Lung Tumorigenesis Alters the Expression of Slit2-exon15 Splicing Variants in Tumor Microenvironment.

Ming-Fang Wu,Jinghua Chang,Cheng-Yen Chuang,Wei-Ting Chen,Shang-Er Su,Ming-Shiou Jan,Pinpin Lin,Chen-Yi Liao

doi:10.3390/cancers11020166

Ming-Fang Wu, Jinghua Chang + Show 6 more

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https://doi.org/10.3390/cancers11020166

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Abstract

Slit2 expression is downregulated in various cancers, including lung cancer. We identified two Slit2 splicing variants at exon15—Slit2-WT and Slit2-ΔE15. In the RT-PCR analyses, the Slit2-WT isoform was predominantly expressed in all the lung cancer specimens and in their normal lung counterparts, whereas Slit2-ΔE15 was equivalently or predominantly expressed in 41% of the pneumothorax specimens. A kRasG12D transgenic mice system was used to study the effects of tumorigenesis on the expressions of the Slit2-exon15 isoforms. The results revealed that a kRasG12D-induced lung tumor increased the Slit2-WT/Slit2-ΔE15 ratio and total Slit2 expression level. However, the lung tumors generated via a tail vein injection of lung cancer cells decreased the Slit2-WT/Slit2-ΔE15 ratio and total Slit2 expression level. Interestingly, the lipopolysaccharide (LPS)-induced lung inflammation also decreased the Slit2-WT/Slit2-ΔE15 ratio. Since Slit2 functions as an anti-inflammatory factor, the expression of Slit2 increases in kRasG12D lungs, which indicates that Slit2 suppresses immunity during tumorigenesis. However, an injection of lung cancer cells via the tail vein and the LPS-induced lung inflammation both decreased the Slit2 expression. The increased Slit2 in the tumor microenvironment was mostly Slit2-WT, which lacks growth inhibitory activity. Thus, the results of our study suggested that the upregulation of Slit2-WT, but not Slit2-ΔE15, in a cancer microenvironment is an important factor in suppressing immunity while not interfering with cancer growth.

Highlights

Slit is a secreted glycoprotein, which was first identified as an axon-repellent molecule expressed by the glia cells along the midline of the CNS in Drosophila
As there were no normal lung specimens available for detecting the Slit2-exon15 splicing variants and both the normal lung bronchial epithelial Beas2B cells and 40% of the pneumothorax specimens expressed a higher level of Slit2-∆E15 than Slit2-WT, we investigated whether lung metastasis affects the Slit2 isoform expression in Balb/c nude mice injected with CL1-5 human lung cancer cells into the tail vein
Our studies showed that lung tumors generated by a tail vein injection of lung cancer cells and a LPS-induced lung inflammation decrease Slit2 expression in the lungs, while lung tumors formed in a transgenic RasG12D animal model increase Slit2 expression, mostly the Slit2-WT form

Summary

Introduction

Slit is a secreted glycoprotein, which was first identified as an axon-repellent molecule expressed by the glia cells along the midline of the CNS in Drosophila. Slit/Robo complex, it prevents axon from re-crossing the midline [1]. Slit/Robo signaling plays an important role in the development of multiple tissues, including lung, kidney, heart, and mammary gland [6,7,8,9,10]. The expression of Slit is repressed by hypermethylation in many cancers [11,12,13]. In addition to its role in embryogenesis, Slit/Robo signaling studies have focused on its role in tumorigenesis, including cancer cell proliferation, motility, and angiogenesis. Contradictory roles of Slit/Robo signaling in tumorigenesis have been discovered in various systems [14]

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