The Role And Mechanism Of Exosormal MiR-17 Derived From Colorectal Cancer Cells In Promoting The Liver Metastasis Of Colorectal Cancer

Tissue microenvironment plays an important role in the initiation and development of tumor.Not only the microenvironment of primary tumor sites can transform into the tumor microenvironment(TME)to promote tumor proliferation and invasion,and tissue in target organ of metastasis may also shift for pre-metastatic niche before metastasis actually happened,forming a suitable environment for circulating tumor cells’ colonization and growth to form secondary lesions,thus promotes the metastasis of malignant tumor.Exosomes are suggested as important factors to regulate the formation of pre-metastatic niche.In liver metastasis of pancreatic cancer and lung metastasis of melanoma in mice model,tumor-cell-derived-exosomes(TEXs)have been proved to accelerate tumor metastasis by promoting formation of pre-metastatic niche,but there were no relative researches in liver metastases of colorectal cancer(CRC)with very high mortality.In order to study the effects of TEXs and its embedded microRNAs on the liver metastasis of CRC,we established xenograft model of liver metastasis by splenic inoculation of tumor cells with different capacity of metastasis.The effects of exosomes on the formation of pre-metastatic niche in liver were observed through sustained intravenous injection of TEXs before tumor cells were inoculated in spleen.We found that TEXs can be uptaken by macrophages in liver tissue,and TEXs form cancer cell lines with higher metastasis capacity(SW620-exo)can induce inflammation in liver tissue,meanwhile the same dose of TEXs from cell lines with low metastasis capacity did not have this effect.Then we compared the microRNA expression profiles of exosomes secreted by CRC cells with different metastasis capicity using the Illumina HiSeq 2500 system.And Exosomal microRNA expression profiling analysis identified several differentially expressed miRNAs related to inflammation and tumor progression including miR-17.Dysregulated expressed miRNAs were then confirmed by individual qRT-PCR in 29 CRC patients and 10 normal controls.We verified the correlation of exosomal miR-17 expression levels with colorectal cancer(CRC)progression and metastasis,thus identified circulating exosomal miR-17-5p as promising prognostic biomarkers for CRC and metastasis patients.In vitro experiments showed that miR-17 was able to activate macrophages via NF-κ B pathway by binding TLR8,inducing the secretion of IL1-β,IL-6,TNF-a and other pro-inflammatory factors.This study reveals that TEXs and exosomal miR-17 from CRC cell lines may promote pre-metastatic niche formation in liver tissue to accelerate tumor metastasis,and circulating exosomal miR-17 can serve as a biomarker for metastasis of CRC patients.