Annual Report 2019
Laboratory of Molecular Carcinogenesis
Naoto Tsuchiya, Yuko Nishiyama, Yuko Fujiwara, Takahiro Shirai, Yuma Nozue
Introduction
To develop new strategies for cancer therapy and diagnosis, understanding molecular networks, formed intercellularly and intracellularly, is a major theme to be tackled. Our laboratory has been focusing on the biological functions of non-coding RNAs (ncRNAs). microRNAs (miRNAs), a class of ncRNAs, are known to be strong regulators of intra- and intercellular connections of molecular networks. We are extensively analyzing tumor-related miRNAs to find intracellular networks required for carcinogenesis, and have a major interest in the extracellular miRNAs as regulators for cancer cells to adapt to their microenvironment.
Research activities
1. Development of diagnosis in early stages of cancers using miRNAs
miRNAs in the body fluids, including serum and plasma, are expected to have applications for the development of cancer diagnosis, especially in the early stages. We reported a serum miRNA classifier for the detection of sarcomas across the various histological subtypes. In addition, a novel biomarker using miRNA isoforms has been created. It has been reported that the production of several isoforms occurs during the biogenesis of miRNAs in normal and malignant cells. These isoforms are generally kept at low levels by degradation processes in normal cells. However, we found that a certain miRNA isoform shows a high level of expression in cancer cells by means of unknown mechanisms. Surprisingly, high expression of one of the miR-21 isoforms is significantly associated with poor prognosis in lung adenocarcinoma (LADC) patients, especially being involved in the recurrences of early stages (I and II) of LADCs. Genome and transcriptome analyses indicate that cell cycle progression and immune checkpoint activation is one of the properties of tumors high in miR-21 isoforms. Detailed analyses are now being conducted to clarify the biological roles of miRNA isoforms and to develop the biomarkers for recurrence case detection of early stages of LADCs.
2. Regulation of tumor microenvironment (TME) by extracellular miRNA
Adaptation of sarcoma cells to their specific tumor microenvironment (TME) is a crucial component of maintenance of their malignant properties. Intracellular communication is generally mediated by cell-cell contact or secreted proteins, including cytokines and chemokines. Accumulating evidence demonstrates that extracellular vesicles (EVs), including those in exosomes and other particles, released by tumor cells play a major role in adaptation of malignant cells to the TME. Extracellular microRNAs (exmiRNAs) embedded in the EVs have been reported to be involved in this adaptation, and also in the initiation of metastasis. We identified miR-451a as a candidate regulator of metastasis of sarcomas. miR-451a, whose high expression is associated with good prognosis of sarcoma patients, was identified by comprehensive expression analysis using clinical samples of sarcomas. Although miR-451a did not affect cell proliferation, it strongly repressed sarcoma cell migration. CMTM6 was identified as a target gene of miR-451a, and its repression induced changes in the expression levels of plasma membrane proteins including growth factor receptors. Furthermore, CMTM6 was found to localize to the membrane structure of cells and be secreted to the extracellular space. Interestingly, we found that CMTM6 vesicles contain a subset of miRNAs. Therefore, our data suggest that CMTM6-containing EVs are involved in the secretion of a subset of miRNAs and this function is a potent feature promoting maintenance of the malignant phenotypes of tumor cells.
3. Understanding the cellular networks specifically formed in p53-inactivated cancer cells
Tumor-suppressor gene, TP53, is mutated and/or inactivated in half of human cancers, and dysfunction of p53 protein, a gene product of TP53, makes a critical contribution to the onset of carcinogenesis. Molecular network(s) specifically activated in p53-deficient contexts may promote proliferation and survival of cancer cells. Therefore, understanding molecular bases for the activation of these networks provides the weaknesses of p53-deficient cancer cells, leading to the development of an ideal strategy for cancer therapy. We previously identified NEK9 as a regulator of the cell cycle in p53-deficient cells. NEK9 depression inhibited cell proliferation only in p53-deficient cells in vitro and in vivo. Parallel analyses identified a cellular network activated in p53 mutant contexts. Lung adenocarcinoma cases with mutation of p53 showed significant up-regulation of this cellular network, suggesting this network-dependent proliferation occurs in p53 mutant cancer cells. Detailed molecular cross talks of NEK9 and this cellular network have been extensively analyzed.
Education
Supervising research and presentation skills for graduate school students and young scientists.
Future prospects
Our studies aim to clarify cellular network(s) formed in cancer cells. Results obtained from these studies will provide the molecular insights into how cancer cells developed and progressed. Especially, research focusing on extracellular miRNA and extracellular vesicles is expected to find a novel molecular mechanism for intercellular communication between cancer cells and surrounding non-tumor cells, and this finding will be the new principle for the development of the next cancer therapeutics.