Multiple functional forms of the integrin VLA-2 can be derived from a single alpha 2 cDNA clone: interconversion of forms induced by an anti-beta 1 antibody.
The integrin VLA-2 was previously found to bind to either collagen alone, or collagen plus laminin, but the mechanism for this cell-specific functional difference was unknown. Here we transfected VLA-2 alpha 2 subunit cDNA into K562 cells and obtained VLA-2 (called Form-O) which bound to neither collagen nor laminin. We then used a Matrigel selection procedure to enrich for a minor subpopulation of K562 cells stably expressing a form of VLA-2 (Form-C) that bound to collagen but not laminin. In contrast, the same alpha 2 cDNA transfected into RD cells yielded VLA-2 (Form-CL) which bound to both collagen and laminin. These Form-O, -C, and -CL activities were stably expressed during extended cell culture, and could not be qualitatively altered by adding phorbol esters or by exchaning the resident divalent cations. However, addition of stimulatory anti-beta 1 antibodies (TS2/16, A-1A5) rapidly converted VLA-2 Form-O and Form-C into Form-CL. Anti-beta 1 antibody stimulation of VLA-2 activity was observed not only on whole cells, but also with solubilized receptors. These results suggest (a) that the ligand binding specificity of VLA-2 can be determined by its cellular environment, rather than by variations in the primary sequence of the alpha 2 subunit, (b) that stably inactive or partly active VLA-2 can be rapidly converted to a fully active form through conformational changes initiated at a nonligand binding site on the beta 1 subunit, and (c) that the mechanisms for VLA-2 stimulation by phorbol ester and by antibody are quite distinct, because the latter does not require an intact cell.
Chan
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BM
Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115.
Hemler
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ME
D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D002448:Cell Adhesion; D002460:Cell Line; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics; D005109:Extracellular Matrix / Q000502:physiology; D006801:Humans; D007700:Kinetics; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive; D046911:Macromolecular Substances; D016029:Receptors, Very Late Antigen / Q000235:genetics* / Q000276:immunology / Q000378:metabolism*; D012208:Rhabdomyosarcoma; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection; D014407:Tumor Cells, Cultured
D000911:Antibodies, Monoclonal; D046911:Macromolecular Substances; D016029:Receptors, Very Late Antigen; D004247:DNA; D013755:Tetradecanoylphorbol Acetate