EGFR Signals through a DOCK180-MLK3 Axis to Drive Glioblastoma Cell Invasion

Abstract

A hallmark of glioblastoma (GBM) tumors is their highly invasive behavior. Tumor dissemination into surrounding brain tissue is responsible for incomplete surgical resection, and subsequent tumor recurrence. Identification of targets that control GBM cell dissemination is critical for developing effective therapies to treat GBM. A majority of GBM tumors have dysregulated EGFR signaling, due most frequently to EGFR amplification or the presence of a constitutively active EGFRvIII mutant. Mixed lineage kinase 3 (MLK3) is a mitogen-activated protein kinase kinase kinase (MAP3K) that can activate multiple MAPK pathways. In this study, evidence is provided that MLK3 is essential for GBM cell migration and invasion, and that an MLK inhibitor blocks EGF-induced migration and invasion. MLK3 silencing or MLK inhibition blocks EGF-induced JNK activation, suggesting that MLK3-JNK signaling promotes invasion of GBM cells. Mechanistically, it is demonstrated that DOCK180, a RAC1 guanine nucleotide exchange factor (GEF) overexpressed in invasive GBM cells, activates the MLK3-JNK signaling axis in a RAC1-dependent manner. In summary, this investigation identifies an EGFR-DOCK180-RAC1-MLK3-JNK signaling axis that drives glioblastoma cell migration and dissemination. On the basis of these findings, MLK3 emerges as a potential therapeutic target for the treatment of glioblastoma. .

MKK7 transcription positively or negatively regulated by SP1 and KLF5 depends on HDAC4 activity in glioma

“…33 Interestingly, recent reports demonstrated that expressing either wild-type EGFR or mutant EGFRvIII signals evoke PKA-dependent phosphorylation of DOCK-180 protein, 34 which subsequently activates the Rac1-MLK3-JNK axis to drive GBM cell invasion and mediate primary resistance to EGFR inhibition or temozolomide treatment. 8,14,35 These findings suggested that the heavy activation of JNK signaling and the oncogenic role of JNK in glioma cells closely depend on the activity of MLKs. As a further test, we demonstrated here that MKK7 directly activates JNK signaling in glioma cells.…”

“…A series of studies examined the activities of basal JNK (the phosphorylated form) and c‐Jun in human GBM tissues and independently confirmed that strongly phosphorylated‐JNK and c‐Jun appear in the majority (>90%) of GBM cases and are associated with the histological grade of a glioma . Interestingly, recent reports demonstrated that expressing either wild‐type EGFR or mutant EGFRvIII signals evoke PKA‐dependent phosphorylation of DOCK‐180 protein, which subsequently activates the Rac1‐MLK3‐JNK axis to drive GBM cell invasion and mediate primary resistance to EGFR inhibition or temozolomide treatment . These findings suggested that the heavy activation of JNK signaling and the oncogenic role of JNK in glioma cells closely depend on the activity of MLKs.…”

“…Similar to the activation of JNK, MKK4 and MKK7 are phosphorylated in their activation by upstream MAP kinase kinase kinases (MKKKs), including mixed lineage kinase (MLK)‐1‐4, DLK, TAK1, ASK1, LZK and ZAK . Recently, it was demonstrated that MLK3 silencing or MLK inhibition blocks JNK activation and both GBM cell migration and invasion, and silencing MLK4 suppresses self‐renewal, motility and radio‐resistance of glioma stem cells, suggesting that the MLK‐JNK axis is crucial for GBM tumourigenesis . However, so far, the critical kinase that directly activates JNK during glioma formation remains unidentified.…”

The Role of Rho GTPases in Motility and Invasion of Glioblastoma Cells

“…Rac1 therefore is part of multiple signaling axes that start at receptor tyrosine kinases and that dictate cell migration and invasion. One such axis is the EGFR-DOCK180/ELMO1-RAC1-MLK3-JNK signaling axis which was found to be a driving factor of glioblastoma invasion [66]. DOCK180 is a Rac1 guanine nucleotide exchange factor (GEF) and is also downstream of other RTKs such as MET, forming a complex with several other proteins and driving Rac1-dependent glioblastoma cell movement [67].…”

The effects of cucurbitacin E on GADD45β‐trigger G2/M arrest and JNK‐independent pathway in brain cancer cells

“…Glioblastomas (GBMs) are highly invasive and recurrence brain tumours, 15 and have been shown to harbour therapy-resistant cancer stem cells (CSCs), and this is the main cause of death. 16,17 Recent studies indicated that GBMs contain a subpopulation of glioma-initiating tumour cells which exhibits stem cell characteristics and may be responsible for in vivo tumour growth.…”