5-hydroxymethylcytosine Deposition Mediates Polycomb Repressive Complex 2 Function in MYCN-amplified Neuroblastoma
Session Number
Project ID: BIO 11
Advisor(s)
Dr. Mark Applebaum; University of Chicago
Mohan Chennakesavulu; University of Chicago
Discipline
Biology
Start Date
19-4-2023 9:20 AM
End Date
19-4-2023 9:35 AM
Abstract
Neuroblastoma, the most common extracranial solid tumor in childhood, is hallmarked by epigenetic deregulation as a driver of oncogenesis. Polycomb Repressive Complex 2 (PRC2) methylates lysine 27 on histone 3 (H3K27me1-2-3), is generally associated with transcriptional silencing through deposition of H3K27me3 at promoter regions. In contrast to H3K27me3, 5-hydroxymethylcytosine (5-hmC) is an intermediate generated in the active demethylation of methylated cytosines (5-mC) and is associated with active transcription. Surprisingly, we found that 5-hmC is enriched at genes targeted by PRC2 in high-risk neuroblastoma tumors. Thus, we hypothesized a cooperative function between 5-hmC and PRC2 to mediate a de-differentiated state in MYCN-amplified neuroblastoma. We found that at the mononucleosome level, DNA associated with H3K27me3 was enriched for 5-hmC, suggesting a possible direct functional relationship between the two marks. Inhibition of EZH2 through treatment with tazemetostat significantly reduced levels of H3K27me3 and upregulated genes associated with differentiation and development, but did not significantly alter patterns of 5-hmC deposition. We found that there was significant overlap in genes upregulated following treatment with either decitabine (a hypomethylating agent) or tazemetostat. In conclusion, we identified an association between 5-hmC deposition and H3K27me3 enrichment at the mononucleosomal level in MYCN-amplified neuroblastoma cell lines.
5-hydroxymethylcytosine Deposition Mediates Polycomb Repressive Complex 2 Function in MYCN-amplified Neuroblastoma
Neuroblastoma, the most common extracranial solid tumor in childhood, is hallmarked by epigenetic deregulation as a driver of oncogenesis. Polycomb Repressive Complex 2 (PRC2) methylates lysine 27 on histone 3 (H3K27me1-2-3), is generally associated with transcriptional silencing through deposition of H3K27me3 at promoter regions. In contrast to H3K27me3, 5-hydroxymethylcytosine (5-hmC) is an intermediate generated in the active demethylation of methylated cytosines (5-mC) and is associated with active transcription. Surprisingly, we found that 5-hmC is enriched at genes targeted by PRC2 in high-risk neuroblastoma tumors. Thus, we hypothesized a cooperative function between 5-hmC and PRC2 to mediate a de-differentiated state in MYCN-amplified neuroblastoma. We found that at the mononucleosome level, DNA associated with H3K27me3 was enriched for 5-hmC, suggesting a possible direct functional relationship between the two marks. Inhibition of EZH2 through treatment with tazemetostat significantly reduced levels of H3K27me3 and upregulated genes associated with differentiation and development, but did not significantly alter patterns of 5-hmC deposition. We found that there was significant overlap in genes upregulated following treatment with either decitabine (a hypomethylating agent) or tazemetostat. In conclusion, we identified an association between 5-hmC deposition and H3K27me3 enrichment at the mononucleosomal level in MYCN-amplified neuroblastoma cell lines.