A STUDY OF THE RELATIONSHIPS AMONG GANGLIOSIDE COMPOSITION, FIBRONECTIN BINDING, AND TUMOR METASTASIS (GLYCOLIPIDS)
Abstract
The hypothesis that fibronectin binds the gangliosides G(,D1b) and G(,T1b) which are lost during tumor metastasis was investigated. Fibronectin bound to erythrocytes and to 96 well dishes coated with gangliosides. The gangliosides, G(,D1a), G(,D1b), and G(,T1b) and mixed rat liver gangliosides bound fibronectin. The apparent dissociation constant for fibronectin binding to rat liver gangliosides was very similar to that of fibronectin binding to plasma membrane fractions isolated from rat liver. Analysis of the distribution of gangliosides in rat liver membrane fractions revealed that gangliosides were nonhomogeneously distributed. Approximately 85% of the total G(,D1b), G(,T1b) and G(,Q1b), but only 15% of the total G(,D1a), was present in the plasma membrane. Assuming a distribution in other cells and tissues similar to that in rat liver, the ganglioside G(,D1a), due to its intracellular localization, should be relatively unimportant in binding of fibronectin to the cell surface. In a series of squamous cell carcinomas and one mammary tumor, reductions in both fibronectin binding and the gangliosides G(,D1b) and G(,T1b) correlated with metastasis. No simple relationship among these three parameters, however, could be demonstrated in seven hepatomas and normal rat liver or eight lines of cultured cells. The complete lack of the gnagliosides G(,D1b) and G(,T1b), provides a demonstration of a block in the biosynthesis of the complex gangliosides of the disialoganglioside pathway in several transplantable and metastatic rodent tumors. In general, hepatomas with higher metastatic incidence bound less fibronectin than did the tumors with lower metastatic incidence. However, since fibronectin binding showed no simple relationship to ganglioside content and since fibronectin binding to rat liver plasma membranes was inhibited by proteases but was stimulated by neuraminidase, evidence for other fibronectin binding molecules was sought. Plasma membrane proteins of 220,000, 140,000, and 67,000 daltons bound fibronectin as demonstrated by western blots and gel overlays. These findings suggest that it may be necessary to evaluate simultaneously several parameters of the mammalian cell surface to account for reductions of fibronectin binding as one of the alterations that may contribute to metastatic ability.
Degree
Ph.D.
Subject Area
Biology
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