Erythropoietin-producing
hepatoma-amplified sequence (
Eph) receptor tyrosine kinases and their cell-surface-bound
ligands, the
ephrins, function as a unique signaling system triggered by cell-to-cell interaction and have been shown to mediate neurodevelopmental processes. In addition, recent studies showed deregulation of some of Eph/
ephrin genes in human
malignancies, suggesting the involvement of this signaling pathway in
tumorigenesis. The ALL1 (also termed MLL) gene on human chromosome 11q23 was isolated by virtue of its involvement in recurrent chromosome translocations associated with acute
leukemias with poor prognosis. The translocations fuse ALL1 to any of >50 partner genes and result in production of chimeric
proteins composed of the ALL1 N terminus and the C terminus of the partner
protein. The most common translocations in ALL1-associated
leukemias are t(4;11) and t(9;11), which generate ALL1/AF4 and ALL1/AF9 fusion
protein, respectively. In the present study, we sought to determine whether ALL1 fusion
proteins are involved in regulation of Eph/
ephrin genes. Screening of K562 cells producing recombinant ALL1/AF4 or ALL1/AF9 fusion
protein revealed transcriptional up-regulation of the EphA7. Consistent with this finding,
siRNA-mediated suppression of ALL1/AF4 in SEMK2 cells carrying the t(4;11) chromosome translocation resulted in down-regulation of EphA7. ChIP analysis demonstrated the occupancy of tagged ALL1 fusion
proteins on the EphA7 promoter, pointing to EphA7 as a direct target of the formers. Further studies demonstrate that EphA7 up-regulation is accompanied by ERK phosphorylation. Finally, we show apoptotic cell death, specific for leukemic cells carrying the t(4;11) chromosome translocation,
after treatment of the cells with an ERK phosphorylation blocker.