Cancer-specific loss of TERT activation sensitizes glioblastoma to DNA damage

Abstract

Most glioblastomas (GBMs) achieve cellular immortality by acquiring a mutation in the telomerase reverse transcriptase (TERT) promoter. TERT promoter mutations create a binding site for a GA binding protein (GABP) transcription factor complex, whose expression is associated with TERT reactivation and telomere maintenance. Here, using biochemical and cell biology approaches, we show direct evidence that a specific GABP complex containing the subunit protein GABPB1L forms predominantly at the mutant TERT promoter, leading to TERT re-expression. Furthermore, we find that TERT promoter mutant GBM cells, unlike wild-type cells, are immediately dependent on GABPB1L for proliferation in cell culture and post-tumor establishment in vivo. Notably, when combined with frontline temozolomide (TMZ) chemotherapy, GABPB1L knockdown and the associated TERT reduction lead to an impaired DNA damage response that results in profoundly reduced growth of intracranial GBM tumors.Together, these findings provide new insights into the mechanism of cancer-specific TERT regulation, uncover rapid effects of TERT suppression in GBM maintenance, and establish GABPB1L inhibition, alone or in combination with chemotherapy, as a therapeutic strategy for TERTp mutant GBM.

Knockdown of the stem cell marker Musashi-1 inhibits endometrial cancer growth and sensitizes cells to radiation

“…While cancer stem cells have generally been associated with radioresistance, there is also specific evidence for the involvement of both TERT and the Notch pathway in radiation response: Loss of TERT is known to sensitize cancer cells to both irradiation and chemotherapy [60] and specifically impairs DNA damage repair [61], a key resistance mechanism after ionizing irradiation. Radioresistance via Notch-1 was reported for malignant gliomas [62] and numb/notch-1 signal pathway inhibition enhanced radiosensitivity in lung cancer [63], melanoma [64] and pancreatic cancer [65].…”

GABP Couples Oncogene Signaling to Telomere Regulation in TERT Promoter Mutant Cancer

“…TERTp mutations seem to be critical throughout tumorigenesis for ongoing telomere maintenance, making them an attractive, cancer-specific therapeutic target (Brastianos et al, 2017;Körber et al, 2019). In this regard, we recently proposed GABP as a potential therapeutic target in combination with chemotherapy (Mancini et al, 2018;Amen et al, 2021). Similarly, others have demonstrated that gene editing of the mutant TERTp reverses cellular immortality (Li et al, 2020).…”

“…Genetic modification of GABP by CRISPR-mediated insertions and deletions led to a reversal of cellular immortality in vitro and decreased tumor growth in vivo (Mancini et al, 2018). Meanwhile, using an inducible system in vivo, we showed that GABP reduction combined with temozolomide, a standard of care for patients with GBM, decreased cellular proliferation and dramatically prolonged survival of mice bearing MGMT methylated GBM, highlighting the therapeutic potential of targeting the GABP-TERT axis (Amen et al, 2021).…”

“…SF7996 (male), LN229 (female), U251 (male), and LN18 (male) were cultured in DMEM/Ham's F-12 1:1 supplemented with 10% Hyclone FBS (GE Life Sciences #SH30071) and 1% Pen-Strep (Gibco #15140-122). NHAPC5 were grown in DMEM (Corning # 10-013-CV) supplemented with 10% FBS and 1% Pen-Strep as previously described (Mancini et al, 2018;Amen et al, 2021). GBM6 (male) tumor-sphere cultures (Sarkaria et al, 2006) were cultured on ultra low attachment plates (Corning #CLS3471) in sterile-filtered Neurocult-A (StemCell #05751) supplemented with GlutaMAX (Gibco #32050-061), sodium pyruvate (Gibco #11360-070), N2 (Gibco #17502-048), and B27-A (Gibco #12587-010), and fed twice weekly with 20ng/mL EGF (Peprotech #AF-100-15) and 20 ng/mL FGF (Peprotech #100-18C).…”

Mutagenesis by RNA-containing telomerase holoenzyme complex or R-loops: a missing piece of the puzzle

“…Telomerase-based lifespan extension remedy is carcinogenic in animal studies, 1 at least partly resulted from the high basic amino acid contents in the protein components of the telomerase holoenzyme complex, accounting for 17.6%, 8.8%, 20.4%, 21.9%, 16.3%, 18.4% of the amino acid residues in TERT, Telomerase Cajal body protein 1, and H/ACA ribonucleoprotein complex subunits DKC1, 1, 2 and 3 respectively. Positively charged basic amino acids, for instance lysine, attract anions such as Cl -.…”