STRUCTURAL BASIS OF BETA-1 INTEGRIN-MEDIATED CELL-ADHESION TO A LARGEHEPARAN-SULFATE PROTEOGLYCAN FROM BASEMENT-MEMBRANES

In a cell attachment assay, several cell lines were found to adhere an d spread on heparan sulfate proteoglycan purified from a basement memb rane-producing tumor. This adhesion was clearly distinct from that on laminin. Cell adhesion to the proteoglycan was completely inhibited by three different antibodies against integrin beta1 subunit, while inhi bitory antibodies against beta3 and alpha2 to alpha6 subunits were wit hout strong effects. Removal of heparan sulfate from the proteoglycan diminished cell attachment, but addition of heparin to the cells did n ot affect adhesion to the proteoglycan. This suggests that both the he paran sulfate side chains and core protein structures are required for efficient cell adhesion. Studies with proteolytic fragments and synth etic RGD peptides showed that the single RGD sequence of mouse proteog lycan is not involved in cellular recognition. Characterization of fra gments also allowed to localize cell adhesion and heparan sulfate atta chment sites to the same 160 kDa core protein structure but not to fra gments derived from the N-terminal portion of the proteoglycan.