Olfactomedin 4 is a key regulator of colon cancer progression

结直肠癌和结肠炎相关癌症是与炎症性肠病（IBD）相关的结直肠癌亚型，是主要的健康风险和主要的死亡原因。结肠癌的发生通常被认为是由多个阶段的癌基因顺序突变和肿瘤抑制所组成。大肠癌发生的最常见起始事件是腺瘤性息肉病（APC）基因的突变，其导致Wnt/β-连环蛋白通路的激活。鉴定APC缺失后调节肿瘤发生的分子事件对于理解结肠癌发生的机制和治疗发展是重要的。Wnt信号通过β-catenin是至关重要的，在调节正常的隐窝细胞的稳态和失调，在结肠癌的发生。几乎所有的结直肠癌都表现出APC或β-连环蛋白的突变，这导致GSK-3对磷酸化的阻断，从而导致β-连环蛋白稳定和增强的Wnt/β-连环蛋白信号传导。在肿瘤发生过程中，通常会获得额外的突变（如KRAS和TP 53）。长期以来，人们一直认为慢性IBD会增加结直肠癌的风险。转录因子NF-B也已被证明是将炎症和免疫与癌症发展和进展联系起来的关键因子。最近的研究表明，NF-B可以增强Wnt信号，导致上皮非干细胞去分化为肿瘤起始细胞。然而，明确定义Wnt信号的调节机制及其在结肠癌发生中的作用仍然是一个挑战。 嗅觉介导蛋白4（OLFM 4）是一种进化上保守的糖蛋白，属于嗅觉介导蛋白家族。它首先在人类造血骨髓细胞中克隆，也在肠隐窝中大量表达。它影响多种细胞过程，包括增殖、分化、凋亡、粘附和针对细菌感染的先天免疫。OLFM 4转录受PU.1、NF-B、Notch和视黄酸调节。其表达也通过启动子甲基化进行表观遗传调控。OLFM 4表达在人IBD中上调，其包括溃疡性结肠炎和克罗恩病。OLFM 4与NOD 1和NOD 2相互作用，NOD 1和NOD 2是已发现与克罗恩病相关的细菌感染的细胞内传感器。最近的一项研究表明，OLFM 4是肠道Lgr 5阳性干细胞的一个强大的标志物。 OLFM 4在早期结肠癌中呈高表达趋势，而在晚期结肠癌中表达减少或消失，提示OLFM 4可能在结肠腺瘤向异型增生的转化过程中发挥作用。在这里，我们探索了这种可能性，发现ApcMin/+小鼠中的Olfm 4缺失导致Wnt/-连环蛋白信号传导基因的上调和远端结肠中的癌形成。我们还观察到Olfm 4缺陷小鼠在氧化偶氮甲烷/葡聚糖硫酸钠（AOM/DSS）诱导的结肠炎相关癌症模型中表现出强烈的肠隐窝增生和严重的炎症。此外，我们发现OLFM 4既是Wnt/β-catenin通路的靶基因，也是Wnt/β-catenin通路的抑制剂。

Colorectal cancer and colitis-associated cancer, a subtype of colorectal cancer associated with inflammatory bowel disease (IBD), are major health risks and leading causes of death. Colon carcinogenesis is generally regarded as being composed of multiple stages of sequential mutations of some oncogenes and tumor suppress. The most common initiating event of colorectal carcinogenesis is mutation of the adenomatous polyposis coli (APC) gene, which leads to activation of the Wnt/β-catenin pathway. Identification of molecular events that regulate tumorigenesis after APC loss is important for understanding the mechanism of colon carcinogenesis and therapeutic development. Wnt signaling via β-catenin is critically important in regulating normal crypt cell homeostasis and is dysregulated in colon carcinogenesis. Almost all colorectal cancers exhibit mutation of either APC or β-catenin, which leads to the blockade of phosphorylation by GSK-3, resulting in β-catenin stabilization and enhanced Wnt/β-catenin signaling. During the course of tumorigenesis, additional mutations (such as KRAS and TP53) are usually acquired. It has long been recognized that chronic IBD increases the risk of colorectal cancer. The transcription factor NF-κB has also been shown to be a key factor linking inflammation and immunity to cancer development and progression. A recent study showed that NF-κB could enhance Wnt signaling, leading to the dedifferentiation of epithelial non-stem cells into tumor-initiating cells. However, clearly defining the regulatory mechanism of Wnt signaling and its role in colon carcinogenesis continues to present a challenge. Olfactomedin 4 (OLFM4) is an evolutionarily conserved glycoprotein that belongs to an olfactomedin family. It was first cloned in human hematopoietic myeloid cells and is also abundantly expressed in intestinal crypts. It affects a diverse set of cellular processes, including proliferation, differentiation, apoptosis, adhesion, and innate immunity against bacterial infections. OLFM4 transcription is regulated by PU.1, NF-κB, Notch, and retinoic acids. Its expression is also regulated epigenetically through promoter methylation. OLFM4 expression is upregulated in human IBD, which comprises ulcerative colitis and Crohns disease. OLFM4 interacts with NOD1 and NOD2, which are intracellular sensors for bacterial infection that have been found to be associated with Crohns disease. A recent study has demonstrated that OLFM4 is a robust marker for intestinal Lgr5-positive stem cells. OLFM4 tends to be overexpressed in early-stage colon cancer, but reduced or lost in advanced stages of the disease .These observations suggest that OLFM4 may play a role in the transition from colon adenoma to dysplastic tumors. Here we explored this possibility and found that Olfm4 deletion in ApcMin/+ mice leads to upregulation of Wnt/β-catenin signaling genes and carcinoma formation in the distal colon. We also observed that Olfm4-deficient mice exhibited robust intestinal crypt hyperplasia and severe inflammation in an azoxymethane/dextran sodium sulfate (AOM/DSS)-induced colitis-associated cancer model. In addition, we showed that OLFM4 is a both a target gene and an inhibitor of the Wnt/β-catenin pathway.