Endocytosis of lutropin by Leydig cells through a pathway distinct from the high-affinity receptor.
In porcine Leydig cells in primary culture, 95% of the internalization of [125I]porcine lutropin ([125I]pLH, which bears sulfated GalNAc) could not be ascribed to the high-affinity LH receptor (LHR). In contrast, >40% of [125I]human choriogonadotropin (hCG, with sialylated sugar chains) uptake was performed by the LHR itself. When the LHR was down-regulated by excess unlabeled hormone, the LHR-independent incorporation of [125I]pLH could be inhibited in a dose-dependent fashion by sulfated polysaccharides such as fucoidan or chondroitin-(4 or 6)-sulfate, but not by other polyanionic compounds, nor by sulfated chondroitin disaccharides. Endocytosis occurred through a clathrin-dependent pathway and was inhibited by low temperature, endocytosis inhibitors, increased ionic strength, or by EDTA and dithiothreitol. Taken together, these results suggest that a Leydig cell membrane protein (possibly a lectin, or a glycosaminoglycan receptor) could perform specific LH clearance in the testis via recognition of its sulfated sugars.
Bozon
V
V
Unité Récepteurs et Communication Cellulaire, Biologie Cellulaire et Moléculaire, INRA-Biotechnologies, Jouy-en-Josas, France.
Pajot-Augy
E
E
Vignon
X
X
Salesse
R
R
D000818:Animals; D002478:Cells, Cultured; D004705:Endocytosis; D006801:Humans; D007985:Leydig Cells / Q000166:cytology / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000378:metabolism*; D008297:Male; D011869:Radioligand Assay; D011974:Receptors, LH / Q000378:metabolism*; D013552:Swine
D011974:Receptors, LH; D007986:Luteinizing Hormone