The HIF-1/SNHG1/miR-199a-3p/TFAM axis explains tumor angiogenesis and metastasis under hypoxic conditions in breast cancer.

ABSTRACT

Activation of hypoxia-inducible factors (HIFs) as a result of intratumoral hypoxia modulates a cascade of molecular pathways thus leading to angiogenesis and metastasis in many solid tumors, including breast cancer (BC). In our paper, we report a regulatory axis of HIF-1, SNHG1, miR-199a-3p, and mitochondrial transcription factor A (TFAM) involved in tumor angiogenesis and metastasis under hypoxic conditions in BC. The expression of SNHG1 was determined in human BC cells cultured in hypoxia (1% O2 , 24 h) and normoxia (20% O2 , 24 h). Cultured MDA-MB-231 cells were assayed for the proliferation, migration, invasion, angiogenesis in vitro by using EdU staining, transwell chamber assays, Matrigel-based angiogenesis assays, tumorigenesis, and lung metastasis in vivo by using an orthotopic-transplant model of human BC. Dual-luciferase reporter assay, chromatin immunoprecipitation quantitative polymerase chain reaction assay, fluorescence in situ hybridization assay, RNA-binding protein immunoprecipitation assay, and RNA pull-down were performed to test interaction between HIF-1 and SNHG1, SNHG1 and miR-199a-3p, miR-199a-3p and TFAM. SNHG1 was increased under hypoxic conditions at a HIF-1-dependent manner. SNHG1 knockdown tempered MDA-MB-231 cell proliferation, migration, invasion, angiogenesis, in vitro, tumorigenesis, and lung metastasis in vitro. SNHG1 was co-expressed with miR-199a-3p and regulated the TFAM, a target gene of miR-199a-3p. SNHG1 increased the TFAM by binding with miR-199a-3p, thus promoting BC development and metastasis. These results support a regulatory axis consisting of HIF-1, SNHG1, miR-199a-3p, and TFAM during BC development and metastasis under hypoxic conditions, providing an opportunity to develop targeted therapeutics for BC.