VHL tumor suppressor regulates Cl-/HCO3- exchange and Na+/H+ exchange activities in renal carcinoma cells
S A Karumanchi1, L Jiang, B Knebelmann
1Renal Division, Beth Israel Deaconess Medical Center, Departments of Medicine and Cell Biology, Harvard Medical School, Boston, Massachusetts 02215, USA.
Abstract:
Mutations in the von Hippel-Lindau (VHL) tumor suppressor gene are thought to play a critical role in the pathogenesis of both sporadic and VHL disease-associated clear-cell renal carcinomas (RCC). Differential display-PCR identified the AE2 anion exchanger as a candidate VHL target gene. AE2 mRNA and polypeptide levels were approximately threefold higher in 786-O VHL cells than in 786-O Neo cells. In contrast, Cl(-)/HCO(3)(-) exchange activity in 786-O VHL cells was 50% lower than in 786-O Neo cells. Since resting intracellular pH (pH(i)) values were indistinguishable, we postulated that Na(+)/H(+) exchange activity (NHE) might be similarly reduced in 786-O VHL cells. NHE-mediated pH(i) recovery from acid load was less than 50% that in 786-O Neo cells, whereas hypertonicity-stimulated, amiloride-sensitive NHE was indistinguishable in the two cell lines. The NHE3 mRNA level was higher in 786-O VHL than 786-O Neo cells, but NHE1 mRNA levels did not differ. AE2 and NHE3 are the first transcripts reported to be upregulated by pVHL. Elucidation of mechanisms responsible for downregulation of both ion exchange activities will require further investigation.
Insights
Mutations in the von Hippel-Lindau (VHL) gene impact clear-cell renal carcinoma (RCC) by altering ion exchangers. VHL cells show increased AE2 and NHE3 mRNA but reduced ion exchange activity, suggesting a complex role in RCC pathogenesis.
Area of Science:
- Molecular Biology
- Oncology
- Cell Physiology
Background:
- Mutations in the von Hippel-Lindau (VHL) tumor suppressor gene are implicated in clear-cell renal carcinoma (RCC) pathogenesis.
- The VHL gene product (pVHL) is crucial for cellular homeostasis and tumor suppression.
- Identifying VHL target genes is key to understanding RCC development.
Purpose of the Study:
- To investigate the role of the AE2 anion exchanger and Na+/H+ exchanger (NHE) in VHL-deficient renal carcinoma cells.
- To determine if AE2 and NHE are direct or indirect targets of VHL.
Main Methods:
- Differential display-PCR to identify VHL target genes.
- Quantitative analysis of AE2 and NHE mRNA and polypeptide levels.
- Measurement of Cl-/HCO3- and Na+/H+ exchange activities.
- Intracellular pH (pHi) measurements following acid loading.
Main Results:
- AE2 mRNA and protein levels were significantly elevated in VHL-mutated cells (786-O VHL) compared to control cells (786-O Neo).
- Despite increased AE2 expression, Cl-/HCO3- exchange activity was reduced by 50% in VHL cells.
- Na+/H+ exchange activity was also impaired in VHL cells, though hypertonicity-stimulated NHE was unaffected.
- NHE3 mRNA levels were upregulated in VHL cells, while NHE1 mRNA levels remained unchanged.
Conclusions:
- AE2 and NHE3 are identified as novel VHL target genes, with their expression upregulated in VHL-deficient renal carcinoma cells.
- The functional downregulation of AE2 and NHE activities in VHL cells suggests a complex regulatory mechanism.
- Further research is needed to elucidate the precise mechanisms underlying the altered ion exchange activities in VHL-associated RCC.
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