CHANGING EXPRESSION OF GTPASE-ACTIVATING PROTEINS WITH DIFFERENTIATION IN NEUROBLASTOMA

p21(ras) is a membrane-associated guanine nucleotide-binding protein w ith intrinsic GTPase activity. Like other guanine nucleotide-binding p roteins p21(ras) is active when GTP bound and inactive when GDP bound. Phosphorylation of p21(ras) is regulated by the GTPase activity of ty pe I GAP(120) and NF1-GRD. In this study we have identified type I GAP (120) and two NF1-GRD mRNAs in three neuroblastoma cell lines, IMR-32, SK-N-SH and SK-N-MC. NF1-GRD mRNA was expressed in all cell lines at a similar level but type I GAP(120) mRNA was more abundant in the IMR- 32 cell line. Retinoic acid induced differentiation of all three cell lines, this effect was most marked in the SK-N-SH line. This different iation was accompanied by an increase in both type I GAP(120) and NF1- GRD mRNAs. Retinoic acid induced differentiation had no effect on the ratio of type I to type II NF1-GRD mRNA. In seven patient tumour sampl es examined type I GAP(120) and NF1-GRD were coexpressed, type I GAP(1 20) at a higher level than NF1-GRD in all tumour stages. Type I was th e predominant NF1-GRD mRNA. The expression of type I GAP(120) was simi lar in all tumour stages but the total level of NF1-GRD was higher in stage 2 and 3 tumours than in stage 4 tumours. In summary, these resul ts suggest increased type I GAP(120) and NF1-GRD mRNA are associated w ith differentiation in neuroblastoma cells.