title: Re-evaluation of milk-fat globule EGF-factor VIII (MFG-E8) as an intrinsic component of the mouse milk-fat globule membrane.
abstract: In lactating mammary glands, milk fat is secreted as fat globules surrounded by a cell plasma membrane containing characteristic membrane-associated proteins. Among these, butyrophilin has been shown to be specific and intrinsic to the fat globule membrane, whereas milk-fat globule EGF-factor VIII (MFG-E8) is uncertain. We characterized in the present study MFG-E8 in milk fat globules and in the culture medium of HC11 mammary epithelial cells. MFG-E8 was immunologically detected in the mammary tissues of both pregnant and lactating mice. Double-immunofluorescence staining for MFG-E8 and butyrophilin showed diversity in the MFG-E8-staining intensity among different fat globules in milk. HC11 cells secreted monomeric MFG-E8 with phosphatidylserine-binding activity, despite no fat globules being detected in the cells. This secretion was upregulated by not only prolactin but also by insulin or EGF. These results suggest that milk MFG-E8 was not equally present among fat globules and not necessarily intrinsic to the fat globules.
authors.affiliation: Department of Applied Molecular Biosciences, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan.
authors.forename: Hajime
authors.initials: H
authors.lastname: Nakatani
authors.forename: Takehiko
authors.initials: T
authors.lastname: Yasueda
authors.forename: Kenzi
authors.initials: K
authors.lastname: Oshima
authors.forename: Daita
authors.initials: D
authors.lastname: Nadano
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Matsuda
mesh_terms: D000818:Animals; D000954:Antigens, Surface / Q000737:chemistry / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D017077:Culture Media, Conditioned / Q000378:metabolism; D005260:Female; D005786:Gene Expression Regulation; D006017:Glycolipids / Q000378:metabolism*; D006023:Glycoproteins / Q000378:metabolism*; D066292:Lipid Droplets; D008321:Mammary Glands, Animal / Q000166:cytology / Q000378:metabolism; D051379:Mice; D008894:Milk Proteins / Q000737:chemistry / Q000378:metabolism*; D010718:Phosphatidylserines / Q000378:metabolism; D011247:Pregnancy; D012995:Solubility
chemical_list: D000954:Antigens, Surface; D017077:Culture Media, Conditioned; D006017:Glycolipids; D006023:Glycoproteins; C490919:Mfge8 protein, mouse; D008894:Milk Proteins; D010718:Phosphatidylserines; C110367:milk fat globule