BETA-1B INTEGRIN INTERFERES WITH MATRIX ASSEMBLY BUT NOT WITH CONFLUENT MONOLAYER POLARITY, AND ALTERS SOME MORPHOGENETIC PROPERTIES OF FRTEPITHELIAL-CELLS

beta 1B is a beta 1 integrin splice variant that differs from the ubiq uitous beta 1A in the terminal portion of the cytosolic tail. The expr ession of this variant in CHO cells results in reduced fibroblast adhe sion and motlity (Balzac, F. et al., J. Cell Biol. 127, 557-565 (1994) ). We have evaluated the phenotypic changes induced by the expression of beta 1B in the FRT epithelial cell line. Stable transfectants of FR T cells expressing beta 1B or beta 1A human integrins were obtained. T he transfected integrins associated with the endogenous alpha subunits and were delivered to the plasma membrane. beta 1B expressing cells a ttached less efficiently and spread less on fibronectin, laminin or ty pe IV collagen coated dishes. A great reduction of fibronectin fibrils associated to the basal membrane of non-confluent beta 1B transfected cells was observed. This was paralleled by the disappearance of micro filament bundles and loss of basally located focal adhesions. On the c ontrary, upon beta 1A transfection, a higher amount of fibronectin fib rils, together with microfilament bundles and focal adhesions, was obs erved. Expression of beta 1B did not significantly modify the ability to manifest the polarized phenotype when cells were grown to confluenc e on filters in two-chamber-systems. beta 1B-transfected cells showed reduced motile properties when embedded as aggregates in type I collag en gels. Moreover, formation of polarized cysts in suspension culture was impaired. The results show that beta 1B, by interfering with focal adhesion organization, microfilament and fibronectin assembly, cell s preading and migration, affects some morphogenetic properties of FRT e pithelial cells.