Induction of microvillar hydrolase activities by cell density and exogenous differentiation inducers in an established kidney epithelial cell line (LLC‐PK1)

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Abstract
Several hydrolase activities characteristic of the apical brush border membrane of renal proximal tubule, leucine aminopeptidase, γ‐ glutamyl transpeptidase, alkaline phosphatase, maltase, and trehalase, were identified in cultures of the LLC‐PK1 kidney epithelial cell line. A coordinate increase in activities of these enzymes was observed upon development of a confluent cell density and functional membrane polarization. Further large progressive increases in individual hydrolase activities were induced after the addition of compounds known as differentiation inducers. Hexamethylene bisacetamide preferentially induced increased trehalase and maltase activities. Induced trehalase activity exhibited an increased Vmax but a similar Km compared with activity in control extracts. Induction required protein synthesis and was dependent on inducer concentration and exposure time. Treatment of confluent cultures with N,N′‐dimethylformamide triggered an induction of maltase, trehalase, alkaline phosphatase, and γ‐glutamyl transpeptidase activities, whereas dimethylsulfoxide induced trehalase and γ‐glutamyl transpeptidase activities. Increased leucine aminopeptidase and maltase activities were observed after addition of the phosphodiesterase inhibitor 1‐methyl‐3‐isobutylxanthine. Induction of trehalase activity by N,N′‐dimethylformamide was reversible over a 4‐day period after removal of inducer, but effects of hexamethylene bisacetamide were irreversible. These results suggest that the LLC‐PK1 cell line reproducibly develops differentiation‐specific characteristics under defined conditions in cell culture, which can be individually modulated by chemicals known as inducers of cell differentiation.