基于EGFR介导的β-catenin浆核穿梭研究AKT1对乳腺癌转移的负性调控

Breast cancer, especially distant metastasis, is still the most common cause of cancer death among women. Although development of novel small molecular AKT inhibitors has become the hot spot in drug research for anticancer treatment because AKT is frequently over-expression in many type tumors, accumulating evidences suggest inhibition of AKT1 accelerated tumor invasion and metastasis in some type breast cancer. These results suggest that not all tumor patients gain profit from treatment of AKT inhibitors. Our previous results have demonstrated that the expression of EGFR, p-EGFR and β-catenin was enhanced after inhibition of AKT1 in MCF-7 and MDA-MB-231 cells, however, whether and how EGFR and β-catenin was involved in AKT1 regulating breast cancer metastasis remains unknown. Therefore, in the present study, breast cancer cell lines, mouse model of metastasis and human breast tumor tissue specimens were used to document the hypothesis: Inhibition of AKT1 and inactivates PIKfyve to reduce the rate of EGFR degradation, reduced EGFR degradation also correlates with increased phosphorylation of EGFR which leads to β-catenin entry into nucleus and promote breast cancer cells metastasis. Together, this study offer new insights into the role of AKT1 in breast cancer metastasis and precise medical treatment of tumor, and also help us seek the potential therapeutic targets.

乳腺癌转移是导致患者死亡的主要原因且机制未明。AKT在多种类型的肿瘤中均高表达并调控肿瘤细胞的增殖及转移，故AKT抑制剂目前已成为抗肿瘤新药研发的一个热点，但我们预实验发现抑制AKT1功能反而促进某些类型的乳腺癌转移并导致EGFR、β-catenin蛋白表达上调，AKT1是否负性调控所有分子分型的乳腺癌的转移及分子机制还不清楚。本课题拟采用体外细胞系、荷瘤动物、临床标本等多种研究模型验证以下科学假说：抑制乳腺癌细胞中AKT1功能阻滞了PIKfyve的磷酸化及其对EGFR的降解能力，导致EGFR下游信号持续激活，促进β-catenin的入核，最终导致乳腺癌转移能力增强。这些问题的阐明为乳腺癌转移的防治提供新思路和新靶点，也有助于乳腺癌的精准医疗及完善AKT抑制剂的抗瘤谱。

AKT在多种类型的肿瘤中均高表达并调控肿瘤细胞的增殖及转移，故AKT抑制剂目前已成为抗肿瘤新药研发的一个热点，但AKT 家族主要有AKT1、AKT2、AKT3 组成，与AKT2、AKT3 亚型不同，AKT1对乳腺癌转移通常发挥着负性调控作用。有研究发现抑制AKT1功能反而促进某些类型的乳腺癌转移，这将带来临床合理用药问题，即AKT抑制剂类药物并不适用于所有AKT高表达的肿瘤患者。但到目前为止，AKT1是否负性调控所有分子分型的乳腺癌的转移及分子机制还不清楚。在本研究中我们发现基因敲减AKT1可促进β-catenin的核移位，进而促进乳腺癌的转移。接下来我们证实基因敲减AKT1可上调EGFR的表达，且抑制AKT1引起的β-catenin核移位可以被 EGFR 酪氨酸激酶抑制剂Gefitinib阻断，这说明EGFR可能参与了AKT1对β-catenin 核移位的调节。通过细胞实验我们进一步证明当基因敲除AKT1后，阻滞了PIKfyve 的磷酸化，使EGFR不能及时降解，导致EGFR下游信号持续激活，促进β-catenin 的入核，最终导致乳腺癌转移能力增强。本研究通过探讨AKT1功能抑制促进乳腺癌转移的分子机制，为乳腺癌转移的防治提供新思路和新靶点，也有助于乳腺癌的精准医疗及AKT抑制剂抗瘤谱的完善。