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Florek, M, Bauer, N, Janich, P, Wilsch-Braeuninger, M, Fargeas, CA, Marzesco, AM, Ehninger, G, Thiele, C, Huttner, WB and Corbeil, D (2007) Prominin-2 is a cholesterol-binding protein associated with apical and basolateral plasmalemmal protrusions in polarized epithelial cells and released into urine. Cell Tissue Res. 328:31-47

Prominin-2 is a pentaspan membrane glycoprotein structurally related to the cholesterol-binding protein prominin-1, which is expressed in epithelial and non-epithelial cells. Although prominin-1 expression is widespread throughout the organism, the loss of its function solely causes retinal degeneration. The finding that prominin-2 appears to be restricted to epithelial cells, such as those found in kidney tubules, raises the possibility that prominin-2 functionally substitutes prominin-1 in tissues other than the retina and provokes a search for a definition of its morphological and biochemical characteristics. Here, we have investigated, by using MDCK cells as an epithelial cell model, whether prominin-2 shares the biochemical and morphological properties of prominin-1. Interestingly, we have found that, whereas prominin-2 is not restricted to the apical domain like prominin-1 but is distributed in a non-polarized fashion between the apical and basolateral plasma membranes, it retains the main feature of prominin-1, i.e. its selective concentration in plasmalemmal protrusions; prominin-2 is confined to microvilli, cilia and other acetylated tubulin-positive protruding structures. Similar to prominin-1, prominin-2 is partly associated with detergent-resistant membranes in a cholesterol-dependent manner, suggesting its incorporation into membrane microdomains, and binds directly to plasma membrane cholesterol. Finally, prominin-2 is also associated with small membrane particles that are released into the culture media and found in a physiological fluid, i.e. urine. Together, these data show that all the characteristics of prominin-1 are shared by prominin-2, which is in agreement with a possible redundancy in their role as potential organizers of plasma membrane protrusions.

PubMed Online version:10.1007/s00441-006-0324-z

Animals; Carrier Proteins/urine; Cell Line; Cell Membrane/drug effects; Cell Membrane/ultrastructure; Cell Polarity/drug effects; Cell Surface Extensions/drug effects; Cell Surface Extensions/metabolism; Cholesterol/deficiency; Detergents/pharmacology; Epithelial Cells/cytology; Epithelial Cells/drug effects; Membrane Glycoproteins/urine; Polyethylene Glycols/pharmacology; Recombinant Fusion Proteins/metabolism