GRANULOSA-CELL LUTEINIZING-HORMONE RECEPTOR EXPRESSION IS MODULATED BY GANGLIOSIDE-SPECIFIC LIGANDS

The ganglioside GM1 (Gal beta 1 --> 3GalNAc beta 1 --> 4[NeuAc alpha 2 --> 3]Gal beta 1 --> 4Glc beta 1 --> 1Cer) was synthesized during gra nulosa cell development in vitro, and the effect of the interaction be tween cell-surface GM1 and its ligands on the luteinizing hormone (LH) receptor expression was investigated. GM1 synthesis, demonstrated by metabolic labeling of glycosphingolipids with [H-3]galactose and bindi ng studies using the I-125-B-subunit of cholera toxin, a specific liga nd for GM1, was increased in follicle-stimulating hormone (FSH)-treate d granulosa cells. When granulosa cells were cultured for 72 h in a me dium containing the B-subunit of cholera toxin, FSH-induced LH-recepto r contents determined by measuring the binding of I-125-deglycosylated human chorionic gonadotropin to intact cells, was augmented. The stim ulatory effect of the B-subunit was dependent on the FSH concentration and culture duration. The augmentation was observed after culture for 48 h, and marked increases were evident after 72 h, which coincided w ith an increase of the I-125-B-subunit binding capacity. Scatchard ana lysis of the LH-receptor binding indicated that treatment with the B-s ubunit increased the number of LH-binding sites (6580 sites/cell after treatment with 20 ng/ml FSH; 11290 sites/cell after FSH plus 100 ng/m l B-subunit), but did not alter the binding affinity. A specific antib ody against GM1 mimicked the stimulatory effect of the B-subunit. The augmentation was not accompanied by granulosa cell proliferation. Thes e findings suggest that binding of exogenous or possible endogenous li gands to cell-surface GM1 produces signals and modulates the cellular behavior during granulosa cell development.