Figure 1.

Mucin (MUC 2) transcription is stimulated by ligation of the flagellin receptor, ASGM1. In A and B, HM3 cells stably transfected with a MUC 2 promoter-driven luciferase reporter were studied. Promoter activity is reported as the fold increase observed in stimulated cells vis-a-vis cells exposed to serum-free medium. (A) Stimulation with flagellin purified from strain PAO1. Proteolysis followed by boiling abolished activity. (B) Stimulation with an antibody directed against the flagellin receptor, asialoGM1 (α-ASGM1). Stimulation was for 4 h before cell lysis. Exposure of cells to an approximately equal concentration of an unrelated polyclonal antibody [CCAAT/enhancer binding protein α (α-c/ebp)] had no effect. (C) RNase protection assay was performed by using a MUC 2 gene-specific probe and a control cyclophilin probe to show MUC 2 mRNA up-regulation by purified flagellin (Flag) and ASGM1 antibody (α-ASGM1). SFM, serum-free medium.