On the basis of transepithelial electrical resistance (TER) measurements, we found that capsaicin (100 mu M)-treated human intestinal Caco-2 cells show a momentary increase in tight-junction (TJ) permeability (decrease in TER) followed by a complete recovery. We used proteome analysis to search for proteins that are associated with the recovery of TJ permeability in capsaicin-treated Caco-2 cells. A protein with a relative molecular mass of 14 kDa was found to be expressed more highly in capsaicin-treated cells than in nontreated cells. Mass spectrometry and sequence analyses revealed that the protein that is expressed significantly upon capsaicin treatment is the ribosomal protein P2; its cDNA sequence was identical to that found in the human genome database. An increase in the amount of cellular filamentous actin (F-actin) was shown after 8 h of incubation with capsaicin. It has been reported that P2 activates elongation factor 2, which stabilizes F-actin filaments, and that the depolymerization of F-actin is associated with the increase in TJ permeability (decrease in TER). Consequently, these results suggest that P2 plays an important role in the recovery of the TJ permeability in capsaicin-treated human intestinal cells.