tailieunhanh - Báo cáo khoa học: The soluble form of the membrane-bound transferrin homologue, melanotransferrin, inefficiently donates iron to cells via nonspecific internalization and degradation of the protein

Melanotransferrin (MTf) is a membrane-bound transferrin (Tf) homologue foundparticularly inmelanoma cells. Apart frommembrane-boundMTf, a soluble formof themolecule (sMTf) has been identified in vitro [Food, ., Rothen-berger, S., Gabathuler, R., Haidl, ., Reid, G. & Jefferies, . (1994)J. Biol. , 3034–3040] and in vivo in Alzheimer’s disease. However, nothing is known about the functionof sMTf or its role inFeuptake. | Eur. J. Biochem. 269 4435-4445 2002 FEBS 2002 doi j The soluble form of the membrane-bound transferrin homologue melanotransferrin inefficiently donates iron to cells via nonspecific internalization and degradation of the protein Michael R. Food Eric O. Sekyere and Des R. Richardson The Heart Research Institute Iron Metabolism and Chelation Group Camperdown Sydney New South Wales Australia Melanotransferrin MTf is a membrane-bound transferrin Tf homologue found particularly in melanoma cells. Apart from membrane-bound MTf a soluble form of the molecule sMTf has been identified in vitro Food . Rothen-berger S. Gabathuler R. Haidl . Reid G. Jefferies . -994 J. Biol. Chem. 269 3034-3040 and in vivo in Alzheimer s disease. However nothing is known about the function of sMTf or its role in Fe uptake. In this study sMTf labelled with 59Fe and -25I was used to examine its ability to donate 59Fe to SK-Mel-28 melanoma cells and other cell types. sMTf donated 59Fe to cells at -4 of the rate of Tf. Analysis of sMTf binding showed that unlike Tf sMTf did not bind to a saturable Tf-binding site. Studies with Chinese hamster ovary cells with and without specific Tf receptors showed that unlike Tf sMTf did not donate its 59Fe via these pathways. This was confirmed by experiments using lysosomotropic agents that markedly reduced 59Fe uptake from Tf but had far less effect on 59Fe uptake from sMTf. In addition an excess of 56Fe-labelled Tf or sMTf had no effect on -25I-labelled sMTf uptake suggesting a nonspecific interaction of sMTf with cells. Protein-free -25I determinations demonstrated that in contrast with Tf sMTf was markedly degraded. We suggest that unlike the binding of Tf to specific receptors sMTf was donating Fe to cells via an inefficient mechanism involving nonspecific internalization and subsequent degradation. Keywords iron iron uptake melanotransferrin transferrin transferrin receptor. Melanotransferrin MTf is a homologue of