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. In vitro STI-571 treatment of CD34(+) cells from patients in blast crisis markedly increased the CXCR4 transcript and CXCR4 membrane expression. Because p210(BCR-ABL) frequently increases with disease progression, we determined the effects of high and low p210(BCR-ABL) expression on CXCR4 protein in the granulocyte macrophage colony-stimulating factor-dependent human cell line MO7e. p210(BCR-ABL) expression distinctly alters CXCR4 protein through two different mechanisms depending on its expression level. At low expression, a signaling defect was detected with no modification of CXCR4 expression. However, higher p210(BCR-ABL) expression induced a marked down-regulation of CXCR4 that is related to its decreased transcription. The effect of p210(BCR-ABL) required its tyrosine kinase activity. Collectively, these data indicate that p210(BCR-ABL) could affect CXCR4 by more than one mechanism and suggest that down-regulation of CXCR4 may have important implications in chronic myelogenous leukemia pathogenesis.