O-GlcNAc expression levels epigenetically regulate colon cancer tumorigenesis by affecting the cancer stem cell compartment via modulating expression of transcriptional factor MYBL1 [Glycobiology and Extracellular Matrices]

To study the regulation of colorectal adenocarcinoma progression by O-GlcNAc, we have focused on the O-GlcNAc-mediated epigenetic regulation of human colon cancer stem cells (CCSC). Xenograft tumors from colon tumor cells with OGT knockdown grew significantly slower than those formed from control cells, indicating a reduced proliferation of tumor cells due to inhibition of OGT expression. Significant reduction of CCSC population was observed in the tumor cells after OGT knockdown, while tumor cells treated with O-GlcNAcase inhibitor showed an increased CCSC population, indicating that O-GlcNAc levels regulated the CCSC compartment. When grown in suspension, tumor cells with OGT knockdown showed a reduced ability to form tumorspheres, indicating a reduced self-renewal of CCSC due to reduced levels of O-GlcNAc. ChIP-seq experiments using an anti-O-GlcNAc antibody revealed significant chromatin enrichment of O-GlcNAc modified proteins at the promoter of the transcription factor MYBL1, which was also characterized by the presence of H3K27me3. RNA-seq analysis showed an increased expression of MYBL1 in tumor cells with OGT knockdown. Forced overexpression of MYBL1 led to a reduced population of CCSC and tumor growth in vivo, similar to the effects of OGT silencing. Moreover, two CpG islands near the TSS site of MYBL1 were identified, and O-GlcNAc levels regulated their methylation status. These results strongly argue that O-GlcNAc epigenetically regulates MYBL1, functioning similarly to H3K27me3. The aberrant CCSC compartment observed after modulating O-GlcNAc levels, therefore, is likely to result, at least in part, from the epigenetic regulation of MYBL1 expression by O-GlcNAc, thereby significantly affecting tumor progression.

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