B-50/GAP-43 mRNA expression in cultured primary Schwann cells is regulated by cyclic AMP.

Following peripheral nerve crush or transection, B-50 mRNA expression increased dramatically in the distal nerve stump. This increase has been fully attributed to an up-regulation of B-50 synthesis in reactive Schwann cells. Here we describe that B-50 mRNA expression in primary Schwann cell cultures is strongly down-regulated by cyclic AMP. Treatment of neonatal Schwann cell cultures with as low as 20 nM forskolin decreased B-50 mRNA expression. We show that B-50 promoter P2, but not P1, is active in Schwann cells and that the activity of P2 is inhibited 2.5 fold by forskolin. P2 does not contain a consensus sequence of a known cyclic AMP responsive element suggesting that the effect of forskolin is indirect.