LncRNA MALAT1 facilitates ovarian cancer progression through promoting chemoresistance and invasiveness in the tumor microenvironment

Upregulation of metastasis-associated lung adenocarcinoma transcript 1 (MALAT1, also known as nuclear-enriched abundant transcript 2 (NEAT2) or LINC00047) was found in various solid tumors, including epithelial ovarian cancer (EOC). MALAT1 is a long noncoding (lnc)RNA that regulates many functional signaling pathways, including tumorigenesis. Herein, we observed the consistent upregulation of MALAT1 in MYST4-overexpressing cell lines, while MALAT1 was frequently found to be upregulated in various types of clinical carcinoma tissues, especially EOC. To further investigate the lncRNA MALAT1 in EOC progression, the transduced overexpression of MALAT1 in EOC cell lines and cancer-associated fibroblasts (CAFs) was employed. We found that MALAT1 overexpression in EOC cell lines significantly increased drug resistance, cell migration, and invasion. Furthermore, the concomitant overexpression of MALAT1 in EOC cells and CAFs dramatically increased EOC cell invasion. Accordingly, a mechanistic investigation of MALAT1 overexpression in EOC cells showed that expressions of the cytokines interleukin (IL)-1β and p-P38/p-NFκB/Cox2/prostaglandin E2 (PGE2) signaling were significantly increased, which stimulated inflammatory responses, whereas cell apoptosis was inhibited due to increased Bcl-2 levels and reduced Caspase3 levels. After MALAT1 was overexpressed in EOC cells, and the cyclin D1, p-PI3K, and p-Akt expressions increased, suggesting the promotion of tumor cell proliferation, while increased zinc finger E-box-binding homeobox-2 (ZEB2), yes-associated protein (YAP), and vimentin expression with E-cadherin downregulation indicated the enhancement of the epithelial-to-mesenchymal transition (EMT) in terms of metastasis, thereby triggering EOC progression. Together, our findings demonstrate how MALAT1 overexpression facilitates an oncogenic function through inhibiting tumor cell apoptosis, combined with increasing tumor cell inflammation, proliferation, and invasion in the EOC tumor microenvironment. MALAT1 is thus a potential diagnostic marker and therapeutic for this malignancy.