Chemical Inducers of Differentiation in a Long-Term Renal Cell Line

Abstract

The long-term renal epithelial cell line LLC-PK1 expresses at confluence several differentiated characteristics of renal proximal tubule including Na/glucose cotransport and several brush border membrane hydrolases. The differentiation-inducing chemical hexamethylene bisacetamide (HMBA) triggers a dramatic induction of Na /glucose symport, trehalase and maltase, expressed as an increase in the number of cells in the culture that express the differentiated phenotype. Characteristics of the induction response are reviewed in terms of proposed mechanisms of inducer action. New evidence suggests that in addition to elevation of intracellular Na levels mediated by partial inhibition of the sodium pump, HMBA treatment also alters polyamine levels via effects on ornithine decarboxylase. These responses may be mediated by HMBA effects on protein kinase C activity. The possible role of polyamine fluctuations and DNA demethylation in mediating HMBA effects on differentiated gene expression is currently being investigated.

Polyamine regulation of Na+/glucose symporter expression in LLC‐PK1 cells

“…Following the development of a confluent cell density, Na+/glucose symport activity increases significantly together with other differentiated markers characteristic of renal proximal tubule Cook, 1982, 1985;Yoneyama and Lever, 1984). Addition of the differentiation inducer hexamethylene bisacetamide (HMBA) (Marks and Rifkind, 1978) t o confluent cultures produced an additional dramatic increase in Na+/glucose symport activity and other differentiated functions (Amsler and Cook, 1982;Yoneyama and Lever, 1984;Lever, 1989). Induction was time-dependent, reaching a maximum after two weeks.…”

Regulation of Na+-coupled Glucose Transport in LLC-PK1 Cells

“…This cell line permits the reconstitution of a fully functional polarized epithelium in vitro. The development of a confluent monolayer is accompanied by the appearance of a number of differentiated functions characteristic of this epithelium including the formation of tight junctions and microvilli, vasopressin responsiveness, transepithelial salt and water transport, several brush-border marker enzyme activities, and apical membrane Na ϩ -coupled glucose transport activity (reviewed in Lever (1989)). Elevation of intracellular levels of cyclic AMP or treatment with the differentiation inducer hexamethylene bisacetamide (HMBA), 1 greatly increased both the levels of expression and rate of appearance of several of these differentiated functions including Na ϩ -coupled glucose transport (Amsler and Cook, 1982;Yoneyama and Lever, 1984;Peng and Lever, 1993;Yet et al, 1994).…”