Department of General Surgery, The First Affiliated Hospital of Nanjing Medical University, 300 Guangzhou Road, Nanjing, 210029, China.
The Jackson Laboratory, Bar Harbor, ME, 04609, USA.
J Exp Clin Cancer Res. 2021 Feb 18;40(1):75. doi: 10.1186/s13046-021-01877-y.
The Mnk2 kinase, encoded by MKNK2 gene, plays critical roles in MAPK signaling and was involved in oncogenesis. Human MKNK2 pre-mRNA can be alternatively spliced into two splicing isoforms, the MKNK2a and MKNK2b, thus yielding Mnk2a and Mnk2b proteins with different domains. The involvement of Mnk2 alternative splicing in colon cancer has been implicated based on RNA-sequencing data from TCGA database. This study aimed at investigating the upstream modulators and clinical relevance of Mnk2 alternative splicing in colon adenocarcinoma (CAC).
PCR, western blotting and immunohistochemistry (IHC) were performed to assess the expression of Mnk2 and upstream proteins in CAC. The function of Mnk2 and its regulators were demonstrated in different CAC cell lines as well as in xenograft models. Two independent cohorts of CAC patients were used to reveal the clinical significance of MKNK2 alternative splicing.
Comparing with adjacent nontumorous tissue, CAC specimen showed a decreased MKNK2a level and an increased MKNK2b level, which were correlated with KRAS mutation and tumor size. The SRSF1 (serine/arginine-rich splicing factor 1) was further confirmed to be the major splicing factor targeting MKNK2 in CAC cells. Higher expression of SRPK1/2 or decreased activity of PP1α were responsible for enhancing SRSF1 phosphorylation and nucleus translocation, subsequently resulted in a switch of MKNK2 alternative splicing.
Our data showed that phosphorylation and subcellular localization of SRSF1 were balanced by SRPK1/2 and PP1α in CAC cells. High nucleus SRSF1 promoted MKNK2 splicing into MKNK2b instead of MNK2a, consequently enhanced tumor proliferation.
Mnk2 激酶，由 MKNK2 基因编码，在 MAPK 信号通路中发挥关键作用，并参与肿瘤发生。人 MKNK2 前体 mRNA 可通过可变剪接形成两种剪接异构体，MKNK2a 和 MKNK2b，从而产生具有不同结构域的 Mnk2a 和 Mnk2b 蛋白。基于 TCGA 数据库的 RNA 测序数据，已经暗示了 Mnk2 可变剪接在结肠癌中的作用。本研究旨在探讨 Mnk2 可变剪接在结肠腺癌（CAC）中的上游调节因子及其临床相关性。
通过 PCR、western blot 和免疫组织化学（IHC）检测 CAC 中 Mnk2 和上游蛋白的表达。在不同的 CAC 细胞系以及异种移植模型中，研究了 Mnk2 及其调节因子的功能。使用两个独立的 CAC 患者队列揭示了 MKNK2 可变剪接的临床意义。
与相邻的非肿瘤组织相比，CAC 标本显示 MKNK2a 水平降低，MKNK2b 水平升高，这与 KRAS 突变和肿瘤大小相关。进一步证实，SRSF1（丝氨酸/精氨酸丰富剪接因子 1）是 CAC 细胞中主要的靶向 MKNK2 的剪接因子。SRPK1/2 表达升高或 PP1α 活性降低导致 SRSF1 磷酸化和核转位增强，从而导致 MKNK2 可变剪接的转换。
我们的数据表明，SRPK1/2 和 PP1α 在 CAC 细胞中平衡 SRSF1 的磷酸化和亚细胞定位。高核 SRSF1 促进 MKNK2 剪接为 MKNK2b 而不是 MNK2a，从而促进肿瘤增殖。
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