ATR maintains chromosomal integrity during postnatal cerebellar neurogenesis and is required for medulloblastoma formation

Abstract

Microcephaly and medulloblastoma may both result from mutations that compromise genomic stability. We report that ATR, which is mutated in the microcephalic disorder Seckel syndrome, sustains cerebellar growth by maintaining chromosomal integrity during postnatal neurogenesis. Atr deletion in cerebellar granule neuron progenitors (CGNPs) induced proliferation-associated DNA damage, p53 activation, apoptosis and cerebellar hypoplasia in mice. Co-deletions of either p53 or Bax and Bak prevented apoptosis in Atr-deleted CGNPs, but failed to fully rescue cerebellar growth. ATR-deficient CGNPs had impaired cell cycle checkpoint function and continued to proliferate, accumulating chromosomal abnormalities. RNA-Seq demonstrated that the transcriptional response to ATR-deficient proliferation was highly p53 dependent and markedly attenuated by p53 co-deletion. Acute ATR inhibition in vivo by nanoparticle-formulated VE-822 reproduced the developmental disruptions seen with Atr deletion. Genetic deletion of Atr blocked tumorigenesis in medulloblastomaprone SmoM2 mice. Our data show that p53-driven apoptosis and cell cycle arrest -and, in the absence of p53, non-apoptotic cell death -redundantly limit growth in ATR-deficient progenitors. These mechanisms may be exploited for treatment of CGNP-derived medulloblastoma using ATR inhibition.

A New Way to Treat Brain Tumors: Targeting Proteins Coded by Microcephaly Genes?

“…Our group has found that Atr deletion in CGNPs causes chromosomal damage and widespread apoptosis but no defect in proliferation at the early postnatal stage, when CGNP proliferation is maximal [134] . Cerebellar hypoplasia was partially rescued by co-deletion of either Bax and Bak or p53 .…”

“…We have found that Atr deletion in two different mouse models of medulloblastoma either significantly reduced tumorigenesis or completely abrogated tumor formation [145] . Our group is currently testing pharmacological ATR inhibition in mice with established medulloblastoma using a novel formulation in which the small molecule ATR inhibitor VE-822 is packaged in polymeric micelle nanoparticles (pVE-822).…”

“…A particular benefit of ATR inhibition for the treatment of brain cancers is that in the adult brain, ATR seems to be dispensable for the survival and function of post-mitotic neurons [145, 148, 149] . It has been shown in mice, however, that ATR is still required for normal proliferation of remaining neural stem cell populations in the adult mouse brain, such as in the hippocampus [150] .…”

“…However, the anti-mitotic agent vincristine has long been paired with alkylating agents and cisplatin in medulloblastoma therapy [153] . Moreover, disruption of ASPM and ATR does not block the cell cycle progression of neural stem/progenitor cells [69–71, 145] . The potential for combining the targeted disruption of microcephaly proteins with conventional radiation and chemotherapy is unknown, and must be investigated before conclusions can be drawn.…”

Nkx2-2as Suppression Contributes to the Pathogenesis of Sonic Hedgehog Medulloblastoma

“…22, 23). MBs were widely accepted to occur due to the transformation of CGNPs (24). We next cultured CGNPs isolated from neonatal mice, and achieved siRNA-based knockdown of Nkx2-2as in these cells (Fig.…”