Decreased levels of heat shock proteins in gut epithelial cells after exposure to plant lectins

Background-The enterocytes of the intestinal epithelium are regularly expos ed to potentially harmful substances of dietary origin, such as lectins. Ex pression of heat shock proteins (HSPs) by this epithelium may be part of a protective mechanism developed by intestinal epithelial cells to deal with noxious components in the intestinal lumen. Aim-To investigate if the lectins PHA, a lectin from kidney beans (Phaseolu s vulgaris) and WGA, a lectin from wheat germ (Triticum aestivum) could mod ify the heat shock response in gut epithelial cells and to establish the ex tent of this effect. Methods-Jejunal tissue sections from PHA and WGA fed rats were screened for expression of HSP70, HSP72, and HSP90 using monoclonal antibodies. Differe ntiated Caco-2 cells, the in vitro counterpart of villus enterocytes, were exposed to 100 mu g/ml of PHA-E-4 or WGA for 48 hours and investigated for changes in DNA and protein synthesis by double labelling with [2-C-14]thymi dine and L-[methyl-H-3]methionine. The relative concentrations of HSP60, HS P70, HSP72, and HSP90 and binding protein (BiP) in these cells exposed to l ectins were analysed by polyacrylamide gel electrophoresis and immunoblotti ng. To establish if lectin exposed differentiated Caco-2 cells were still c apable of producing a heat shock response, these cells received a heat shoc k (40 degrees C, 41 degrees C, and 42 degrees C) for one hour and were allo wed to recover for six hours at 37 degrees C. During heat shock and recover y periods, lectin exposure was continued. Results-Constitutive levels of HSPs were measured in the intestinal cells o f lactalbumin fed (control) rats, as may be expected from the function of t his tissue. However, in PHA and WGA fed rats a marked decline in the bindin g of antibodies against several HSPs to the intestinal epithelium was found . These results were confirmed by in vitro experiments using differentiated Caco-2 cells exposed to PHA-E-4 and WGA. However, after exposure to lectin s, these cells were still capable of heat induced heat shock protein synthe sis, and total protein synthesis was not impaired indicating specific inhib ition of HSP synthesis in non-stressed cells. Conclusions-We conclude that PHA and WGA decrease levels of stress proteins in rat gut and enterocyte-like Caco-2 cells, leaving these cells less well protected against the potentially harmful content of the gut lumen.