NG108-15 CELLS EXPRESS NEUREGULIN THAT INDUCES ACHR ALPHA-SUBUNIT SYNTHESIS IN CULTURED MYOTUBES

A cholinergic neuroblastoma x glioma hybrid cell line NG108-15 is able to form functional synapses, and contains both AChR-aggregating and A ChR-inducing activities when cocultured with myotubes, Several lines o f evidence indicate that the AChR-inducing activity of NG108-15 cells is derived from neuregulin, The conditioned medium of cultured NG108-1 5 cells induced the expression of AChR alpha-subunit as well as the ty rosine phosphorylation of erbB-3 receptor. NG108-15 cells expressed ne uregulin with a protein of similar to 100 kDa in size and transcripts of similar to 6.8 kbp, similar to 2.6 kbp and similar to 1.8 kbp; mRNA s encoding beta 1 and alpha 2 isoforms of neuregulin were revealed. NG 108-15 cells were induced to differentiate by chemicals, and the chemi cal-induced differentiation of NG108-15 cells increased the level of n euregulin mRNA expression similar to 3-fold while the expression of a housekeeping gene remained relatively unchanged, The activity of neure gulin in the conditioned medium of NG108-15 cells was reduced by treat ing the medium with heparin and anti-neuregulin antibody, In addition, NG108-15 tells were transfected with antisense neuregulin cDNA and it s expression of neuregulin was reduced, while its neuregulin-induced t yrosine phosphorylation activity was markedly decreased. This is the f irst direct demonstration that the NG108-15 cell-induced AChR upregula tion on cultured myotubes is mediated by neuron-derived neuregulin. (C ) 1997 Federation of European Biochemical Societies.