Effect of mutational inactivation of tyrosine kinase activity on BCR/ABL-induced abnormalities in cell growth and adhesion in human hematopoietic progenitors

Chronic myelogenous leukemia (CML) results from transformation of a primitive hematopoietic cell by the BCR/ABL gene. The specific BCR/ABL signaling mechanisms responsible for transformation of primitive human hematopoietic cells are not well defined. Previous studies have suggested that constitutively activated tyrosine kinase activity plays an important role for in abnormal proliferation of CML progenitors but has not clearly defined its role in abnormal adhesion and migration. We established a human progenitor model of CML by ectopic expression of BCR/ABL in normal CD34+ cells using retrovirus-mediated gene transfer. CD34+ cells expressing BCR/ABL demonstrated several features characteristic of primary CML progenitors including increased proliferation in committed and primitive progenitor culture, reduced adhesion to fibronectin, and reduced chemotaxis to stroma-derived factor-1α. We expressed a kinase-inactive BCR/ABL gene to directly investigate the role of kinase activity in abnormal progenitor function. Abnormalities in proliferation were completely reversed, whereas defects in adhesion and migration were significantly improved but not completely reversed in cells expressing a kinase-inactive BCR/ABL. Furthermore, the BCR/ABL kinase inhibitor imatinib mesylate markedly inhibited proliferation of BCR/ABL-expressing progenitors but did not fully correct the adhesion and migration defects. Expression of BCR/ABL genes with deletions of either the COOH-terminal actin binding or proline-rich domains resulted in enhanced adhesion and chemotaxis compared with wild-type BCR/ABL but did not affect progenitor proliferation. We conclude that abnormal kinase activity is essential for abnormal proliferation and survival of CML progenitors but that abnormal adhesion and migration result from both kinase-dependent and -independent mechanisms.