| Background:Nowadays,cancer is still the main leathal disease worldwide,and the main cause of the death for cancer is the metastasis or recurrence.Malignant tumors usually develop metastasis even after radical surgery,and in that case the chemotherapy effect is always not good then,which iducing the bad prognosis to patients.Therefore,to block the cancer prognosis and reduce the death rate,it is very important to well understand the underling mechanism of metastasis.The basic steps of metastasis can be simplified as:local invasion,intravasation,survival in the circulation,extravasation and colonization.Besides the metastatic hallmarkers of tumor cells,researchers commonly think the microenvironment also play a crucial role in metastatic process from tumor cell dissemination to organ-specific colonization.And Paget’s theory of "Seed and Soil" has already emphasized the significance of tumor microenvironment in metastasis."Cancer Epigentics" is a newly rapid developing area of research,which is the study of post-trancriptional modification of genome,involving none of nucleotide change,but heritable epigenetic change such as DNA methylation,microRNA regulation and histone modification.And recently,Epigenetics is found to be closely related to the tumor progress including metastasis.Not only the tumor cells,but also the stroma components of tumor microenvironment such as fibroblasts can be commonly epigenetically regulated in the tumor metastatic progression.Methods and Results:In this thesis,due to their high rate of metastasis,colorectal cancer and pancreatic cancer were taken as the models to investigate the epigenetic regulation in the tumor metastasis,especially the microRNA regulation and DNA methylation.The two main parts of the thesis are as followings:1.MicroRNAs regulation in the liver metastasis of colorectal cancer;2.Tumor-induced DNA methylation of cancer associated fibroblasts in the liver metastasis of pancreatic cancer.Considering the limited reseach in the microRNAs in the liver metastasis of colorectal cancer,a microRNA microarray analysis was conducted between the primary colorectal adenocarcinomas with or without liver metastasis at the time of diagnosis.Twelve microRNAs were found significantly disregulated in the primary colorectal tumor with liver metastasis,including miR-320b was significantly increased.By the proliferation and invasion assay,miR-320b was proved to promote the proliferation and invasion of colorectal cancer cells.And the expression of their target protein further uncovered that miR-320b promotes colorectal cancer proliferation and invasion by competing with its homologous miR-320a in targeting their downstream target proteins:β-catenin,Rac-1 and Neuropilin-1.In the second part,pancreatic cancer was taken as a model to explore the epigenetic regulation in microenvironment in cancer metastasis,because the stoma of pancreatic cancer is identified as the extensive desmoplastic stroma.Based on the KPC mouse model,we successfully isolated the primary tumor cell lines and cancer associated fibroblasts(CAFs)cell lines,derived from primary KPC pancreatic cancer tumor,liver and lung metastasis.It is found and validated in vitro that ALDH1a3 and NQO1 were specifically elevated methylated in CAFs in the microenvironment of liver metastasis.And the meth-microarray result of the human mesenchymal stem cells(hMSC)induced by human pancreatic cancer cells showed that the human pancreatic cancer cell can induce the high methylation of many important genes in the glucose and ATP metabolic pathway in hMSC,including the ALDHla3 and NQO1 we found.Thus,we propose a hypothesis here:pancreatic metastatic tumor cell may suppress the glucose and ATP metabolism of CAFs in the microenvironment,resulting in a low lactate microenvironment,then creat a lactate gradient for the tumor cells exporting out the high concentration of lactate accumulated in the tumor cells due to the Warburg effect.Conclusion:Until now,there was still limited research on the micoRNAs in liver metastasis of colorectal cancer.In the first part of the thesis,the number of the colorectal cancer patients with liver metastasis enrolled is the biggest until now.And for the first time,this study suggested that one nucleotide different between microRNA-320a and microRNA-320b results in opposite functions in controlling cell proliferation and invasion of colorectal cancer.It initiates new thoughts in exploring the unknown functions among the commom exsiting microRNA homologs in mammals.Similarly,it is also obscue that how the interaction between tumor cells and CAFs works in the metastasis of pancreatic cancer,involving the unknown epigenetic regulation in the metastasis.For the first time,we proved that the pancreatic tumor cell can induce the methylation of ALDHla3 and NQO1 in the CAFs,specifically in the liver metastatic microenvironment.And the "lactate gradien" hypothesis may open a brand new area for the investigation in the interaction between tumor cells and CAFs.Due to the complexity of tumor microenvironment with multiple cell components,the comprehensive understanding of the tumor microenvironment is still limited.In this part,we explore the tumor microenvironment function with the respect of epigenetic regulation,which is still a brand new area until now. |
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