ABSTRACT
The gene encoding the kinase Mnk2 (MKNK2) is alternatively spliced to produce two isoforms-Mnk2a and Mnk2b. We previously showed that Mnk2a is downregulated in several types of cancer and acts as a tumor suppressor by activation of the p38-MAPK stress pathway, inducing apoptosis. Moreover, Mnk2a overexpression suppressed Ras-induced transformation in culture and in vivo. In contrast, the Mnk2b isoform acts as a pro-oncogenic factor. In this study, we designed modified-RNA antisense oligonucleotides and screened for those that specifically induce a strong switch in alternative splicing of the MKNK2 gene (splice switching oligonucleotides or SSOs), elevating the tumor suppressive isoform Mnk2a at the expense of the pro-oncogenic isoform Mnk2b. Induction of Mnk2a by SSOs in glioblastoma cells activated the p38-MAPK pathway, inhibited the oncogenic properties of the cells, re-sensitized the cells to chemotherapy and inhibited glioblastoma development in vivo. Moreover, inhibition of p38-MAPK partially rescued glioblastoma cells suggesting that most of the anti-oncogenic activity of the SSO is mediated by activation of this pathway. These results suggest that manipulation of MKNK2 alternative splicing by SSOs is a novel approach to inhibit glioblastoma tumorigenesis.
Subject(s)
Brain Neoplasms/therapy , Glioblastoma/therapy , Intracellular Signaling Peptides and Proteins/genetics , Oligonucleotides/genetics , Protein Serine-Threonine Kinases/genetics , Alternative Splicing , Animals , Apoptosis , Brain Neoplasms/genetics , Cell Line, Tumor , Genes, Tumor Suppressor , Glioblastoma/genetics , Humans , Intracellular Signaling Peptides and Proteins/metabolism , MAP Kinase Signaling System , Mice , Mice, Inbred NOD , Mice, SCID , Neoplasm Transplantation , Oligonucleotides, Antisense , Phosphorylation , Protein Isoforms , Protein Serine-Threonine Kinases/metabolism , RNA Splicing , p38 Mitogen-Activated Protein Kinases/metabolismABSTRACT
Several long noncoding RNAs (lncRNA) are abrogated in cancer but their precise contributions to oncogenesis are still emerging. Here we report that the lncRNA MALAT1 is upregulated in hepatocellular carcinoma and acts as a proto-oncogene through Wnt pathway activation and induction of the oncogenic splicing factor SRSF1. Induction of SRSF1 by MALAT1 modulates SRSF1 splicing targets, enhancing the production of antiapoptotic splicing isoforms and activating the mTOR pathway by modulating the alternative splicing of S6K1. Inhibition of SRSF1 expression or mTOR activity abolishes the oncogenic properties of MALAT1, suggesting that SRSF1 induction and mTOR activation are essential for MALAT1-induced transformation. Our results reveal a mechanism by which lncRNA MALAT1 acts as a proto-oncogene in hepatocellular carcinoma, modulating oncogenic alternative splicing through SRSF1 upregulation. Cancer Res; 77(5); 1155-67. ©2016 AACR.
