Caveolin-1 is enriched in the peroxisomal membrane of rat hepatocytes.
Caveolae are a subtype of cholesterol-enriched lipid microdomains/rafts that are routinely detected as vesicles pinching off from the plasma membrane. Caveolin-1 is an essential component of caveolae. Hepatic caveolin-1 plays an important role in liver regeneration and lipid metabolism. Expression of caveolin-1 in hepatocytes is relatively low, and it has been suggested to also reside at other subcellular locations than the plasma membrane. Recently, we found that the peroxisomal membrane contains lipid microdomains. Like caveolin-1, hepatic peroxisomes are involved in lipid metabolism. Here, we analyzed the subcellular location of caveolin-1 in rat hepatocytes. The subcellular location of rat hepatocyte caveolin-1 was analyzed by cell fractionation procedures, immunofluorescence, and immuno-electron microscopy. Green fluorescent protein (GFP)-tagged caveolin-1 was expressed in rat hepatocytes. Lipid rafts were characterized after Triton X-100 or Lubrol WX extraction of purified peroxisomes. Fenofibric acid-dependent regulation of caveolin-1 was analyzed. Peroxisome biogenesis was studied in rat hepatocytes after RNA interference-mediated silencing of caveolin-1 and caveolin-1 knockout mice. Cell fractionation and microscopic analyses reveal that caveolin-1 colocalizes with peroxisomal marker proteins (catalase, the 70 kDa peroxisomal membrane protein PMP70, the adrenoleukodystrophy protein ALDP, Pex14p, and the bile acid-coenzyme A:amino acid N-acyltransferase BAAT) in rat hepatocytes. Artificially expressed GFP-caveolin-1 accumulated in catalase-positive organelles. Peroxisomal caveolin-1 is associated with detergent-resistant microdomains. Caveolin-1 expression is strongly repressed by the peroxisome proliferator-activated receptor-alpha agonist fenofibric acid. Targeting of peroxisomal matrix proteins and peroxisome number and shape were not altered in rat hepatocytes with 70%-80% reduced caveolin-1 levels and in livers of caveolin-1 knockout mice.


CONCLUSIONS
Caveolin-1 is enriched in peroxisomes of hepatocytes. Caveolin-1 is not required for peroxisome biogenesis, but this unique subcellular location may determine its important role in hepatocyte proliferation and lipid metabolism.
Department of Gastroenterology and Hepatology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands.
Jannes
J
Woudenberg
Krzysztof P
KP
Rembacz
Fiona A J
FA
van den Heuvel
Titia E
TE
Woudenberg-Vrenken
Manon
M
Buist-Homan
Mariska
M
Geuken
Mark
M
Hoekstra
Leo E
LE
Deelman
Carlos
C
Enrich
Rob H
RH
Henning
Han
H
Moshage
Klaas Nico
KN
Faber
D018528:ATP-Binding Cassette Transporters / Q000378:metabolism; D000217:Acyltransferases / Q000378:metabolism; D000818:Animals; D051242:Caveolin 1 / Q000378:metabolism*; D011345:Fenofibrate / Q000031:analogs & derivatives / Q000494:pharmacology; D022781:Hepatocytes / Q000378:metabolism*; D008297:Male; D021962:Membrane Microdomains / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D000074401:Peroxins; D020675:Peroxisomes / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D013347:Subcellular Fractions / Q000378:metabolism
D018528:ATP-Binding Cassette Transporters; C489272:Abcd3 protein, rat; D051242:Caveolin 1; D008565:Membrane Proteins; D000074401:Peroxins; C490454:Pex11a protein, rat; C006012:fenofibric acid; D000217:Acyltransferases; C026953:bile acid-CoA amino acid N-acyltransferase; D011345:Fenofibrate