ABSTRACT
Large-scale, genome-wide studies report that RNA binding proteins are altered in cancers, but it is unclear how these proteins control tumor progression. We found that the RNA-editing protein ADAR (adenosine deaminase acting on double-stranded RNA) acted as a facilitator of lung adenocarcinoma (LUAD) progression through its ability to stabilize transcripts encoding focal adhesion kinase (FAK). In samples from 802 stage I LUAD patients, increased abundance of ADAR at both the mRNA and protein level correlated with tumor recurrence. Knocking down ADAR in LUAD cells suppressed their mesenchymal properties, migration, and invasion in culture. Analysis of gene expression patterns in LUAD cells identified ADAR-associated enrichment of a subset of genes involved in cell migration pathways; among these, FAK is the most notable gene whose expression was increased in the presence of ADAR. Molecular analyses revealed that ADAR posttranscriptionally increased FAK protein abundance by binding to the FAK transcript and editing a specific intronic site that resulted in the increased stabilization of FAK mRNA. Pharmacological inhibition of FAK blocked ADAR-induced invasiveness of LUAD cells, suggesting a potential therapeutic application for LUAD that has a high abundance of ADAR.
Subject(s)
Adenocarcinoma/enzymology , Adenosine Deaminase/metabolism , Cell Movement , Focal Adhesion Kinase 1/metabolism , Lung Neoplasms/enzymology , Neoplasm Proteins/metabolism , RNA-Binding Proteins/metabolism , Adenocarcinoma/drug therapy , Adenocarcinoma/genetics , Adenocarcinoma/pathology , Adenocarcinoma of Lung , Adenosine Deaminase/genetics , Cell Line , Enzyme Stability , Focal Adhesion Kinase 1/antagonists & inhibitors , Focal Adhesion Kinase 1/genetics , Humans , Lung Neoplasms/drug therapy , Lung Neoplasms/genetics , Lung Neoplasms/pathology , Neoplasm Proteins/antagonists & inhibitors , Neoplasm Proteins/genetics , RNA-Binding Proteins/geneticsABSTRACT
The identity of the RNA-binding proteins (RBPs) that govern cancer stem cells remains poorly characterized. The MSI2 RBP is a central regulator of translation of cancer stem cell programs. Through proteomic analysis of the MSI2-interacting RBP network and functional shRNA screening, we identified 24 genes required for in vivo leukemia. Syncrip was the most differentially required gene between normal and myeloid leukemia cells. SYNCRIP depletion increased apoptosis and differentiation while delaying leukemogenesis. Gene expression profiling of SYNCRIP-depleted cells demonstrated a loss of the MLL and HOXA9 leukemia stem cell program. SYNCRIP and MSI2 interact indirectly though shared mRNA targets. SYNCRIP maintains HOXA9 translation, and MSI2 or HOXA9 overexpression rescued the effects of SYNCRIP depletion. Altogether, our data identify SYNCRIP as a new RBP that controls the myeloid leukemia stem cell program. We propose that targeting these RBP complexes might provide a novel therapeutic strategy in leukemia.
Subject(s)
Gene Expression Regulation, Leukemic , Heterogeneous-Nuclear Ribonucleoproteins/genetics , Leukemia, Myeloid/genetics , RNA-Binding Proteins/metabolism , Animals , Cell Survival , Female , Hematopoiesis/genetics , Heterogeneous-Nuclear Ribonucleoproteins/metabolism , Homeodomain Proteins/genetics , Humans , Leukemia, Biphenotypic, Acute/genetics , Leukemia, Biphenotypic, Acute/pathology , Leukemia, Myeloid/pathology , Mice, Inbred C57BL , Mice, Knockout , Myeloid Progenitor Cells/metabolism , Myeloid Progenitor Cells/pathology , RNA, Small Interfering , RNA-Binding Proteins/genetics , Xenograft Model Antitumor AssaysABSTRACT
The angiogenic capability of colorectal carcinomas (CRC), and their susceptibility to anti-angiogenic therapy, is determined by expression of vascular endothelial growth factor (VEGF) isoforms. The intracellular protein T-cell Intracellular Antigen (TIA-1) alters post-transcriptional RNA processing and binds VEGF-A mRNA. We therefore tested the hypothesis that TIA-1 could regulate VEGF-A isoform expression in colorectal cancers. TIA-1 and VEGF-A isoform expression was measured in colorectal cancers and cell lines. We discovered that an endogenous splice variant of TIA-1 encoding a truncated protein, short TIA-1 (sTIA-1) was expressed in CRC tissues and invasive K-Ras mutant colon cancer cells and tissues but not in adenoma cell lines. sTIA-1 was more highly expressed in CRC than in normal tissues and increased with tumour stage. Knockdown of sTIA-1 or over-expression of full length TIA-1 (flTIA-1) induced expression of the anti-angiogenic VEGF isoform VEGF-A165b. Whereas flTIA-1 selectively bound VEGF-A165 mRNA and increased translation of VEGF-A165b, sTIA-1 prevented this binding. In nude mice, xenografted colon cancer cells over-expressing flTIA-1 formed smaller, less vascular tumours than those expressing sTIA-1, but flTIA-1 expression inhibited the effect of anti-VEGF antibodies. These results indicate that alternative splicing of an RNA binding protein can regulate isoform specific expression of VEGF providing an added layer of complexity to the angiogenic profile of colorectal cancer and their resistance to anti-angiogenic therapy.
Subject(s)
Alternative Splicing , Bevacizumab , Colonic Neoplasms/metabolism , Drug Resistance, Neoplasm , Gene Expression Regulation, Neoplastic , Neoplasm Proteins/biosynthesis , Neovascularization, Pathologic/metabolism , Poly(A)-Binding Proteins/biosynthesis , Vascular Endothelial Growth Factor A/biosynthesis , Animals , Colonic Neoplasms/blood supply , Colonic Neoplasms/genetics , Colonic Neoplasms/pathology , HEK293 Cells , HeLa Cells , Heterografts , Humans , Mice, Nude , Neoplasm Proteins/genetics , Neoplasm Transplantation , Neovascularization, Pathologic/genetics , Neovascularization, Pathologic/pathology , Poly(A)-Binding Proteins/genetics , Protein Isoforms/biosynthesis , Protein Isoforms/genetics , T-Cell Intracellular Antigen-1 , Vascular Endothelial Growth Factor A/geneticsABSTRACT
Angiogenesis is regulated by the balance of proangiogenic VEGF(165) and antiangiogenic VEGF(165)b splice isoforms. Mutations in WT1, the Wilms' tumor suppressor gene, suppress VEGF(165)b and cause abnormal gonadogenesis, renal failure, and Wilms' tumors. In WT1 mutant cells, reduced VEGF(165)b was due to lack of WT1-mediated transcriptional repression of the splicing-factor kinase SRPK1. WT1 bound to the SRPK1 promoter, and repressed expression through a specific WT1 binding site. In WT1 mutant cells SRPK1-mediated hyperphosphorylation of the oncogenic RNA binding protein SRSF1 regulated splicing of VEGF and rendered WT1 mutant cells proangiogenic. Altered VEGF splicing was reversed by wild-type WT1, knockdown of SRSF1, or SRPK1 and inhibition of SRPK1, which prevented in vitro and in vivo angiogenesis and associated tumor growth.