Ten Hypermethylated lncRNA Genes Are Specifically Involved in the Initiation, Progression, and Lymphatic and Peritoneal Metastasis of Epithelial Ovarian Cancer

<b></b> Our work aimed to evaluate and differentiate the role of ten lncRNA genes (<i>GAS5</i>, <i>HAND2-AS1</i>, <i>KCNK15-AS1</i>, <i>MAGI2-AS3</i>, <i>MEG3</i>, <i>SEMA3B-AS1</i>, <i>SNHG6</i>, <i>SSTR5-AS1</i>, <i>ZEB1-AS1</i>, and <i>ZNF667-AS1</i>) in the development and progression of epithelial ovarian cancer (EOC). A representative set of clinical samples was used: 140 primary tumors from patients without and with metastases and 59 peritoneal metastases. Using MS-qPCR, we demonstrated an increase in methylation levels of all ten lncRNA genes in tumors compared to normal tissues (<i>p</i> < 0.001). Using RT-qPCR, we showed downregulation and an inverse relationship between methylation and expression levels for ten lncRNAs (<i>r_s</i> < -0.5). We further identified lncRNA genes that were specifically hypermethylated in tumors from patients with metastases to lymph nodes (<i>HAND2-AS1</i>), peritoneum (<i>KCNK15-AS1</i>, <i>MEG3</i>, and <i>SEMA3B-AS1</i>), and greater omentum (<i>MEG3</i>, <i>SEMA3B-AS1</i>, and <i>ZNF667-AS1</i>). The same four lncRNA genes involved in peritoneal spread were associated with clinical stage and tumor extent (<i>p</i> < 0.001). Interestingly, we found a reversion from increase to decrease in the hypermethylation level of five metastasis-related lncRNA genes (<i>MEG3</i>, <i>SEMA3B-AS1</i>, <i>SSTR5-AS1</i>, <i>ZEB1-AS1</i>, and <i>ZNF667-AS1</i>) in 59 peritoneal metastases. This reversion may be associated with partial epithelial-mesenchymal transition (EMT) in metastatic cells, as indicated by a decrease in the level of the EMT marker, CDH1 mRNA (<i>p</i> < 0.01). Furthermore, novel mRNA targets and regulated miRNAs were predicted for a number of the studied lncRNAs using the NCBI GEO datasets and analyzed by RT-qPCR and transfection of SKOV3 and OVCAR3 cells. In addition, hypermethylation of <i>SEMA3B-AS1</i>, <i>SSTR5-AS1</i>, and <i>ZNF667-AS1</i> genes was proposed as a marker for overall survival in patients with EOC.