THE LH CG AND FSH RECEPTORS - DIFFERENT MOLECULAR-FORMS AND INTRACELLULAR TRAFFIC/

Monoclonal antibodies have been raised against the LH/CG receptor [1] and have allowed to perform immunochemical studies of the receptor in target cells. Three different forms of the LH/CG receptor are physiolo gically expressed: a mature similar to 85 kDa transmembrane species co rresponding to the full length receptor, a similar to 65 kDa high mann ose containing species corresponding to a precursor which accumulates inside the cells, and truncated soluble similar to 45-48 kDa molecular weight species corresponding to the variant messanger RNAs generated by alternative splicing. Monoclonal antibodies against the human FSH r eceptor were also prepared. They allow to observe the existence of two forms of the FSH receptor in the ovaries: a major similar to 87 kDa s pecies corresponding to the mature receptor and a minor similar to 81 kDa species corresponding to a high mannose rich precursor. No variant forms of the receptor corresponding to alternative mRNA transcripts w ere detected. The transport of hCG was examined in rat testicular micr ovasculature by electron microscopy and by analyzing the transfer of r adiolabeled hormone and antireceptor antibodies. LH/CG receptors were present in endothelial cells and were involved in hormone transcytosis through these cells. Immunocytochemical experiments have shown that t he FSH receptor has a polarized expression in the Sertoli cells of the testes whereas the LH/CG receptor is spread on the surface of thecal granulosa and luteal cells in the ovary and Leydig cells in the testes . To study the mechanism of this polarization FSH, LH and TSH receptor s were expressed in polarized MDCK cells. The mechanism of basolateral localization and of transcytosis of the receptors was studied using t his model. The effect of hormone, cAMP and agents acting on G proteins was examined. Copyright (C) 1996 Elsevier Science Ireland Ltd.