The HGF-MET axis coordinates liver cancer metabolism and autophagy for chemotherapeutic resistance

Notwithstanding the numerous drugs available for liver cancer, emerging evidence suggests that chemotherapeutic resistance is a significant issue. HGF and its receptor MET play critical roles in liver carcinogenesis and metastasis, mainly dependent on the activity of receptor tyrosine kinase. However, for unknown reasons, all HGF-MET kinase activity-targeted drugs have failed or have been suspended in clinical trials thus far. Macroautophagy/autophagy is a protective ‘self-eating’ process for resisting metabolic stress by recycling obsolete components, whereas the impact of autophagy-mediated reprogrammed metabolism on therapeutic resistance is largely unclear, especially in liver cancer. In the present study, we first observed that HGF stimulus facilitated the Warburg effect and glutaminolysis to promote biogenesis in multiple liver cancer cells. We then identified the pyruvate dehydrogenase complex (PDHC) and GLS/GLS1 as crucial substrates of HGF-activated MET kinase; MET-mediated phosphorylation inhibits PDHC activity but activates GLS to promote cancer cell metabolism and biogenesis. We further found that the key residues of kinase activity in MET (Y1234/1235) also constitute a conserved LC3-interacting region motif (Y1234-Y1235-x-V1237). Therefore, on inhibiting HGF-mediated MET kinase activation, Y1234/1235-dephosphorylated MET induced autophagy to maintain biogenesis for cancer cell survival. Moreover, we verified that Y1234/1235-dephosphorylated MET correlated with autophagy in clinical liver cancer. Finally, a combination of MET inhibitor and autophagy suppressor significantly improved the therapeutic efficiency of liver cancer in vitro and in mice. Together, our findings reveal an HGF-MET axis-coordinated functional interaction between tyrosine kinase signaling and autophagy, and establish a MET-autophagy double-targeted strategy to overcome chemotherapeutic resistance in liver cancer. Abbreviations: ALDO: aldolase, fructose-bisphosphate; CQ: chloroquine; DLAT/PDCE2: dihydrolipoamide S-acetyltransferase; EMT: epithelial-mesenchymal transition; ENO: enolase; GAPDH: glyceraldehyde-3-phosphate dehydrogenase; GLS/GLS1: glutaminase; GLUL/GS: glutamine-ammonia ligase; GPI/PGI: glucose-6-phosphate isomerase; HCC: hepatocellular carcinoma; HGF: hepatocyte growth factor; HK: hexokinase; LDH: lactate dehydrogenase; LIHC: liver hepatocellular carcinoma; LIR: LC3-interacting region; PDH: pyruvate dehydrogenase; PDHA1: pyruvate dehydrogenase E1 alpha 1 subunit; PDHX: pyruvate dehydrogenase complex component X; PFK: phosphofructokinase; PK: pyruvate kinase; RTK: receptor tyrosine kinase; TCGA: The Cancer Genome Atlas

尽管目前已有多种用于肝癌治疗的临床药物，但越来越多的研究证据表明，化疗耐药仍是制约肝癌治疗效果的重大难题。肝细胞生长因子（hepatocyte growth factor, HGF）及其受体MET在肝癌发生与转移过程中发挥关键调控作用，其功能主要依赖于受体酪氨酸激酶（receptor tyrosine kinase, RTK）的活性。然而，受限于未知的分子机制，迄今为止所有靶向HGF-MET激酶活性的药物均在临床试验中失败或被暂停研发。
巨自噬（macroautophagy，以下简称自噬）是一种通过降解胞内废弃组分以抵抗代谢应激的保护性‘自我吞噬’过程，但目前学界对自噬介导的代谢重编程在治疗耐药中的作用仍知之甚少，在肝癌领域尤其如此。
本研究首先发现，HGF刺激可增强多种肝癌细胞的瓦博格效应（Warburg effect）与谷氨酰胺分解代谢，进而促进癌细胞的生物合成过程。随后，我们鉴定出丙酮酸脱氢酶复合物（pyruvate dehydrogenase complex, PDHC）与谷氨酰胺酶（glutaminase, GLS/GLS1）是HGF激活的MET激酶的关键底物；MET介导的磷酸化修饰可抑制PDHC活性，但激活GLS，从而促进癌细胞代谢与生物合成。
我们进一步发现，MET的激酶活性关键残基Y1234/1235同时构成了一个保守的LC3相互作用区域（LC3-interacting region, LIR）基序（Y1234-Y1235-x-V1237）。因此，当抑制HGF介导的MET激酶激活后，去磷酸化的Y1234/1235 MET可诱导自噬，以维持癌细胞存活所需的生物合成过程。此外，我们在临床肝癌样本中验证了去磷酸化Y1234/1235 MET的表达水平与自噬活性呈正相关。最后，MET抑制剂与自噬抑制剂联合给药，可显著提升体外细胞实验及小鼠体内模型的肝癌治疗效果。
综上，本研究揭示了HGF-MET轴协同调控的酪氨酸激酶信号通路与自噬之间的功能性互作机制，并确立了MET-自噬双靶点策略以克服肝癌化疗耐药。
缩写说明：
ALDO：醛缩酶，果糖双磷酸酯；
CQ：氯喹；
DLAT/PDCE2：二氢硫辛酰胺S-乙酰转移酶；
EMT：上皮间质转化；
ENO：烯醇化酶；
GAPDH：甘油醛-3-磷酸脱氢酶；
GLS/GLS1：谷氨酰胺酶；
GLUL/GS：谷氨酰胺连接酶；
GPI/PGI：葡萄糖-6-磷酸异构酶；
HCC：肝细胞癌；
HGF：肝细胞生长因子；
HK：己糖激酶；
LDH：乳酸脱氢酶；
LIHC：肝脏肝细胞癌；
LIR：LC3相互作用区域；
PDH：丙酮酸脱氢酶；
PDHA1：丙酮酸脱氢酶E1α1亚基；
PDHX：丙酮酸脱氢酶复合物组分X；
PFK：磷酸果糖激酶；
PK：丙酮酸激酶；
RTK：受体酪氨酸激酶；
TCGA：癌症基因组图谱（The Cancer Genome Atlas）