The oncogenic mechanisms underlying acute lymphoblastic leukemia (ALL) in adolescents and young adults (AYA; 15-39 years old) remain largely elusive. Here we have searched for new oncogenes in AYA-ALL by performing RNA-seq analysis of Philadelphia chromosome (Ph)-negative AYA-ALL specimens (n = 73) with the use of a next-generation sequencer. Interestingly, insertion of D4Z4 repeats containing the DUX4 gene into the IGH locus was frequently identified in B cell AYA-ALL, leading to a high level of expression of DUX4 protein with an aberrant C terminus. A transplantation assay in mice demonstrated that expression of DUX4-IGH in pro-B cells was capable of generating B cell leukemia in vivo. DUX4 fusions were preferentially detected in the AYA generation. Our data thus show that DUX4 can become an oncogenic driver as a result of somatic chromosomal rearrangements and that AYA-ALL may be a clinical entity distinct from ALL at other ages.

Targeted disruption of the gene encoding MEK kinase 1 (MEKK1), a mitogen-activated protein kinase (MAPK) kinase kinase, defined its function in the regulation of MAPK pathways and cell survival. MEKK1(-/-) embryonic stem cells from mice had lost or altered responses of the c-Jun amino-terminal kinase (JNK) to microtubule disruption and cold stress but activated JNK normally in response to heat shock, anisomycin, and ultraviolet irradiation. Activation of JNK was lost and that of extracellular signal-regulated protein kinase (ERK) was diminished in response to hyperosmolarity and serum factors in MEKK1(-/-) cells. Loss of MEKK1 expression resulted in a greater apoptotic response of cells to hyperosmolarity and microtubule disruption. When activated by specific stresses that alter cell shape and the cytoskeleton, MEKK1 signals to protect cells from apoptosis.

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