HETEROLOGOUS EXPRESSION OF ALPHA-1-INTEGRIN CDNA GENERATES VARIABLE LIGAND SPECIFICITIES AND ALTERATIONS IN CELL-SHAPE

Integrins can mediate a diverse variety of functions that are regulate d by unknown mechanisms. Integrin alpha 1 beta 1 can serve as a recept or for laminin-l and collagen in certain cell types, but is a receptor for only collagen in others. To examine the molecular basis of this d ifference in specificity, three cell types were transfected with cDNA for the rat alpha 1 subunit. Following transfection with rat alpha 1, pluripotential hematopoietic human K562 cells exhibited -dependent att achment to collagen IV, but not laminin-1, unless activating antibody TS2/I6 was added. The attachment to collagen IV stimulated the elabora tion of a spread morphology resembling a differentiated megakarocyte w ith extensive processes which were absent in response to all other sub strates. When MRC-5 cells, a human fibroblastic cell, or RD cells, a h uman rhabdomyosarcoma line, were transfected with the identical alpha 1-integrin construct, rat alpha 1 beta 1-dependent attachment to both collagen IV and laminin-l was seen. Therefore differences in ligand sp ecificity can be generated by translation of an identical integrin alp ha 1 beta 1 mRNA in different cell types. Despite differences in ligan d binding, alpha 1 cDNA-transfected K562 and RD cells express an al su bunit that appears to be antigenically and electrophoretically similar . Small differences in glycosylation were apparent, and correlated wit h changes in ligand specificity. Together these results show for the f irst time that identical cDNAs, absent activating antibodies or other manipulations, can change ligand selectivity and better establish the importance of cellular context in determining integrin function. Moreo ver they show that select integrins can shift the differentiated state of pluripotential cells.