Ocadaic acid treatment causes tyrosine phosphorylation of caveolin-2 and induces internalization of caveolae in rat peritoneal macrophages.
In this paper, we provide evidences that protein phosphatases could regulate the internalization cycle of caveolae in rat peritoneal cells. Ocadaic acid (OA)--a serine/threonine phosphatase inhibitor--was used in various concentrations (4 and 100 nM) to study the internalization of horseradish peroxidase (HRP) in resident and elicited macrophages. We have found that OA in both concentrations has significantly decreased HRP uptake in resident and elicited cells. The results of our morphometrical analysis showed that in OA-treated cells, the number of surface-connected caveolae has been dramatically decreased. Simultaneously large, endosome-like vacuoles containing small vesicles appeared in the cytoplasm. The membrane of these small vesicles was labeled with anti-caveolin-1 antibody. Immunoprecipitation and Western blot analysis revealed that in OA-treated cells an approximately 29 kDa protein identified as caveolin-2 in macrophages was phosphorylated on tyrosine residues. These data support the idea that there is a close correlation between the phosphorylation of caveolin-2 and endocytosis of caveolae: the tyrosine phosphorylation of this approximately 29 kDa protein can drive caveolae to pinch off from the plasma membrane and causes accumulation of caveolae in a multivesicular body-like cellular compartment, which was never found to contain lysosomal enzymes. As a result of OA treatment caveolin-2 remains phosphorylated and the phosphorylation of these protein might inhibit the recycling of caveolae.
Department of Human Morphology and Developmental Biology, Semmelweis University of Medicine, H-1450 Budapest, Tûzoltó u. 58, Hungary. KissA@ana2.sote.hu
Anna L
AL
Kiss
Erzsébet
E
Botos
Agnes
A
Turi
Nándor
N
Müllner
D000818:Animals; D021941:Caveolae / Q000187:drug effects* / Q000648:ultrastructure; D051243:Caveolin 2; D022461:Caveolins / Q000378:metabolism*; D017737:Macrophages, Peritoneal / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D008297:Male; D019319:Okadaic Acid / Q000494:pharmacology*; D010766:Phosphorylation; D051381:Rats; D014443:Tyrosine / Q000378:metabolism*
D051243:Caveolin 2; D022461:Caveolins; D019319:Okadaic Acid; D014443:Tyrosine