NF-KAPPA-B-DEPENDENT EXPRESSION OF NITRIC-OXIDE SYNTHASE IS REQUIRED FOR MEMBRANE-FUSION OF CHICK EMBRYONIC MYOBLASTS

The activity of nitric oxide synthase (NOS) has recently been shown to increase transiently but dramatically in chick embryonic myoblasts th at are competent for fusion and that NO acts as a messenger for the ce ll fusion. Here we show that the rise in NOS activity is tightly corre lated with an increase in NOS protein level, and its synthesis is unde r transcriptional control. In addition, a partial cDNA sequence of NOS obtained by reverse transcription PCR on total RNA. from chick myobla sts was found to be identical with that of the inducible type of NOS ( iNOS) from chick macrophage. Thus chick myoblast NOS must belong to th e family of iNOS. Consistently, pyrrolidine dithiocarbamate, a potent inhibitor of nuclear factor kappa B (NF-kappa B), prevented the expres sion of myoblast NOS. Furthermore the antioxidant also strongly inhibi ted cell fusion, and its inhibitory effect was reversed by treatment w ith sodium nitroprusside, an NO-generating agent. In addition, nuclear extracts obtained from myoblasts that were competent for fusion, but not those from proliferating cells or from fully differentiated myotub es, were capable of binding to the consensus NF-kappa B site in the pr omoter region of the gene encoding iNOS. These results suggest that NF -kappa B-dependent expression of NOS is an important step in membrane fusion of chick embryonic myoblasts.