ROLES OF THE SNF2-LIKE HELICASE HELLS IN MYC-DRIVEN GENE TRANSCRIPTION

Helicase, lymphoid specific (HELLS) is a SNF2-like ATP-dependent chromatin remodeler that participates in transcriptional repression and activation in mammalian cells (von Eyss et al., 2012; Myant and Stancheva, 2008). HELLS has long been described as a proliferation-associated protein (Jarvis et al., 1996; Lee et al., 2000; Raabe et al., 2001), but its role in neoplastic diseases, which are characterized by cellular hyperproliferation, has not been widely investigated. This dissertation presents work that addresses how the expression and molecular function of HELLS may have pathologic relevance to human cancers. Through immunohistochemistry and RNA sequencing (RNA-seq), we found that HELLS is abundantly expressed in proliferative compartments of normal human tissues and broadly overexpressed in a number of cancers. We used chromatin immunoprecipitation followed by sequencing (ChIP-seq) to identify HELLS binding sites in human Burkitt lymphoma, glioblastoma multiforme, and small cell lung carcinoma cell line genomes and found that HELLS predominantly targets the promoters of transcribed genes, leading us to conclude that in human cancers, HELLS function is likely to be associated with transcriptional activation rather than repression. Expressed HELLS-bound genes are significantly enriched for targets of MYC, which has well-described oncogenic effects. Using ChIP- seq and co-immunoprecipitation (co-IP), we found that HELLS and MYC colocalize extensively at transcribed gene promoters and physically interact in human cells, which suggests that the proteins may functionally interact as well. We modeled partial loss of HELLS function in human cells through CRISPR/Cas9-mediated engineering of a hypomorphic HELLS allele and found that genes previously identified as HELLS targets exhibited altered expression levels. In human osteosarcoma cells with inducible MYC, we tested the effects of RNA interference (RNAi)-induced HELLS knockdown on MYC- driven transcription. While MYC target gene induction was not wholly impaired, a subset of MYC targets exhibited decreased expression. We conclude that HELLS is a bona fide MYC-interacting protein that may contribute to regulating the expression of some MYC targets, which could have implications for human tumor biology