Forskolin induction of S-100 protein in glioma and hybrid cells

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Abstract
The S‐100 protein level in mouse neuroblastoma (N18TG‐2 and NIE‐115), rat glioma (C6, C6BU‐1, and C6V‐1), and hybrid (NG108‐15, 140‐3, 141‐B, NBr10A, NBr20A, NCB20, and NX3IT) 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 μM forskolin for 48 hr, the S‐100 protein level increased 2–2.5‐fold in C6BU‐1 glioma cells whose mean control level was 60 ± 26 ng/mg protein (± 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 μM. The increase by forskolin was initiated from 10–15 hr after incubation with it and was inhibited with cycloheximide and actinomycin D. In NG108‐15 hybrid cells the induction of S‐100 protein was also observed by forskolin as well as prostaglandin (PG) E1 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.