Cotargeting signaling pathways driving survival and cell cycle circumvents resistance to Kit inhibitors in leukemia.

Oncogenic mutations leading to persistent kinase activities are associated with malignancies. Therefore, deciphering the signaling networks downstream of these oncogenic stimuli remains a challenge to gather insights into targeted therapy. To elucidate the biochemical networks connecting the Kit mutant to leukemogenesis, in the present study, we performed a global profiling of tyrosine-phosphorylated proteins from mutant Kit-driven murine leukemia proerythroblasts and identified Shp2 and Stat5 as proximal effectors of Kit.

Erythropoietin down-regulates stem cell factor receptor (Kit) expression in the leukemic proerythroblast: role of Lyn kinase.

Overexpression of the transcription factor Spi-1/PU.1 by transgenesis in mice induces a maturation arrest at the proerythroblastic stage of differentiation. We have previously isolated a panel of spi-1 transgenic erythroleukemic cell lines that proliferated in the presence of either erythropoietin (Epo) or stem cell factor (SCF).

EKLF restricts megakaryocytic differentiation at the benefit of erythrocytic differentiation.

Previous observations suggested that functional antagonism between FLI-1 and EKLF might be involved in the commitment toward erythrocytic or megakaryocytic differentiation. We show here, using inducible shRNA expression, that EKLF knockdown in mouse erythroleukemia (MEL) cells decreases erythrocytic and increases megakaryocytic as well as Fli-1 gene expression. Chromatin immunoprecipitation analyses revealed that the increase in megakaryocytic gene expression is associated with a marked increase in RNA pol II and FLI-1 occupancy at their promoters, albeit FLI-1 protein levels are only minimally affected.

p210BCR-ABL inhibits SDF-1 chemotactic response via alteration of CXCR4 signaling and down-regulation of CXCR4 expression.

It has been shown that p210(BCR-ABL) significantly impairs CXCR4 signaling. We report here that the migratory response to SDF-1 was profoundly altered in blast crisis, whereas chronic-phase CD34(+) cells migrated normally to this chemokine. This migratory defect was associated with a low CXCR4 membrane expression.

Intracellular localization and constitutive endocytosis of CXCR4 in human CD34+ hematopoietic progenitor cells.

CXCR4, the stromal cell-derived factor-1 receptor, plays an important role in the migration of hematopoietic progenitor/stem cells. The surface and cytoplasmic expression of CXCR4 on human hematopoietic CD34(+) cells was investigated. We show that its surface expression is low, whereas a large part of CXCR4 protein is sequestered intracellularly.

Down-regulation of BRCA1 in BCR-ABL-expressing hematopoietic cells.

BCR-ABL fusion oncogene is the molecular hallmark of chronic myelogenous leukemia (CML), a condition characterized by a progression from a chronic to acute phase leukemia because of secondary genetic events, the nature of which remains largely unknown. Here, we report that the expression of the p210 BCR-ABL fusion protein leads to a down-regulation of BRCA1 protein, a gene product involved in the maintenance of genome integrity. BRCA1 protein is nearly undetectable in leukemia cells from patients with CML, both during the chronic phase and in blast crisis.