Cytokine Regulation of Normal and Neoplastic Hematopoietic Cell Growth

在造血过程中，需要从少量干细胞中不断产生8种不同谱系的大量成熟细胞，这需要一系列高度复杂的事件。造血干细胞（HSC）可以保持数月的静止状态，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是由可溶性或细胞外介质调节的，这些介质可以在给定的细胞类型上具有重叠，附加和/或相反的功能。转化生长因子β -1 （TGF-b1）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-b是造血所有阶段的调节因子。当前的重点是进一步确定TGF-b的生理相关性，并确定其发挥各种复杂作用的机制。重要的问题仍有待回答。TGF-b对造血的多效作用是由细胞内介质Smad2和Smad3的不同作用引起的，还是与其他信号转导途径的串扰引起的？自分泌和旁分泌TGF-b在HSC调节中的相对作用是什么？细胞内TGF-b信号的改变能改变分化结果吗？我们发现TGF-b1通过自分泌和旁分泌机制调节HSC的沉默和存活。此外，造血干细胞中自分泌TGF-b的中和导致骨髓移植所需的细胞更少，移植速度更快。相反，在造血干细胞因子存在的情况下，人造血干细胞中自分泌TGF-b的中和会在红细胞生成素缺乏的情况下刺激红细胞祖细胞的产生。明确自分泌TGF-b调控HSC的机制将提供新的治疗机会。此外，我们发现Smad2/3是细胞内传感器，在药物作用下调节髓细胞分化的承诺。全反式维甲酸（ATRA）通过刺激磷酸酶活性刺激粒细胞分化，使Smad2/3去磷酸化；而维生素D3通过磷酸化Smad2/3刺激单核细胞分化。此外，MAPK信号通路的不同成员和Smad通路之间的串扰会改变髓系和红系分化的结果。此外，我们已经证明Smad2和Smad3对早期造血功能有不同的影响。因此，特定信号的衰减对造血结果有深远的影响。由于TGF-b、其受体和下游效应物（smad）的改变都与肿瘤发生有关，这些研究可以为恶性过程提供见解。TGF-b1通过限制细胞周期的G1期来抑制增殖，部分是通过细胞周期抑制剂等基因的快速转录激活。我们最近发现了另一种肿瘤抑制基因tuberlin sclerosis gene product 2，可导致G1期生长停滞，它直接与Smad2相互作用，并由TGF-b介导转录激活。此外，我们已经证明，在髓细胞中，tuberin是tgf -b1调控的转录和分化事件的强大刺激物。因此，失去功能性结节蛋白和/或Smads可导致细胞增殖失控，分化受阻。因此，TGF-b1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合作能力为研究癌症的发展提供了一个令人兴奋和重要的新途径。这一点最近得到了国会的认可，它要求NCI研究结节性硬化症（TSC），这是一种遗传性疾病，会引发身体多个器官的不可控肿瘤生长，包括大脑、心脏、肾脏、肺、肝、眼睛或皮肤。鉴于它与癌细胞不受控制的生长有相似之处。许多科学家认为，确定TSC中肿瘤生长的原因也可能为癌症的治愈和治疗开辟道路。委员会鼓励NCI支持研究TSC的分子和细胞基础以及TSC在肿瘤发展中的作用的项目。它与tgf - β途径相互作用的能力是理解这一过程的一个新环节。

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. This was recently recognized by congress in that it asked the NCI to study Tuberous sclerosis complex (TSC),a genetic disorder that triggers uncontrollable tumor growth in multiple organs of the body, including the brain, heart, kidneys, lungs, liver, eyes or skin. In light of its similarities to the uncontrolled growth of cancer cells. Many scientists believe that determining the cause of tumor growth in TSC could open the way for cures and treatments for cancer as well. The Committee encourages NCI to support programs examining the molecular and cellular basis of TSC, and the role of TSC in tumor development. Its ability to interact with TGF-beta pathway is an new link in understanding this process.