Role of ASCL1 and Its Interactors in Neuroblastoma
Neuroblastoma (NB) arises due to incomplete differentiation of sympathoadrenal cells during development, and is maintained by either an adrenergic or mesenchymal core transcriptional regulatory circuitry (CRC). Differentiation therapies are an attractive therapeutic approach for NB. However, it is still not fully understood how to modulate NB cell behaviour to limit proliferation and potentiate differentiation. Achaete-scute complex-like 1 (ASCL1) is a transcription factor required for both progenitor maintenance and neuronal differentiation in normal sympathoadrenal development. In NB, ASCL1 also has a dual role - as a component of the adrenergic CRC, ASCL1 supports cell proliferation, while promoting differentiation and cell-cycle exit on ASCL1 over expression. The mechanism behind these two functions is not fully understood but is likely to involve ASCL1 interactors regulating its transcriptional activity on chromatin. In this dissertation, the mechanisms by which ASCL1 induces differentiation are explored by characterising its genome-wide transcriptional targets, chromatin binding, whole proteome and protein-protein interactor differences between two pairs of NB cell lines overexpressing exogenous ASCL1. Each cell line was chosen to represent different genetic and epigenetic backgrounds of neuroblastoma disease. It was found that ASCL1 overexpression inhibited proliferation and induced morphological and transcriptional features of neuronal differentiation to a differing extent in each cell line. In the cell lines more responsive to ASCL1-induced differentiation, ASCL1 was found to associate more with proteins known to positively impact neuronal differentiation during development, such as BCL11B, PBX1, PHOX2B, SOX11, and others. On the other hand, in the cell lines less responsive to ASCL1-induced differentiation, ASCL1 associated more with proteins involved in cell-cycle regulation, such as CDKs and cyclins, or showed weaker association with most of its interactors, including E-protein TCF4, compared to a more responsive cell line. This work suggests understanding ASCL1 interactors could help explain whether this key transcriptional regulator promotes cell proliferation or differentiation of NB, allowing modulation of ASCL1-mediated differentiation to improve therapeutic options for this devastating disease.
ASCL1, cell cycle, differentiation, neuroblastoma, neuronal, protein-protein interactions
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