谷氨酰胺酶GLS的琥珀酰化修饰及其在胰腺导管腺癌中的作用与机制研究

Pancreatic ductal adenocarcinoma (PDAC) is a kind of tumor with high malignancy and lethality, but effective treatment is still devoid now. Strong dependence on glutamine is observed in the progress of tumor cell proliferation, which is called “glutamine addiction”. Glutaminase (GLS) is a key enzyme in glutaminolysis which converts glutamine into glutamate. Here we found that the PDAC cells also showed enhanced glutaminolysis and were more sensitive to glutamine depletion. Knock-down of GLS or treatment with GLS inhibitor significantly inhibited the growth of PDAC cells. In addition, we identified that GLS could be succinylated by Succinyl-CoA directly, and K311 is the main succinylation site. Succinylation of GLS enhanced its glutaminase activity and hence promoted the growth of PDAC cells. Next, we will try to clarify the mechanisms of the upregulated GSL activity induced by succinylation, to investigate the roles of Succinyl-CoA Ligase β subunit A2 (SUCLA2) in the regulation of GLS succinylation, and to explore the possibility of treating PDAC via targeting GLS. This study will benefit our understanding of the regulation of GLS activity and the mechanism of protein succinylation, and provide new ideas on PDAC diagnosis and treatment.

胰腺导管腺癌（PDAC）是恶性程度非常高、严重致死性的恶性肿瘤，目前仍无很好的治疗手段。肿瘤细胞的增生会强烈依赖谷氨酰胺，被称之为“谷氨酰胺成瘾”。谷氨酰胺酶（GLS）可以将谷氨酰胺转变为谷氨酸，是谷氨酰胺代谢中的关键酶。我们前期研究发现PDAC细胞对于谷氨酰胺缺乏更为敏感，敲低GLS或使用GLS抑制剂可以显著抑制细胞的生长。我们还发现琥珀酰辅酶A可以直接将GLS琥珀酰化，并鉴定出其修饰位点（K311）。GLS被琥珀酰化后可以增强其酶活性，从而促进肿瘤细胞对于谷氨酰胺的利用和细胞的生长。基于以上发现，我们拟进一步研究琥珀酰化调控GLS活性的具体机理，以及琥珀酰辅酶A连接酶β亚基A2（SUCLA2）对于GLS琥珀酰化的调控作用，并初步探索GLS作为治疗PDAC的有效靶点的可能性。这些将加深我们对于GLS活性调控和蛋白质琥珀酰化修饰的理解，也将为PDAC诊治手段的发展提供新的思路。

谷氨酰胺酶调节谷氨酰胺分解促进癌细胞增殖。然而，谷氨酰胺酶活性调节的机制尚不清楚。在此研究中，我们发现谷氨酰胺酶（GLS）在人胰腺导管腺癌（PDAC）标本中高度表达，并促进PDAC细胞产生更强的谷氨酰胺依赖性。在肿瘤细胞发生氧化应激后，琥珀酰辅酶A连接酶β亚基A2（SUCLA2）的S79位点可以被MAP激酶p38磷酸化，导致SUCLA2与GLS解离，进而导致GLS K311琥珀酰化升高，这促进了GLS的多聚化和活性增强。激活的GLS增加谷氨酰胺分解和NADPH、谷胱甘肽的生成，从而抵消小鼠肿瘤细胞存活和肿瘤生长中的氧化应激。此外，SUCLA2 pS79和GLS K311琥珀酰化水平相互关联，与PDAC晚期和患者预后不良呈正相关。我们的发现揭示了SUCLA2偶联的GLS琥珀酰化调节对GLS活性的重要调控作用，并展示了代谢物在谷氨酰胺分解和PDAC发生发展中的重要调节作用。