Brown T R, Stonehouse T J, Branch J S, Brickell P M, Katz D R
Department of Molecular Pathology, University College London Medical School, United Kingdom.
Exp Cell Res. 1997 Oct 10;236(1):94-102. doi: 10.1006/excr.1997.3704.
Although retinoic acid (RA) has been known for many years to be a modulating agent that plays a role in generating both granulocytes and monocytes, the molecular mechanism underlying this role has not been defined in the monoblast lineage. In particular, the part played by the retinoid X receptors (RXRs), which are members of the steroid/thyroid hormone nuclear receptor family, has not been explored. In this study, therefore, the human monoblastic leukemia cell line U937 has been used as a model system to investigate the role of one of the RXRs, RXR-alpha, in monoblast differentiation. RXR-alpha mRNA was present in untreated U937 cells, and levels increased after induction of differentiation with phorbol ester. The same was found for RXR-beta mRNA. Using plasmids containing sense or antisense RXR-alpha sequences under the control of an inducible promoter, we generated stably transfected cell lines which expressed either increased or decreased levels of RXR-alpha, respectively. The sense cell lines (U alpha S and its clonal derivative alpha G2S) showed increased sensitivity to RA, while the antisense cell lines (U alpha A and its clonal derivative alpha B5A) showed decreased sensitivity to RA, as demonstrated by growth inhibition and by regulation of an RA-responsive reporter gene. Both U alpha A and alpha B5A also failed to respond to another modulating agent, 1 alpha,25-dihydroxycholecalciferol (DHCC), but only U alpha S and not alpha G2S showed an enhanced response to DHCC. The combination of RA and DHCC together inhibited growth of both sense and antisense cell lines. In addition, alpha G2S exhibited increased expression of CD11b and CD54, while alpha B5A cells showed increased expression of CD102, suggesting that RXR-alpha has a role in regulating expression of cell adhesion molecules in U937 cells. These results demonstrate that RXR-alpha has a role in mediating growth inhibition and cell adhesion during myelomonocytic differentiation, and suggest that different species of heterodimers involving RXR-alpha may control the acquisition of different features of mature monocyte/macrophage function.
尽管多年来已知视黄酸（RA）是一种调节因子，在粒细胞和单核细胞的生成中发挥作用，但单核母细胞谱系中这一作用的分子机制尚未明确。特别是，作为类固醇/甲状腺激素核受体家族成员的视黄酸X受体（RXRs）所起的作用尚未得到探索。因此，在本研究中，人类单核母细胞白血病细胞系U937被用作模型系统，以研究RXR之一的RXR-α在单核母细胞分化中的作用。未处理的U937细胞中存在RXR-α mRNA，在用佛波酯诱导分化后其水平升高。RXR-β mRNA也有同样的情况。使用在可诱导启动子控制下含有RXR-α序列的正义或反义质粒，我们分别生成了稳定转染的细胞系，其RXR-α水平分别升高或降低。正义细胞系（UαS及其克隆衍生物αG2S）对RA的敏感性增加，而反义细胞系（UαA及其克隆衍生物αB5A）对RA的敏感性降低，这通过生长抑制和对RA反应性报告基因的调节得以证明。UαA和αB5A对另一种调节因子1α,25-二羟基胆钙化醇（DHCC）也无反应，但只有UαS而非αG2S对DHCC表现出增强的反应。RA和DHCC联合使用可抑制正义和反义细胞系的生长。此外，αG2S表现出CD11b和CD54表达增加，而αB5A细胞表现出CD102表达增加，这表明RXR-α在调节U937细胞中细胞黏附分子的表达中起作用。这些结果表明，RXR-α在骨髓单核细胞分化过程中介导生长抑制和细胞黏附，并且提示涉及RXR-α的不同种类的异二聚体可能控制成熟单核细胞/巨噬细胞功能不同特征的获得。
