SIK在肾癌中参与SAV1负性调控Akt磷酸化的机制研究

Akt is a serine/threonine protein kinase, and its overactivation plays an important role in the development of renal cell carcinoma. Previous study found that SAV1 negatively regulates Akt phosphorylation and inhibits the growth of renal cell carcinoma by interacting with Akt protein. At present, the mechanism of regulating the interaction between SAV1 and Akt is not clear. SIK is a highly conserved serine/threonine protein kinase, which plays an important regulatory role in tumor proliferation, apoptosis and other signaling pathways. Research has shown that Sik2 and Sik3 can bind to Sav and phosphorylate it in Drosophila melanogaster. Besides, it has been reported that the high expression of SIK2 and SIK3 is a poor prognostic factor of cancer. Inhibiting SIK2 expression can down-regulate Akt phosphorylation and inhibit tumor growth. Based on previous experimental results, we propose the following hypothesis: SIK may be involved in SAV1 negative regulation of Akt phosphorylation by binding to and phosphorylating SAV1. On the basis of previous work, this study aims to elucidate the molecular mechanism of SIK involvement in SAV1 negative regulation of Akt phosphorylation, which is expected to provide a new mechanism for the occurrence and development of renal cell carcinoma and a new molecular target for the treatment of renal cell carcinoma.

Akt是一种丝氨酸/苏氨酸蛋白激酶，它的过度激活在肾癌发生发展中起重要作用。本研究前期实验发现，SAV1在肾癌中通过与Akt蛋白相互作用，负性调控Akt磷酸化，抑制肾癌细胞生长。目前调控SAV1和Akt相互作用的机制尚不清楚。SIK是一种高度保守的丝氨酸/苏氨酸蛋白激酶，在肿瘤增殖、凋亡等信号通路中起重要调控作用。有研究表明，在果蝇中Sik2、Sik3可以与Sav结合并使其磷酸化；SIK2、SIK3高表达是肿瘤预后不良因素，抑制SIK2表达可以下调 Akt磷酸化水平，抑制肿瘤生长。基于上述研究背景和前期实验基础，我们提出以下项目假说：SIK在肾癌中可能通过与SAV1结合并使其磷酸化从而参与SAV1对Akt磷酸化的负性调控。本研究在前期工作基础上，以阐明SIK参与SAV1负性调控Akt磷酸化的分子机制为目的，有望为肾癌的发生发展提供新的机制，为肾癌的治疗提供新的分子靶点。

肾癌对放疗、化疗均不敏感。目前抗血管生成药物是晚期肾癌的主要治疗手段之一，然而缓解率并不高，且容易出现耐药。肾癌中存在Akt过度激活；持续性PI3K/Akt通路激活是引起舒尼替尼获得性耐药的原因之一。我们前期研究发现，SAV1在肾癌中可以与Akt蛋白相互作用，负性调控Akt磷酸化，抑制肾癌细胞增殖。然而调控SAV1和Akt相互作用的机制尚不清楚。在本研究中，我们通过外源性和内源性免疫沉淀实验明确了SIK2可以与SAV1相互作用；并且，SIK2可以增强SAV1与Akt的相互作用。为了明确SIK2是否通过影响SAV1与Akt的相互作用调控Akt磷酸化，我们构建了多种敲低SIK2表达的肾癌细胞系，结果发现在部分肾癌细胞中，下调SIK2表达可以增加Akt磷酸化，促进肿瘤生长。我们进一步对肾癌组织及癌旁组织进行免疫组化检测发现，SIK2在癌组织中低表达，癌旁组织中高表达，两者表达有显著差异；SIK2表达与肿瘤大小呈负相关。TCGA数据分析结果显示，SIK2表达与肾癌预后呈正相关。我们的研究结果揭示了肾癌中Akt磷酸化调控的新机制，为寻找新的治疗靶点提供了基础。