The role of extrahepatic retinol binding protein in the mobilization of retinoid stores.
Although the major tissue site of retinol binding protein (RBP) synthesis in the body is the liver, other sites of synthesis have been reported. The physiological role(s) of circulating RBP that is produced and secreted extrahepatically has not been systematically investigated. To address this question, we used as a model a mouse strain (hRBP(-/-)) that expresses human RBP (hRBP) cDNA under the control of the mouse muscle creatine kinase promoter in an rbp-null background (RBP(-/-)). By comparing hRBP(-/-), RBP(-/-), and wild-type mice, we asked whether extrahepatic RBP can perform all of the physiological functions of RBP synthesized in the liver. We demonstrate that extrahepatically synthesized hRBP, unlike RBP expressed in liver, cannot mobilize liver retinoid stores. Consistent with this conclusion, we find that circulating hRBP is not taken up by hepatocytes. RBP has been proposed to play an essential role in distributing hepatic retinoids between hepatocytes and hepatic stellate cells. We find, however, that the distribution of retinoid in the livers of the three mouse strains described above is identical. Thus, RBP is not required for intrahepatic transport and storage of retinoid. These and other observations are discussed.
Institute of Cancer Research, College of Physicians and Surgeons, Columbia University, New York, NY 10032, USA.
Loredana
L
Quadro
William S
WS
Blaner
Leora
L
Hamberger
Phyllis M
PM
Novikoff
Silke
S
Vogel
Roseann
R
Piantedosi
Max E
ME
Gottesman
Vittorio
V
Colantuoni
D000284:Administration, Oral; D000821:Animal Feed; D000818:Animals; D001692:Biological Transport; D015153:Blotting, Western; D002851:Chromatography, High Pressure Liquid; D003402:Creatine Kinase / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D022781:Hepatocytes / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D011401:Promoter Regions, Genetic; D012177:Retinol-Binding Proteins / Q000378:metabolism*; D013997:Time Factors; D014212:Tretinoin / Q000378:metabolism*; D014801:Vitamin A / Q000008:administration & dosage / Q000378:metabolism*
D018076:DNA, Complementary; D012177:Retinol-Binding Proteins; D014801:Vitamin A; D014212:Tretinoin; D003402:Creatine Kinase