Effects of TIG1 isoforms on cAMP levels. Control (Ctrl), TIG1A and TIG1B stable HCT116 cells were incubated with 5 nM MFP for 24 h, serum starved for 16 h, and then treated with or without PGE2 (10 nM) for 5 min. Levels of cAMP were measured using an enzyme immunoassay. Representative results from triplicate samples were expressed as mean ± SD. *, P < 0.05; **, P < 0.01.