Seternes Ole-Morten, Mikalsen Theresa, Johansen Bjarne, Michaelsen Espen, Armstrong Chris G, Morrice Nick A, Turgeon Benjamin, Meloche Sylvain, Moens Ugo, Keyse Stephen M
Department of Pharmacology, Institute of Medical Biology, University of Tromsø, Tromsø, Norway.
EMBO J. 2004 Dec 8;23(24):4780-91. doi: 10.1038/sj.emboj.7600489. Epub 2004 Dec 2.
Extracellular signal-regulated kinase 3 (ERK3) is an atypical mitogen-activated protein kinase (MAPK), which is regulated by protein stability. However, its function is unknown and no physiological substrates for ERK3 have yet been identified. Here we demonstrate a specific interaction between ERK3 and MAPK-activated protein kinase-5 (MK5). Binding results in nuclear exclusion of both ERK3 and MK5 and is accompanied by ERK3-dependent phosphorylation and activation of MK5 in vitro and in vivo. Endogenous MK5 activity is significantly reduced by siRNA-mediated knockdown of ERK3 and also in fibroblasts derived from ERK3-/- mice. Furthermore, increased levels of ERK3 protein detected during nerve growth factor-induced differentiation of PC12 cells are accompanied by an increase in MK5 activity. Conversely, MK5 depletion causes a dramatic reduction in endogenous ERK3 levels. Our data identify the first physiological protein substrate for ERK3 and suggest a functional link between these kinases in which MK5 is a downstream target of ERK3, while MK5 acts as a chaperone for ERK3. Our findings provide valuable tools to further dissect the regulation and biological roles of both ERK3 and MK5.
细胞外信号调节激酶3（ERK3）是一种非典型的丝裂原活化蛋白激酶（MAPK），其受蛋白质稳定性调控。然而，其功能尚不清楚，且尚未鉴定出ERK3的生理底物。在此，我们证明了ERK3与丝裂原活化蛋白激酶激活的蛋白激酶5（MK5）之间存在特异性相互作用。这种结合导致ERK3和MK5均被排除在细胞核外，并且在体外和体内均伴随着ERK3依赖性的MK5磷酸化和激活。通过小干扰RNA介导的ERK3敲低以及在源自ERK3基因敲除小鼠的成纤维细胞中，内源性MK5活性均显著降低。此外，在神经生长因子诱导PC12细胞分化过程中检测到的ERK3蛋白水平升高伴随着MK5活性增加。相反，MK5缺失导致内源性ERK3水平显著降低。我们的数据鉴定出了ERK3的首个生理蛋白底物，并表明这些激酶之间存在功能联系，其中MK5是ERK3的下游靶点，而MK5作为ERK3的伴侣蛋白发挥作用。我们的研究结果为进一步剖析ERK3和MK5的调控及生物学作用提供了有价值的工具。
