The HHIP-AS1 lncRNA promotes tumorigenicity through stabilization of dynein complex 1 in human SHH-driven tumors

Most lncRNAs display species-specific expression patterns suggesting that animal models of cancer may only incompletely recapitulate the regulatory crosstalk between lncRNAs and oncogenic pathways in humans. Among these pathways, Sonic Hedgehog (SHH) signaling is aberrantly activated in several human cancer entities. We unravel that aberrant expression of the primate-specific lncRNA HedgeHog Interacting Protein-AntiSense 1 (HHIP-AS1) is a hallmark of SHH-driven tumors including medulloblastoma and atypical teratoid/rhabdoid tumors. HHIP-AS1 is actively transcribed from a bidirectional promoter shared with SHH regulator HHIP. Knockdown of HHIP-AS1 induces mitotic spindle deregulation impairing tumorigenicity in vitro and in vivo. Mechanistically, HHIP-AS1 binds directly to the mRNA of cytoplasmic dynein 1 intermediate chain 2 (DYNC1I2) and attenuates its degradation by hsa-miR-425-5p. We uncover that neither HHIP-AS1 nor the corresponding regulatory element in DYNC1I2 are evolutionary conserved in mice. Taken together, we discover an lncRNA-mediated mechanism that enables the pro-mitotic effects of SHH pathway activation in human tumors.

Long non-coding RNAs (lncRNAs) can contribute to cancers that are driven by Sonic hedgehog (SHH) signaling. Here the authors report that lncRNA HHIP-AS1 stabilises the mRNA of dynein complex 1, thereby, promoting the pro-mitotic effects of SHH-driven tumors.

MEDB-15. Dynamic chromatin alteration induces oncogenic hijacking by essential transcriptional factors during SHH medulloblastoma tumorigenesis

Medulloblastoma is a malignant brain tumor that occurs in the cerebellum, most frequently in children. Medulloblastoma is molecularly classified into four major groups, and therapies are now being developed according to the nature of these groups and subgroups. However, there are currently no effective molecularly targeted drugs for most of these groups. In recent years, we have been analyzing the genomes of medulloblastomas to identify genetic mutations involved in tumorigenesis. Among them, mutations in chromatin modifiers are frequently detected in medulloblastoma, suggesting the importance of alterations in the epigenome in tumor development. However, it remains unclear how epigenomic changes are involved in tumorigenesis. Here, we have used the SHH-group medulloblastoma (MB-SHH) mouse model to understand the epigenomic changes during tumor development and identify new therapeutic targets for medulloblastoma. To this end, we utilized an Atoh1-EGFP:Ptch1+/- mice that specifically label cerebellar granule cell progenitors (GNPs) that are known to be the cellular origin of MB-SHH, preneoplastic (PNCs) and tumor cells with EGFP during MB-SHH formation. Following FACS-based collection of EGFP-positive cells, comparative ATAC-seq analysis revealed that the open chromatin regions dynamically changed during transformation of GNPs into PNCs with enrichment of nuclear factor I (NFI) binding motifs. Cut & Tag analysis on these cells showed that NFI proteins bound chromatin regions that become more accessible during tumorigenesis, suggesting that NFI could play an important role in tumorigenesis after the epigenomic changes. Indeed, CRISPR-engineered in vivo somatic deletion of Nfia and/or Nfib prevented hyperplasia formation, confirming their essential role in tumor initiation. Knockdown of either NFIA or NFIB in patient-derived xenograft models also attenuated tumor growth. Thus, our study has uncovered a novel oncogenic mechanism that contributes to the development of MB-SHH tumors via alterations of accessible chromatin and aberrant DNA binding of NFI transcription factors.