Sonic hedgehog accelerates DNA replication to cause replication stress promoting cancer initiation in medulloblastoma

Menée in vitro et à l'aide de modèles murins, cette étude met en évidence un mécanisme par lequel la protéine "Sonic hedgehog", en accélérant la réplication de l'ADN, cause un stress de réplication qui favorise le développement d'un médulloblastome

Résumé en anglais

The mechanisms generating cancer-initiating mutations are not well understood. Sonic hedgehog (SHH) pathway activation is frequent in medulloblastoma (MB), with PTCH1 mutations being a common initiating event. Here we investigated the role of the developmental mitogen SHH in initiating carcinogenesis in the cells of origin: granule cell progenitors (GCPs). We delineate a molecular mechanism for tumor initiation in MB. Exposure of GCPs to Shh causes a distinct form of DNA replication stress, increasing both origin firing and fork velocity. Shh promotes DNA helicase loading and activation, with increased Cdc7-dependent origin firing. The S-phase duration is reduced and hyper-recombination occurs, causing copy number neutral loss of heterozygosity—a frequent event at the PTCH1/ptch1 locus. Moreover, Cdc7 inhibition to attenuate origin firing reduces recombination and preneoplastic tumor formation in mice. Therefore, tissue-specific replication stress induced by Shh promotes loss of heterozygosity, which in tumor-prone Ptch1+/− GCPs results in loss of this tumor suppressor—an early cancer-initiating event.