The comparative analysis of proenkephalin mRNA expression induced by cholera toxin and pertussis toxin in primary cultured rat cortical astrocytes

In rat astrocytes, incubation with cholera toxin (CTX; 0.1 mug/ml) for 8 h increased proenkephalin (proENK) mRNA level (10-fold), which was further in creased by dexamethasone (DEX; 1 muM) (2.2-fold as much as CTX alone). Alth ough pertussis toxin (PTX; 0.1 mug/ml) did not affect the basal proENK mRNA level, DEX significantly increased proENK mRNA level in PTX-treated cells (6-fold). The inhibition of protein synthesis by cycloheximide (CHX; 15 muM ) also increased proENK mRNA level in PTX-treated cells (5.2-fold), but not in CTX-stimulated cells. The treatment with CTX, but not PTX, increased c- Fos and Fra-2 protein levels as well as AP-1, CRE, or ENKCRE-2 DNA binding activity, but neither toxin affected Fra-1, c-Jun, JunB, and JunD protein l evels. CHX significantly attenuated CTX-induced increase of c-Fos or Fra-2 protein level and AP-1, CRE, or ENKCRE-2 DNA binding activity, although CHX alone did not affect the basal AP-1, CRE, and ENKCRE-2 DNA binding activit ies. Phosphorylated CREB level was increased by both CTX and PTX, although the magnitude of phosphorylation of CREB by PTX was much less than that by CTX. In addition, CHX further or persistently increased PTX- or CTX-induced phosphorylated CREB levels in parallel with increases in proENK mRNA. Howe ver, DEX did not alter the basal or stimulated phosphorylated-CREB level. T hese results suggest that the elevation of phosphorylation of CREB rather t han AP-1 level may be involved in CTX-induced and CHX-dependent-PTX-induced increase of proENK mRNA level. In addition, AP-1 expression or CREB phosph orylation appears not to be involved the potentiative action of DEX on proE NK mRNA expression in CTX- and PTX-treated astrocytes. (C) 2001 Elsevier Sc ience BN. All rights reserved.