These studies focus on fibronectin (FN)-mediated adhesion mechanisms of human and rodent neuroblastoma cells in culture model systems, as well as the mechanisms of immortalized hybrid F11 cells (rat dorsal root neurons X mouse neuroblastoma cells). They examine the significance of these mechanisms in neuritogenesis in vitro and tumorigenesis in vivo. Subcloning of F11 cells and several experimental approaches have led to isolation and classification of stable subpopulations that have segregated multiple and overlapping mechanisms of differentiation on FN and other molecularly-specific matrices. Proteolytic fragments of FNs and model matrix binding proteins have been used to map at least four independent or cooperative mechanisms of neuritogenesis, utilizing four different cell surface """"""""receptors"""""""" of these neuronal tumor cells--RGDS (Arg-Gly-Asp-Ser)- dependent integrin binding of FNs; a new cell-binding site in FNs--RGDS- independent, located N-terminal of alternately-spliced Edb sequences, and directed to an unidentified receptor; binding to cell surface heparin sulfate proteoglycan; and ganglioside GM1-dependent binding. In addition proteoglycan or ganglioside binding in some experimental contexts can modulate neuritogenesis mediated by other receptor classes on the cell surface. To analyze further the FN adhesion mechanisms of these neuronal tumor cells and their biological significance, three specific aims are proposed: (1) We will characterize a newly-discovered cell adhesion mechanism that mediates neuritogenesis of neuronal tumor cells on FN matrices, the cell surface receptor that mediates its action, its cell-type specificity, and the interplay between this mechanism and other known adhesion mechanisms of FNs. (II) We will evaluate regulation of the multiple mechanisms of neuritogenesis in dorsal root neuron hybrid subclones by the interaction of """"""""cis-acting"""""""" proteoglycans and/or gangliosides with FN receptor molecules at the cell surface, as well as intercellular regulation of differentiation by medium-secreted components in mixed cell populations. (III) We will characterize the early events in neuronal tumor progression in an athymic nude mouse model system, using novel bacterial marker genes for ease of identification of neuronal tumor cells in various organ sites, and the significance of cell type-specific adhesion mechanisms in neuronal tumor progression. Overall, these analyses are demonstrating the complexity and multiplicity of FN binding reactions for mediating adhesion processes by these neuronal tumor derivative cells in two biological contexts - as model systems of neuritogenesis of the embryonic neuronal populations from which these tumor cells were derived and as evaluators of the specialized tumor progression events of these nervous system-derived tumor systems.
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