Regulation of the Tumor Microenvironment by KSHV

描述（由申请人提供）：卡波西肉瘤（KS）仍然是HIV/AIDS患者中最常见的肿瘤，累及口腔是该肿瘤最常见的临床表现之一。卡波西肉瘤相关疱疹病毒（KSHV）的复制和靶细胞的持续感染在KS发病机制中起重要作用。氨基酸膜转运蛋白亚基xCT维持细胞内谷胱甘肽的储存，以提高产生活性氮（RNS）的细胞的存活，xCT最近被确定为KSHV的融合进入受体（Kaleeba和Berger， Science, 2006）。许多细胞内和细胞外的触发因素调节xCT的表达，包括转录调控因子结合xCT启动子和RNS激活正转录调控因子。我们最近已经确定，xCT在KS病变中的多种细胞类型和HIV感染患者的循环单核细胞中表达，其中KSHV/HIV合并感染患者的细胞中xCT表达最高。然而，尚不清楚KSHV本身是否调节xCT表达以促进KSHV在局部环境中的感染和持续。KSHV感染KS病变内的巨噬细胞，巨噬细胞是RNS的主要来源。通过一种新的巨噬细胞培养系统，我们的初步数据表明，KSHV microRNA抑制xCT表达的负转录调节因子bach1，并且KSHV诱导巨噬细胞分泌RNS。基于这些初步数据，我们假设KSHV通过旁分泌和自分泌机制上调xCT表达来促进自身在局部环境中的持久性，并且靶向xCT调节途径可以减少KSHV在微环境中的感染和持久性。为了解决这一假设，我们提出了两个独立的目标：1)确定KSHV调节xCT的机制和功能结果；2)确定KSHV感染、xCT表达和RNS产生在KS高危hiv感染者中的临床关系。通过这些努力，我们希望通过靶向xCT和减少KSHV感染和肿瘤微环境中的持久性，为开发新的KS治疗策略提供框架。

DESCRIPTION (provided by applicant): Kaposi's sarcoma (KS) remains the most common tumor arising in patients with HIV/AIDS, and involvement of the oral cavity represents one of the most common clinical manifestations of this tumor. Kaposi's sarcoma-associated herpesvirus (KSHV) replication and ongoing infection of target cells plays an important role in KS pathogenesis. An amino acid membrane transport protein subunit, xCT, maintains intracellular glutathione stores to enhance the survival of cells producing reactive nitrogen species (RNS), and xCT was recently identified as a fusion-entry receptor for KSHV (Kaleeba and Berger, Science, 2006). A number of intracellular and extracellular triggers regulate xCT expression, including binding of the xCT promoter by transcription regulators and the activation of positive transcription regulators by RNS. We have determined recently that xCT is expressed by multiple cell types within KS lesions and circulating mononuclear cells from HIV-infected patients, with cells from KSHV/HIV co-infected patients exhibiting the highest xCT expression. However, it is unknown whether KSHV itself regulates xCT expression to promote KSHV infection and persistence in the local environment. KSHV infects macrophages within KS lesions, and macrophages are a principal source of RNS. Using a novel macrophage cell culture system, our preliminary data suggest that KSHV microRNA suppress BACH-1, a negative transcription regulator of xCT expression, and that KSHV induces RNS secretion by macrophages. Based on these preliminary data, we hypothesize that KSHV promotes its own persistence in the local environment by upregulating xCT expression through both paracrine and autocrine mechanisms, and that targeting xCT regulatory pathways reduces KSHV infection and persistence in the microenvironment. To address this hypothesis, we propose two independent aims: 1) to determine mechanisms and functional outcomes for xCT regulation by KSHV; and 2) to determine clinical relationships between KSHV infection, xCT expression and RNS production in HIV-infected patients at greatest risk for KS. Through these efforts, we hope to provide the framework for developing novel therapeutic strategies for KS through the targeting of xCT and the reduction of KSHV infection and persistence within the tumor microenvironment. PUBLIC HEALTH RELEVANCE: Tumors etiologically linked to the Kaposi's sarcoma-associated herpesvirus (KSHV/HHV8), including Kaposi's sarcoma (KS), are among the most common tumors encountered in the setting of HIV infection and other forms of immune suppression. KS remains an important cause of morbidity and mortality for these patients in the modern era, and the efficacy and toxicity of available therapies for KS are limiting. Therefore, understanding mechanisms for how KSHV regulates expression of its own receptors and the longevity of KSHV-infected cells could provide a scientific basis for developing novel preventive and therapeutic targets for KS.