REGULATION AND LOCALIZATION OF CELLULAR RETINOL-BINDING PROTEIN, RETINOL-BINDING PROTEIN, CELLULAR RETINOIC ACID-BINDING PROTEIN (CRABP), AND CRABP-II IN THE UTERUS OF THE PSEUDOPREGNANT RAT

Three members of the superfamily of small intracellular carrier protei ns for Lipophilic compounds are cellular retinol-binding protein (CRBP ), cellular retinoic acid-binding protein (CRABP), and cellular retino ic acid-binding protein II (CRABP II). Retinol-binding protein (RBP) i s a secreted protein that binds and solubilizes vitamin A for transpor t. Here we report the coordinate regulation of RBP, CRBP, retinol, and CRABP II in the uterus of the pseudopregnant rat. In the proliferativ e stage of the uterus, which was induced by PMSG, the messenger RNA (m RNA) and protein levels of RBP and CRBP as well as retinol levels sign ificantly decreased. This pattern of regulation was duplicated by estr ogen treatment of prepubertal rats. In addition, CRBP and RBP were fou nd to be colocalized to the stromal cells of the rat uterus by immunoh istochemistry and [S-35]methionine-labeled affinity chromatography, re spectively, and were not detected in other cell populations. CRABP II mRNA and protein expression were up-regulated in the proliferative pha se of the uterus brought about by PMSG injection or, alternatively, by estrogen treatment of prepubertal rats. CRABP II was localized to the surface epithelium, but was not seen elsewhere, including glandular e pithelium. Immunolocalization of CRABP showed staining of the smooth m uscle and stromal cells of the uterus. The appearance of CRABP in the stroma of the uterus also correlated with PMSG injection as well as es trogen treatment. Although estrogen induced the appearance of both bin ding proteins, CRABP mRNA levels peaked between 4-24 h postestrogen tr eatment, whereas CRABP II mRNA levels continued to rise 48 h postestro gen treatment. These data demonstrate an important role for vitamin A and retinoid-binding proteins in rat uterine physiology.