Opposing effects of ERK and p38‐JNK MAP kinase pathways on formation of prions in GT1‐1 cells

Abstract

Brain‐derived neurotrophic factor, which activates the extracellular regulated kinase (ERK) pathway, increases formation of prions in scrapie‐infected gonadotropin‐releasing hormone (GT1–1) cells. This indicates that conversion of the cellular prion protein PrP to its pathogenic isoform, PrP Sc , can be regulated by physiological stimuli acting on specific signal transduction pathways. In the present study, we examined the involvement of different mitogen‐activated protein (MAP) kinase cascades and the cAMP‐PKA pathway in formation of proteinase K‐resistant PrP Sc (rPrP Sc ). Long‐term depolarization of GT1‐1 cells infected with the Rocky Mountain Laboratory strain of scrapie increased the formation of rPrP Sc . This effect was associated to ERK activation and was blocked by the MAPK/ERK kinase (MEK) inhibitor U0126. Treatment with forskolin caused a similar increase in rPrP Sc formation that was prevented by the protein kinase A (PKA) inhibitor H89. Both depolarization and forskolin treatment were accompanied by increased phosphorylation of the S6 ribosomal protein, while phosphorylation of histone H3 occurred only after forskolin treatment. Inhibitors of p38‐ and c‐Jun NH 2 ‐terminal kinase (JNK) promoted the formation of rPrP Sc , in contrast to the clearance of rPrP Sc produced by inhibitors of the ERK pathway. Thus, the ERK and the p38‐JNK MAP kinase pathways appear to exert opposing effects on rPrP Sc formation, suggesting that balances between these intracellular signaling cascades may regulate replication of prions.— Nordström, E., Fisone, G., Kristensson, K. Opposing effects of ERK and p38‐JNK MAP kinase pathways on formation of prions in GT1‐1 cells. FASEB J. 23, 613–622 (2009)