Bhatia R, McCarthy J B, Verfaillie C M
Department of Medicine, University of Minnesota, Minneapolis, USA.
Blood. 1996 May 1;87(9):3883-91.
Chronic myelogenous leukemia (CML) progenitors show decreased adhesion to stroma and fibronectin (FN) through beta 1 integrin receptors. We have previously shown that interferon-alpha (IFN-alpha) restores beta 1 integrin-mediated adhesion of CML progenitors to stroma. Because beta1 integrins transmit proliferation inhibitory signals from the microenvironment to normal hematopoietic progenitors, we hypothesized that decreased integrin-mediated adhesion of CML progenitors contributes to their continuous proliferation when in contact with stroma and that IFN-alpha treatment, by restoring integrin-mediated adhesion, also restores integrin-mediated microenvironmental inhibition of CML progenitor proliferation. We show here that, in contrast to normal colony-forming cells (CFC), the percentage of malignant CML CFC in S-phase was not significantly reduced following coculture with stromal layers. However, IFN-alpha treatment resulted in a significant reduction in the proliferation of CML CFC on coculture with stroma. This effect was not because of a direct antiproliferative effect of IFN-alpha on CML CFC because the proliferation of IFN-alpha treated CML CFC kept in suspension culture was not reduced. We examined the role of restored signaling through beta 1 integrin receptors in IFN-alpha induced inhibition of CML progenitors in two sets of experiment. In the first set of experiments, we demonstrated that proliferation of IFN-alpha-treated CML CFC, but not untreated CML CFC, was significantly reduced following coculture with 33/66-kD and 75-kD FN fragments, recognized by alpha 4 beta 1 and alpha 5 beta 1 integrins respectively. In a second set of experiments, we demonstrate that direct stimulation of integrin receptors by crosslinking with blocking antibodies to alpha 4, alpha 5, and beta 1 integrins and secondary goat antimouse antibodies resulted in significant reduction in proliferation of normal and IFN-alpha treated CML progenitors but not untreated CML CFC. These studies indicate that CML hematopoietic progenitors are unresponsive to beta 1-integrin mediated proliferation inhibition and that IFN-alpha not only restores beta 1 integrin-mediated adhesion but also beta1-mediated microenvironmental inhibition of CML progenitor proliferation. These observations may explain, at least in part, the therapeutic efficacy of IFN-alpha in CML.
慢性粒细胞白血病（CML）祖细胞通过β1整合素受体对基质和纤连蛋白（FN）的黏附能力下降。我们之前已经表明，α干扰素（IFN-α）可恢复β1整合素介导的CML祖细胞与基质的黏附。由于β1整合素可将增殖抑制信号从微环境传递至正常造血祖细胞，我们推测CML祖细胞整合素介导的黏附能力下降导致其与基质接触时持续增殖，而IFN-α治疗通过恢复整合素介导的黏附，也恢复了整合素介导的对CML祖细胞增殖的微环境抑制作用。我们在此表明，与正常集落形成细胞（CFC）不同，恶性CML CFC在与基质层共培养后，S期的百分比并未显著降低。然而，IFN-α治疗导致CML CFC与基质共培养时的增殖显著降低。这种效应并非由于IFN-α对CML CFC的直接抗增殖作用，因为悬浮培养的经IFN-α处理的CML CFC的增殖并未降低。我们在两组实验中研究了通过β1整合素受体恢复信号传导在IFN-α诱导的对CML祖细胞的抑制中的作用。在第一组实验中，我们证明，与分别被α4β1和α5β1整合素识别的33/66-kD和75-kD FN片段共培养后，经IFN-α处理的CML CFC的增殖显著降低，而未经处理的CML CFC则未降低。在第二组实验中，我们证明，用针对α4、α5和β1整合素的阻断抗体和二抗山羊抗小鼠抗体交联直接刺激整合素受体，导致正常和经IFN-α处理的CML祖细胞的增殖显著降低，但未经处理的CML CFC则未降低。这些研究表明，CML造血祖细胞对β1整合素介导的增殖抑制无反应，且IFN-α不仅恢复了β1整合素介导的黏附，还恢复了β1介导的对CML祖细胞增殖的微环境抑制作用。这些观察结果至少可以部分解释IFN-α在CML中的治疗效果。
