PROPERTIES OF WNT-1 PROTEIN THAT ENABLE CELL-SURFACE ASSOCIATION

Members of the highly conserved Wnt gene family serve key functions in cellular growth and differentiation. Regulated expression of the muri ne Wnt-1 protooncogene is essential for normal development of the embr yonic nervous system and when misexpressed in the mammary gland leads to hyperplasias and tumorigenic progression. Wnt-1 encodes a cysteine rich glycoprotein that is secreted and tightly associated with the cel l surface and/or extracellular matrix. This restricted diffusion of Wn t-1 protein is important for specifying a spatially defined pattern of Wnt-activity necessary for cell to cell signaling in cell growth and differentiation. Since the receptors and cell surface molecules that b ind Wnt proteins are as yet unknown we have sought to define the seque nces within Wnt-1 protein that enable cell surface association and to define the nature of the cell surface structures with which Wnt-1 prot ein associates. First, site directed mutagenesis was used to identify a basic amino acid sequence motif within Wnt-1 protein that is require d for this protein to accumulate on the cell surface. Second, wild typ e Wnt-1 protein was expressed in a series of proteoglycan-deficient CH O cell lines to show that, contrary to expectations, cellular glycosam inoglycans are not required for processing, secretion, cell surface as sociation and accumulation of Wnt-1 protein.