Regulation of Differentiation of Pediatric Embryonal Tumors- Neuroblastoma

Division Of Basic Sciences - Nci

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Abstract

The amplification of MYCN inhibits the ability of Neuroblastoma tumor cells to control growth and differentiate into a post-mitotic neuronal state. We know that decreasing MYCN levels will lead to inhibition of the ability of cells to proliferate and the implementation of a differentiation program. Targeting transcription factors such as MYCN has been difficult due to their structure in which a large region is intrinsically disordered. This intrinsically disordered region (IDR) enables MYC to interact with numerous other proteins to variably regulate different transcriptional programs. Our studies have shown that by decreasing MYCN protein levels, tumor cell growth is inhibited and the tumor cells express a more differentiated state similar to normal neural cells. The studies in this Project are aimed at identifying MYCN interacting proteins, identifying how these protein interaction regulate gene programs and then targeting these interacting proteins, many of which have enzymatic activities that are more readily druggable. Key findings in this research period identified MYCN interacting protein WDR5 that positivly regulated a "canonical MYC program" to support cell growth and ribosomal biogenesis. MYCN also interacted with G9a at enhancers to negatively regulated genes that would induce a neuronal differentiation program. Thus MYCN was both stimulating cell proliferation and blocking the cells ability to differentiate. By using a combination of small molecule inhibitors that targeted WDR5 and G9a we could block tumor cell growth and induce differentiation. This paper was published in PLOS Biology. We also identified that MYCN stimulates KAT2A expression and interacts with KAT2A to bind DNA while KAT2A, a histone acetylase, acetylates MYCN increasing the stability of the MYCN protein. By establishing this feed-forward interaction loop there is global gene regulation that stabilizes the malignant phenoype. We tested a KAT2A Protac degrader that caused a reduction in MYCN levels, interfered with the feedforward loop and suppressed MYCN transcription and cell proliferation. This was published in Oncogenesis. These studies supported our hypothesis that by targeting MYCN protein interactors one could target oncogenic programs driven by MYCN. Independent studies carried out by our collaborator confirmed G9a as an oncogenic mediator in Neuroblastoma,