Legume lectin phytohemagglutinin reduces transepithelial electrical resistance by counteracting the chaperone function of heat shock protein-70

Abstract

Legume lectins represent a broad class of environmental toxicants that bind to cell surface glycoproteins. Raw red kidney beans (RRKB), a widely consumed common source of dietary protein, are rich in the lectin phytohemagglutinin (PHA). Consumption of improperly cooked (which may require overnight presoaking and boiling at least at 100°C for 45 min) red kidney beans causes severe gastrointestinal symptoms. Since the relationship between lectin toxicity and the cellular chaperone machinery remains unknown, the study aimed to determine the effects of heat-denatured PHA on epithelial barrier function and heat shock protein 70 (HSP70) expression and its function as a molecular chaperone in PHA-treated Caco-2 cells and animals. Twelve male Sprague-Dawley rats were randomised to an ad libitum diet of either standard rat chow or chow containing 26% crude red kidney beans. We measured HSP70 and heat shock factor 1 gene expressions in the small intestine and HSP70 protein expression in Caco-2 cells. In Caco-2 cells, luciferase activity was measured to investigate protein folding. Fluorescein-5-isothiocyanate (FITC)-labelled lectin was used to study its intracellular uptake by Caco-2 cells. PHA lectin reduced transepithelial electrical resistance in Caco-2 cells. FITC-labelled PHA entered Caco-2 cells within 3 h of treatment. PHA treatment significantly reduced HSP70 levels and luciferase activity in Caco-2 cells, which was prevented by HSP70 overexpression. In rats fed RRKB chow consisting of legume lectins, we found reduced levels of HSP70 and heat shock factor 1. These observations suggest that lectins counter the protective function of HSP70 on intestinal barrier function.

Keywords

• HSF1
• HSP70
• Lectins
• Phytohemagglutinin (PHA)
• Protein folding