The ternary complex factor Net contains two distinct elements that mediate different responses to MAP kinase signalling cascades

Abstract

The ternary complex factors (TCFs), Elk-1, Sap-1a and Net, are key integrators of the transcriptional response to different signalling pathways. Classically, three MAP kinase pathways, involving ERK, JNK, and p38, transduce various extracellular stimuli to the nucleus. Net is a repressor that is converted into an activator by Ras/ERK signalling. Net is also exported from the nucleus in response to stress stimuli transduced through the JNK pathway, leading to relief from repression. Here we show that ERK and p38 bind to the D box and that binding is required for phosphorylation of the adjacent C-terminally located C-domain. The D box as well as the phosphorylation sites in the C-domain (the DC element) are required for transcription activation by Ras. On the other hand, JNK binds to the J box in the middle of the protein, and binding is required for phosphorylation of the adjacent EXport motif. Both the binding and phosphorylation sites (the JEX element) are important for Net export. In conclusion, specific targeting of Net by MAP kinase pathways involves two different docking sites and phosphorylation of two different domains. These two elements, DC and JEX, mediate two distinct functional responses.