Expression of JNK cascade scaffold protein JSAPl in the mouse nervous system

The mitogen-activated protein kinase (MAPK) cascades consist of MAPK. MAPK kinase (MAPKK). and MAPKK kinase (MAPKKK). The specificity of activation of MAPK cascades may be determined, in part, by scaffold proteins that organi ze multi-enzyme complexes. We have earlier reported a, scaffold protein JSA P1 (also known as JIP3) in the JNK MAPK cascade. We also showed that, of th e adult mouse tissues tested. JSAP1 mRNA was predominantly expressed in bra in. Here we report the localization of JSAP1 protein in mouse embryos and a dult blain by immunohistochemistry analysis. In embryos (E11-16), JSAP1 imm unoreactivity was mainly found in the central and peripheral nervous system s, where it was localized to the cell bodies and/or axons of developing neu rons, but not neural precursor cells. In the adult brain. immunoreactive JS AP1 was localized mostly to cell bodies in almost all neurons. We also show ed that the expression of JSAP1 transcripts and proteins gradually increase d Juring the neural differentiation of mouse P19 embryonal carcinoma (EC) c ells. Furthermore, we showed that overexpressed JSAP1 facilitated the effic ient activation of JNK by MEKK1 in P19 cells. These results suggest that JS AP1 may function as: a scaffold protein for the JNK signaling module in neu ronal cells. (C) 2001 Elsevier Science Ireland Ltd and the Japan Neuroscien ce Society. All rights reserved.