Delineating how retinoic acids regulate lipid metabolism in glioblastoma and their resistance mechanisms

摘要 胶质母细胞瘤(GBM)是最常见的原发脑肿瘤，也是所有癌症中最致命的癌症之一。主 GBM治疗面临的挑战是肿瘤细胞对各种治疗手段迅速产生耐药性。鉴于 我们对基底膜生物学的部分了解是阐明潜在耐药性的主要障碍。 机械装置。我们的实验室最近发现，GBM可以极大地改变脂质代谢，从而获得足够的脂质 因为它的快速增长。我们鉴定了固醇调节元件结合蛋白-1(SREBP-1)，它是一种 控制脂肪酸合成的转录因子在GBM中高表达，对肿瘤至关重要 成长。我们的发现最近得到了多个小组的验证，表明SREBP-1在不同的 其他癌症。然而，显著改变的脂代谢是否促进了肿瘤的抗药性 完全未知。此外，上调癌细胞中SREBP-1表达的机制仍然存在 难以捉摸。有趣的是，我们最近发现全反式维甲酸(ATRA)和13-顺式维甲酸可以显著 抑制GBM细胞SREBP-1和造脂酶的表达，并呈剂量依赖性。这些 维甲酸是治疗急性早幼粒细胞白血病的有效药物，也被用于治疗GBM 和其他实体瘤，但对肿瘤的耐药性一直非常具有挑战性。到目前为止，他们的抗肿瘤和 抗性机制仍然知之甚少。我们检测了它们的结合伙伴维甲酸的表达。 酸性核受体α(RARα)在胶质瘤患者组织中的表达，并发现其在肿瘤组织和 与SREBP-1的表达呈正相关，而与较差的患者存活率呈负相关。 有趣的是，我们的数据进一步表明，13-顺式-维甲酸和全反式维甲酸处理显著增加了 肉毒碱棕榈酰基转移酶1A是将脂肪酸运送到线粒体进行β氧化的关键酶 和能源生产。CPT1a联合维甲酸的药理抑制作用 明显的基底膜细胞死亡。总之，这些新的初步数据有力地支持了13-顺式-RA的假设 或全反式维甲酸可显著改变基底膜的脂代谢，促进脂肪酸氧化以支持肿瘤细胞 生存和抵抗。我们进一步假设，维甲酸治疗与抑制 SREBP-1活化或脂肪酸氧化可有效抑制GBM生长，克服肿瘤耐药性。 这项研究的目的是确定以前未报道的维甲酸和视黄酸受体α的作用和机制 在脂代谢调节和基底膜生长方面(目标1)，并开发有效的组合方法 目标GBM(目标2)。这项研究的完成将揭示上调SREBP-1的潜在机制 GBM的表达和脂肪生成，为理解抗肿瘤和耐药提供了重要的见解 维甲酸的作用机制，并确定靶向GBM和克服维甲酸耐药性的新策略。

ABSTRACT Glioblastoma (GBM) is the most common primary brain tumor and one of the most lethal of all cancers. The main challenge in treating GBM is the quickly developing resistance to all kinds of treatments by tumor cells. Whereas our partial understanding of GBM biology is a major roadblock to elucidate the underlying resistance mechanisms. Our laboratory recently uncovered that GBM greatly alters lipid metabolism to gain sufficient lipids for its rapid growth. We identified that sterol regulatory element-binding protein-1 (SREBP-1), a master transcription factor that controls fatty acid synthesis, is highly expressed in GBM and is essential for tumor growth. Our findings were recently validated by multiple groups showing that SREBP-1 is also elevated in various other cancers. However, whether the dramatically altered lipid metabolism facilitates tumor resistance is completely unknown. Moreover, the mechanism that upregulates SREBP-1 expression in cancer cells remains elusive. Interestingly, we recently found that all-trans retinoic acid (ATRA) and 13-cis-RA could significantly reduce the expression of SREBP-1 and lipogenic enzymes in a dose-dependent manner in GBM cells. These retinoic acids are effective drugs in treating acute promyelocytic leukemia and have also been used to treat GBM and other solid tumors, but tumor resistance has been very challenging. To date, both their antitumor and resistance mechanisms remain poorly understood. We examined the expression of their binding partner, retinoic acid nuclear receptor α (RARα) in GBM patient tissues and found it to be highly expressed in tumor tissues and positively correlated with SREBP-1 expression, while inversely associated with poor patient survival. Interestingly, our data further show that 13-cis-RA and ATRA treatment significantly increased the expression of carnitine palmitoyltransferase 1A (CPT1A), a key enzyme shuttling fatty acids into mitochondria for β-oxidation and energy production. Pharmacological inhibition of CPT1A combined with retinoic acid treatment resulted in marked GBM cell death. Together, these novel preliminary data strongly support the hypothesis that 13-cis-RA or ATRA can significantly alter lipid metabolism in GBM and promote fatty acid oxidation to support tumor cell survival and resistance. We further hypothesize that retinoic acid treatment in combination with suppression of SREBP-1 activation or fatty acid oxidation will effectively inhibit GBM growth and overcome tumor resistance. The goal of this study is to identify the previously unreported roles and mechanisms of retinoic acids and RARα in lipid metabolism regulation and GBM growth (Aim 1), and to develop effective combination approaches to target GBM (Aim 2). Completion of this study will uncover the underlying mechanism upregulating SREBP-1 expression and lipogenesis in GBM, provide great insights into understanding the antitumor and resistance mechanisms of retinoic acids, and identify novel strategies to target GBM and overcome retinoic acid resistance.