Inorganic phosphate uptake is a universal function accomplished by transporters that are present across the living world. In contrast, no phosphate exporter has ever been identified in metazoans. Here, we show that depletion of XPR1, a multipass membrane molecule initially identified as the cell-surface receptor for xenotropic and polytropic murine leukemia retroviruses (X- and P-MLV), induced a decrease in phosphate export and that reintroduction of various XPR1 proteins, from fruit fly to human, rescued this defect. Inhibition of phosphate export was also obtained with a soluble ligand generated from the envelope-receptor-binding domain of X-MLV in all human cell lines tested, as well as in diverse stem cells and epithelial cells derived from renal proximal tubules, the main site of phosphate homeostasis regulation. These results provide new insights on phosphate export in metazoans and the role of Xpr1 in this function.
The metabolic state of quiescent hematopoietic stem cells (HSCs) is an important regulator of self-renewal, but it is unclear whether or how metabolic parameters contribute to HSC lineage specification and commitment. Here, we show that the commitment of human and murine HSCs to the erythroid lineage is dependent upon glutamine metabolism. HSCs require the ASCT2 glutamine transporter and active glutamine metabolism for erythroid specification. Blocking this pathway diverts EPO-stimulated HSCs to differentiate into myelomonocytic fates, altering in vivo HSC responses and erythroid commitment under stress conditions such as hemolytic anemia. Mechanistically, erythroid specification of HSCs requires glutamine-dependent de novo nucleotide biosynthesis. Exogenous nucleosides rescue erythroid commitment of human HSCs under conditions of limited glutamine catabolism, and glucose-stimulated nucleotide biosynthesis further enhances erythroid specification. Thus, the availability of glutamine and glucose to provide fuel for nucleotide biosynthesis regulates HSC lineage commitment under conditions of metabolic stress.
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