Splicing factors PTBP1 and PTBP2 promote proliferation and migration of glioma cell lines

Abstract

Polypyrimidine tract-binding protein 1 (PTBP1) is a multi-functional RNA-binding protein that is aberrantly overexpressed in glioma. PTBP1 and its brain-specific homologue polypyrimidine tract-binding protein 2 (PTBP2) regulate neural precursor cell differentiation. However, the overlapping and non-overlapping target transcripts involved in this process are still unclear. To determine why PTBP1 and not PTBP2 would promote glial cell-derived tumours, both PTBP1 and PTBP2 were knocked down in the human glioma cell lines U251 and LN229 to determine the role of these proteins in cell proliferation, migration, and adhesion. Surprisingly, removal of both PTBP1 and PTBP2 slowed cell proliferation, with the double knockdown having no additive effects. Decreased expression of both proteins individually and in combination inhibited cell migration and increased adhesion of cells to fibronectin and vitronectin. A global survey of differential exon expression was performed following PTBP1 knockdown in U251 cells using the Affymetrix Exon Array to identify PTBP1-specific splicing targets that enhance gliomagenesis. In the PTBP1 knockdown, previously determined targets were unaltered in their splicing patterns. A single gene, RTN4 (Nogo) had significantly enhanced inclusion of exon 3 when PTBP1 was removed. Overexpression of the splice isoform containing exon 3 decreased cell proliferation to a similar degree as the removal of PTBP1. These results provide the first evidence that RNA-binding proteins affect the invasive and rapid growth characteristics of glioma cell lines. Its actions on proliferation appear to be mediated, in part, through alternative splicing of RTN4.

Significance of Polypyrimidine Tract–Binding Protein 1 Expression in Colorectal Cancer

“…It is involved in polyadenylation of the pre-mRNA 3 0 end (31-33) and also plays an important role in translational regulation of a subset of RNA transcription through internal ribosome entry sites (21,(34)(35)(36)(37). As for malignancies, PTBP1 is overexpressed in glioblastoma (7,8) and breast cancer (38), suppresses p27 expression, and contributes largely to cell proliferation (21,39). In zebrafish, PTBP1 ablation leads to increased proliferation and cell apoptosis (40).…”

“…PTBP1 is reported to promote cell proliferation in embryonic stem cells (20) and glioblastoma cells (7). To assess the effect of PTBP1 in proliferation of colorectal cancer cells, we performed a proliferation assay.…”

“…PTBP1 has been reported to play a key role in pre-mRNA splicing in cancer. Actually, PTBP1 have a critical effect on pyruvate kinase (PKM) alternative splicing in glioma, and this splicing strongly influences cancer progression (7,8). PTBP1 also has multiple functions other than pre-mRNA splicing and affects glioma cell invasion (7).…”

“…Actually, PTBP1 have a critical effect on pyruvate kinase (PKM) alternative splicing in glioma, and this splicing strongly influences cancer progression (7,8). PTBP1 also has multiple functions other than pre-mRNA splicing and affects glioma cell invasion (7). In ovarian cancer, PTBP1 levels correlate with the degree of malignancy (9).…”

Alternative pre-mRNA splicing regulation in cancer: pathways and programs unhinged

“…PTB has been shown to be overexpressed in ovarian cancer as well as gliomas (Jin et al 2003;He et al 2007;David et al 2010). Like hnRNP A2, PTB promotes invasive behavior in a number of cancer cell types (He et al 2007;Cheung et al 2009). In glioma-derived cells, the increased inclusion of exon 3 in the RTN4 transcript, which is inhibited by PTB, appears to underlie the adverse effects of PTB depletion on cell migration (Cheung et al 2009).…”