Prefectural Colony, Kasugai, Aichi 480-03, (M.S., K. K.) Japan.
The S-100 protein level in mouse neuroblastoma (N18TG-2 and NIE-l15), rat glioma (C6, C6BU-1, and C6V-1), and hybrid (NG108-15, 140-3, 141-B, NBrlOA, NBr20A, NCB20, and NX31T) cells was determined with a sensitive enzyme immunoassay system that uses a rabbit antibody to bovine brain S-100 protein. S-100 protein was detected in glioma but not in neuroblastoma cells. All seven hybrid cells derived from neuroblastoma and glioma or other types of cells were found to possess a very little or undetectable S-100 protein. The induction of S-100 protein level in prestationary phase cultures of glioma C6BU-1 cells was examined by forskolin, which was a highly specific activator of adenylate cyclase of the cells and produced morphological differentiation. After incubation with 10 pM forskolin for 48 hr, the 5100 protein level increased 2-2.5-fold in C6BU-1 glioma cells whose mean control level was 60 f 26 ng/mg protein (f SD). The forskolin induction of S-100 protein in the cells was dose dependent, and the concentration of forskolin required for 50% activation of S-100 protein was about 0.6 pM. The increase by forskolin was initiated from 10-15 h r after incubation with it and was inhibited with cycloheximide and actinomycin D. In NG108-15 hybrid cells the induction of S-I00 protein was also observed by forskolin as well as prostaglandin (PG) El plus theophylline which are known to activate adenylate cyclase of the cells. The results indicate that S-100 protein biosynthesis is genetically controlled in these clonal cells, and that S-100 protein can be regulated in a CAMP-dependent fashion in prestationary cultures.