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Modification of the epidermal growth factor response by ammonia in renal cell hypertrophy
1Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, Georgia, and Atlanta Veterans Affairs Medical Center, Decatur, Georgia.
Abstract:
Epidermal growth factor (EGF) causes proliferation in renal tubular cells but, when it is combined with transforming growth factor-beta1, it causes hypertrophy by a mechanism that requires the activity of the retinoblastoma family of proteins. In contrast, ammonia causes hypertrophy by decreasing lysosomal proteolysis; in some cell types, it also decreases cellular proliferation. These studies were designed to determine whether ammonia, like transforming growth factor-beta1, could convert EGF-induced hyperplasia to hypertrophy. Cultured NRK-52E cells were incubated with EGF and/or ammonia and the protein/DNA ratio was measured, as a marker of hypertrophy. Addition of ammonia to EGF-treated NRK-52E cells converted EGF-induced hyperplasia to hypertrophy, because of a decrease in DNA synthesis. The mechanism involved no change in EGF-induced protein synthesis. Inhibition of lysosomal function with a proton pump inhibitor or lysosomal protease inhibitors also converted the response of EGF-treated cells to hypertrophy. Expression of the human papilloma virus 16 E7 protein (which inactivates all members of the retinoblastoma family) prevented ammonia from converting EGF-induced hyperplasia to hypertrophy. It is concluded that ammonia converts EGF-induced hyperplasia to hypertrophy by a mechanism that involves suppression of lysosomal function and this response can be blocked by inhibiting the activity of the retinoblastoma family of proteins.
Insights
Ammonia converts epidermal growth factor (EGF)-induced renal tubular cell hyperplasia to hypertrophy by suppressing lysosomal function. This effect is mediated by the retinoblastoma family of proteins.
Area of Science:
- Cell Biology
- Renal Physiology
- Molecular Biology
Background:
- Epidermal growth factor (EGF) promotes renal tubular cell proliferation.
- Transforming growth factor-beta1 converts EGF-induced hyperplasia to hypertrophy via retinoblastoma proteins.
- Ammonia induces hypertrophy by decreasing lysosomal proteolysis and potentially inhibiting proliferation.
Purpose of the Study:
- To investigate if ammonia can convert EGF-induced hyperplasia to hypertrophy, similar to transforming growth factor-beta1.
- To elucidate the cellular mechanisms underlying ammonia's effect on renal tubular cell growth.
Main Methods:
- Cultured NRK-52E cells were treated with EGF and/or ammonia.
- Protein/DNA ratio was measured as a marker of hypertrophy.
- Lysosomal function was inhibited using a proton pump inhibitor and protease inhibitors.
- Retinoblastoma protein activity was modulated using HPV16 E7 protein.
Main Results:
- Ammonia converted EGF-induced hyperplasia to hypertrophy by decreasing DNA synthesis without altering protein synthesis.
- Inhibition of lysosomal function mimicked ammonia's effect, converting hyperplasia to hypertrophy.
- The HPV16 E7 protein blocked ammonia's ability to convert hyperplasia to hypertrophy.
Conclusions:
- Ammonia induces hypertrophy in EGF-treated renal tubular cells by suppressing lysosomal proteolysis.
- The retinoblastoma family of proteins is crucial for mediating ammonia's hypertrophic effect.
- This study reveals a novel mechanism for regulating renal tubular cell size involving ammonia and lysosomal pathways.