Differential regulation of M3/6 (DUSP8) signaling complexes in response to arsenite-induced oxidative stress.

Mitogen-activated protein kinase (MAPK) cascades are involved in the regulation of cellular proliferation, differentiation, survival, apoptosis, as well as in inflammatory responses. Signal intensity and duration have been recognized as crucial parameters determining MAPK signaling output. Phosphatases play a particularly important role in this respect, by tightly controlling MAPK phosphorylation and activation. M3/6 (DUSP8) is a dual-specificity phosphatase implicated in the dephosphorylation and inactivation of JNK and, to a lesser extent, p38 MAPKs and is found in a complex with these kinases, along with other pathway components, held together by scaffold proteins. The JNK family consists of three genes, giving rise to at least ten different splice variants. Some functional differences between these gene products have been demonstrated, but the underlying molecular mechanisms and the roles of individual splice variants are still incompletely understood. We have investigated the interaction of M3/6 with JNK isoforms, as well as scaffold proteins of the JNK interacting protein (JIP) family, in order to elucidate the contribution of M3/6 to the regulation of distinct JNK signaling modules. M3/6 exhibited stronger binding towards JNK1β and JNK2α isoforms and this was reflected in higher enzymatic activity towards JNK2α2 when compared to JNK1α1 in vitro. After activation of the pathway by exposure of cells to arsenite, the interaction of M3/6 with JNK1α and JNK3 was enhanced, whereas that with JNK1β or JNK2α decreased. The modulation of binding affinities was found to be independent of JNK-mediated M3/6 phosphorylation. Furthermore, arsenite treatment resulted in an inducible recruitment of M3/6 to JNK-interacting protein 3 (JIP3) scaffold complexes, while its interaction with JIP1 or JIP2 was constitutive. The presented data suggest an isoform-specific role for the M3/6 phosphatase and the dynamic targeting of M3/6 towards distinct JNK-containing signaling complexes.