Background & Aims

Polycomb group proteins are epigenetic factors that silence gene expression; they are dysregulated in cancer cells and contribute to carcinogenesis by unclear mechanisms. We investigated whether BMI1 proto-oncogene, polycomb ring finger (BMI1), and polycomb group ring finger 2 (PCGF2, also called MEL18) are involved in the initiation and progression of colitis-associated cancer (CAC) in mice.

Methods

We generated mice containing floxed alleles of Bmi1 and/or Mel18 and/or Reg3b using the villin-Cre promoter (called Bmi1^ΔIEC, Mel18^ΔIEC, DKO, and TKO mice). We also disrupted Bmi1 and/or Mel18 specifically in intestinal epithelial cells (IECs) using the villin-CreER^T2-inducible promoter. CAC was induced in cre-negative littermate mice (control) and mice with conditional disruption of Bmi1 and/or Mel18 by intraperitoneal injection of azoxymethane (AOM) followed by addition of dextran sulfate sodium (DSS) to drinking water. Colon tissues were collected from mice and analyzed by histology and immunoblots; IECs were isolated and used in cDNA microarray analyses.

Results

Following administration of AOM and DSS, DKO mice developed significantly fewer polyps than control, Bmi1^ΔIEC, Mel18^ΔIEC, Reg3b^ΔIEC, or TKO mice. Adenomas in the colons of DKO mice were low-grade dysplasias, whereas adenomas in control, Bmi1^ΔIEC, Mel18^ΔIEC, Reg3b^ΔIEC, or TKO mice were high-grade dysplasias with aggressive invasion of the muscularis mucosa. Disruption of Bmi1 and Mel18 (DKO mice) during late stages of carcinogenesis significantly reduced the numbers of large adenomas and the load of total adenomas, reduced proliferation, and increased apoptosis in colon tissues. IECs isolated from DKO mice after AOM and DSS administration had increased expression of Reg3b compared with control, Bmi1^ΔIEC, or Mel18^ΔIEC mice. Expression of REG3B was sufficient to inhibit cytokine-induced activation of STAT3 in IECs. The human REG3β protein, the functional counterpart of mouse REG3B, inhibited STAT3 activity in human 293T cells, and its expression level in colorectal tumors correlated inversely with pSTAT3 level and survival times of patients.

Conclusions

BMI1 and MEL18 contribute to the development of CAC in mice by promoting proliferation and reducing apoptosis via suppressing expression of Reg3b. REG3B negatively regulates cytokine-induced activation of STAT3 in colon epithelial cells. This pathway might be targeted in patients with colitis to reduce carcinogenesis.

中文翻译：

---

BMI1和MEL18通过REG3B和STAT3促进小鼠结肠炎相关癌症

背景与目标

聚梳蛋白是使基因表达沉默的表观遗传因子。它们在癌细胞中失调，并通过不清楚的机制促进癌变。我们调查了BMI1原癌基因，多梳无名指（BMI1）和多梳组无名指2（PCGF2，也称为MEL18）是否参与小鼠结肠炎相关癌症（CAC）的发生和发展。

方法

我们生成包含的两侧装接loxP的等位基因的小鼠的Bmi1和/或Mel18和/或REG3B使用绒毛Cre重组启动子（称为Bmi1的^ΔIEC，Mel18 ^ΔIEC，DKO和TKO只小鼠）。我们还使用villin-CreER ^T2诱导型启动子特异性破坏了肠上皮细胞（IEC）中的Bmi1和/或Mel18。在cre-阴性同窝小鼠（对照）和有条件破坏Bmi1和/或Mel18的小鼠中诱导CAC通过腹膜内注射乙氧基甲烷（AOM），然后向饮用水中添加右旋糖酐硫酸钠（DSS）。从小鼠收集结肠组织，并通过组织学和免疫印迹进行分析。分离出IEC，并将其用于cDNA微阵列分析。

结果

继AOM和DSS的管理，DKO小鼠发展比对照息肉显著较少，Bmi1的^ΔIEC，Mel18 ^ΔIEC，REG3B ^ΔIEC，或者TKO小鼠。在DKO小鼠的结肠腺瘤低档发育异常，而在控制腺瘤，Bmi1的^ΔIEC，Mel18 ^ΔIEC，REG3B ^ΔIEC，或TKO小鼠高档发育异常与粘膜肌层的侵略性入侵。Bmi1和Mel18的破坏（DKO小鼠）在癌变的晚期阶段显着减少了大腺瘤的数量和总腺瘤的负荷，减少了结肠组织的增殖并增加了细胞凋亡。的IEC从DKO小鼠分离AOM和DSS给药增加了的表达后REG3B与对照相比的Bmi1 ^ΔIEC，或Mel18 ^ΔIEC小鼠。REG3B的表达足以抑制IEC中细胞因子诱导的STAT3激活。人REG3β蛋白是小鼠REG3B的功能配对物，可抑制人293T细胞中的STAT3活性，其在结肠直肠肿瘤中的表达水平与pSTAT3水平和患者生存时间成反比。

结论

BMI1和MEL18通过抑制Reg3b的表达促进增殖和减少细胞凋亡来促进小鼠CAC的发育。REG3B在结肠上皮细胞中负调节细胞因子诱导的STAT3激活。该途径可能针对结肠炎患者以减少致癌作用。