CircSMARCA5 Inhibits Migration of Glioblastoma Multiforme Cells by Regulating a Molecular Axis Involving Splicing Factors SRSF1/SRSF3/PTB

Abstract

Circular RNAs (circRNAs) have recently emerged as a new class of RNAs, highly enriched in the brain and very stable within cells, exosomes and body fluids. To analyze their involvement in glioblastoma multiforme (GBM) pathogenesis, we assayed the expression of twelve circRNAs, physiologically enriched in several regions of the brain, through real-time PCR in a cohort of fifty-six GBM patient biopsies and seven normal brain parenchymas. We focused on hsa_circ_0001445 (circSMARCA5): it was significantly downregulated in GBM biopsies as compared to normal brain tissues (p-value < 0.00001, student’s t-test), contrary to its linear isoform counterpart that did not show any differential expression (p-value = 0.694, student’s t-test). Analysis of a public dataset revealed a negative correlation between the expression of circSMARCA5 and glioma’s histological grade, suggesting its potential negative role in the progression to malignancy. Overexpressing circSMARCA5 in U87MG cells significantly decreased their migration, but not their proliferation rate. In silico scanning of circSMARCA5 sequence revealed an enrichment in binding motifs for several RNA binding proteins (RBPs), specifically involved in splicing. Among them, serine and arginine rich splicing factor 1 (SRSF1), a splicing factor known to be a positive controller of cell migration and known to be overexpressed in GBM, was predicted to bind circSMARCA5 by three different prediction tools. Direct interaction between circSMARCA5 and SRSF1 is supported by enhanced UV crosslinking and immunoprecipitation (eCLIP) data for SRSF1 in K562 cells from Encyclopedia of DNA Elements (ENCODE). Consistently, U87MG overexpressing circSMARCA5 showed an increased expression of serine and arginine rich splicing factor 3 (SRSF3) RNA isoform containing exon 4, normally skipped in a SRSF1-dependent manner, resulting in a non-productive non-sense mediated decay (NMD) substrate. Interestingly, SRSF3 is known to interplay with two other splicing factors, polypyrimidine tract binding protein 1 (PTBP1) and polypyrimidine tract binding protein 2 (PTBP2), that positively regulate glioma cells migration. Collectively, our data show circSMARCA5 as a promising druggable tumor suppressor in GBM and suggest that it may exert its function by tethering the RBP SRSF1.

CircZNF609/miR-134-5p/BTG-2 axis regulates proliferation and migration of glioma cell

“…CircRNA is more diverse in neuronal tissue than other tissues and plays critical roles in brain diseases, such as cerebrovascular disease and neurodegenerative disease . Recently, evidences suggested that the key role of circRNAs in the molecule mechanism of glioma development, where some circRNA promote glioma malignancy and some circRNA inhibit glioma progression . It is still few evidences of the role of circZNF609 in glioma carcinogenesis.…”

“…[3,4] Recently, evidences suggested that the key role of circRNAs in the molecule mechanism of glioma development, [5,6] where some circRNA promote glioma malignancy [7,8] and some circRNA inhibit glioma progression. [9] It is still few evidences of the role of circZNF609 in glioma carcinogenesis. As previous study, circZNF609 was indispensable for the growth of central nervous system.…”

circKIF4A promotes tumorogenesis of glioma by targeting miR-139-3p to activate Wnt5a signaling

“…Therefore, identifying the underlying mechanisms of glioma development and finding new therapeutic targets is an urgent issue. A growing body of evidence that circRNAs are involved in the development of glioma as an oncogene or tumor suppressor (Xie 2018;He et al 2018;Barbagallo et al 2018). It has been reported that circKIF4A expression is significantly increased in glioma tissues.…”

BRWSP: Predicting circRNA‐Disease Associations Based on Biased Random Walk to Search Paths on a Multiple Heterogeneous Network

“…According to the reports of Liu et al [21], the function of circRNAs was also versatile to function as microRNA (miRNA) sponges [5,13] and protein sponges [22,23]. For example, the circSMARCA5 [24] and circCFH [25] have been found to be expressed in a glioma-speci c pattern which may be used as the tumor biomarkers. CircNFIX [26] and circNT5E [27] have been found that they play oncogenic roles in glioma, whereas circFBXW7 and circSHPRH have been reported to function as the tumor suppressors.…”