Olfactomedin 4- a key regulator of human neutrophil function, role in small intestinal adenocarcinoma.

小肠腺癌是一种罕见的肠道恶性肿瘤，具有独特的临床和分子实体。最近，肠干细胞标志物OLFM 4（Olfactomedin 4）和原癌基因RET的融合已在小肠腺癌患者中报道。但这种新发现的融合基因在肿瘤发生中的潜在作用尚不清楚。在我们目前的研究中，我们研究了OLFM 4-RET融合构建体的生物学后果，以确定它是否可以启动小肠组织中的肿瘤发生。首先，我们发现OLFM 4表达在小肠癌中经常丢失或减少，其下调与低分化和晚期肿瘤阶段相关。然后我们研究了OLFM 4-RET是否可以诱导细胞转化。在HEK 293细胞中，OLFM 4-RET的表达诱导早期细胞快速增殖和晚期细胞凋亡。OLFM 4-RET融合蛋白保留在细胞膜上，并在Y509处组成性磷酸化，并导致Ras-Raf-MAPK通路和STAT 3通路的激活。OLFM 4-RET可上调多个癌症相关基因家族，包括AP 1、EGFR、MMPs。OLFM 4-RET在HuTu 80小肠癌细胞中的表达增加MAPK、STAT 3和PI 3-Akt通路的活化，并中和RET诱导的凋亡和集落生长抑制。最后，我们已经表明，OLFM 4-RET在小肠中的靶向表达导致转基因小鼠中隐窝增生、腺瘤和腺癌的发展。我们的研究表明OLFM 4-RET是小肠癌发生的启动子。OLFM 4-RET融合激酶可能是小肠腺癌的一个靶向癌基因。

Small intestine adenocarcinoma is a rare intestinal malignancy with a distinct clinical and molecular entity. Recently, the fusion of intestinal stem cell marker OLFM4 (Olfactomedin 4) and the proto-oncogene RET has been reported in a patient with small intestine adenocarcinoma. But this newly discovered fusion genes potential role in carcinogenesis is not known. In our current study, we investigated the biological consequences of a OLFM4-RET fusionconstruct in order to determine whether it can initiate the tumorigenesis in small intestine tissue. First, we show that OLFM4 expression is frequently lost or reduced in small intestine carcinoma and its downregulation is correlated with poor differentiation and advanced tumor stage. Then we investigated whether OLFM4-RET can induce cellular transformation. In HEK293 cells, expression of OLFM4-RET induces early rapid cell proliferation and apoptosis at later stage. The OLFM4-RET fusion protein remains on cell membrane and is constitutively phosphorylated at Y509 and leads to activation of Ras-Raf-MAPK pathway and STAT3 pathway. Multiple cancer-related family of genes including AP1, EGRs, MMPs have been upregulated by OLFM4-RET. Expression of OLFM4-RET in HuTu80 small intestine cancer cells increased activation of MAPK, STAT3 and PI3-Akt pathway and neutralized RET-induced apoptosis and inhibition of colony growth. Finally, we have shown that targeted expression of OLFM4-RET in the small intestine leads to the development of crypt hyperplasia, adenoma and adenocarcinoma in transgenic mice. Our study suggests that OLFM4-RET is an initiator of small intestine carcinogenesis. OLFM4-RET fusion kinase may prove to be a targetable oncogene in small intestine adenocarcinoma.