Ligation of flagellin receptor activates the MAP kinase cascade, which is required for mucin induction. (A) HM3 cells grown in six-well plates were lysed with SDS sample buffer 5 min after the addition of agonist antibody, α-ASGM1. Equal amounts of lysate were run on a 12% SDS gel, transferred to nitrocellulose, immunoblotted with a phospho-specific Erk 1/2 antibody, and visualized by chemiluminescence. Blots were stripped and reprobed with Erk 1/2 antibody to show equal loading. P-Erk Cntrl, positive control from vendor. (B) Effect of MEK 1/2 inhibitor PD98059 (37 μM, 30 min) and dominant negative mutant MEK K97R on MUC 2 promoter activity. (c) Inhibition of Erk phosphorylation by the calcium chelator, BAPTA/AM (30 μM, 45 min). Fold increase expressed as the ratio of phosphorylated Erk to baseline Erk 1/2 as determined by densitometry.