The DEAD-box RNA Helicase DDX28 Suppresses Cell Migration and 3D Growth and Invasion in MDA-MB-231 Cells by Altering Bioenergetics

Hypoxia is a common characteristic of the tumor microenvironment leading to aggressive phenotypes. A major response to hypoxia is through the induction of gene programs by the hypoxia-inducible factors (HIF). Previously, we showed that the DEAD-box RNA helicase DDX28 negatively regulates hypoxic eIF4E2-directed translation through its interaction with HIF-2α. We hypothesized that DDX28 is a tumor suppressor that represses the oncogenic HIF-2α axis. Here, we overexpress DDX28 in MDA-MB-231 breast cancer and U87MG glioblastoma cells that have very low and normal endogenous levels of DDX28, respectively, compared with noncancerous HEK293. We show that DDX28 suppresses cell migration, spheroid growth, and invasion in MDA-MB-231, but not U87MG cells. However, suppression is not through the HIF-2α gene program, but through DDX28 impacting cellular bioenergetics. DDX28 levels altered how cells utilized mitochondrial respiration and glycolysis for ATP generation. Furthermore, the pharmacological inhibition of these processes specifically reversed the effects of DDX28 overexpression. This study shows that low endogenous DDX28 levels promote hypoxic migration, and growth/invasion in three-dimensional structures in cells that have a bioenergetic profile that favors glycolysis such as MDA-MB-231.