title: Reverse overshot water-wheel retroendocytosis of apotransferrin extrudes cellular iron.
abstract: Iron (Fe), a vital micronutrient for all organisms, must be managed judiciously because both deficiency or excess can trigger severe pathology. Although cellular Fe import is well understood, its export is thought to be limited to transmembrane extrusion through ferroportin (also known as Slc40a1), the only known mammalian Fe exporter. Utilizing primary cells and cell lines (including those with no discernible expression of ferroportin on their surface), we demonstrate that upon Fe loading, the multifunctional enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH), which is recruited to the cell surface, 'treadmills' apotransferrin in and out of the cell. Kinetic analysis utilizing labeled ligand, GAPDH-knockdown cells, (55)Fe-labeled cells and pharmacological inhibitors of endocytosis confirmed GAPDH-dependent apotransferrin internalization as a prerequisite for cellular Fe export. These studies define an unusual rapid recycling process of retroendocytosis for cellular Fe extrusion, a process mirroring receptor mediated internalization that has never before been considered for maintenance of cellular cationic homeostasis. Modulation of this unusual pathway could provide insights for management of Fe overload disorders.
authors.affiliation: Institute of Microbial Technology, CSIR, Sector 39A, Chandigarh 160036, India.
authors.forename: Navdeep
authors.initials: N
authors.lastname: Sheokand
authors.affiliation: Institute of Microbial Technology, CSIR, Sector 39A, Chandigarh 160036, India.
authors.forename: Himanshu
authors.initials: H
authors.lastname: Malhotra
authors.affiliation: Institute of Microbial Technology, CSIR, Sector 39A, Chandigarh 160036, India.
authors.forename: Anoop Singh
authors.initials: AS
authors.lastname: Chauhan
authors.affiliation: Institute of Microbial Technology, CSIR, Sector 39A, Chandigarh 160036, India.
authors.forename: Manoj
authors.initials: M
authors.lastname: Kumar
authors.affiliation: Institute of Microbial Technology, CSIR, Sector 39A, Chandigarh 160036, India.
authors.forename: Surbhi
authors.initials: S
authors.lastname: Chaudhary
authors.affiliation: Institute of Microbial Technology, CSIR, Sector 39A, Chandigarh 160036, India.
authors.forename: Anil
authors.initials: A
authors.lastname: Patidar
authors.affiliation: National Institute of Pharmaceutical Education & Research, Phase X, Sector 67, SAS Nagar, Punjab 160062, India.
authors.forename: Vishant Mahendra
authors.initials: VM
authors.lastname: Boradia
authors.affiliation: National Institute of Pharmaceutical Education & Research, Phase X, Sector 67, SAS Nagar, Punjab 160062, India.
authors.forename: Chaaya Iyengar
authors.initials: CI
authors.lastname: Raje
authors.affiliation: Institute of Microbial Technology, CSIR, Sector 39A, Chandigarh 160036, India manoj@imtech.res.in.
authors.forename: Manoj
authors.initials: M
authors.lastname: Raje
mesh_terms: D000818:Animals; D001059:Apoproteins / Q000378:metabolism*; D002460:Cell Line; D004705:Endocytosis; D007501:Iron / Q000378:metabolism*; D051379:Mice; D021381:Protein Transport; D014168:Transferrin / Q000378:metabolism*
chemical_list: D001059:Apoproteins; D014168:Transferrin; C028284:apotransferrin; D007501:Iron
keywords: Apotransferrin; GAPDH; Glyceraldehyde-3-phosphate dehydrogenase; Iron; Microscopy; Moonlighting protein; Protein trafficking; Retroendocytosis