Two complementary approaches have been used to provide insight into the molecular mechanisms of adhesion of human or rodent neuroblastoma tumor cells to a model fibronectin-containing extracellular matrix--(a) biochemical analyses of the components in substratum adhesion sites after EGTA-mediated detachment of cells from the tissue culture substratum and (b) evaluation of adhesive responses of neural tumor cells to substrata coated with specific binding domains of the fibronectin moleculle or model proteins with specific binding activities. These studies reveal that (a) the mechanisms of adhesion of the growth cone and the cell body of neuroblastoma cells are distinctly different, (b) neuroblastoma tumor cells from the central nervous system of the animal resond to defined matrices very differently than peripheral neurons and possible CNS neurons indicating strong selection for a particular matrix-adhering type of tumor cell, and (c) heparan sulfate proteoglycan on the cell surface plays a central role in cell body adhesion of neuroblastoma whereas the unidentified receptor for fibronectin plays a critical role in growth cone adhesion. In addition, neurite-containing neuroblastoma cells display on their surfaces and in their substratum adhesion sites a unique and very high molecular weight glycoconjugate, called Io, that is not observed on a host of other cells, including glioma tumor cells and nonneurite neuroblastoma.
Three specific aims will now be pursued. A more detailed investigation of the heparan sulfate proteoglycan in the substratum adhesion sites of neuroblastoma cells will be undertaken, including their aggregation competence and ability to bind to affinity matrices for correlation with adhesion functional analyses. Secondly, the structure of the unique Io glycoconjugate will be investigated based on preliminary hints as to its composition; included here is the raising of antibodies for both structural and cell biological studies of this neurite-""""""""associated"""""""" molecule. And, finally, adhesive responses to specific binding domains of fibronectin or laminin, as well as model binding proteins, will be used to define the receptor-dependent processes for growth cone or cell body adhesion of these neural tumor cells. These experiments will define similarities and differences in matrix adhesion of these tumor cells in concert with parallel studies with embryonic peripheral or central nervous system neurons, as well as the nature of the selection processes that give rise to tumor cells competent for penetrating fibronectin- and/or laminin-containing matrices.
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