Quercetin increases claudin-4 expression through multiple transcription factors in intestinal Caco-2 cells

We previously reported that quercetin increases tight junction (TJ) barrier integrity in intestinal Caco-2 cells. This study was aimed at determining the molecular mechanism underlying the quercetin-mediated effect with a particular focus on the transcriptional regulation of claudin-4. Quercetin aglycone, but not its glycosides, enhanced TJ barrier integrity of Caco-2 cells, indicated by transepithelial electrical resistance. Immunoblot analysis, qPCR, and luciferase promoter assay revealed that quercetin transcriptionally increased the claudin-4 expression. Narrowing the claudin-4 promoter sequences from 1866 bp to 200 bp did not affect quercetin-mediated promoter activation. Site-directed mutation of SP1, AP-1 and GATA binding sites within the 200 bp sequence partially suppressed the effects of quercetin on claudin-4 promoter activity. Taken together, quercetin enhances the TJ barrier integrity in intestinal Caco-2 cells, with the transcription factors, SP1, AP-1, and GATA, involved in the quercetin-mediated transcriptional regulation of claudin-4.