The Role of Polycomb Repressive Complex 1 in HL-60 Acute Promyelocytic Leukemia Cells

Abstract

Polycomb group (PcG) proteins are known to form multimeric complexes that suppress gene expression by epigenetic modifications1. Functionally, it consists of two distinct complexes, Polycomb Repressive Complex (PRC) 1 and PRC2. In acute promyelocytic leukemia (APL) disease model with PML-RAR fusion oncoprotein, PRC2, but not PRC1, is reported to cooperate with DNA methyltransferases and histone deacetylase 1 to suppress PML-RAR target genes2. Thus, we investigated the role of PRC1 genes in HL-60 APL cell line with wild type RAR . Upon induction of myeloid differentiation of HL-60 cells with all-trans retinoic acid (ATRA), expression of Mel18, a PRC1 gene, was reduced both at the transcript and protein levels in a time-dependent manner. Cell growth was reduced upon Mel18 gene knockdown with lentiviral shRNA (shMel18) infection. In addition, granulocytic differentiation was enhanced upon Mel18 gene knockdown as assessed by Wright-Giemsa staining, nitroblue tetrazolium staining, and quantification of differentiation marker genes. Notably, expression of a homeobox gene HOXA7 was significantly enhanced upon Mel18 gene knockdown. Reduced binding of Mel18 protein on the HOXA7 promoter was seen in ATRA-treated or shMel18-infected HL-60 cells, suggesting the role of HOXA7 gene in myeloid differentiation. Taken together, these results support the role of a PRC1 gene, Mel18, as a differentiation regulator in HL-60 APL cells with wild type RAR .