THE L-ARGININE: NO PATHWAY IN MAMMARY TUMOR PROGRESSION

虽然一氧化氮（NO）调节肿瘤的发展已成为共识，但它是否抑制或刺激血管生成和转移扩散仍不确定。 NO的细胞抑制作用支持了它具有抗肿瘤作用的信念。 然而，来自非可比性实验系统的相互矛盾的数据使NO对肿瘤进展的影响不确定。 因此，需要全面研究NO对肿瘤进展的影响。 它需要一个适当的模型系统，考虑到两个协调事件，合作产生NO：（i）激活NOS 2基因表达，和（ii）运输足够量的NO底物L-精氨酸。 高度有用的肿瘤模型系统采用多瘤中T致癌转基因（PyV-mT）。 它在100%的女性中显示了快速、可重复、多灶性转移性乳腺癌。 通过转录控制的诱导型一氧化氮合酶（NOS 2）酶产生持续和大量的NO。 L-精氨酸是NO生成的唯一底物，其转运由特异性转运蛋白（CAT）介导。 当PyV-mT在Nos 2-/-和Cat 2-/-小鼠中表达时，该模型用于定义它们在乳腺肿瘤进展中的个体作用。 我们假设CAT 2精氨酸转运蛋白在通过NOS 2调节NO产生中发挥核心作用。 将通过使用“设计者”双基因和三基因小鼠测量乳腺癌的发生、生长、血管生成和转移来评估由NOS 2产生的NO和经由CAT 2的精氨酸转运的后果。 PyV-mT转基因是受体酪氨酸激酶（特别是cErbB 2）的替代物，是一种极致癌的转基因。 然而，cErbB 2转基因是一种更惰性的癌基因，表现出较慢的肿瘤动力学。 移植研究将确定NO对乳腺肿瘤形成的刺激作用是否是上皮细胞自主的。或者，移植实验将揭示循环和/或基质组织是否是Nos 2-/-和Nos 2 +/+小鼠之间观察到的肿瘤进展差异的原因。 将使用微血管密度分析来测量血管生成，并评估细胞凋亡的程度。 将在肿瘤细胞系和适当的荷瘤小鼠中评估CAT 2介导的L-精氨酸转运对NO产生的作用。 所提出的实验直接测试Nos 2和Cat 2基因在该模型中对血管生成、肿瘤生长和转移的作用。 这些模型系统所表现出的乳腺肿瘤进展与人类乳腺癌发展具有重要的形态学和病因学相似性。 因此，所获得的知识将是值得的，因为精氨酸的转运和NO的产生都可以通过饮食和/或改变NOS 2活性或底物通量的精氨酸类似物来调节。

Although there is consensus that nitric oxide (NO) modulates tumor development, it is unsettled whether it inhibits or stimulates angiogenesis and metastatic spread. The cytostatic effect of NO lends support to the belief that it has antitumor action. However, conflicting data from non-comparable experimental systems leave unsettled the effect of NO on tumor progression. Hence, a comprehensive investigation of the effects of NO on tumor progression is needed. It requires an adequate model system that takes into account two coordinate events that cooperate to produce NO: (i) The activation of NOS2 gene expression, and (ii) The transport of adequate amounts of the NO substrate L-arginine. A highly useful tumor model system employs the polyoma middle T oncogenic transgene (PyV-mT). It elicits rapid, reproducible, multifocal metastatic mammary adenocarcinoma in 100 percent of females. Sustained and copious NO production occurs via the transcriptionally controlled inducible nitric oxide synthase (NOS2) enzyme. Transport of the sole substrate for NO production, L-arginine is mediated by specific transporters (CATs). When PyV-mT is expressed in either Nos2-/- and Cat2-/- mice, the models serve to define their individual roles in breast tumor progression. We postulate that the CAT2 arginine transporter plays a central role in the regulated production of NO via NOS2. The consequences of NO produced from NOS2 and arginine transport via CAT2, will be assessed by measuring the occurrence, growth, angiogenesis and metastasis of mammary adenocarcinoma using "designer" bigenic and trigenic mice. The PyV-mT transgene is a surrogate for receptor tyrosine kinase (specifically cErbB2) and is an extremely oncogenic transgene. However, the cErbB2 transgene is a more indolent oncogene exhibiting slower tumor kinetics. Transplantation studies will determine whether the stimulatory effect of NO on mammary tumor formation is epithelial cell autonomous. Alternatively, transplant experiments will reveal if circulating and/or stromal tissues are responsible for the differences in tumor progression observed between Nos2-/- and Nos2+/+ mice. An analysis of the microvascular density will be used to measure angiogenesis and the extent of apoptosis will be assessed. The role of CAT2 mediated L-arginine transport on NO production will be assessed in tumor cell lines and in appropriate tumor bearing mice. The proposed experiments directly test the role of Nos2 and Cat2 genes on angiogenesis, tumor growth, and metastasis in this model. The mammary tumor progression exhibited by these model systems have important morphological and etiological similarities with human breast cancer development. Hence, the knowledge gained will be worthwhile since both the transport of arginine and the production of NO can be modulated by diet and/or arginine analogues that modify NOS2 activity or substrate flux.