Dysregulation of the Tumor Microenvironment in Hepatocellular Carcinoma

描述(申请人提供)：肝细胞癌是全球第三大癌症死亡原因。肝细胞癌发生和发展的间质改变很重要，但还不完全清楚。慢性炎症导致的肝硬变是肝细胞癌发生发展的最重要的危险因素，因此间质微环境的改变在肝细胞癌的发生发展中具有重要意义。肝硬变的特征是星状细胞/周细胞的激活和增殖以及随之而来的细胞外基质(ECM)的扩张。星状细胞的激活依赖于血小板衍生生长因子(PDGF)和转化生长因子(TGF-β)的信号传递，PDGF是一种肝素结合生长因子，转化生长因子-β储存在与潜在的转化生长因子-β结合蛋白结合的ECM中，并由硫酸乙酰肝素蛋白多糖(HSPG)辅受体转化生长因子-βR3呈递给转化生长因子-β2激活受体。作为对PDGF的反应，周细胞产生成纤维细胞生长因子、肝细胞生长因子和血管内皮生长因子，这些细胞反过来又可以作用于肿瘤细胞和内皮细胞，产生正反馈循环，推动癌症的发生。我们已经证明，最近发现的肝素降解硫酸酯酶SULF2与人肝癌的肿瘤复发和较差的预后有关，并促进了肝癌裸鼠移植瘤的生长；相反，相关的硫酸酯酶SULF1具有肿瘤抑制作用。SULF2是由肿瘤细胞分泌到细胞外基质中，并在氨基葡萄糖的6-O位脱除HSPG。肝素结合生长因子与HSPGs的结合需要6-O硫代反应。通过脱除HSPGs，SULF2减少了HSPGs与生长因子的结合，将它们从细胞表面和细胞外基质中释放出来，并使它们能够与其受体结合。我们推测SULF2释放PDGF和转化生长因子β，促进星状细胞激活、血管生成和肿瘤生长。在特定的目标1中，我们将测试SULF2通过在ECM和星状细胞表面脱硫HSPG来从存储位置释放PDGF和TGF-β的假设。在特定的目标2中，我们将检验这样一种假设，即肝癌细胞表达SULF2增强了PDGF和转化生长因子β对星形细胞的激活，并刺激了肿瘤的生长。在特定的目标3中，我们将检验SULF1拮抗SULF2对PDGF和TGF-β介导的星状细胞激活的影响的假设。这些研究的成功完成将为肿瘤-间质相互作用在肝癌分子发病机制中的作用提供新的见解，并可能导致针对肝癌的合理靶向治疗策略的发展。与公共卫生相关：在过去20年中，美国的原发性肝癌发病率翻了一番，这主要是由于丙型肝炎病毒感染率的增加。如果及早发现，肝癌可以通过手术或移植治疗，但在其他情况下，由于没有有效的晚期疾病化疗方法，肝癌很快就会致命。这项研究将调查最近发现的促进肝癌生长的硫酸酶的功能，目的是为这种毁灭性的疾病开发有效的治疗方法。

DESCRIPTION (provided by applicant): Hepatocellular carcinoma (HCC) is the third leading cause of cancer death worldwide. The stromal changes underlying the development and progression of HCC are important but incompletely understood. Chronic inflammation resulting in liver cirrhosis is the most important risk factor for the development of HCC, hence changes in the stromal microenvironment must be important in the development and progression of HCC. Cirrhosis is characterized by activation and proliferation of stellate cells/pericytes and consequent expansion of the extracellular matrix (ECM). Stellate cell activation is dependent on signaling by platelet-derived growth factor (PDGF), a heparin-binding growth factor, and transforming growth factor-¿ (TGF-¿) which is stored in the ECM bound to latent TGF-¿ binding proteins and is presented to the TGF¿R2 activating receptor by the heparan sulfate proteoglycan (HSPG) coreceptor TGF¿R3. In response to PDGF, pericytes produce FGF, HGF, and VEGF, which, in turn, can act on tumor cells and endothelial cells, creating positive feedback loops that drive carcinogenesis. We have shown that the recently identified heparin-degrading endosulfatase, SULF2, is associated with tumor recurrence and worse prognosis of human HCC and promotes the growth of HCC xenografts in nude mice; in contrast, the related sulfatase SULF1 has a tumor suppressor effect. SULF2 is secreted by tumor cells into the ECM and desulfates HSPGs at the 6-O position of glucosamine. 6-O sulfation is required for binding of heparin-binding growth factors to HSPGs. By desulfating HSPGs, SULF2 decreases the binding of HSPGs to growth factors, releases them from the cell surface and ECM, and makes them available for binding to their receptors. We hypothesize that SULF2 releases PDGF and TGF-¿ and promotes stellate cell activation, angiogenesis and tumor growth. In Specific Aim 1 we will test the hypothesis that SULF2 releases PDGF and TGF-¿ from storage sites by desulfating HSPGs in the ECM and at the stellate cell surface. In Specific Aim 2 we will test the hypothesis that expression of SULF2 by HCC tumor cells enhances stellate cell activation by PDGF and TGF-¿ and stimulates tumor growth. In Specific Aim 3, we will test the hypothesis that SULF1 antagonizes the effects of SULF2 on PDGF- and TGF-¿-mediated stellate cell activation. Successful completion of these studies will provide novel insight into the role of tumor-stromal interactions in the molecular pathogenesis of HCC, and may lead to the development of rational targeted therapeutic strategies against HCC. PUBLIC HEALTH RELEVANCE: The rates of development of primary liver cancer in the US have doubled over the past 20 years, primarily due to increases in hepatitis C virus infection rates. Liver cancer can be treated by surgery or transplantation if detected early, but is otherwise rapidly fatal because there are no effective chemotherapy treatments for advanced disease. This study will investigate the function of recently discovered sulfatase enzymes that enhance growth of liver cancers, with the goal of developing effective treatments for this devastating disease.