PTBP2 and glioblastoma: In GBM, splicing regulatory factor SRSF1 was found to bind to circSMARCA5 at multiple sites, circSMARCA5 functioned as a tumor suppressor by regulating the activity of SRSF1, thus affecting the splicing and expression of SRSF3 and polypyrimidine tract binding protein 1(PTBP1) and polypyrimidine tract binding protein 2(PTBP2) [60].