Gangliosides as bimodal regulators of cell growth.

Abstract

The B subunit of cholera toxin, which binds specifically to several molecules of ganglioside galactosyl-(,B1--3)-N-acetylgalactosyminyl(fi1---4)- [N-acetylneuramin-yl(a2-+3)]-galactosyl(fi1--+4)glucosyl(fl-d)ceramide (GM1) on the cell surface, stimulated DNA synthesis and cell division in quiescent, nontransformed mouse 3T3 cells in a dosedependent manner. In addition, the B subunit potentiated the response of the 3T3 cells to other mitogens, such as epidermal growth factor, platelet-derived growth factor, and insulin. This synergistic effect indicates that the B subunit does not act identically to any of these growth factors but probably modulates a common effector system crucial for cell proliferation. In distinct contrast, the B subunit inhibited the growth of rastransformed 3T3 cells as well as rapidly dividing normal 3T3 cells. Thus, the same cells, depending on their state of growth, exhibited a bimodal response to the B subunit. We conclude that endogenous gangliosides may be bimodal regulators of positive and negative signals for cell growth.Gangliosides, sialic acid-containing glycosphingolipids, have long been recognized as characteristic constituents of the plasma membrane of mammalian cells (1, 2). Although gangliosides have been identified as receptors for bacterial toxins (2) and viruses (3), relatively little is known about their normal function in membranes. In recent years, interest in these membrane constituents has increased due to the discovery that many monoclonal antibodies raised against tumor cells recognize carbohydrate sequences present on gangliosides and these determinants appear to be tumor-specific antigens (reviewed in refs. 4-6). Furthermore, the alterations in ganglioside metabolism and organization related to oncogenic transformation, cell cycle, and density-dependent growth inhibition (1, 6) raised the possibility that gangliosides play an important role in the regulation of cell growth. Such a possibility was reinforced by observations that exogenously added gangliosides altered the growth of a variety of cell types (7-13). In particular, exogenous gangliosides inhibited the action of several growth factors as well as the tyrosine kinase activity associated with the growth factor receptors (8, 9), suppressed the proliferation of lymphocytes induced by lectins, antigens, and interleukin 2 (4, 10), and sensitized tumor cells to growth inhibitors (11). In contrast, exogenous gangliosides stimulated the proliferation of astroglial (12) oncogenes. Stock cultures of murine 3T3 cells were maintained in Dulbecco's modified Eagle's medium (DMEM), supplemented with 10% (vol/vol) fetal bovine serum in a humidified atmosphere of 5% C02/95% air at 37°C.Measurement of DNA Synthesis in Quiescent 3T3 Cells.Swiss, NIH, and BALB/c 3T3 cells were subcultured into 24-well tissue culture plates (Costar, Cambridge, MA) at a density of 2.5 x 104 cells per well in 1 ml ofDMEM containing 10% fetal bovine serum and refed with the same medium after 2 days. Such cultures were used at least ...

Inhibition of Invasiveness and Motility of Human Breast Cancer Cells by Sphingosine-1-Phosphate.

“…Radioactive bands were quantified using a Storm densitometer with the ImageQuant program (Molecular Dynamics). Sphingosine production was measured as described [25].…”

“…Radioactive bands were quantified using a Storm densitometer with the ImageQuant program (Molecular Dynamics). Sphingosine production was measured as described [25].Immunoprecipitation. Cells were treated with the indicated sphingolipids, washed twice with PBS, and lysed at 4°C in 500 /ill of lysis buffer consisting of 50 mM Hepes, pH 7.4/1% (v/v) Triton X-100/ 150 mM NaCl/1 mM EDTA/1 mM 4-(2-aminoethyl)benzenesulfonyl fluoride/50 mM NaF/4 mM sodium pyrophosphate/2 mM Na 3 V0 4 / leupeptin and aprotinin (2.5 /u,g/ml each).…”

Gangliosides and energy substrates in brown adipose tissue of cold-acclimated rat.

“…In any event, these results suggest that a correlation may exist between the GM3 content and the functional changes of the tissues other than neural tissue. In relation to the present study, the suggestions by SPIEGEL and FISHMAN (1987) and HANAI et al (1987) are worthy of notice, i.e., that endogenous gangliosides or modified gangliosides may be biomodulators of positive and negative growth signals for cells, depending on their state of growth, by means of regulating the growth of cells in response to insulin and growth factor such as epidermal growth factor. From the present result, together with these findings, it is implied that GM3 or modified GM3 compounds are involved in the cold-induced proliferation of brown adipocytes as membrane transducer of positive signals for cell growth.…”

Angiogenic and Angiostatic Microenvironment in Tumors:Role of Gangliosides

“…It is not clear whether this release is the result of an aberrant over-production as a consequence of the neoplastic transformation or if it is the expression of abnormal amounts of membrane components shed by rapidly growing cells (4). Gangliosides are cell-membrane constituents involved in signalling events for growth and cell adhesion (5)(6)(7)(8). Tumor shedding of these components in the microenvironment is often so extensive as to alter the ganglioside composition of the host serum (9,10).…”