DMT1-mediated endosome-mitochondria interactions regulates iron homeostasis and mitochondrial metabolism

Mitochondria-early endosome (EE) interactions have been shown to facilitate the translocation of iron into mitochondria. Here we show that Divalent Metal Transporter 1 (DMT1) modulates iron exit from endosomes and transport into mitochondria via regulation of EE-mitochondria interactions. In cancer cells, mitochondria are the ultimate cellular iron sink, where iron can be either stored or used for example to shift cellular metabolism towards glycolysis (Warburg effect), a key adaptive mechanism of cancer cells. Moreover, a gene signature associated with reduced intracellular iron content, including low transferrin receptor (TfR) (anti-import) and high ferroportin (FPN) (pro-export) expression levels, has been related to favorable breast cancer prognosis. Similarly, reduced DMT1 expression associates with improved breast cancer patient survival. We evaluated the role of DMT1 in two distinct breast cancer cell lines: estrogen receptor positive T47D and triple-negative MDAMB231. In both cell lines, we demonstrate colocalization between EE, DMT1 and mitochondria. Interestingly, DMT1 is localized to the surface contact area between endosomes and mitochondria. To demonstrate that DMT1 plays a role in endosome-mitochondria interactions and Mitochondrial Iron Translocation (MIT), we have generated MDAMB231 as well as T47D CRISPR/Cas9 based DMT1 knockout (KO) stable cell lines. Several lines of evidence show that DMT1 regulates MIT and labile iron pool (LIP) levels via modulation of EE-mitochondria interactions in MDAMB231 cells. MIT decrease via DMT1 silencing was partially rescued by re-expression of DMT1 in MDAMB231, but not in T47D cells. MDAMB231 DMT1 KO cells showed increased Ferro-Orange staining, indicating higher LIP levels, as well as decreased TfR and increased FPN protein levels. Importantly, DMT1 silencing significantly reduced EE-mitochondria interactions and EE speed in MDAMB231 but not in T47D. Thus, DMT1 regulates MIT and LIP levels via EE-mitochondria interactions in MDAMB231. These results are in agreement with previous results showing that MDAMB231 display a delay in iron release in comparison to T47D, making them more sensitive to disruptions in MIT. Since mitophagy has been shown to act as a tumor suppressor in breast cancer, we tested whether it could be modulated by DMT1-mediated MIT. We found that DMT1 silencing increases mitochondrial ferritin, global autophagy marker LC3B and PINK1/Parkin-dependent mitophagy markers in MDAMB231; levels of all proteins evaluated were rescued to basal levels upon re-expression of DMT1 in DMT KO cells. Moreover, DMT1 silencing decreases Tom 20 (outer mitochondrial membrane marker) with PMPCB, a known DMT1 interactor that is required for PINK1 turnover. Concurring with the role of DMT1 in mitophagy and iron metabolism, both mitochondrial metabolism and invasive cell migration are significantly impaired by DMT1 silencing and are partially rescued by re-expression of DMT1. Overall, our results implicate DMT1 in the regulation of EE dynamics and EE-mitochondria interactions to support higher MIT/lower LIP levels, which are necessary for sustaining mitochondrial bioenergetics and invasive cell migration. Thus, we propose DMT1 as a key player associated with aggressive phenotypes in breast cancer. © FASEB.