Assistant Professor
Ph.D. University of Manitoba, Canada 1999
Research in my laboratory is focused on studying the role of MAP3Ks in cell proliferation and cancer. Mitogen activated protein kinases (MAPKs) respond to diverse extracellular stimuli (growth factors, hormones, cytokines) and directly regulate gene expression. The MAPKs are activated as part of a three-tiered core signaling pathway by a concomitant tyrosine and threonine phosphorylation that is catalyzed by members of the MAPK-kinase (MAPKK) family. MAPKKs are activated by serine/threonine phosphorylation catalyzed by MAPKK-kinases (MAP3Ks). The extracellular stimuli and upstream activators that regulate MAP3K activation remain poorly understood. The MAP3K mixed-lineage kinase 3 (MLK3) is a member of a family of serine/threonine protein kinases that phosphorylate and activate MAPKKs, which in turn activate the JNK pathway. Stimuli that activate MLK3 include TNF? and ceramide.
In our previous studies we observed activation of endogenous MLK3 by epidermal growth factor (EGF). This finding placed MLK3 in the context of receptor tyrosine kinase signaling and prompted us to investigate the role of MLK3 in regulation of ERK MAPK signaling. Silencing mlk3 with RNAi significantly inhibited ERK activation by EGF. Furthermore, these studies revealed an unexpected requirement for MLK3 in the proliferation of normal fibroblasts and of all tumor-derived cell lines having an activated Ras (eg. ovarian-, osteocarcinoma-, NF1-schwannoma-, colon-). Interestingly, MLK3 is not required for proliferation of tumor cells bearing an activating V599E mutation in B-Raf. Wild type B-Raf undergoes two activating phosphorylations on residues Thr598 and Ser601. The V599E mutation, which occurs in approximately 70% of human melanomas, is believed to mimic these activating phosphorylations, yielding a constitutively active enzyme. These studies also showed that MLK3 is required for mitogen-induced phosphorylation of B-Raf on these key residues (Thr598 and Ser601). Thus, MLK3 plays an important role in mitogen activation of B-Raf, ERK and cell proliferation. Blocking cell proliferation by targeting MLK3 could represent a novel therapeutic approach for the treatment of specific types of cancer.
Our research is focused on deciphering the biochemical regulation of MLK3 by growth factor and cytokine signaling pathways and in defining the biological role of MLK3 and other MAP3Ks in cell proliferation and cancer.
Very little is known about the signaling molecules that relay growth factor or cytokine signals from receptors to MLK3 and other MAP3Ks. We are interested in identifying the intracellular signaling molecules that recruit MLK3 to growth factor (EGF) or cytokine (TNF) receptors. We are also interested in determining the mechanism by which MLK3 regulates B-Raf phosphorylation and kinase activity. Previously, we have observed that silencing mlk3 in mammalian cells blocks cell proliferation of normal and tumor cells. Thus, we are interested in determining if silencing mlk3 affects specific regulators of cell cycle progression and leads to cell cycle arrest at a specific phase of the cell cycle. We are also interested in analyzing MLK3 protein expression and kinase activity in normal and tumor cells to determine if MLK3 is deregulated in tumor cells in comparison to normal cells. In addition, we will explore the role of MLK3 in the different aspects of cellular transformation and tumorigenesis.
Chadee, D.N., Xu, D., Hung, G., Andalibi, A., Lim, D.J., Luo, Z., Gutmann, D.H., and Kyriakis, J.M. (2006) MLK3 regulates B-Raf through a mechanism that involves maintenance of the B-Raf/Raf-1 complex and inhibition by the NF2 tumor suppressor protein. Proc. Natl. Acad. Sci. USA, Mar 21;103(12):4463-8.
Chadee, D.N. and Kyriakis, J.M. (2004) A novel role for MLK3 in B-Raf activation and cell proliferation. Cell Cycle, Oct 3(10), 1227-9.
Chadee, D.N. and Kyriakis, J.M. (2004) MLK3 is required for mitogen activation of B-Raf, ERK, and cell proliferation. Nat. Cell Biol., Aug 6(8), 770-6.
Kyriakis, J.M., Liu, H., and Chadee, D.N. (2004) Activation of SAPKs/JNKs and p38s in vitro. Methods Mol. Biol., 250, 61-88.
Roelen, B.A., Cohen, O.S., Raychowdhury, M.K., Chadee, D.N., Zhang, Y., Kyriakis ,J.M., Alessandrini, A.A., Lin, H.Y. (2003) Phosphorylation of threonine 276 in Smad4 is involved in transforming growth factor-beta-induced nuclear accumulation. Am J. Physiol. Cell Physiol., 285(4), C823-30.
Chadee, D.N., Peltier, C.P. and Davie, J.R. (2002) Histone H1(S)-3 phosphorylation in Ha-ras oncogene-transformed mouse fibroblasts. Oncogene, 21(55), 8397-403.
Chadee, D.N., Yuasa, T. and Kyriakis, J.M. (2002) Direct activation of mitogen-activated protein kinase kinase kinase MEKK1 by the Ste-20p homologue GCK and the adapter protein TRAF2. Mol. Cell. Biol., 22, 737-749.
Chadee, D.N., Hendzel, M.J., Tylipski, C.P., Allis, C.D., Bazett-Jones, D.P., Wright, J.A., and Davie, J.R. (1999) Increased Ser-10 phosphorylation of histone H3 in oncogene-transformed and mitogen-stimulated mouse fibroblasts. J. Biol. Chem., 274, 24914-20.
Davie, J.R. and Chadee, D.N. (1998) Regulation and regulatory parameters of histone modifications. J. Cell. Biochem., 30/31, 203-213.
Holth, L.T., Chadee, D.N., Spencer, V., Samuel, S.K., Safneck, J., and Davie J.R. (1998) Structural organization of the nucleus in cancer. Int. J. Oncology, 13, 827-837.
Fischer, A.H., Chadee, D.N., Wright, J.A., Gansler, T.S., and Davie, J.R. (1998) A Ras-associated nuclear structural change appears functionally significant and independent of the mitotic signalling pathway. J. Cell. Biochem., 70, 130-140.
Chadee, D.N., Allis C.D., Wright, J.A., and Davie. J.R. (1997) Histone H1b phosphorylation is dependent upon ongoing transcription and replication in normal and ras-transformed mouse fibroblasts. J. Biol. Chem., 272, 8113-8116.
Chadee, D.N., Taylor, W.R., Hurta, R.A., Allis, C.D., Wright, J.A., and Davie, J.R. (1995) Increased phosphorylation of histone H1 in mouse fibroblasts transformed with oncogenes or constitutively active MAP kinase kinase. J. Biol. Chem., 270, 20098-20105.