title: Involvement of Lgl and Mahjong/VprBP in cell competition.
abstract: During the initial stages of carcinogenesis, transformation events occur in a single cell within an epithelial monolayer. However, it remains unknown what happens at the interface between normal and transformed epithelial cells during this process. In Drosophila, it has been recently shown that normal and transformed cells compete with each other for survival in an epithelial tissue; however the molecular mechanisms whereby "loser cells" undergo apoptosis are not clearly understood. Lgl (lethal giant larvae) is a tumor suppressor protein and plays a crucial role in oncogenesis in flies and mammals. Here we have examined the involvement of Lgl in cell competition and shown that a novel Lgl-binding protein is involved in Lgl-mediated cell competition. Using biochemical immunoprecipitation methods, we first identified Mahjong as a novel binding partner of Lgl in both flies and mammals. In Drosophila, Mahjong is an essential gene, but zygotic mahjong mutants (mahj(-/-)) do not have obvious patterning defects during embryonic or larval development. However, mahj(-/-) cells undergo apoptosis when surrounded by wild-type cells in the wing disc epithelium. Importantly, comparable phenomena also occur in Mahjong-knockdown mammalian cells; Mahjong-knockdown Madin-Darby canine kidney epithelial cells undergo apoptosis, only when surrounded by non-transformed cells. Similarly, apoptosis of lgl(-/-) cells is induced when they are surrounded by wild-type cells in Drosophila wing discs. Phosphorylation of the c-Jun N-terminal kinase (JNK) is increased in mahj(-/-) or lgl(-/-) mutant cells, and expression of Puckered (Puc), an inhibitor of the JNK pathway, suppresses apoptosis of these mutant cells surrounded by wild-type cells, suggesting that the JNK pathway is involved in mahj- or lgl-mediated cell competition. Finally, we have shown that overexpression of Mahj in lgl(-/-) cells strongly suppresses JNK activation and blocks apoptosis of lgl(-/-) cells in the wild-type wing disc epithelium. These data indicate that Mahjong interacts with Lgl biochemically and genetically and that Mahjong and Lgl function in the same pathway to regulate cellular competitiveness. As far as we are aware, this is the first report that cell competition can occur in a mammalian cell culture system.
authors.affiliation: Department of Biological Science, Florida State University, Tallahassee, Florida, United States of America.
authors.forename: Yoichiro
authors.initials: Y
authors.lastname: Tamori
authors.forename: Carl Uli
authors.initials: CU
authors.lastname: Bialucha
authors.forename: Ai-Guo
authors.initials: AG
authors.lastname: Tian
authors.forename: Mihoko
authors.initials: M
authors.lastname: Kajita
authors.forename: Yi-Chun
authors.initials: YC
authors.lastname: Huang
authors.forename: Mark
authors.initials: M
authors.lastname: Norman
authors.forename: Nicholas
authors.initials: N
authors.lastname: Harrison
authors.forename: John
authors.initials: J
authors.lastname: Poulton
authors.forename: Kenzo
authors.initials: K
authors.lastname: Ivanovitch
authors.forename: Lena
authors.initials: L
authors.lastname: Disch
authors.forename: Tao
authors.initials: T
authors.lastname: Liu
authors.forename: Wu-Min
authors.initials: WM
authors.lastname: Deng
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Fujita
mesh_terms: D000818:Animals; D017209:Apoptosis; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D002999:Clone Cells; D004285:Dogs; D029721:Drosophila Proteins / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000166:cytology* / Q000378:metabolism*; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D004848:Epithelium / Q000378:metabolism; D055785:Gene Knockdown Techniques; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases; D025521:Tumor Suppressor Proteins / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases; D014921:Wings, Animal / Q000166:cytology / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D029721:Drosophila Proteins; C553038:Mahj protein, Drosophila; D025521:Tumor Suppressor Proteins; C081435:l(2)gl protein, Drosophila; D044767:Ubiquitin-Protein Ligases; C530533:DCAF1 protein, human; D017346:Protein Serine-Threonine Kinases; D048031:JNK Mitogen-Activated Protein Kinases