Biochemical markers in colon tumorigenesis: retinoic acid and dihydrotestosterone-binding proteins

A specific retinoic acid-binding protein (RABP) and a dihydrotestosterone-binding protein (DHTBP) appeared in colon tumors as well as in tissues surrounding the the tumors, but the proteins were nondetectable in normal adult human colon tissues. We have analyzed a total of 105 human colon tumors and related specimens for the presence of RABP and DHTBP as possible biochemical markers in colon tumorigenesis. The tissue or tumor extracts after incubation with (3H) retinoic acid or (3H) dihydrotestosterone were sedimented on sucrose gradients, and the binding proteins were detected from the 2S (RABP) or 6-7S (DHTBP) radioactive peaks. The overall results of the analysis illustrate that about 78% of the 74 human colon, rectum, cecum, and colorectum tumors analyzed contained RABP in detectable amounts. Thirty percent of the 20 colon tissues isolated from subjects suspected for colon cancer and 18% of the 11 normal colon tissues from autopsies contained detectable amounts of the binding protein. A comparative study on the quantitative amounts of RABP and DHTBP in colon tumors and related tissues indicates that the amount of retinoic acid or dihydrotestosterone bound per mg protein ranged from 0.8 to 5.1 pmoles in the binding protein-positive specimens. However, the relative amounts of the two binding proteins in these tissues were not in the same proportions. Appearance of RABP and/or DHTBP in the surrounding tissues of colon tumors correlated with the amounts of the binding protein(s) in the tumors. RABP of human colon tumor shared the same ligand specificity and other physicochemical characteristics as RABP of other species.