Embryonal rhabdomyosarcoma (ERMS) is a childhood cancer that expresses myogenic master regulatory factor MYOD but fails to differentiate. Here, we show that the zinc finger transcription factor CASZ1 up-regulates MYOD signature genes and induces skeletal muscle differentiation in normal myoblasts and ERMS. The oncogenic activation of the RAS-MEK pathway suppresses CASZ1 expression in ERMS. ChIP-seq, ATAC-seq and RNA-seq experiments reveal that CASZ1 directly up-regulates skeletal muscle genes and represses non-muscle genes through affecting regional epigenetic modifications, chromatin accessibility and super-enhancer establishment. Next generation sequencing of primary RMS tumors identified a single nucleotide variant in the CASZ1 coding region that potentially contributes to ERMS tumorigenesis. Taken together, loss of CASZ1 activity, due to RAS-MEK signaling or genetic alteration, impairs ERMS differentiation, contributing to RMS tumorigenesis.

No abstract

The MYCN gene encodes the transcription factor N-Myc, a driver of neuroblastoma (NB). Targeting G-quadruplexes (G4s) with small molecules is attractive strategy to control the expression of undruggable proteins such as N-Myc. However, selective binders to G4s are challenging to identify due to the structural similarity of many G4s. Here, we report the discovery of a small molecule ligand (4) that targets the noncanonical, hairpin containing G4 structure found in the MYCN gene using small molecule microarrays (SMMs). Unlike many G4 binders, the compound was found to bind to a pocket at the base of the hairpin region of the MYCN G4. This compound stabilizes the G4 and has affinity of 3.5 ± 1.6 μM. Moreover, an improved analog, MY-8, suppressed levels of both MYCN and MYCNOS (a lncRNA embedded within the MYCN gene) in NBEB neuroblastoma cells. This work indicates that the approach of targeting complex, hybrid G4 structures that exist throughout the human genome may be an applicable strategy to achieve selectivity for targeting disease-relevant genes including protein coding (MYCN) as well as non-coding (MYCNOS) gene products.