Increased expression of O-acetyl disialoganglioside synthase during rat liver fibrogenesis relates to stellate cell activation

The activation of the hepatic stellate cell (HSC) is a key step in liver fibrogenesis. Utilizing large scale sequencing of a 3'-directed cDNA library, we investigated expression profiles of quiescent and activated rat HSCs. During the activation process, O-acetyl disialoganglioside synthase (OAcGD3S) was identified as one of the significant upregulated factors. Upregulation of OAcGD3S in cultured HSCs was confirmed by both Northern and Western blot analyses. OAcGD3S expression in models of experimental liver fibrosis was investigated at the mRNA level using RT-PCR. The expression of OAcGD3S protein in activated rat HSCs and in experimental fibrotic livers was demonstrated by immunohistochemistry. In situ hybridization revealed OAcGD3S mRNA expression in areas of ductular proliferation. Furthermore, O-acetyl GD3 protein was detected in activated rat HSCs and human cirrhosis livers. This study shows that OAcGD3S is strongly expressed during liver fibrogenesis and HSCs seem to be the major cellular sources of OAcGD3S in the liver.     

Monoclonal antibody (5F3) defining renal cell carcinoma-associated antigen disialosyl globopentaosylceramide (V3NeuAcIV6NeuAcGb5), and distribution pattern of the antigen in tumor and normal tissues

Renal cell carcinoma (RCC) has been characterized by high expression of three types of disialogangliosides: two based on lacto-series type 1 structure (disialosyl Lc₄, GalNAc disialosyl Lc₄), the other based on globo-series structure (disialosyl globopentaosylceramide; disialosyl Gb5). The present study established a mAb, 5F3, directed to disialosyl Gb5. 5F3 was established after immunization with RCC cell line ACHN. The major disialoganglioside antigen isolated from ACHN cells, showing specific reactivity with 5F3, was characterized unequivocally as disialosyl Gb5 (V³NeuAcIV⁶NeuAcGb5) by identification of the core structure as globopentaosylceramide (Gb5) after enzymatic and acid hydrolysis, and by 2-dimensional ¹H-NMR spectroscopy. 5F3 does not react with monosialosyl Gb5 (V³NeuAcGb5), Gb5, or any lacto-series structures. 5F3 strongly stained 19 of 41 cases of primary RCC tissue. It reacted with proximal tubules (but not distal tubules) of kidney, microglial cells of cerebrum and cerebellum, goblet cells of stomach and intestine, smooth muscle of various organs. It did not react with parenchymatous cells of various organs, except for kidney epithelia and prostate stroma. Immunostaining of RCC tissue by mAb 5F3, in combination with staining by other antibodies directed to globo-series and lacto-series structures, has prognostic significance in defining metastatic potential of RCC.     

Gangliosides do not raise cyclic AMP levels during inhibition of lymphocyte mitogenesis

The effect of bovine brain gangliosides on the intrathymocyte levels of cyclic AMP as a potential mediator of ganglioside action has been studied. Commercial tri-, and disialogangliosides, at 2.5 to 5 μM were found to produce a rapid and profound increase (eg., 10 fold within 2 min by trisialoganglioside). When the preparations were purified on Florisil, this effect on cyclic AMP content was lost, but not the immunoinhibitory potency of the ganglioside (as tested on Concanavalin A induced DNA synthesis). The water soluble “ganglioside associated protein” fractions separated from commercial di- and trisialo gangliosides by Florisil chromatography did not alter the cyclic AMP levels of thymocytes. Previous reports of an effect of commercial gnagliosides on the enzymes of cyclic AMP metabolism in nervous tissue should be re-evaluated.