We have examined the binding of
tetanus toxin (TT) to surface receptors of
neuroblastoma cells by flow cytometry following chemically induced differentiation. Cells were treated with
mitomycin C,
bromodeoxyuridine,
prostaglandin E1 or cyclic
adenosine monophosphate at different doses, alone or in combination for 4 days. Cells extended long neurites within 24 h in the presence of
prostaglandin/
cyclic AMP or
mitomycin/
bromodeoxyuridine treatment while single-
drug treatment was less efficient in morphological differentiation of these cells. Cells exposed to the
drug combinations stopped growing after 3 days while flow-cytometric analysis of
DNA levels of each cell stained with
propidium iodide indicated that at least 60% of these cells were arrested in phase G0/G1 of the cell cycle.
Drug-treated cultures were stained for TT binding by immunofluorescence of cells in
suspension and analyzed by flow cytometry. Chemically differentiated N2AB-1 cells were shown to bind significantly more TT than control cultures. Receptors for TT could be saturated by increasing doses of TT and differentiated cells bound twice as much toxin at saturation as did control cells. Immunofluorescence of TT binding to monolayers revealed staining in a stippled fashion along all neurites and cell bodies. These data support the concept that drugs which stimulate differentiation of
neuroblastoma cells as determined by morphological and cell-cycle criteria also increase the presence of
ganglioside receptors on the cell surface available for toxin binding.