AUTHOR=Jin Yan , Zhang Zhengming , Yu Qiao , Zeng Zhu , Song Hong , Huang Xiaoxu , Kong Qi , Hu Hao , Xia Yabin 

TITLE=Positive Reciprocal Feedback of lncRNA ZEB1-AS1 and HIF-1α Contributes to Hypoxia-Promoted Tumorigenesis and Metastasis of Pancreatic Cancer

JOURNAL=Frontiers in Oncology

VOLUME=11

YEAR=2021

URL=https://www.frontiersin.org/journals/oncology/articles/10.3389/fonc.2021.761979

DOI=10.3389/fonc.2021.761979

ISSN=2234-943X

ABSTRACT=<sec><title>Background</title><p>Many studies have reported the roles of the extracellular hypoxia microenvironment in the tumorigenesis and metastasis of multiple cancers. However, long noncoding RNAs (<italic>lncRNA</italic>s) that induce cancer oncogenicity and metastasis of pancreatic cancer (PC) under hypoxia conditions remain unclear.</p></sec><sec><title>Methods</title><p>In PC cells, the expression levels of <italic>lncRNA</italic>s in different conditions (normoxia or hypoxia) were compared through RNA sequencing (RNA-seq). The effects of the zinc finger E-box-binding homeobox 1 (<italic>ZEB1-AS1</italic>) antisense <italic>lncRNA</italic> on PC cells cultured in normoxia/hypoxia medium were measured through gain and loss-of-function experiments. Fluorescence <italic>in situ</italic> hybridization and luciferase reporter assays in addition to <italic>in vivo</italic> studies were utilized to explore the adaptive mechanisms of <italic>ZEB1-AS1</italic> in the hypoxia-promoted proliferation, migration, and invasion ability of PC cells. Moreover, the level of <italic>ZEB1-AS1</italic> and its associated targets or pathways were investigated in both PC and pancreatic normal tissues.</p></sec><sec><title>Results</title><p>RNA-seq revealed that <italic>ZEB1-AS1</italic> was significantly upregulated in PC cells under hypoxia conditions. The <italic>ZEB1-AS1</italic> expression level was closely associated with poor prognosis of PC patients. Knockdown of <italic>ZEB1-AS1</italic> suppressed the proliferation, migration, and invasion of PC cells <italic>in vitro</italic> as well as PC xenograft tumor growth <italic>in vivo</italic>. In PC cells, RNAi-mediated reduction of <italic>ZEB1-AS1</italic> inhibited zinc finger E-box-binding homeobox 1 (<italic>ZEB1</italic>), while <italic>ZEB1-AS1</italic> overexpression rescued <italic>ZEB1</italic> expression, indicating that <italic>ZEB1-AS1</italic> promotes <italic>ZEB1</italic> expression. Moreover, hypoxia-inducible factor-1α (<italic>HIF-1</italic>α)induced the expression of <italic>ZEB1-AS1</italic> by binding to the <italic>ZEB1-AS1</italic> promoter, which contains a putative hypoxia response element (HRE). Mechanistically, <italic>ZEB1-AS1</italic> scaffolded the interaction among <italic>HIF-1</italic>α, <italic>ZEB1</italic>, and histone deacetylase 1 (<italic>HDAC1</italic>), leading to deacetylation-mediated stabilization of <italic>HIF-1</italic>α. We further revealed that <italic>ZEB1</italic> induced the deacetylase capacity of <italic>HDAC1</italic> to suppress the acetylation or degradation of <italic>HIF-1</italic>α, improving <italic>HIF-1</italic>α assembly. Thus, hypoxia-induced <italic>ZEB1-AS1</italic> facilitated <italic>ZEB1</italic> transcription and the stability of <italic>HIF-1</italic>α, which promoted the metastasis of PC cells. Clinically, dysregulated <italic>ZEB1</italic> and <italic>HIF-1</italic>α expression was significantly correlated with histological grade, lymphatic metastasis, and distant metastasis in PC patients.</p></sec><sec><title>Conclusions</title><p>Our results emphasized that the positive reciprocal loop of <italic>HIF-1</italic>α/<italic>ZEB1-AS1</italic>/<italic>ZEB1</italic>/<italic>HDAC1</italic> contributes to hypoxia-promoted oncogenicity and PC metastasis, indicating that it might be a novel therapeutic target for PC.</p></sec>