Developmental Mutators and Early Onset Cancer

Childhood cancer mutagenesis caused by transposase-derived PGBD5

Genomic rearrangements are a hallmark of most childhood tumors, including medulloblastoma, one of the most common brain tumors in children, but their causes remain largely unknown. Here, we show that PiggyBac transposable element derived 5 (Pgbd5) promotes tumor development in multiple developmentally accurate mouse models of Sonic Hedgehog (SHH) medulloblastoma. Most Pgbd5-deficient mice do not develop tumors, while maintaining normal cerebellar development. Ectopic activation of SHH signaling is sufficient to enforce cerebellar granule cell progenitor-like cell states, which exhibit Pgbd5-dependent expression of distinct DNA repair and neurodevelopmental factors. Mouse medulloblastomas expressing Pgbd5 have increased numbers of somatic structural DNA rearrangements, some of which carry PGBD5-specific sequences at their breakpoints. Similar sequence breakpoints recurrently affect somatic DNA rearrangements of known tumor suppressors and oncogenes in medulloblastomas in 329 children. This identifies PGBD5 as a medulloblastoma mutator and provides a genetic mechanism for the generation of oncogenic DNA rearrangements in childhood cancer.

Why do young people get cancer?

Oncologists and cancer biologists are frequently confronted by the question of what causes cancer? This is particularly vexing for cancers affecting children and young adults who have had limited exposure to environmental mutagens and the effects of aging. Here, I focus on a general framework of the causes of early-onset cancer development in children and young adults by relating inherited and constitutional cancer predisposition, oncogenic pathogens, and developmental mutations. This framework has implications not only for mechanistic investigation of young cancers, but should also clarify improved strategies for their treatment, screening, and potential prevention.