Gallo, Kathleen A.

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. Implications: On the basis of these findings, MLK3 emerges as a potential therapeutic target for the treatment of glioblastoma. Mol Cancer Res; 15(8); 1085–95. ©2017 AACR.

Some 5 years ago, it was first discovered that mutations in the gene encoding LRRK2 (leucine-rich repeat protein kinase 2) are tightly linked with a subset of familial PD (Parkinson's disease). Before this genetic association, LRRK2 had never been investigated biochemically. Now it is of utmost importance to establish whether LRRK2 is a bona fide kinase in vitro and in vivo and to understand how mutations of LRRK2 lead to the specific loss of dopaminergic neurons in the substantia nigra to cause PD. In spite of tremendous efforts in the research community, there is no consensus with regard to the magnitude of the enzymatic activity of LRRK2 mutant forms that segregate with PD owing, in part, to the lack of a highly sensitive kinase assay system, and it is still unclear whether an abnormal increase in kinase activity is responsible for LRRK2-associated PD. As described in this issue of the Biochemical Journal, Nichols et al. have developed an extensive set of molecular tools, including an optimized peptide substrate for determining in vitro kinase activity of LRRK2, a set of kinase inhibitors that can be used to explore LRRK2 substrate specificity and biology, a much-needed murine-specific antibody for immunoprecipation, and efficient gene-silencing approaches. In the present commentary, we discuss some of the components of this new LRRK2 biochemical toolbox and how they can be used to better understand this enigmatic kinase.