Takamatsu Y, Simmons P J, Lévesque J P
Matthew Roberts Foundation Laboratory, Leukaemia Research Unit, Hanson Centre for Cancer Research, Adelaide, Australia.
Cell Adhes Commun. 1998 Jul;5(5):349-66. doi: 10.3109/15419069809010781.
Beta-1 integrins have essential functions in hemopoietic and immune systems by controlling phenomenons such as cell homing and cell activation. The function alpha 4 beta 1 and alpha 5 beta 1 integrins is regulated by divalent cations and, as demonstrated more recently, by mitogenic cytokines which activate them by "inside-out" mechanisms. Using the adhesive interaction of a cytokine-dependent human hemopoietic cell line to immobilized fibronectin, we have analyzed the requirements in divalent cations Mn2+, Mg2+ and Ca2+ for alpha 4 beta 1 and alpha 5 beta 1 activation by "inside-out" mechanisms triggered by cytokines such as granulocyte-macrophage colony stimulating factor or KIT ligand, or by external conformational constraints with the function-activating anti-beta 1 integrin monoclonal antibody 8A2. The intrinsic difference between these two modes of beta 1 integrin activation was revealed by their different requirements in divalent cations. We found that in the absence of any divalent cations, alpha 4 beta 1 and alpha 5 beta 1 were non-functional even after further stimulation by cytokines or 8A2. However, whilst either Ca2+, Mg2+ or Mn2+ were able to restore adhesive functions of alpha 4 beta 1 and alpha 5 beta 1 when activated by 8A2, only Mg2+ and Mn2+ were able to support activation of alpha 4 beta 1 and alpha 5 beta 1 by cytokines. Furthermore, high concentrations of Ca2+ exceeding 20 mM dramatically inhibited cell adhesion to fibronectin induced by Mn2+ and cytokines but not by 8A2. On the contrary, in the presence of both Ca2+ and Mg2+, Mn2+ had an additive effect on the activation of alpha 4 beta 1 and alpha 5 beta 1 by mitogenic cytokines. The presence of the absence of these divalent cations did not inhibit early tyrosine phosphorylation induced by the binding of KIT ligand to its tyrosine-kinase receptor KIT. Therefore, we propose that in hemopoietic cells, Ca2+, Mg2+ and Mn2+ may modulate in vivo alpha 4 beta 1 and alpha 5 beta 1 regulation by mitogenic cytokines, a phenomenon involved in the regulation of hemopoietic progenitor cell homing within the bone marrow.
β1整合素在造血和免疫系统中发挥着重要作用，可控制细胞归巢和细胞激活等现象。α4β1和α5β1整合素的功能受二价阳离子调节，最近的研究表明，有丝分裂细胞因子也可通过“由内向外”机制激活它们。利用一种依赖细胞因子的人造血细胞系与固定化纤连蛋白的黏附相互作用，我们分析了二价阳离子Mn2+、Mg2+和Ca2+对α4β1和α5β1通过“由内向外”机制激活的需求，这些机制由粒细胞-巨噬细胞集落刺激因子或KIT配体等细胞因子触发，或由功能激活的抗β1整合素单克隆抗体8A2产生的外部构象限制触发。这两种β1整合素激活模式的内在差异通过它们对二价阳离子的不同需求得以揭示。我们发现，在没有任何二价阳离子的情况下，即使在细胞因子或8A2进一步刺激后，α4β1和α5β1也无功能。然而，当由8A2激活时，Ca2+、Mg2+或Mn2+中的任何一种都能够恢复α4β1和α5β1的黏附功能，只有Mg2+和Mn2+能够支持细胞因子对α4β1和α5β1的激活。此外，超过20 mM的高浓度Ca2+会显著抑制Mn2+和细胞因子诱导的细胞与纤连蛋白的黏附，但不会抑制8A2诱导的黏附。相反，在同时存在Ca2+和Mg2+的情况下，Mn2+对有丝分裂细胞因子激活α4β1和α5β1具有累加效应。这些二价阳离子的存在与否并不抑制KIT配体与其酪氨酸激酶受体KIT结合诱导的早期酪氨酸磷酸化。因此，我们提出，在造血细胞中，Ca2+、Mg2+和Mn2+可能在体内调节有丝分裂细胞因子对α4β1和α5β1的调控，这一现象参与了造血祖细胞在骨髓内归巢的调控。
