Evidence for the presence of a low-mass beta1 integrin on the cell surface.
Although the cell line K562 reportedly expresses a single species of beta1 integrin, alpha5beta1, surface staining with monoclonal antibodies JB1A, 12G10 and B3B11 to the beta1 chain clearly demonstrated differences in the expression levels of the epitopes detected by these antibodies. The present studies were initiated to determine the basis for this molecular heterogeneity in the integrins. Cross-linking of surface integrins with B3B11 caused their selective aggregation. This distribution was similar to that observed for the alpha5 chain. In contrast, cross-linking the beta1 chains with 12G10 did not cause codistribution of alpha5, suggesting that these two species were not associated on the cell surface. Immunoprecipitates of the surface integrins of K562 cells indicated the presence of 120 and 140 kDa forms of the beta1 chain which were detected by 12G10 and B3B11, respectively. Immunological, biochemical and mass spectrometric analysis of K562 surface integrins also failed to demonstrate the presence of any alpha chain in association with the 120 kDa species of beta1 of K562 cells. Treatment of the two forms of beta1 with PGNase reduced their masses to approximately 90 kDa, suggesting that N-glycosylation was responsible for the mass differences. Collectively, these results provide evidence for a novel species of beta1 on the cell surface, which does not appear to be associated with any alpha chain. The data also suggest that differences in glycosylation may be involved in defining the association between the integrin alpha and beta chains and the functional properties of these integrins.
Meng
Xiaobo
X
Manitoba Centre for Proteomics and Systems Biology, Department of Internal Medicine, University of Manitoba, 715 McDermot Avenue, Winnipeg, MB, Canada R3E 3P4.
Cheng
Keding
K
Krohkin
Oleg
O
Mould
A Paul
AP
Humphries
Martin J
MJ
Ens
Werner
W
Standing
Kenneth
K
Wilkins
John A
JA
D000911:Antibodies, Monoclonal / Q000378:metabolism*; D003432:Cross-Linking Reagents / Q000378:metabolism; D000939:Epitopes; D006801:Humans; D047468:Immunoprecipitation; D039482:Integrin alpha5 / Q000378:metabolism; D019012:Integrin beta1 / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism*; D020014:K562 Cells; D013058:Mass Spectrometry; D008565:Membrane Proteins / Q000737:chemistry / Q000276:immunology / Q000378:metabolism*; D008970:Molecular Weight; D020033:Protein Isoforms / Q000737:chemistry* / Q000276:immunology / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D003432:Cross-Linking Reagents; D000939:Epitopes; D039482:Integrin alpha5; D019012:Integrin beta1; D008565:Membrane Proteins; D020033:Protein Isoforms