Cellular binding proteins for vitamin A in colorectal adenocarcinoma of rat.

Rat colorectal mucosa was examined during the course of carcinogenesis, induced by chronic administration of 1,2-dimethylhydrazine (DMH), for the presence and amount of cellular retinol-binding protein (CRBP) and cellular retinoic acid-binding protein. These two binding proteins are implicated in the action of vitamin A in normal and neoplastic tissue. Induced adenocarcinomas were found to contain low levels of cellular retinoic acid-binding protein (10 pmol/g), similar to the levels found in adjacent mucosa of the same animal and also in colorectal mucosa from normal rats or rats chronically treated with DMH. However, the adenocarcinomas had high levels of CRBP (300 to 500 pmol/g), and these levels were dramatically higher than levels of CRBP in adjacent mucosa of the same animal (40 to 100 pmol/g), colorectal mucosa from normal rats (20 pmol/g), or colorectal mucosa from rats chronically treated with DMH (22 to 25 pmol/g). Consequently, the increase in CRBP occurred only with tumor appearance and not with the general hyperplasia of the crypts caused by DMH administration. The CRBP of the tumor was associated with endogenous retinol (77 to 100% saturation) and was similar to, if not identical with, CRBP of normal tissue, as judged by fluorescence spectra, sedimentation behavior, and elution position on Sephadex G-75.