PLEK2磷酸化修饰经CAND1抑制EGFR泛素化降解促进胆囊癌侵袭转移的机制研究

Gallbladder cancer (GBC) is a malignant tumor with low R0 resection and high mortality due to its strong propensity to invasion and metastasis. Our clinical findings showed for the first time that PLEK2 had a much higher expression in metastatic GBC tissues. In addition, PLEK2 expression was positively correlated with lymph node and distant metastasis, while negatively correlated with prognosis. Our preliminary investigations clarified for the first time that PLEK2 could interact with EGFR and might suppress EGFR ubiquitination by CAND1 competitive binding with ubiquitin ligases. Consequently, the EGFR downstream signaling pathways were activated and triggered EMT (epithelial – mesenchymal transition). Ultimately, the invasion and metastasis of GBC cells were promoted. Furthermore, YY (332, 333) in PLEK2 was first identified as a functional phosphorylation site which might play crucial roles in its biological function. In this study, we aim to reveal and verify that PLEK2 YY (332, 333) phosphorylation promotes the binding of PLEK2 and EGFR. Then EGFR can’t interact with ubiquitin ligases due to the competitive binding of CAND1. Accordingly, the EGFR degradation by ubiquitination is suppressed. The increased EGFR stability leads to persistent activation of AKT and ERK. Then GBC cells generate EMT, the invasion and metastasis of GBC are reinforced. Taken together, this study will provide profound evidence for whether PLEK2 and its phosphorylation site can be a specific therapeutic target for GBC patients.

侵袭与转移是胆囊癌手术切除率低、预后差的重要原因。我们前期研究首次发现，PLEK2在转移的胆囊癌组织中异常高表达，且PLEK2的表达与淋巴结转移和远处转移正相关，与胆囊癌病人预后负相关。预实验首次阐明PLEK2与EGFR相互作用，并可能通过CAND1竞争性结合泛素化连接酶，EGFR与泛素化连接酶结合受到抑制，使得EGFR的泛素化降解减弱，其下游信号通路促使胆囊癌细胞发生EMT转化，胆囊癌的侵袭转移增强。同时，我们首次发现PLEK2存在YY（332，333）磷酸化位点，该位点的磷酸化修饰可能与PLEK2的功能活化密切相关。本研究首次揭示：PLEK2 YY（332，333）位点磷酸化→PLEK2结合EGFR→CAND1阻止EGFR与泛素化连接酶结合→EGFR蛋白泛素化降解减少→AKT和ERK持续激活→EMT转化发生→胆囊癌侵袭转移增强的新机制，为PLEK2作为胆囊癌转移的治疗靶点提供理论依据。

胆囊癌是最常见的胆道恶性肿瘤，平均生存期不到1年，5年总生存率仅为 17.8%-21.7%。胆囊癌的侵袭转移是影响胆囊癌患者长期存活的重要因素。本研究预实验首先发现PLEK2在转移的胆囊癌组织中异常高表达，且PLEK2的表达与淋巴结转移和远处转移正相关，与胆囊癌病人预后负相关。PLEK2能够调控EGFR的蛋白稳定性，增强胆囊癌细胞EMT转化来促进胆囊癌的侵袭转移。我们进一步研究发现PLEK2与EGFR的胞内酪氨酸激酶结构域相互结合，同时PLEK2能竞争性结合泛素化连接酶c-CBL，使得EGFR不能结合c-CBL，从而抑制EGFR的泛素化-蛋白酶体降解，最终通过调控STAT3/CCL2信号通路促进胆囊癌的侵袭转移。本研究对于阻断肿瘤进展、发现靶向药物，从而改善病人预后具有重要意义。