Fibroblast membrane sterol kinetic domains: modulation by sterol carrier protein-2 and liver fatty acid binding protein.
The mechanism(s) of intracellular sterol trafficking among subcellular organelle membranes is not well understood. Relative contributions of vesicular, sterol carrier protein, and membrane sterol domain pathways are not resolved. A sterol kinetic assay was used to resolve multiple sterol domains in microsome (MICRO), mitochondria (MITO), and plasma (PM) membrane: exchangeable, 20-40% of total; non-exchangeable, 60-80% of total. Spontaneous sterol transfer between dissimilar donor and acceptor membranes was vectorial and depended both on acceptor and donor membrane properties. For example, sterol transfer from PM to MICRO or to MITO, or from MICRO to MITO was 3- to 5-fold slower as compared to sterol movement in the opposite direction. Sterol carrier protein-2 (SCP-2) stimulated sterol transfer in most donor/acceptor membrane combinations by decreasing exchange half-time but not domain size. SCP-2 enhanced sterol transfer selectively: PM-MICRO (12-fold); MITO-MITO, MICRO-MICRO, MICRO-PM (3-fold); PM-PM (1.4-fold); PM-MITO, MICRO-MITO (no effect). Thus, SCP-2-mediated sterol movement was vectorial and not necessarily down a membrane sterol concentration gradient. In contrast, liver fatty acid binding protein (L-FABP) revealed a modest (2-fold) stimulatory effect on sterol transfer only between PM-MITO and MICRO-MICRO. In conclusion, in vitro studies of sterol transfer among isolated subcellular membranes provided kinetic evidence for sterol domains in microsomes and mitochondria as well as plasma membranes. Furthermore, both spontaneous and protein-mediated sterol transfer appeared vectorial and selective in nature.
Department of Physiology and Pharmacology, Texas A & M University, TVMC, College Station 77843-4466, USA.
A
A
Frolov
J K
JK
Woodford
E J
EJ
Murphy
J T
JT
Billheimer
F
F
Schroeder
D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism*; D004875:Ergosterol / Q000031:analogs & derivatives / Q000378:metabolism; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D005454:Fluorescence Polarization; D006801:Humans; D007425:Intracellular Membranes / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D007739:L Cells; D051379:Mice; D008861:Microsomes / Q000737:chemistry / Q000378:metabolism; D008928:Mitochondria / Q000737:chemistry / Q000378:metabolism; D008962:Models, Theoretical; D018996:Myelin P2 Protein / Q000235:genetics / Q000378:metabolism*; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D010940:Plant Proteins; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D013261:Sterols / Q000378:metabolism*; D025521:Tumor Suppressor Proteins
D002352:Carrier Proteins; C493319:FABP1 protein, human; C107608:FABP7 protein, human; C493320:Fabp1 protein, mouse; C493321:Fabp1 protein, rat; C082667:Fabp5 protein, mouse; C086936:Fabp7 protein, mouse; C490174:Fabp7 protein, rat; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D018996:Myelin P2 Protein; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D010940:Plant Proteins; D011994:Recombinant Proteins; D013261:Sterols; D025521:Tumor Suppressor Proteins; C072087:sterol carrier proteins; C010905:dehydroergosterol; D004875:Ergosterol