4EBP1在肿瘤雷帕霉素耐药中的作用及分子机制

The deregulation of mTOR signaling plays a key role in the development of cancer. Rapamycin and its analogues, which can specially bind to mTORC1 and inhibit its kinase activity, have been approved for the treatment of multiple cancers by the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA). However, Rapamycin and its analogues gave modest clinical performance in treatment of a number of neoplastic diseases due to the existence of Rapamycin resistance. Three mechanisms for this resistance have been proposed: the feedback activation of PI3K/AKT signaling; the resistance of 4EBP1 phosphorylation to long-term Rapamycin treatment; the existence of mTORC2. However, the downstream effecter of PI3K and mTORC2 and the mechanism underlying the resistance of 4EBP1 phosphorylation to long-term Rapamycin treatment are unknown. Our previous study showed that suppression of the feedback activation of PI3K signaling or inhibition of mTORC2 significantly enhanced the sensitivity of 4EBP1 phosphorylation and tumor growth to Rapamycin, suggesting that the feedback activation of PI3K signaling and the kinase activity of mTORC2 may contribute to the resistance of 4EBP1 phosphorylation to Rapamycin, which lead to Rapamycin resistance. Based on these observations, we will further investigate the the role and mechanism of the resistance of 4EBP1 phosphorylation to Rapamycin mediated by the feedback activation of PI3K signaling and the kinase activity of mTORC2 and its effect to Rapamycin resistance, laying a solid foundation for enhancing rapalogue clinical efficacy.

mTOR信号通路的异常激活在肿瘤的恶性进展中发挥重要作用。雷帕霉素及衍生物能够特异性结合mTORC1并抑制其激酶活性，已被FDA和EMA批准用于肿瘤的临床治疗，但临床研究发现多数肿瘤细胞能够产生雷帕霉素耐药性。目前已经发现耐药机制主要是：① PI3K/AKT信号通路的反馈激活；② 雷帕霉素处理下4EBP1磷酸化的恢复；③ mTORC2的存在。但是，PI3K/AKT反馈激活和mTORC2的下游效应分子及4EBP1磷酸化恢复的分子机制仍不清楚。我们的前期研究发现，阻断PI3K反馈激活或抑制mTORC2活性后能够显著增加4EBP1磷酸化及肿瘤细胞对雷帕霉素的敏感性，这些结果提示我们PI3K的反馈激活及mTORC2可能介导了4EBP1磷酸化的恢复，从而导致雷帕霉素耐药。本申请拟在此研究基础上，阐明4EBP1在肿瘤雷帕霉素耐药中的作用及分子机制，为提高雷帕霉素的临床治疗效果提供理论依据。

目前，已在多数恶性肿瘤中发现了mTOR信号通路的异常激活。雷帕霉素及衍生物能够特异性抑制mTORC1激酶活性，已被批准用于部分肿瘤的临床治疗，但是临床研究发现多数肿瘤细胞能够产生雷帕霉素耐药性。4EBP1是mTOR信号通路下游重要分子，主要负责调控帽子依赖的翻译。近年来研究发现4EBP1的磷酸化与肿瘤细胞对雷帕霉素的耐药密切相关。我们研究发现，阻断PI3K反馈激活或抑制mTORC2活性后能够显著增加4EBP1磷酸化及肿瘤细胞对雷帕霉素的敏感性，提示我们PI3K的反馈激活及mTORC2可能介导了4EBP1磷酸化的恢复，从而导致雷帕霉素耐药。本研究整合了目前的三种耐药机制，通过研究雷帕霉素处理后4EBP1 磷酸化恢复与eIF4F 翻译起始复合物活性之间的关联，证明4E-BP1 是雷帕霉素耐药的下游效应分子。我们用 CRISPR-Cas9技术构建了敲除 SGK3 的乳腺癌细胞系，发现SGK3 和 4EBP1 磷酸化以及乳腺癌细胞的增殖、生长和存活及细胞耐药密切相关，是重要的 4EBP1 磷酸化调节分子，通过抑制 SGK3 介导的 4EBP1 磷酸化改善肿瘤细胞对雷帕霉素的耐药，从而提高雷帕霉素及其衍生物的临床治疗效果。这些发现为肿瘤的联合用药治疗提供了新的理论依据。