MLL gene rearrangements (MLLr) are a common cause of aggressive, incurable acute lymphoblastic leukemias (ALL) in infants and children, most of which originate in utero. The most common MLLr produces an MLL-AF4 fusion protein. MLL-AF4 promotes leukemogenesis by activating key target genes, mainly through recruitment of DOT1L and increased histone H3 lysine-79 methylation (H3K79me2/3). One key MLL-AF4 target gene is PROM1, which encodes CD133 (Prominin-1). CD133 is a pentaspan transmembrane glycoprotein that represents a potential pan-cancer target as it is found on multiple cancer stem cells. Here we demonstrate that aberrant PROM1/CD133 expression is essential for leukemic cell growth, mediated by direct binding of MLL-AF4. Activation is controlled by an intragenic H3K79me2/3 enhancer element (KEE) leading to increased enhancer–promoter interactions between PROM1 and the nearby gene TAPT1. This dual locus regulation is reflected in a strong correlation of expression in leukemia. We find that in PROM1/CD133 non-expressing cells, the PROM1 locus is repressed by polycomb repressive complex 2 (PRC2) binding, associated with reduced expression of TAPT1, partially due to loss of interactions with the PROM1 locus. Together, these results provide the first detailed analysis of PROM1/CD133 regulation that explains CD133 expression in MLLr ALL.

MLL 基因重排 (MLLr) 是婴儿和儿童侵袭性、无法治愈的急性淋巴细胞白血病 (ALL) 的常见原因，其中大多数起源于子宫内。最常见的 MLLr 产生 MLL-AF4 融合蛋白。MLL-AF4 通过激活关键靶基因促进白血病发生，主要是通过募集 DOT1L 和增加组蛋白 H3 赖氨酸 79 甲基化 (H3K79me2/3)。一个关键的 MLL-AF4 靶基因是PROM1，它编码 CD133 (Prominin-1)。CD133 是一种五跨跨膜糖蛋白，代表潜在的泛癌靶点，因为它存在于多个癌症干细胞上。在这里，我们证明了异常的PROM1/CD133 表达对白血病细胞生长至关重要，由 MLL-AF4 直接结合介导。激活由基因内 H3K79me2/3 增强子元件 (KEE) 控制，导致PROM1和附近基因TAPT1之间的增强子-启动子相互作用增加。这种双基因座调控反映在白血病表达的强相关性中。我们发现在PROM1 /CD133 非表达细​​胞中，PROM1基因座受到多梳抑制复合物 2 (PRC2) 结合的抑制，这与TAPT1的表达减少有关，部分原因是与PROM1基因座的相互作用丧失。总之，这些结果提供了对PROM1的第一次详细分析/CD133 调节，解释 MLLr ALL 中的 CD133 表达。