PROSTAGLANDIN E-2 INCREASES PROENKEPHALIN MESSENGER-RNA LEVEL IN RAT ASTROCYTE-ENRICHED CULTURE

The effect of prostaglandin E-2 (PGE(2)) on proenkephalin (proENK) mRN A expression in primary cultured rat astrocytes was studied. The proEN K mRNA level was significantly increased about 3.3-fold 4 h after PGE( 2) (10 mu M) treatment and this increase was potentiated by the pre-tr eatment with cycloheximide (CHX; 15 mu M) about 1.7-fold as much as PG E(2) alone treated cells. The pretreatment with staurosporine (1 mu M) completely inhibited the increase of PGE(2)-induced proENK mRNA level , although only a partial inhibition of PGE(2)-induced proENK mRNA lev el (approximate to 1.5-fold) by H89 (10 mu M) was observed. The increa se of PGE(2)-induced proENK mRNA level was not affected by the pretrea tment with PD98059 (1, 5, and 10 mu M), omega-conotoxin GIVA (1 mu M), nimodipine(1 mu M), calmidazolium (1 mu M), or KN-62 (1 mu M) In addi tion to the proENK mRNA level, PGE(2) also increased c-Fos (approximat e to 4.3-fold), Fra-1 (approximate to 3.8 fold), and Fra-2(approximate to 8.2-fold) protein levels at 4 h after drug treatment. However, c-J un, JunB, and JunD protein levels were not affected by PGE(2). Indeed, PGE(2) failed to up-regulate c-jun mRNA expression as well as its pro tein product. Surprisingly, although three Jun proteins were not induc ed by PGE(2), AP-I and ENKCRE-2 DNA binding activities were increased by PGE(2), (approximate to 5 and approximate to 2.8-fold, respectively ) and which were effectively reduced by CHX (approximate to 2.5 and 2- fold, respectively). In western blot analyses, PGE(2) enhanced the pho sphorylation of CREB (approximate to 2.6-fold at 1 h), and CHX showed a potentiative effect on PGE(2)-induced CREB phosphorylation (approxim ate to 1.7 fold at 1 h) which is similar to the action on proENK mRNA regulation. Our results suggest that PGE, increases proENK mRNA expres sion via activating serine/threonine protein kinase such as PKA, but n ot calcium/calmodulin dependent protein kinase and MAPK. In addition, phosphorylation of CREB rather than the increase of AP-I may have a po ssible role at least early stage in PGE(2)-induced proENK mRNA level a nd CHX-evoked potentiation. (C) 1998 Elsevier Science B.V. All rights reserved.