The epithelial-mesenchymal transition (EMT) is a highly conserved cellular process that transforms epithelial cells into mesenchymal cells; EMT is involved in normal embryogenesis and tissue repair and contributes to tumor progression, including tumor metastasis, therapy resistance and disease recurrence. Cancer stem cells (CSCs) represent a fraction of undifferentiated cancer cells that exhibit stem cell-like features. They have the ability to self-renew and can seed new tumors. Thus, CSCs might represent the cellular resource that causes metastases and accounts for therapy resistance. Recent studies have highlighted a link between EMT and CSC formation. EMT is relevant to the acquisition and maintenance of stem cell-like characteristics and is sufficient to endow differentiated normal and cancer cells with stem cell properties. Moreover, CSCs often exhibit EMT properties. This reciprocal relationship between EMT and CSCs might have many implications in tumor progression. In this paper, we review current studies related to EMT and CSCs in tumor progression and therapeutic resistance, with a special focus on the common characteristics and links between these processes, and explore the importance of these links in the development of improved antitumor therapies.

MicroRNAs (miRNAs) regulate tumor progression and invasion via direct interaction with target messenger RNAs (mRNAs). We defined miRNAs involved in cancer metastasis (metastamirs) using an established in vitro colorectal cancer (CRC) model of minimally metastatic cells (SW480 line) from a colon adenocarcinoma primary lesion and highly metastatic cells (SW620 line) from a metastatic lymph node from the same patient 1 year later. We used microarray analysis to identify miRNAs differentially expressed in SW480 and SW620 cells, focusing on miR-499-5p as a novel candidate prometastatic miRNA whose functions in cancer had not been studied. We confirmed increased miR-499-5p levels in highly invasive CRC cell lines and lymph node-positive CRC specimens. Furthermore, enhancing the expression of miR-499-5p promoted CRC cell migration and invasion in vitro and lung and liver metastasis in vivo, while silencing its expression resulted in reduced migration and invasion. Additionally, we identified FOXO4 and PDCD4 as direct and functional targets of miR-499-5p. Collectively, these findings suggested that miR-499-5p promoted metastasis of CRC cells and may be useful as a new potential therapeutic target for CRC.

Hypoxia has been implicated as a crucial microenvironmental factor that induces cancer metastasis. We previously reported that hypoxia could promote gastric cancer (GC) metastasis, but the underlying mechanisms are not clear. Long noncoding RNAs (lncRNAs) have recently emerged as important regulators of carcinogenesis that act on multiple pathways. However, whether lncRNAs are involved in hypoxia-induced GC metastasis remains unknown. In this study, we investigated the differentially expressed lncRNAs resulting from hypoxia-induced GC and normoxia conditions using microarrays and validated our results through real-time quantitative polymerase chain reaction. We found an lncRNA, AK058003, that is upregulated by hypoxia. AK058003 is frequently upregulated in GC samples and promotes GC migration and invasion in vivo and in vitro. Furthermore, AK058003 can mediate the metastasis of hypoxia-induced GC cells. Next, we identified γ-synuclein (SNCG), which is a metastasis-related gene regulated by AK058003. In addition, we found that the expression of SNCG is positively correlated with that of AK058003 in the clinical GC samples used in our study. Furthermore, we found that the SNCG gene CpG island methylation was significantly increased in GC cells depleted of AK058003. Intriguingly, SNCG expression is also increased by hypoxia, and SNCG upregulation by AK058003 mediates hypoxia-induced GC cell metastasis. These results advance our understanding of the role of lncRNA-AK058003 as a regulator of hypoxia signaling, and this newly identified hypoxia/lncRNA-AK058003/SNCG pathway may help in the development of new therapeutics.