Cytokine Regulation of Normal and Neoplastic Hematopoiet

在造血中，需要从少量干细胞连续产生大量八种不同谱系的成熟细胞，这需要一系列高度复杂的事件。造血干细胞（HSC），可以保持静止数月，必须保持分化成所有谱系，自我更新和长期再生骨髓（LTRA）的能力。控制造血的许多关键相互作用由可溶性或细胞外介质调节，所述介质可以对给定细胞类型具有重叠、相加和/或相反的功能。转化生长因子β-1（TGF-β 1）是造血的关键调节因子之一，因为我们的体外和体内研究表明TGF-β 1是造血所有阶段的调节因子。目前的优先事项是进一步确定TGF-β的生理相关性，并确定其发挥其各种复杂作用的机制。重要的问题仍有待回答。TGF-β对造血的多效性作用是由细胞内介质Smad 2和Smad 3的不同作用引起的，还是与其他信号转导途径的串扰？自分泌和旁分泌TGF-β在HSC调节中的相对作用是什么？细胞内TGF-β信号的改变能否改变分化结果？我们发现TGF-β 1通过自分泌和旁分泌机制调节HSC的静止和存活。此外，HSC中自分泌TGF-β的中和导致骨髓移植所需细胞更少的更快速的植入。相反，在干细胞因子存在下，人HSC中自分泌TGF-β的中和在促红细胞生成素不存在下刺激红系祖细胞的产生。明确TGF-β自分泌调节HSC的作用机制将带来新的治疗机会。此外，我们已经发现，Smad 2/3是细胞内传感器，调节承诺的髓样分化，以响应药物。全反式视黄酸（ATRA）通过刺激磷酸酶活性（其使Smad 2/3去磷酸化）来刺激粒细胞分化;而维生素D3通过Smad 2/3的磷酸化来刺激单核细胞分化。此外，MAPK信号通路和Smad通路的不同成员之间的串扰改变了髓系和红系分化的结果。此外，我们已经表明Smad 2和Smad 3对早期造血功能有不同的影响。因此，特异性信号的衰减对造血结果具有深远的影响。由于TGF-β、其受体和下游效应子（SMADs）的改变都与肿瘤发生有关，因此这些研究可以为恶性过程提供见解。TGF-β 1通过限制通过细胞周期的G1期来抑制增殖，部分是通过快速转录激活基因如细胞周期抑制剂。我们最近发现tuberlin硬化症基因产物2，另一种在G1期引起生长停滞的肿瘤抑制基因，直接与Smad 2相互作用，这是一种由TGF-β介导的转录激活。此外，我们已经表明，块茎蛋白是一个强大的刺激因子TGF-β 1调节转录和分化的髓细胞的事件。因此，功能性块茎蛋白和/或Smads的损失可导致不受控制的细胞增殖，并阻断分化。因此，TGF-β 1调节的微妙而慢性的变化可导致病理生理状态。这两个肿瘤抑制基因家族在细胞功能上的协作能力为有关癌症发展的研究提供了一个令人兴奋和重要的新途径。

In hematopoiesis, the need to continuously generate large numbers of maturing cells of eight distinct lineages from small numbers of stem cells requires a highly complex series of events. Hematopoietic stem cells (HSC), which can remain quiescent for months, must retain the abilities to differentiate into all lineages, to self-renew and to long-term repopulation marrow (LTRA). Numerous critical interactions controlling hematopoiesis are regulated by soluble or extracellular mediators which can have overlapping, additive and/or opposing functions on a given cell type. Transforming growth factor beta-1 (TGF-b1) is one of these critical regulators of hematopoiesis since our in vitro and in vivo work indicates that TGF-b is a regulator of all stages of hematopoiesis. A current priority is to further define the physiological relevance of TGF-b and determine the mechanisms by which it exerts its varied and complex effects. Important questions remain to be answered. Are the pleiotropic effects of TGF-b on hematopoiesis caused by distinct roles for intracellular mediators, Smad2 and Smad3, or crosstalk with other signal transduction pathways? What are the relative contributions of autocrine and paracrine TGF-b in HSC regulation? Can alteration of intracellular TGF-b signals alter differentiation outcomes? We have found that TGF-b1 regulates both HSC quiesence and survival through autocrine and paracrine mechanisms. Furthermore, neutralization of autocrine TGF-b in HSC causes a more rapid engraftment with fewer cells needed for bone marrow transplantation. In contrast, neutralization of autocrine TGF-b in human HSC in the presence of stem cell factor stimulates the production of erythroid progenitors in the absence of erythropoietin. Defining the mechanism(s) of autocrine TGF-b actions on regulating HSC will present new therapeutic opportunities. Furthermore, we have found that Smad2/3 are intracellular sensors that regulate commitment to myeloid differentiation in response to pharmacologic agents. All trans retinoic acid (ATRA) stimulates granulocytic differentiation by stimulating a phosphatase activity which dephosphorylates Smad2/3; while vitamin D3 stimulates monocytic differentiation through phosphorylation of Smad2/3. In addition, crosstalk between different members of the MAPK signaling pathways and the Smad pathway alters the outcomes of myeloid and erythroid differentiation. In addition, we have shown that Smad2 and Smad3 have different effects on early hematopoietic function. Thus, attenuation of specific signals has profound effects on hematopoietic outcomes. Since alterations in TGF-b, its receptors and downstream effectors (SMADs) have all been implicated in tumorigenesis, these studies could provide insights into malignant processes. TGF-b1 inhibits proliferation by restricting passage through the G1 phase of the cell cycle, in part through rapid transcriptional activation of genes such as cell cycle inhibitors. We recently found the tuberlin sclerosis gene product 2, another tumor suppressor gene that causes growth arrest in G1, directly interacts with Smad2 an transcriptional activation mediated by TGF-b (manuscript in press). Moreover, we have shown that tuberin is a powerful stimulator of TGF-b1-regulated transcription and differentiation events in the myeloid cells. Thus, the losses of functional tuberin and/or Smads can result in uncontrolled cell proliferation with a block in differentiation. Thus, subtle yet chronic changes in TGF-b1 regulation can lead to pathophysiological states. This ability of two tumor suppressor gene families to collaborate in cellular functions provides an exciting and important new avdenue of study pertaining to the development of cancers.