REGULATION OF WNT5A MESSENGER-RNA EXPRESSION IN HUMAN MAMMARY EPITHELIAL-CELLS BY CELL-SHAPE, CONFLUENCE, AND HEPATOCYTE GROWTH-FACTOR

The Wnts are a family of genes with a role in cell fate and morphologi cal development in numerous embryonic and adult tissues, In mouse mamm ary tissue a subset of the Wnts have a function in the normal developm ent of the gland, and abberant expression of Wnts normally silent in t his tissue causes mammary carcinomas. We have previously shown that Wn t5a expression is elevated in the epithelial component of proliferativ e lesions of human breast and have therefore examined the regulation o f Wnt5a mRNA expression in the human mammary epithelial cell line HB2, which has a luminal phenotype and thus represents the most commonly t ransformed cell type in human breast cancer, Wnt5a was up-regulated 30 -fold at confluence, This up-regulation was induced specifically by co nfluence and not by the growth arrest that accompanied it, In addition , Wnt5a was down-regulated 3-fold by changes in cell shape associated with the transition from growth on a two-dimensional surface (flat cel l morphology) to growth in three-dimensional gels (spherical cell morp hology), Cytoskeletal disruption with non-toxic doses of colchicine al so induced a spherical morphology and brought about a dose dependent d own-regulation of Wnt5a. Wnt5a was also down-regulated 10-fold during the hepatocyte growth factor-induced branching of HB2 cell aggregates in collagen gels, The down-regulation of Wnt5a preceded the branching process, A similar result was obtained with primary human breast epith elial populations and the breast cancer cell line MDA468. We conclude that regulation of Wnt5a expression is a downstream effect of signalin g by hepatocyte growth factor, These results are consistent with a rol e for Wnt5a in mammary epithelial cell motility and are in accord with Xwnt5a's function in embryonal cell migration, If Wnt5a's function in human mammary epithelial cells is similar to that of Xwnt5a, its up-r egulation at confluence may be a mechanism for inhibition of cell migr ation beyond confluence.