PTBP1‐dependent regulation of USP5 alternative RNA splicing plays a role in glioblastoma tumorigenesis

Abstract

Aberrant RNA splicing is thought to play a key role in tumorigenesis. The assessment of its specific contributions is limited by the complexity of information derived from genome-wide array-based approaches. We describe how performing splicing factor-specific comparisons using both tumor and cell line datasets may more readily identify physiologically relevant tumor-specific splicing events. Affymetrix exon array data derived from glioblastoma (GBM) tumor samples with defined PTBP1 levels were compared with data from U251 GBM cells with and without PTBP1 knockdown. This comparison yielded overlapping gene sets that comprised only a minor fraction of each dataset. The identification of a novel GBM-specific splicing event involving the USP5 gene led us to further examine its role in tumorigenesis. In GBM, USP5 generates a shorter isoform 2 through recognition of a 5′ splice site within exon 15. Production of the USP5 isoform 2 was strongly correlated with PTBP1 expression in GBM tumor samples and cell lines. Splicing regulation was consistent with the presence of an intronic PTBP1 binding site and could be modulated through antisense targeting of the isoform 2 splice site to force expression of isoform 1 in GBM cells. The forced expression of USP5 isoform 1 in two GBM cell lines inhibited cell growth and migration, implying an important role for USP5 splicing in gliomagenesis. These results support a role for aberrant RNA splicing in tumorigenesis and suggest that changes in relatively few genes may be sufficient to drive the process.

Regulation of mRNA Abundance by Polypyrimidine Tract-Binding Protein-Controlled Alternate 5′ Splice Site Choice

“…Of note, Ptbp1 had been previously proposed to regulate the A5C event in the Usp5 gene identified by our analysis [43]. This positive control and 11 examples of newly identified targets representing the four AS patterns (Ptbp1-induced bias towards u5′ss, d5′ss, u3′ss or d3′ss) were selected for RT-PCR validation.…”

The deubiquitinase Leon/USP5 regulates ubiquitin homeostasis during Drosophila development

“…Thus, different DUBs may target the same substrate, providing a multi-facet regulation or a cell-context dependent regulation. Until now, USP5 has been shown to link two carcinomas: alterations of USP5 isoforms in glioblastoma tumorigenesis and USP5 linked-suppression of p53 in melanoma [25,26]. Treatment of DUBs inhibitor EOAI3402143, targeting to USP9X and USP5, succeed to suppress melanoma growth [26].…”

TGF-β1 Induces Polypyrimidine Tract-Binding Protein to Alter Fibroblasts Proliferation and Fibronectin Deposition in Keloid

“…PKM2 promotes aerobic glycolysis to support cell growth and is predominantly expressed in tumor cells, while PKM1 is the dominant isoform in normal cells. Modulation of USP5 splicing generates a shorter isoform 2 without exon 15 that is strongly correlated with cell proliferation and overexpressed in glioblastoma39, whereas USP5 isoform 1 with exon 15 is associated with reduced cell growth and motility in glioblastoma. In human glioma cells, depletion of PTB slowed cell proliferation with enhanced inclusion of exon 3 of RTN4, and the overexpression of RTN4 splicing isoform with exon 3 resulted in a similar degree of decreased cell proliferation as the removal of PTB19.…”