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Identification of caveolin-1 in lipoprotein particles secreted by exocrine cells

Abstract

Caveolin-1 is a protein component (of relative molecular mass 22,000) of the striated coat that decorates the cytoplasmic surface of caveolae membranes. Previous biochemical and molecular tests have indicated that caveolin-1 is an integral membrane protein that is co-translationally inserted into endoplasmic-reticulum membranes of fibroblast and epithelial cells such that its carboxy- and amino-terminal ends are in the cytoplasm. Here we identify caveolin-1 in the secretory pathway of exocrine cells. Secretion of caveolin-1 from pancreatic acinar cells and a transfected exocrine cell line, but not from Chinese hamster ovary cells, is stimulated by the secretagogues secretin, cholecystokinin and dexamethasone. The secreted caveolin-1 co-fractionates with apolipoproteins, indicating that it may be secreted in a complex with lipids.

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Figure 1: Indirect immunofluorescence and immunogold localization of caveolin-1 and caveolin-2 in mouse pancreas.
Figure 2: Distribution of caveolin-1, protein, EGF receptor, amylase and ApoA1 in the supernatant and high-speed pellet fractions of rat pancreas (Pan) and human fibroblasts (Fibro).
Figure 3: Negative staining of the caveolin-rich fractions from the CsCl gradient, plasma HDL or plasma LDL.
Figure 4: Immunopurification of caveolin-1, ApoA1 and ApoE from soluble pancreas homogenates.
Figure 5: Stimulation of caveolin-1 secretion from rat and ApoA1-deficient mouse pancreas, and flotation of secreted rat caveolin-1 on CsCl gradients.
Figure 6: Secretion of transfected caveolin-1 as a lipoprotein by AR42J (a–c, h, i) cells but not CHO (d), fibroblast (e), endothelial (f) or lung epithelial (g) cells.
Figure 7: Immunocytochemical localization of caveolin-1 to secretory vesicles, and secretion of caveolin-1 and amylase from stimulated AR42J cells.

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Acknowledgements

We thank M. Zhu for valuable technical assistance; S. Knight for administrative assistance; D. Spady for his assistance with the ApoA1-deficient mice; and M. Brown and J. Goldstein for helpful suggestions during the preparation of the manuscript. This work was supported by grants from the NIH (HL20948 and GM52016) and by the Perot Family Foundation. T.M. was supported by a postdoctoral fellowship from the Deutsche Forschungsgemeinschaft.

Correspondence and requests for materials should be addressed to R.G.W.A.

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Correspondence to Richard G.W. Anderson.

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Liu, P., Li, WP., Machleidt, T. et al. Identification of caveolin-1 in lipoprotein particles secreted by exocrine cells. Nat Cell Biol 1, 369–375 (1999). https://doi.org/10.1038/14067

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