Intracellular trafficking of vitamin E in hepatocytes: the role of tocopherol transfer protein.
The term vitamin E denotes a family of tocopherols and tocotrienols, plant lipids that are essential for vertebrate fertility and health. The principal form of vitamin E found in humans, RRR-alpha-tocopherol (TOH), is thought to protect cells by virtue of its ability to quench free radicals, and functions as the main lipid-soluble antioxidant. Regulation of vitamin E homeostasis occurs in the liver, where TOH is selectively retained while other forms of vitamin E are degraded. Through the action of tocopherol transfer protein (TTP), TOH is then secreted from the liver into circulating lipoproteins that deliver the vitamin to target tissues. Presently, very little is known regarding the intracellular transport of vitamin E. We utilized biochemical, pharmacological, and microscopic approaches to study this process in cultured hepatocytes. We observe that tocopherol-HDL complexes are efficiently internalized through scavenger receptor class B type I. Once internalized, tocopherol arrives within approximately 30 min at intracellular vesicular organelles, where it co-localizes with TTP, and with a marker of the lysosomal compartment (LAMP1), before being transported to the plasma membrane in a TTP-dependent manner. We further show that intracellular processing of tocopherol involves a functional interaction between TTP and an ABC-type transporter.
Qian
Jinghui
J
Division of Nutritional Sciences, Cornell University, Ithaca, NY, 14853, USA.
Morley
Samantha
S
Wilson
Kathleen
K
Nava
Phil
P
Atkinson
Jeffrey
J
Manor
Danny
D
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000818:Animals; D006528:Carcinoma, Hepatocellular; D002352:Carrier Proteins / Q000502:physiology*; D045744:Cell Line, Tumor; D004318:Doxycycline / Q000494:pharmacology; D005905:Glyburide / Q000494:pharmacology; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D051381:Rats; D014810:Vitamin E / Q000378:metabolism*
D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D002352:Carrier Proteins; C017763:alpha-tocopherol transfer protein; D014810:Vitamin E; D004318:Doxycycline; D005905:Glyburide