α6β1-Integrin, a Major Cell Surface Carrier of β1-6-branched Oligosaccharides, Mediates Migration of EJ-ras-transformed Fibroblasts on Laminin-1 Independently of Its Glycosylation State

Abstract EJ- ras oncogene-induced malignant transformation is characterized by a series of changes in cell surface carbohydrates and cell-cell and cell-matrix interactions. Here, we show that EJ- ras -transformed NIH-3T3 fibroblasts acquired a migratory phenotype on laminin-1 surfaces. Such a phenotype was accompanied by overexpression of: ( a ) functional α6β1, but not other laminin binding β1-integrins; and ( b ) glycoconjugates on the cell surface bearing large oligosaccharides recognized by leukoagglutinin from Phaseolus vulgaris (L-PHA). The internal pool of pre-β1-integrins was differently regulated in EJ- ras -transformed cells compared with nontransfected fibroblasts. Conversion of pre-β1- into mature β1-integrins was faster in EJ- ras -transformed cells, a process associated with the overexpression of the α6-chain. Overexpression of L-PHA-reactive oligosaccharides is dependent on the activity of N -acetylglucosaminyltransferase V, which is increased in transformed cells [J. W. Dennis et al. , Science (Washington DC), 236: 582–585, 1987]. We show that β1-integrins were the major carriers of L-PHA-reactive oligosaccharides on the cell surface. This glycosylation pattern, however, was not necessary for either the cell surface expression of β1-integrins or their functional activity in the migratory response to laminin-1. Moreover, EJ- ras -transformed fibroblasts aggregated spontaneously. These effects were not observed in c- jun -transfected fibroblasts, which were unable to migrate on laminin, did not overexpress either β1-integrins or L-PHA-reactive oligosaccharides, and did not self-aggregate.