PROMININ, A NOVEL MICROVILLI-SPECIFIC POLYTOPIC MEMBRANE-PROTEIN OF THE APICAL SURFACE OF EPITHELIAL-CELLS, IS TARGETED TO PLASMALEMMAL PROTRUSIONS OF NONEPITHELIAL CELLS

Using a new mAb raised against the mouse neuroepithelium, we have iden tified and cDNA-cloned prominin, an 858-amino acid-containing, 115-kDa glycoprotein, Prominin is a novel plasma membrane protein with an N-t erminal extracellular domain, five transmembrane segments flanking two short cytoplasmic loops and two large glycosylated extracellular doma ins, and a cytoplasmic C-terminal domain, DNA sequences from Caenorhab ditis elegans predict the existence of a protein with the same feature s, suggesting that prominin is conserved between vertebrates and inver tebrates, Prominin is found not only in the neuroepithelium but also i n various other epithelia of the mouse embryo, In the adult mouse, pro minin has been detected in the brain ependymal layer, and in kidney tu bules, In these epithelia, prominin is specific to the apical surface, where it is selectively associated with microvilli and microvilli-rel ated structures, Remarkably, upon expression in CHO cells, prominin is preferentially localized to plasma membrane protrusions such as filop odia, lamellipodia, and microspikes, These observations imply that pro minin contains information to be targeted to, and/or retained in, plas ma membrane protrusions rather than the planar cell surface, Moreover, our results show that the mechanisms underlying targeting of membrane proteins to microvilli of epithelial cells and to plasma membrane pro trusions of non-epithelial cells are highly related.