Abstract 4134: HELLS is upregulated in Sonic hedgehog-associated medulloblastoma and proliferating cerebellar progenitors in a YAP-dependent manner

Abstract

Abstract Aberrant hedgehog signaling has been implicated in many human cancers, including medulloblastoma (MB), the most common malignant pediatric brain tumor. In fact, 30% of MB tumors are driven by aberrant activity of the Sonic hedgehog (SHH) signaling pathway. Our efforts focus on unraveling the downstream components of this pathway to better understand medulloblastoma and better inform therapeutic treatment development and decisions. While some of the signaling alterations in SHH MB are due to gene mutations or amplifications, others may have their roots in epigenetics. Therefore, we examined expression levels of several candidate epigenetic regulators in our systems and identified lymphoid-specific helicase (HELLS) as a gene whose expression is markedly induced by SHH. HELLS is a unique member of the SNF2 family of chromatin remodelers with multiple epigenetic functions in DNA methylation, histone acetylation and methylation, and chromatin remodeling. Additional roles in transcription activation and DNA repair have also been reported. Of interest, HELLS was shown to delay senescence by inhibiting the expression of CDKN2A, the genetic locus of P16INK4A, a key tumor suppressor whose inactivation has recently been reported as critical to MB progression. Confirming our initial finding, we observed considerably higher levels of HELLS in primary cultures of cerebellar granule neuron precursors (CGNPs) treated with SHH and in SmoA1 mouse MB tumor tissue when compared to adjacent normal cerebellum. Our preliminary analysis of a large cohort of MB patients also indicates overexpression of HELLS in human SHH MB. Bioinformatic promoter analysis and experiments with SHH pathway inhibitors suggest regulation of HELLS expression through members of the SHH proliferation program. Downstream effectors of SHH include GLI1/2 and YAP1. Inhibition of GLI1 and GLI2 with Gant61 in both CGNPs and cultured mouse MB cells resulted in a reduction of HELLS, but an increase of apoptosis markers may indicate this reduction is due to cell death rather than specific downregulation of HELLS. In contrast, verteporfin, an inhibitor of the interaction between the transcriptional co-activator YAP1 and the transcription factor TEAD1, resulted in a reduction of HELLS at the mRNA and protein level without a concomitant increase of apoptosis markers. These results suggest that transcriptional upregulation of HELLS in mouse cerebellar progenitors and MB tumors is mediated by the SHH effector YAP1. Experiments to confirm direct involvement of YAP1 in HELLS gene transcription are underway. Future studies to understand the role of HELLS in SHH MB have the potential to provide a better understanding of the disease and new avenues for development of targeted treatments to improve the lives of these patients. Citation Format: M. Hope Robinson, Anna M. Kenney. HELLS is upregulated in Sonic hedgehog-associated medulloblastoma and proliferating cerebellar progenitors in a YAP-dependent manner [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4134.