CYTOSKELETAL REGULATION OF HCG-INDUCED RECEPTOR CLUSTERING IN TRANSFORMED LEYDIG-CELLS

The gonadotropins, human choriogonadotropin (hCG) and lutropin (LH), a ct through the same G protein-coupled receptor to stimulate steroidoge nesis in target cells, an action that is generally associated with a c hange in cell morphology in vitro. However, it is not understood how r eceptors and the cytoskeleton function during the course of steroidoge nesis. Using immunofluorescence microscopy, we have examined the distr ibution of receptors on the plasma membrane of the clonal murine-trans formed Leydig cell line, MA-10, utilizing a monoclonal antibody direct ed against the hCG/LH receptor. Untreated cells exhibit a random and d iffuse distribution of surface receptors which, after incubation with hCG, undergo a time-dependent rearrangement in the plasma membrane to form a polar aggregate or cap structure. There is a correlation betwee n the localization of these aggregated membrane receptors and certain cytoskeletal proteins, e.g. actin, myosin, alpha-lactinin, and cytoker atin, that may be responsible for directing receptor movement and/or s ubsequent morphological changes. In addition, agents that interfere wi th cytoskeletal function inhibit hCG-induced receptor capping and ster oidogenesis, suggesting that those processes involve the cytoskeleton and that cytoskeletal-dependent receptor aggregation may be required f or steroidogenesis. This system may prove useful for understanding the role of receptor redistribution in hormone signal transduction, as we ll as the expression of a cellular differentiated response.