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MLK3 is required for mitogen activation of B-Raf, ERK and cell proliferation

Nature Cell Biology volume 6, pages 770–776 (2004)Cite this article

Abstract

The ERK group of mitogen-activated protein kinases (MAPKs) is essential for cell proliferation stimulated by mitogens, oncogenic ras and raf (ref. 1). All MAPKs are activated by MAP3K/MEK/MAPK core pathways1 and the Raf proto-oncoproteins, especially B-Raf, are ERK-specific MAP3Ks (refs 1–3). Mixed lineage kinase-3 (MLK3) is a MAP3K that was thought to be a cytokine-activated, and comparatively selective, regulator of the JNK group of MAPKs (refs 1, 4–6). Here we report that silencing of mlk3 by RNAi suppressed mitogen and cytokine activation not only of JNK but of ERK and p38 as well. Silencing mlk3 also blocked mitogen-stimulated phosphorylation of B-Raf at Thr 598 and Ser 601, a step required for B-Raf activation7,8. Furthermore, silencing mlk3 prevented serum-stimulated cell proliferation and the proliferation of tumour cells bearing either oncogenic Ki-Ras or loss-of-function neurofibromatosis-1 (NF1) or NF2 mutations. The proliferation of tumour cells containing activating B-raf or raf-1 mutations was unaffected by silencing mlk3. Our results define an unexpected role for MLK3 in mitogen regulation of B-Raf, ERK and cell proliferation.

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Figure 1: Activation of MLK3 by mitogen.
Figure 2: Activation of MAPKs, but not Akt, by mitogens and cytokines requires MLK3.
Figure 3: Activation of B-Raf (by phosphorylation at Thr 598/Ser 601)7,8,9 requires MLK3.
Figure 4: MLK3 is necessary for serum stimulation of cell proliferation.
Figure 5: MLK3 is necessary for maximal proliferation of human tumour cells with activating Ki-ras, but not B-raf, mutations.

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Acknowledgements

We thank J. Avruch and N. Birnberg for MEK1 cDNA and discussions; A. McLatchey for F3439 cells; A. Guha and J. Fletcher for ST88-14 cells; Q.P. Weng and N. Birnberg for Ki-ras-transformed NIH3T3 cells; A. Agarwal and A. Kuliopulos for SKOV3 cells; R. Gerszten for HUVECs; and M. Comb for anti-p-Thr598/Ser601-B-Raf antibody. This work was supported by grants from the US National Institute of General Medical Sciences and the Arthritis Foundation (to J.M.K.) and the American Heart Association, Massachusetts Chapter (to D.N.C.).

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  1. Department of Medicine, Tufts-New England Medical Center and The Department of Medicine, The Molecular Cardiology Research Institute, Tufts University School of Medicine, 750 Washington Street, Box 8486, Boston, 02111, MA, USA

    Deborah N. Chadee & John M. Kyriakis

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Correspondence to John M. Kyriakis.

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Chadee, D., Kyriakis, J. MLK3 is required for mitogen activation of B-Raf, ERK and cell proliferation. Nat Cell Biol 6, 770–776 (2004). https://doi.org/10.1038/ncb1152

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