Rabbit polyclonal antibodies to ZO-1, -2, -3; claudin; or occludin were obtained from Zymed (Carlsbad, CA). Mouse monoclonal antibodies to α-tubulin and a protease inhibitor cocktail were from Sigma-Aldrich (St. Louis, MO). Antibodies to total or phosphorylated forms of ERK1 or -2 (ERK1/2), p38 MAPK, JNK, or c-Jun were obtained from Cell Signaling (Beverly, MA). Horseradish peroxidase–conjugated secondary antibodies to rabbit or mouse immunoglobulin-G or -M were from Promega (Madison, WI). PD098059, SB203580, and JNK inhibitor II were obtained from Calbiochem (San Diego, CA). Dulbecco’s modified Eagle’s medium (DMEM)-F12 mixture (50:50, vol/vol), fetal bovine serum, and Alexa Fluor 488-labeled goat antibodies to rabbit immunoglobulin G were obtained from Invitrogen-Gibco (Rockville, MD), and bovine serum albumin (BSA) was from Nacalai Tesque (Kyoto, Japan). All media and reagents used for cell culture were endotoxin minimized.