The role of MEKK3 in osteosarcoma invasion and metastasis

1819 Osteosarcoma is the most commonly diagnosed bone tumor in adolescents and young adults. Despite effective control of the primary tumor and aggressive adjuvant chemotherapy, death from pulmonary metastasis occurs in approximately 40-50% of patients and has not improved in over 2 decades despite multiple changes in the chemotherapy regimens. Osteosarcoma is an excellent model to study the molecular mechanisms involved in tumor metastasis to the lung. Evidence indicated that the mitogen-activated protein kinase (MAPK) activity is linked to early osteosarcoma metastasis through activation of the membrane-cytoskeleton linker ezrin, but the molecular mechanisms involved in the intracellular signal transduction remain largely unknown. The purpose of this study is to understand the role of MEKK3, a member of the MAPK kinase kinase (MAP3K) family, in metastasis and invasion of osteosarcoma. MEKK3 belongs to the MEKK/TE11 subgroup of the MAP3K family. Upon phosphorylation, MEKK3 is activated and subsequently phosphorylate and activate downstream signaling molecules, including c-Jun N-terminal kinase and p38. This activation not only links diverse extracellular stimuli to subsequent signaling molecules but also amplifies the initiating signals to ultimately activate the effector molecules and induce cell proliferation, differentiation, and survival. We established an MEKK3 down-regulated murine osteosarcoma cell line (Dunn) by lentiviral-mediated delivery of small interfering RNA. This system successfully knocked down the MEKK3 level to only 5% of the normal level, as determined by immunoprecipitation and western blotting analysis. We examined tumor cell migration and invasion and found that the migration rate was dramatically reduced in cells with down regulated MEKK3. This initial study suggested that MEKK3 may play a role in osteosarcoma tumor invasion and metastasis.