title: Oncogenic Raf-1 disrupts epithelial tight junctions via downregulation of occludin.
abstract: Occludin is an integral membrane protein of the epithelial cell tight junction (TJ). Its potential role in coordinating structural and functional events of TJ formation has been suggested recently. Using a rat salivary gland epithelial cell line (Pa-4) as a model system, we have demonstrated that occludin not only is a critical component of functional TJs but also controls the phenotypic changes associated with epithelium oncogenesis. Transfection of an oncogenic Raf-1 into Pa-4 cells resulted in a complete loss of TJ function and the acquisition of a stratified phenotype that lacked cell-cell contact growth control. The expression of occludin and claudin-1 was downregulated, and the distribution patterns of ZO-1 and E-cadherin were altered. Introduction of the human occludin gene into Raf-1-activated Pa-4 cells resulted in reacquisition of a monolayer phenotype and the formation of functionally intact TJs. In addition, the presence of exogenous occludin protein led to a recovery in claudin-1 protein level, relocation of the zonula occludens 1 protein (ZO-1) to the TJ, and redistribution of E-cadherin to the lateral membrane. Furthermore, the expression of occludin inhibited anchorage-independent growth of Raf-1-activated Pa-4 cells in soft agarose. Thus, occludin may act as a pivotal signaling molecule in oncogenic Raf- 1-induced disruption of TJs, and regulates phenotypic changes associated with epithelial cell transformation.
authors.affiliation: Department of Pharmaceutical Research and Development, Genentech Inc., South San Francisco, California 94080, USA.
authors.forename: D
authors.initials: D
authors.lastname: Li
authors.forename: R J
authors.initials: RJ
authors.lastname: Mrsny
mesh_terms: D000818:Animals; D015820:Cadherins / Q000032:analysis; D002455:Cell Division; D002461:Cell Line, Transformed; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D048429:Cell Size; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D062445:Claudin-1; D002999:Clone Cells / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D003260:Contact Inhibition / Q000235:genetics / Q000502:physiology; D015536:Down-Regulation; D004847:Epithelial Cells / Q000166:cytology / Q000201:enzymology / Q000378:metabolism / Q000473:pathology*; D006801:Humans; D020935:MAP Kinase Signaling System; D008565:Membrane Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D062793:Occludin; D010750:Phosphoproteins / Q000032:analysis; D019908:Proto-Oncogene Proteins c-raf; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D015682:Retroviridae Proteins, Oncogenic / Q000235:genetics / Q000378:metabolism*; D012685:Sepharose; D019108:Tight Junctions / Q000737:chemistry / Q000378:metabolism*; D014162:Transfection; D062826:Zonula Occludens-1 Protein
chemical_list: C568108:CLDN1 protein, human; D015820:Cadherins; D062445:Claudin-1; C568114:Cldn1 protein, rat; D008565:Membrane Proteins; C568985:OCLN protein, human; D062793:Occludin; C568987:Ocln protein, rat; D010750:Phosphoproteins; D012333:RNA, Messenger; D015682:Retroviridae Proteins, Oncogenic; C569042:TJP1 protein, human; C569044:Tjp1 protein, rat; D062826:Zonula Occludens-1 Protein; D012685:Sepharose; D019908:Proto-Oncogene Proteins c-raf; C107753:proto-oncogene protein v-RAF1, pig; D020928:Mitogen-Activated Protein Kinases