The VEGF-A exon 8 splicing-sensitive fluorescent reporter mouse is a novel tool to assess the effects of splicing regulatory compounds in vivo

Design of a GFP reporter for splicing analysis in mammalian cells

Eukaryotic genes are formed by exons and introns. Pre-mRNA splicing promotes exon ligation and intron removal and is performed by a specialized macromolecular machinery named spliceosome, composed of five small ribonucleoprotein particles (snRNPs) and more than one hundred proteins. The activity of this complex is highly accurate due to the coordinated activity of its components. Altered splicing has been related to the development of several diseases, including neurodegenerative disorders, such as amyotrophic lateral sclerosis, and different types of cancer. Detailed understanding of splicing regulation in eukaryotic cells can be achieved using splicing reporter systems. We designed a reporter plasmid suitable for splicing analysis in cultured mammalian cells. Our reporter is based on GFP expression, and the splicing outcome can be easily visualized by fluorescence microscopy. We quantified splicing activity in two human cell lines, HEK-293T and MDA-MB-231, confirming its suitability for use in live cells in culture.

VEGF gene polymorphisms regulate human retinal vascular endothelial cell proliferation and apoptosis through ASF/SF2-associated alternative splicing

This study investigated the effects of single nucleotide polymorphisms (SNPs) of the VEGF （vascular endothelial growth factor） gene, which are associated with susceptibility to age-related macular degeneration (AMD), on the expression of VEGF proteins (VEGF165 and VEGF165b) and their role in cell proliferation and apoptosis in human retinal vascular endothelial cells (hRVECs). Cell viability and VEGF165 and VEGF165b expressions were evaluated in hRVECs transfected with VEGF genes containing different SNPs (rs3025039, rs3025033, and rs10434). The Cell Counting Kit 8 assay, quantitative real-time PCR, western blotting, TUNEL assay, and enzyme-linked immunosorbent assay were used to examine the effects of VEGF gene SNPs on cell viability, VEGF165 and VEGF165b expressions, and cell apoptosis in hRVECs. The interaction and localization of the RNA-binding protein alternative splicing factor/splicing factor 2 (ASF/SF2) were assessed using RNA pull-down. Although VEGF165 expression decreased, VEGF165b levels increased significantly in hRVECs transfected with rs3025039, which decreased cell viability and induced apoptosis. The SNPs rs3025033 and rs10434 had no significant effects on VEGF165b protein production and apoptosis; however, they promoted cell proliferation. SNPs affected the interaction between RNA and ASF/SF2, a splicing factor for intron retention. Insulin-like growth factor-1 treatment induced the expression of VEGF165, but not VEGF165b, whereas SRPIN340 treatment, an inhibitor of ASF/SF2, increased VEGF165b protein levels. VEGF gene sequence variations affected hRVEC proliferation and apoptosis via alternative gene splicing. Thus, the regulation of splicing via ASF/SF2 could be a potential strategy in treating pathological neovascularization in patients with AMD.

Identification of novel somatic fusions of ERG-VEGFA, TMPRSS2-ERG, and VEGFA-TMPRSS2 in prostate cancer treated with anlotinib and androgen deprivation therapy: A case report

The TMPRSS2-ERG fusion gene has frequently been found in prostate cancer and is associated with malignancy. Identifying novel fusions will help to stratify patients and establish patient-tailored therapies. A 78-year-old man presented to our hospital with severe symptoms of urinary urgency and frequency for 2 years, as well as severe bone pain for 1 year. He was diagnosed with metastatic prostate cancer with a Gleason score of 5 + 5. Three gene fusions, ERG_VEGFA, TMPRSS2_ERG, and VEGFA_TMPRSS2, were identified in the patient's prostate cancer tissue. Notably, administration of the tyrosine kinase inhibitor, anlotinib, in combination with a gonadotropin-releasing hormone agonist (GnRHa) and abiraterone, reduced the patient's bone pain and also stabilized his prostate cancer for more than 2 years. This is the first report of somatic fusions among the VEGFA, ERG, and TMPRSS2 genes in cancer tissues from a patient with prostate cancer who responded well to antiangiogenic treatment combined with a GnRHa and abiraterone.

A drug-repositioning screen using splicing-sensitive fluorescent reporters identifies novel modulators of VEGF-A splicing with anti-angiogenic properties

Alternative splicing of the vascular endothelial growth factor A (VEGF-A) terminal exon generates two protein families with differing functions. Pro-angiogenic VEGF-A_xxxa isoforms are produced via selection of the proximal 3' splice site of the terminal exon. Use of an alternative distal splice site generates the anti-angiogenic VEGF-A_xxxb proteins. A bichromatic splicing-sensitive reporter was designed to mimic VEGF-A alternative splicing and was used as a molecular tool to further investigate this alternative splicing event. Part of VEGF-A's terminal exon and preceding intron were inserted into a minigene construct followed by the coding sequences for two fluorescent proteins. A different fluorescent protein is expressed depending on which 3' splice site of the exon is used during splicing (dsRED denotes VEGF-A_xxxa and EGFP denotes VEGF-A_xxxb). The fluorescent output can be used to follow splicing decisions in vitro and in vivo. Following successful reporter validation in different cell lines and altering splicing using known modulators, a screen was performed using the LOPAC library of small molecules. Alterations to reporter splicing were measured using a fluorescent plate reader to detect dsRED and EGFP expression. Compounds of interest were further validated using flow cytometry and assessed for effects on endogenous VEGF-A alternative splicing at the mRNA and protein level. Ex vivo and in vitro angiogenesis assays were used to demonstrate the anti-angiogenic effect of the compounds. Furthermore, anti-angiogenic activity was investigated in a Matrigel in vivo model. To conclude, we have identified a set of compounds that have anti-angiogenic activity through modulation of VEGF-A terminal exon splicing.