MicroRNA-101 (miR-101) is a regulator of histone methyltransferase EZH2 in cancer. The study shows that miR-101 inhibits EZH2 expression and function in cancer cells. Analysis of human prostate tumors revealed that miR-101 expression decreases during cancer progression, paralleling an increase in EZH2 expression. Genomic loss of miR-101 was found in 37.5% of clinically localized prostate cancers and 66.7% of metastatic disease. This loss leads to overexpression of EZH2 and dysregulation of epigenetic pathways, resulting in cancer progression. EZH2 is a component of the Polycomb Repressive Complex 2 (PRC2), which regulates gene expression by tri-methylating histone H3 lysine 27 (H3K27). EZH2 has oncogenic properties, promoting cell proliferation, colony formation, and invasion. Knock-down of EZH2 in cancer cells results in growth arrest and reduced tumor growth and metastasis. The study found that miR-101 regulates EZH2 expression by binding to its 3'UTR. Overexpression of miR-101 decreases EZH2 transcript and protein levels, while miR-101 overexpression inhibits cell proliferation, invasion, and tumor growth. AntagomiR technology was used to inhibit miR-101, leading to increased EZH2 expression and enhanced invasive potential. The study also showed that miR-101 overexpression reduces H3K27 tri-methylation, leading to decreased promoter occupancy of PRC2 target genes and increased gene expression. miR-101 expression inversely correlates with EZH2 levels in human tumors. Genomic loss of miR-101 loci was found in prostate cancer progression, with miR-101-1 and miR-101-2 loci being lost in a significant proportion of cases. This loss is somatic and leads to increased EZH2 expression and cancer progression. The findings suggest that miR-101 loss may represent a progressive molecular lesion in the development of more aggressive disease. Re-introducing miR-101 into tumors may have therapeutic benefit by reverting the epigenetic program of tumor cells to a more normal state.MicroRNA-101 (miR-101) is a regulator of histone methyltransferase EZH2 in cancer. The study shows that miR-101 inhibits EZH2 expression and function in cancer cells. Analysis of human prostate tumors revealed that miR-101 expression decreases during cancer progression, paralleling an increase in EZH2 expression. Genomic loss of miR-101 was found in 37.5% of clinically localized prostate cancers and 66.7% of metastatic disease. This loss leads to overexpression of EZH2 and dysregulation of epigenetic pathways, resulting in cancer progression. EZH2 is a component of the Polycomb Repressive Complex 2 (PRC2), which regulates gene expression by tri-methylating histone H3 lysine 27 (H3K27). EZH2 has oncogenic properties, promoting cell proliferation, colony formation, and invasion. Knock-down of EZH2 in cancer cells results in growth arrest and reduced tumor growth and metastasis. The study found that miR-101 regulates EZH2 expression by binding to its 3'UTR. Overexpression of miR-101 decreases EZH2 transcript and protein levels, while miR-101 overexpression inhibits cell proliferation, invasion, and tumor growth. AntagomiR technology was used to inhibit miR-101, leading to increased EZH2 expression and enhanced invasive potential. The study also showed that miR-101 overexpression reduces H3K27 tri-methylation, leading to decreased promoter occupancy of PRC2 target genes and increased gene expression. miR-101 expression inversely correlates with EZH2 levels in human tumors. Genomic loss of miR-101 loci was found in prostate cancer progression, with miR-101-1 and miR-101-2 loci being lost in a significant proportion of cases. This loss is somatic and leads to increased EZH2 expression and cancer progression. The findings suggest that miR-101 loss may represent a progressive molecular lesion in the development of more aggressive disease. Re-introducing miR-101 into tumors may have therapeutic benefit by reverting the epigenetic program of tumor cells to a more normal state.