Loss of ATRX Suppresses Resolution of Telomere Cohesion to Control Recombination in ALT Cancer Cells

Abstract

Summary The chromatin-remodeler ATRX is frequently lost in cancer cells that use ALT (alternative lengthening of telomeres) for telomere maintenance, but its function in telomere recombination is unknown. Here we show that loss of ATRX suppresses the timely resolution of sister telomere cohesion that normally occurs prior to mitosis. In the absence of ATRX, the histone variant macroH2A1.1 binds to the poly(ADP-ribose) polymerase tankyrase 1, preventing it from localizing to telomeres and resolving cohesion. The resulting persistent telomere cohesion promotes recombination between sister telomeres, while it suppresses inappropriate recombination between non-sisters. Forced resolution of sister telomere cohesion induces excessive recombination between non-homologs, genomic instability, and impaired cell growth, indicating the ATRX-macroH2A1.1-tankyrase axis as a potential therapeutic target in ALT tumors.

Loss of Tumor Suppressor STAG2 Promotes Telomere Recombination and Extends the Replicative Lifespan of Normal Human Cells

“…Immunoblots were incubated separately with the following primary antibodies: goat anti-SA1 C-term A300-157A (0.5 µg/ml) (Bethyl Laboratories, Inc.); goat anti-SA1 N-term A300-156A (0.5 µg/ml) (Bethyl Laboratories, Inc.); rabbit anti-SA1 172 (0.5 µg/ml) (8); rabbit anti-SA2 N-term A300-580A (0.20 µg/ml) (Bethyl Laboratories, Inc.); goat anti-SA2 C-term A300-158A (0.20 µg/ml) (Bethyl Laboratories, Inc.); rabbit anti-SMC3 – ChIP grade ab9263 (0.5 µg/ml) (Abcam); rabbit anti-SMC1 A300-055A-T (1.0 µg/ml) (Bethyl Laboratories, Inc.); rabbit anti-Rad21 A300-080A (0.5 µg/ml) Bethyl Laboratories, Inc.); rabbit anti-ATRX sc15408 (0.5 µg/ml) (Santa Cruz); mouse anti-DAXX VMA00318 (1:1000) (Biorad) and mouse anti-α-tubulin (1:10,000) (Sigma Aldrich, T5768), followed by horseradish peroxidase-conjugated donkey anti-rabbit or anti-mouse IgG (Amersham) or donkey ant-goat (Bethyl Laboratories, Inc.) (1:2500). Bound antibody was detected with Super Signal West Pico (Thermo Scientific).…”

“…The remaining 15% of cancers activate ALT (alternative lengthening of telomeres) (5) a recombination-based mechanism marked by high rates of telomere sister chromatid exchange (T-SCE) (6, 7). ALT cells exhibit defective (persistent) sister telomere cohesion into mitosis that contributes to the high level of T-SCE (8). …”

Mutant ATRX: uncovering a new therapeutic target for glioma

“…This complex acts as a telomere cap and protects chromosome ends from the inappropriate activity of the DNA surveillance and repair pathways and also mediate the specialized mechanisms required for their replication and cohesion [5, 8]. Dysfunction in H3.3-ATRX-DAXX chromatin remodeling complex leads to reduced incorporation of H3.3 at telomeric chromatin allowing for a permissive environment for telomere-telomere recombination.…”

“…Dysfunction in H3.3-ATRX-DAXX chromatin remodeling complex leads to reduced incorporation of H3.3 at telomeric chromatin allowing for a permissive environment for telomere-telomere recombination. The telomere sister chromatid exchange (T-SCE) model proposes that loss of ATRX suppresses the proper resolution of sister telomere cohesion that normally occurs prior to mitosis [8]. In the absence of ATRX, the histone variant macroH2A1.1 inhibitis the ability of the telomere-associated poly-ADP ribose polymerase tankyrase to dissociate components of the shelterin complex that mediates telomere cohesion.…”

“…There is a correlation between ATRX mutations and Alternative Lengthening of Telomeres (ALT), a non-telomerase-dependent telomere lengthening mechanism [4, 5, 6, 7, 8]. ATRX loss in gliomas has been demonstrated to promote ALT.…”