Role of Lipocalin 24p3 in Apoptosis and Leukemia

描述（申请人提供）：程序性细胞死亡，细胞凋亡，是正常生理以及癌症发生和治疗的关键方面。某些凋亡通路受到转录调控；在这些情况下，细胞凋亡是由编码促凋亡蛋白的基因的转录激活诱导的。本应用的重点是24p3/24p3R转录调控的促凋亡通路，这是我们实验室在过去几年里发现并一直在研究的。我们最初确定24p3是在白细胞介素3 （IL-3）依赖细胞的细胞因子剥夺诱导凋亡后转录刺激最大的基因。24p3是一种分泌性脂钙蛋白，我们发现当加入到多种淋巴样细胞中时可诱导细胞凋亡。这些和其他结果揭示了IL-3剥夺激活24p3转录的模型，导致24p3的合成和分泌，并通过自分泌/旁分泌途径诱导细胞凋亡。我们分离了24p3细胞表面受体（24p3R），发现24p3通过一种新的途径诱导细胞凋亡，最终导致细胞内铁水平的降低。细胞内铁的减少诱导凋亡前蛋白Bim的表达，导致细胞凋亡。细胞内铁传递阻断了Bim的诱导，抑制了24p3添加或IL-3剥夺导致的细胞凋亡。在本申请中，我们提出通过细胞系、患者样本和动物模型来研究24p3/24p3R促凋亡通路在正常生理和骨髓增生性疾病中的作用。细胞内铁减少诱导细胞凋亡的基础尚不清楚。我们将继续表征24p3和铁螯合剂诱导的凋亡途径。表达谱分析和RNA干扰将用于鉴定参与24p3和铁螯合剂介导的细胞凋亡的转录激活基因。我们的初步结果表明，24p3/24p3R通路可能在糖皮质激素介导的细胞凋亡和糖皮质激素抵抗中发挥作用，我们将继续对此进行研究。我们发现BCR-ABL癌蛋白通过错调控24p3和24p3R的表达来抵消24p3/24p3R促凋亡通路。这些结果揭示了BCR-ABL促进细胞存活的机制的一个新的和意想不到的方面。我们将继续分析这一结果的普遍性，并研究24p3和24p3R转录失调的基础。我们已经获得了24p3纯合子敲除小鼠，将用于研究24p3/ 24p3r促凋亡通路在BCR/ abl诱导的骨髓增增殖性疾病中的作用。

DESCRIPTION (provided by applicant): Programmed cell death, apoptosis, is a critical aspect of normal physiology as well as the genesis and treatment of cancer. Certain apoptotic pathways are transcriptionally regulated; in these cases, apoptosis is induced by the transcriptional activation of genes encoding proapoptotic proteins. This application focuses on the 24p3/24p3R transcriptionally-regulated proapoptotic pathway that our laboratory discovered and has been studying for the past several years. We originally identified 24p3 as the gene undergoing maximum transcriptional stimulation following induction of apoptosis by cytokine-deprivation of interleukin 3 (IL-3) dependent cells. 24p3 is a secreted lipocalin, which we have found induces apoptosis when added to a variety of lymphoid cells. These and other results revealed a model in which IL-3 deprivation activates 24p3 transcription, leading to synthesis and secretion of 24p3, which induces apoptosis through an autocrine/paracrine pathway. We have isolated the 24p3 cell surface receptor (24p3R) and found that 24p3 induces apoptosis through a novel pathway culminating in a decrease in intracellular iron levels. The decrease in intracellular iron induces expression of the proapoptotic protein Bim, resulting in apoptosis. Intracellular iron delivery blocks induction of Bim and suppresses apoptosis due to 24p3 addition or IL-3 deprivation. In this application we propose experiments to study the role of the 24p3/24p3R proapoptotic pathway in normal physiology and myeloproliferative disease using cell lines, patient samples and animal models. The basis by which decreased intracellular iron induces apoptosis is not well understood. We will continue to characterize the apoptotic pathway induced by 24p3 and by iron chelators. Expression profiling and RNA interference will be used to identify transcriptionally activated genes involved in 24p3- and iron chelator-mediated apoptosis. Our preliminary results suggest a possible role for the 24p3/24p3R pathway in glucocorticoid-mediated apoptosis and glucocorticoid-resistance, which we will continue to investigate. We have found that the BCR-ABL oncoprotein counteracts the 24p3/24p3R proapoptotic pathway by misregulating expression of 24p3 and 24p3R. These results reveal a new and unanticipated aspect of the mechanism by which BCR-ABL promotes cell survival. We will continue to analyze the generality of this result and study the basis by which 24p3 and 24p3R transcription is misregulated. We have derived 24p3 homozygous knockout mice, which will be used to study the contribution of the 24p3/24p3R proapoptotic pathway to BCR/ABL-induced myeloproliferative disease.