis↗

PubMed2002

Human epidermal growth factor receptor-1 expression renders Chinese hamster ovary cells sensitive to alternative aldosterone signaling.

The epidermal growth factor (EGF) regulates cell proliferation, differentiation, and ion transport using ERK1/2 as a downstream effector. Furthermore, the EGF receptor (EGFR) is involved in signaling by G-protein-coupled receptors, growth hormone, and cytokines via transactivation. It has been suggested that steroids interact with peptide hormones. Previously, we have shown that aldosterone modulates EGF responses in Madin-Darby canine kidney cells (Gekle, M., Freudinger, R., Mildenberger, S., and Silbernagl, S. (2002) Am. J. Physiol. 282, F669-F679). Here, we tested the hypothesis that human EGFR-1 can confer alternative aldosterone responsiveness with respect to ERK1/2 phosphorylation to Chinese hamster ovary cells, which do not express EGFR. Wild-type Chinese hamster ovary cells did not respond to EGF or aldosterone. After transfection of human EGFR-1, the cells responded to EGF, but not to aldosterone. However, when submaximal concentrations of EGF were used, nanomolar concentrations of aldosterone potentiated the action of EGF within minutes, resulting in a leftward shift of the EGF dose-response curve. This was not the case in mock-transfected cells. The EGFR kinase inhibitor tyrphostin AG1478 or the MEK1/2 inhibitor U0126 completely prevented the effect. Furthermore, aldosterone enhanced Tyr phosphorylation of c-Src and EGFR, and an inhibitor of cytosolic tyrosine kinases (4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyriociaine) prevented the action of aldosterone. Our data show that aldosterone uses the EGF-EGFR-MEK1/2-ERK1/2 signaling cascade to elicit its alternative effects. In the presence of EGF, aldosterone leads to EGFR transactivation via cytosolic tyrosine kinases of the Src family.

Aldosterone↗