Mammalian Homolog of Drosophila Tumor Suppressor Lethal (2) Giant Larvae Interacts with Basolateral Exocytic Machinery in Madin-Darby Canine Kidney Cells

摘要

The Drosophila tumor suppressor protein lethal (2) giantlarvae [l(2)gl] is involved in the establishment of epithelialcell polarity during development. Recently, a yeast homolog of theprotein has been shown to interact with components of the post-Golgiexocytic machinery and to regulate a late step in protein secretion.Herein, we characterize a mammalian homolog of l(2)gl, called Mlgl, inthe epithelial cell line Madin-Darby canine kidney (MDCK). Consistentwith a role in cell polarity, Mlgl redistributes from a cytoplasmiclocalization to the lateral membrane after contact-naive MDCK cellsmake cell-cell contacts and establish a polarized phenotype.Phosphorylation within a highly conserved region of Mlgl is required torestrict the protein to the lateral domain, because a recombinantphospho-mutant is distributed in a nonpolar manner. Membrane-bound Mlglfrom MDCK cell lysates was coimmunoprecipitated with syntaxin 4, acomponent of the exocytic machinery at the basolateral membrane, butnot with other plasma membrane solubleN-ethylmaleimide-sensitive factor attachmentreceptor (SNARE) proteins that are either absent from or notrestricted to the basolateral membrane domain. These data suggest thatMlgl contributes to apico-basolateral polarity by regulatingbasolateral exocytosis.