Transforming Growth Factor-β, a Whey Protein Component, Strengthens the Intestinal Barrier by Upregulating Claudin-4 in HT-29/B6 Cells

TGF beta (isoforms 1-3) has barrier-protective effects in the intestine. The mechanisms involved in regulating tight junction protein expression are poorly understood. The aim of this study was to elucidate TGF beta-dependent protective effects with special attention to promoter regulation of tight junction proteins using the HT-29/B6 cell model. In addition, the effects of whey protein concentrate 1 (WPC1), a natural source of TGF beta in human nutrition, were examined. For this purpose, the claudin-4 promoter was cloned and tested for its activity. It exhibited transactivation in response to TGF beta 1, which was intensified when Smad-4 was cotransfected, indicating a Smad-4 dependent regulatory component. Shortening and mutation of the promoter altered and attenuated this effect. WPC1 induced an increase in the claudin-4 protein level and resistance of HT-29/B6 cell monolayers. Anti-TGF beta(1-3) antibodies blocked these whey protein effects, suggesting that a main part of this function was mediated through TGF beta. This effect was observed on intact monolayers as well as when barrier function was impaired by preexposure to IFN gamma. In conclusion, TGF beta 1 affects claudin-4 gene expression via Smad-4-dependent and -independent transcriptional regulation, resulting in barrier protection, a cytokine effect that is also found in whey protein concentrates used in enteral nutrition. J. Nutr. 141: 783-789, 2011.