title: Molecular determinants of milk lipid secretion.
abstract: Mammary epithelial cells secrete lipids by an envelopment process that produces lipid droplets coated by membranes derived from the plasma membrane and possibly secretory vesicles. This secretion process, which resembles viral budding, is hypothesized to be mediated by specific interactions between molecules on the surface of intracellular lipids and membrane elements of the cell. Multiple lines of evidence indicate that milk lipid secretion occurs through a tripartite complex between the integral transmembrane protein, butyrophilin (BTN); the soluble metabolic enzyme, xanthine oxidoreductase (XOR); and the lipid droplet surface protein, adipophilin (ADPH). However, topological evidence from freeze-fracture replica immunolabelling (FRIL) challenge this model and suggests that milk lipid secretion is mediated by butyrophilin alone. Advances in our understanding of the molecular, structural, and functional properties of these proteins now make it possible to understand the physiological functions of each of these molecules in detail and to identify the specific molecular determinants that mediate milk lipid secretion.
authors.affiliation: Department of Obstetrics and Gynecology, University of Colorado Denver and Health Sciences Center, Aurora, CO, USA. jim.mcmanaman@uchsc.edu
authors.forename: James L
authors.initials: JL
authors.lastname: McManaman
authors.forename: Tanya D
authors.initials: TD
authors.lastname: Russell
authors.forename: Jerome
authors.initials: J
authors.lastname: Schaack
authors.forename: David J
authors.initials: DJ
authors.lastname: Orlicky
authors.forename: Horst
authors.initials: H
authors.lastname: Robenek
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D007774:Lactation; D050356:Lipid Metabolism; D008892:Milk / Q000378:metabolism*; D008954:Models, Biological