The effects of neuraminidase and gangliosides on ovarian LH/hCG receptors during rat development

Gangliosides GD1b, GT1b, and GQ1b suppress the growth of human melanoma by inhibiting interleukin-8 production: the inhibition of adenylate cyclase

We studied the effects of various gangliosides on in vitro growth of human metastatic melanoma WM266-4. GD1b, GT1b, and GQ1b inhibited 3H-thymidine uptake and growth rate of WM266-4 whereas the other gangliosides were ineffective. The growth inhibition by GD1b, GT1b, and GQ1b was counteracted by interleukin-8 but not by the other growth factors. The growth inhibition by gangliosides was not detected in the presence of anti-interleukin-8 antibody. GD1b, GT1b, and GQ1b reduced the constitutive interleukin-8 secretion and mRNA levels in WM266-4. Transient transfection showed that GD1b, GT1b, and GQ1b inhibited the constitutive chloramphenicol acetyltransferase expression driven by interleukin-8 promoter in WM266-4. Transfection with a series of 5'-deleted mutants demonstrated that the sequences between -98 and -62 bp on interleukin-8 promoter may be involved in the transcriptional repression by these gangliosides. Cyclic AMP analog dibutyryl cAMP counteracted GD1b, GT1b, and GQ1b-induced inhibition of interleukin-8 production at the levels of protein secretion, mRNA expression, and promoter activity. GD1b, GT1b, and GQ1b reduced cAMP level and protein kinase A activity in WM266-4. These gangliosides suppressed adenylate cyclase activity without altering that of cyclic nucleotide phosphodiesterase in WM266-4. The data indicate that GD1b, GT1b, and GQ1b may suppress the growth of melanoma by inhibiting interleukin-8 production via the inhibition of adenylate cyclase.

Masked gonadotropin-binding sites in human corpora lutea during menstrual cycle and pregnancy

To evaluate the possible existence of masked receptors for luteinizing hormone (LH)/human chorionic gonadotropin (hCG) in the human corpus luteum, we examined the effect of neuraminidase pretreatment on the specific binding of (125I)hLH to luteal particulates obtained from 11 patients during the menstrual cycle and 4 patients during early pregnancy. The pretreatment with neuraminidase significantly enhanced the specific binding of hLH to corpora lutea at the different stages of the luteal phase. Scatchard analyses revealed that neuraminidase increased the number of LH binding sites without altering the affinity for LH. Furthermore, the specific binding of hLH to human corpora lutea during pregnancy significantly increased after the pretreatment with neuraminidase. The data suggest that distinct populations of receptors for LH/hCG are masked within the human luteal cells.

Effect of neuraminidase on luteinizing hormone/chorionic gonadotrophin binding to the ovarian and testicular membranes from different mammalian species

After treatment of the ovarian and testicular membranes from several mammalian species an elevation in the specific binding of human [125I]-labelled CG could be observed. With the assumption that this effect is due to sialic acid-masked receptors, the presence of such receptors seem to be a common property of most mammalian gonads. An interesting observation was the abnormally high hormone binding capacity of the Syrian hamster ovary, as compared to other hamster species, and the lack of a neuraminidase effect in the ovary of the Syrian hamster.