Naked2 acts as a cargo recognition and targeting protein to ensure proper delivery and fusion of TGF-alpha containing exocytic vesicles at the lower lateral membrane of polarized MDCK cells.

Li C, Hao M, Cao Z, Ding W, Graves-Deal R, Hu J, Piston DW, Coffey RJ
Mol Biol Cell. 2007 18 (8): 3081-93

PMID: 17553928 · PMCID: PMC1949375 · DOI:10.1091/mbc.e07-02-0172

Transforming growth factor-alpha (TGF-alpha) is the major autocrine EGF receptor ligand in vivo. In polarized epithelial cells, proTGF-alpha is synthesized and then delivered to the basolateral cell surface. We previously reported that Naked2 interacts with basolateral sorting determinants in the cytoplasmic tail of a Golgi-processed form of TGF-alpha and that TGF-alpha is not detected at the basolateral surface of Madin-Darby canine kidney (MDCK) cells expressing myristoylation-deficient (G2A) Naked2. By high-resolution microscopy, we now show that wild-type, but not G2A, Naked2-associated vesicles fuse at the plasma membrane. We further demonstrate that Naked2-associated vesicles are delivered to the lower lateral membrane of polarized MDCK cells independent of mu1B adaptin. We identify a basolateral targeting segment within Naked2; residues 1-173 redirect NHERF-1 from the apical cytoplasm to the basolateral membrane, and internal deletion of residues 37-104 results in apical mislocalization of Naked2 and TGF-alpha. Short hairpin RNA knockdown of Naked2 leads to a dramatic reduction in the 16-kDa cell surface isoform of TGF-alpha and increased cytosolic TGF-alpha immunoreactivity. We propose that Naked2 acts as a cargo recognition and targeting (CaRT) protein to ensure proper delivery, tethering, and fusion of TGF-alpha-containing vesicles to a distinct region at the basolateral surface of polarized epithelial cells.

MeSH Terms (19)

Adaptor Protein Complex 1 Animals Carrier Proteins Cell Membrane Cell Polarity Cell Survival Cytosol Dogs Exocytosis Humans Membrane Fusion Microscopy, Fluorescence Protein Structure, Tertiary Protein Transport RNA, Small Interfering Swine Tannins Transforming Growth Factor alpha Transport Vesicles

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