The supernatant of U87EGFRvIII when HM13 knockdown regulated the activity of the TGF‐β signaling pathway in vitro. (A) Luciferase reporter assay indicated that the supernatant of U87EGFRvIII when HM13 was knocked down inhibited TGF‐β transcriptional activity in different GBM cells (P < 0.01). (B) Western blot results showed the total, cytoplasm, and nuclear expression of smad2, p‐smad2, smad3, and p‐smad3 in U87 cells when cultured with supernatant of U87EGFRvIII infected with Lenti‐NC or Lenti‐siHM13. GAPDH or H3 was used as a loading control. (C) Confocal microscopy showed results consistent with Western blot. Compared with Lenti‐siHM13 cultured cells, Lenti‐NC‐treated cells exhibited higher p‐smad2 and p‐smad3 expression in the nucleus (magnification: 1000×).