Characterization of the structure and subcellular distribution of the rat hepatic prolactin receptor

The structure of rat hepatic prolactin (PRL) receptors was examined in various subcellular fractions by immunoblotting. In all subcellular fractions, a single 42 kDa species was identified. Tri- and/or tetrantennary complex carbohydrates compose $ sp sim$7 kDa of the weight of the receptor. Enzymatic deglycosylation of the mature receptor does not appreciably reduce ligand binding or antibody recognition of the receptor. However, core glycosylation of the receptor is necessary for the acquisition of binding capacity and antibody recognition.The intracellular distribution of PRL receptors was determined by Percoll gradient centrifugation and application of the diaminobenzidine (DAB)-shift methodology. There was a sex-dependent distribution of PRL receptors, with females having a 3-fold higher concentration of receptors in early endosomes than males. This discrepancy disappeared when male rats were treated with estrogen. No such sex-dependent distribution of intracellular receptors were discovered for insulin receptors.Colchicine treatment of estrogen-induced male rats prevented newly synthesized receptors from reaching the cell surface, and allowed the accumulation of at least some of these receptors into an endosomal compartment. These studies suggest that under conditions of colchicine blockade, PRL receptors may access an endosomal compartment by an entirely intracellular route. To date, such a route has only been described for mannose-6-phosphate receptors