Human Endogenous Retroviral Sequences (HERVs) in the development and progression of human glioblastoma

胶质瘤是美国最常见的恶性脑肿瘤，其中约20%是胶质母细胞瘤，是最具侵袭性且几乎无法治愈的肿瘤。耐药通常与离散的细胞群体的存在有关，这些细胞表现为干细胞样表型。在胶质母细胞瘤中，这些细胞被称为胶质瘤初始细胞(GICs)，它们的扩张通常与肿瘤复发有关。人类内源性逆转录病毒序列(HERV)是病毒来源的可移动元件，占人类基因组的近8%。在HERV中，就像在所有逆转录病毒中一样，编码病毒蛋白的基因两侧有长末端重复序列(LTRs)。作为启动子，LTRs尤其富含转录因子的结合基序。重要的是，最近的研究表明，在人类早期发育，包括中枢神经系统发育期间，当细胞多能性和干细胞样表型占主导地位时，HERV转录本上调。HERV基因的重新激活也与不同的肿瘤相关，然而，HERV与癌症之间的因果关系尚未建立。因此，HERV对胶质母细胞瘤干细胞样表型的形成和维持的影响以及相关的耐药性，需要进一步的研究。我们推测，在胶质母细胞瘤临床标本中发现的HERV的异常表达有助于胶质母细胞瘤干细胞样表型的增强和相关的耐药性。我们将通过执行由两个独立但逻辑相连的特定目标组成的实验计划来验证这一一般假设：在目标1中，我们将确定HERV在神经胶质瘤中的转录水平，并分析HERV的高转录是否与：a)特定的胶质母细胞瘤亚型：前神经性(17个月存活)、经典型(14个月存活)、间叶性(11.5个月存活)，与低级别胶质瘤(90%可治愈)相比；b)胶质母细胞瘤干细胞特异性转录模式。在目标2中，我们将分析基于可诱导的Crisp/Cas的HERV转录上调和下调分别对低级别胶质瘤和胶质母细胞瘤的干样表型和恶性生长的影响。长期目标是确定HERV转录本在建立高度恶性的胶质母细胞瘤表型中的作用，并利用这一知识开发针对这些终末期脑肿瘤的新的治疗策略。

Glial tumors are the most commonly occurring malignant brain tumor in the United States, among which approximately 20% are glioblastomas, which are the most aggressive and practically incurable. Drug resistance is often associated with the existence of a discrete population of cells, which demonstrate a stemlike phenotype. In glioblastoma, these cells are known as glioma initialing cells (GICs), and their expansion is often linked with tumor recurrence. Human endogenous retroviral sequences (HERVs) are mobile elements of the viral origin that comprise nearly 8% of the human genome. In HERVs, like in all retroviruses, genes encoding viral proteins are flanked by long terminal repeats (LTRs). Serving as promoters, LTRs are particularly enriched in binding motifs for transcription factors. Importantly, recent studies show that HERV transcripts are upregulated during early human development, including CNS development, when cellular pluripotency and stem-like phenotype predominate. Reactivation of HERV loci are also associated with different tumors, however, the cause and effect relationship between HERVs and cancer have not been established. Therefore, the effect/s of HERVs on the development and maintenance of stem-like phenotype in glioblastoma tumors, and the associated drug resistance, require further investigation. We hypothesize that aberrant expression of HERVs found in glioblastoma clinical samples contributes to the enhanced glioblastoma stem-like phenotype and associated drug resistance. We will test this general hypothesis by executing our experimental plan that consists of two independent but logically connected Specific Aims: In Aim 1 we will determine HERV transcript levels in glial tumors, and analyze if high HERV transcription correlates with: a) specific glioblastoma subtype: pro-neural (17 months survival), classical (14 months survival), mesenchymal (11.5 months survival), as compared to low-grade gliomas (90% curable); b) glioblastoma stem-specific transcription pattern. In Aim 2 we will analyze effects of inducible Crisp/Cas-based -upregulation and -downregulation of HERV transcripts on stem-like phenotype and malignant growth of low grade gliomas and glioblastomas, respectively. The long-term objective is to establish the role of HERV transcripts in establishing highly malignant phenotype of glioblastoma, and to use this knowledge in the development of new therapeutic strategies against these terminal brain neoplasms.