DIFFERENTIAL REGULATION OF AMOUNTS OF THE GUANINE-NUCLEOTIDE-BINDING PROTEINS GI AND GO IN NEURO-BLASTOMA X GLIOMA HYBRID-CELLS IN RESPONSE TO DIBUTYRYL CYCLIC-AMP

Incubation of the neuroblastoma .times. glioma hybrid cell line NG108015 in tissue culture with dibutyryl cyclic AMP (1 mM) for up to 8 days produced a morphological differentiation of the cells, during which they extended neurite-like processes. Pertussis-toxin-catalysed ADP-ribosylation indicated that amounts of guanine-nucleotide-binding proteins (G-protein), which are substrates for this toxin, were approximately doubled in membranes from the ''differentiated'' cells in comparison with the control cells. Immunoblotting of membranes derived from either untreated or dibutyryl cyclic AMP-treated cells with anti-peptide antisera specific for the .alpha. subunits of the pertussis-toxin-sensitive G-proteins Gi and Go demonstrated that amounts of these G-proteins were reciprocally modulated during the differentiation process. In comparison with the untreated cells, the amount of Gi in the ''differentiated'' cells was decreased, whereas the amount of Go was substantially increased. Stimulation of high-affinity GTPase activity in response to opioid peptides, which in this cell line interact with an opioid receptor of the .delta. subclass, was much decreased, and inhibition of adenylate cyclase activity was almost entirely attenuated in the ''differentiated''-cell membranes in comparison with membranes of untreated cells. Opioid receptor number was also decreased in membranes of the dibutyryl cyclic AMP-treated cells in comparison with the control cells. These data demonstrate that relatively small changes in the observed pattern of pertussis-toxin-catalysed ASP-ribosylation of membranes can mask more dramatic alterations in amounts of the individual pertussis-toxin-sensitive G-proteins, and further demonstrate the importance of methodologies able to discriminate between the different gene products.