Binds to bile acids and is involved in enterohepatic bile acid metabolism. Required for efficient apical to basolateral transport of conjugated bile acids in ileal enterocytes (By similarity). In vitro binds to bile acids in the order: deoxycholic acid > cholic acid > chenodeoxycholic acid and respective BA conjugation modifies affinities in the order taurine-conjugated > glycine-conjugated > unconjugated bile acids. Stimulates gastric acid and pepsinogen secretion (By similarity). Essential for the survival of colon cancer cells to bile acid-induced apoptosis. Localized close to nucleus on the apical side of both normal and neoplastic cells. Isoform 1 is expressed in the jejunum, ileum, cecum and ascending colon intestine. Isoform 2 is xpressed in the gallbladder, duodenum, jejunum, ileum, cecum, ascending, transverse and descending colon, sigmoid colon and rectum. Isoform 2 is expressed in colorectal adenocarcinomas and their adjacent normal mucosa (at protein level). Isoform 1 is up-regulated by chenodeoxycholic acid (CDCA) via the FXR transcription pathway. Isoform 2 is up-regulated by NF-kappa-B and in all stages of colorectal adenocarcinoma. Isoform 1 is not up-regulated in all stages of colorectal adenocarcinoma. Forms a beta-barrel structure that accommodates the hydrophobic ligand in its interior. Can bind at least two ligands per molecule, however, the stoichiometry is debated. Belongs to the calycin superfamily. Fatty-acid binding protein (FABP) family.