A scaffold protein in the c-Jun NH2-terminal kinase signaling pathways suppresses the extracellular signal-regulated kinase signaling pathways.
We previously reported that c-Jun NH(2)-terminal kinase (JNK)/stress-activated protein kinase-associated protein 1 (JSAP1) functions as a putative scaffold factor in the JNK mitogen- activated protein kinase ( MAPK) cascades. In that study we also found MEK1 and Raf-1, which are involved in the extracellular signal-regulated kinase ( ERK) MAPK cascades, bind to JSAP1. Here we have defined the regions of JSAP1 responsible for the interactions with MEK1 and Raf-1. Both of the binding regions were mapped to the COOH-terminal region (residues 1054-1305) of JSAP1. We next examined the effect of overexpressing JSAP1 on the activation of ERK by phorbol 12-myristate 13-acetate in transfected COS-7 cells and found that JSAP1 inhibits ERK's activation and that the COOH-terminal region of JSAP1 was required for the inhibition. Finally, we investigated the molecular mechanism of JSAP1's inhibitory function and showed that JSAP1 prevents MEK1 phosphorylation and activation by Raf-1, resulting in the suppression of the activation of ERK. Taken together, these results suggest that JSAP1 is involved both in the JNK cascades, as a scaffolding factor, and the ERK cascades, as a suppressor.[1]References
- A scaffold protein in the c-Jun NH2-terminal kinase signaling pathways suppresses the extracellular signal-regulated kinase signaling pathways. Kuboki, Y., Ito, M., Takamatsu, N., Yamamoto, K.I., Shiba, T., Yoshioka, K. J. Biol. Chem. (2000) [Pubmed]
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