NH4Cl-induced hypertrophy is mediated by weak base effects and is independent of cell cycle processes

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Abstract
Renal hypertrophy occurs in a number of clinical conditions, some of which are associated with increases in ambient ammonia concentrations. NH4Cl induces hypertrophy in cultured renal epithelial cells. The present studies examined the mechanism of NH4Cl-induced hypertrophy in NRK-52E cells. Hypertrophy was also induced by methylammonium chloride, a related weak base, but not by tetramethylammonium chloride, a weak base analogue that can neither accept nor donate protons. Bafilo-mycin A1, an inhibitor of vacuolar proton pumps, also induced hypertrophy. Together, these studies suggest that NH4Cl-induced hypertrophy is mediated by its weak base property, allowing it to enter and alkalinize acid vesicular compartments. Additional studies demonstrated that NH4Cl-induced hypertrophy is not mediated by modulation of cell cycle processes. NH4Cl addition had no effect on the following: c-fos mRNA abundance, typically associated with entrance into the cell cycle; cyclin E protein abundance, which increases as cells progress through G1; or protein synthesis, which also increases during G1. In addition, inactivation of pRB by overexpression of human papilloma virus-16 carrying the E7 gene, which inhibits cell cycle-dependent hypertrophy, had no effect on the ability of NH4Cl to induce hypertrophy. Based on these data, we postulate that, in hypertrophic conditions associated with increased ammoniagenesis, hypertrophy is mediated by vesicular alkalinization and occurs independently of processes that govern progression through the cell cycle.