Vicious amplification loops involving a myriad of PcG proteins and miRNAs. Repression of PRC1-repressing miRNAs by PRC2 (A) establishes a positive-feedback loop ensuring coexpression and cooperation of 2 main PcG repressor complexes in stem and cancer cells; c-MYC, which is frequently translocated or overexpressed in Burkitt lymphoma and other B-cell lymphoma types, assembles a gene-silencing complex with PRC2 and HDACs to downregulate a list of tumor-suppressive miRNAs that can repress EZH2 and DNMT3A (B), hence establishing positive-feedback loops to enforce expression and functionality of PRC2 in B-cell lymphomas. Me3, trimethylation. Ub1, mono-ubiquitination.