Desmogleins and desmocollins are the major adhesive components of desmosomes and form two distinct subtypes of the cadherin superfamily of cell-cell adhesion and morphoregulatory proteins. The adhesive properties and cytoskeletal connections of these and other cadherin-type proteins are modulated by their association with several cytoplasmic proteins. Plakoglobin physically associates with both desmogleins and desmocollins at the desmosome as well as with classical cadherins which concentrate in the adherens junction. As the only component to interact with all three of the major cell-cell adhesive proteins of epithelia, plakoglobin is uniquely positioned to play a key role in co-ordinating the adhesive properties of the cell. Plakoglobin is also the structural and functional homologue of a protein involved in cell fate determination in Drosophila and has been shown to participate in Wnt-l transformation of PC12 cells. Furthermore plakoglobin has recently been shown to form cytosolic complexes with another structurally related protein, APC, the product of a gene linked to an inherited form of colon cancer. This family of proteins may therefore be considered central players in cell-cell adhesion and tumor suppression. Given the involvement of plakoglobin in the important cellular processes outlined above I propose to further investigate the role of this protein and its receptors.
My specific aims are: 1. To examine the effect on cell adhesion and proliferation of overexpressing native and mutant forms of plakoglobin. These mutants are designed to saturate specifically binding sites on cadherins , or, APC and to potentate or negate the interactions of these proteins with the cytoskeleton. 2. To identify the additional interactions of desmoglein/plakoglobin complexes: a) purify and clone a 70 kDa cytoplasmic partner of plakoglobin b) identify the novel partners binding to the cytoplasmic domain of desmoglein expressed as a fusion protein by screening libraries with the same fusion protein and employing the yeast two-hybrid system. 3) To characterize desmosomal cadherin receptors and functionally interfere with desmosome formation by use of an alkaline phosphatase tagged soluble ectodomain of desmoglein.
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