Abstract：
Studying the mechanisms underlying clear cell renal cell carcinoma (ccRCC), the most common subtype of kidney cancer, may address an unmet need in ccRCC-targeted drug research. Growing evidences indicate that protein phosphatase 4 (PP4) plays an important role in cancer biology. Here, we characterized the upregulation of PP4 core component SMEK1 in ccRCC using tissue microarrays and revealed that its high expression is closely associated with reduced patient survival. We then conducted cell function experiments and animal experiments to prove the tumor-promoting effect of SMEK1. Next, RNA-seq was performed to explore its underlying mechanism, and the results revealed that SMEK1-regulated genes were extensively involved in cell motility, and the canonical tyrosine kinase receptor EGFR was one of its targets. Moreover, we verified the regulatory effect of SMEK1 on EGFR and its downstream MAPK and AKT pathway through molecular experiments, in which erlotinib, a tyrosine kinase inhibitor, can partially block this regulation, demonstrating that SMEK1 mediates its effects dependent on the tyrosine kinase activity of EGFR. Mechanistically, SMEK1 bond to PRMT5 and facilitated PRMT5-mediated histone methylation to promote the transcription of EGFR. Furthermore, we studied the upstream regulators of SMEK1 and demonstrated that the transcription factor E2F1 could directly bind to the SMEK1 promoter by chromatin immunoprecipitation. Functionally, E2F1 could also induce ccRCC progression by manipulating the expression of SMEK1. Collectively, our findings demonstrate the overexpression of SMEK1 in ccRCC, and reveal a novel E2F1/SMEK1/PRMT5/EGFR-tyrosine-kinase-dependent pathway for ccRCC progression.
摘要：
研究透明细胞肾细胞癌（ccRCC）的潜在机制，最常见的肾癌亚型,可以解决ccRCC靶向药物研究中未满足的需求。越来越多的证据表明，蛋白磷酸酶4（PP4）在癌症生物学中起着重要作用。这里,我们使用组织微阵列表征了ccRCC中PP4核心组分SMEK1的上调,并揭示其高表达与患者生存率降低密切相关.然后我们进行了细胞功能实验和动物实验来证明SMEK1的促肿瘤作用。接下来,进行RNA-seq以探索其潜在的机制，结果表明，SMEK1调控的基因广泛参与细胞运动，典型的酪氨酸激酶受体EGFR是其靶点之一。此外，通过分子实验验证了SMEK1对EGFR及其下游MAPK和AKT通路的调节作用,其中厄洛替尼，酪氨酸激酶抑制剂，可以部分阻止这一规定，证明SMEK1介导其作用依赖于EGFR的酪氨酸激酶活性。机械上,SMEK1与PRMT5结合并促进PRMT5介导的组蛋白甲基化以促进EGFR的转录。此外，我们研究了SMEK1的上游调节因子，并证明转录因子E2F1可以通过染色质免疫沉淀直接结合SMEK1启动子。功能上,E2F1还可以通过操纵SMEK1的表达来诱导ccRCC的进展。总的来说，我们的发现表明SMEK1在ccRCC中过度表达，并揭示了一种新的E2F1/SMEK1/PRMT5/EGFR-酪氨酸激酶依赖性途径用于ccRCC进展。
