Regulation of integrin function by CD47 ligands. Differential effects on alpha vbeta 3 and alpha 4beta1 integrin-mediated adhesion.
We examined the regulation of alpha4beta1 integrin function in melanoma cells and T cells by ligands of CD47. A CD47 antibody (B6H12) that inhibited alphavbeta3-mediated adhesion of melanoma cells induced by CD47-binding peptides from thrombospondin-1 directly stimulated alpha4beta1-mediated adhesion of the same cells to vascular cell adhesion molecule-1 and N-terminal regions of thrombospondin-1 or thrombospondin-2. B6H12 also stimulated alpha4beta1- as well as alpha2beta1- and alpha5beta1-mediated adhesion of CD47-expressing T cells but not of CD47-deficient T cells. alpha4beta1 and CD47 co-purified as a detergent-stable complex on a CD47 antibody affinity column. CD47-binding peptides based on C-terminal sequences of thrombospondin-1 also specifically enhanced adhesion of melanoma cells and T cells to alpha4beta1 ligands. Unexpectedly, activation of alpha4beta1 function by the thrombospondin-1 CD47-binding peptides also occurred in CD47-deficient T cells. CD47-independent activation of alpha4beta1 required the Val-Val-Met (VVM) motif of the peptides and was sensitive to inhibition by pertussis toxin. These results indicate that activation of alpha4beta1 by the CD47 antibody B6H12 and by VVM peptides occurs by different mechanisms. The antibody directly activates a CD47-alpha4beta1 complex, whereas VVM peptides may target an unidentified Gi-linked receptor that regulates alpha4beta1.
Barazi
Heba O
HO
Laboratory of Pathology, NCI, National Institutes of Health, Bethesda, Maryland 20892, USA.
Li
Zhuqing
Z
Cashel
Jo Anne
JA
Krutzsch
Henry C
HC
Annis
Douglas S
DS
Mosher
Deane F
DF
Roberts
David D
DD
D000595:Amino Acid Sequence; D015703:Antigens, CD / Q000502:physiology*; D001665:Binding Sites; D051928:CD47 Antigen; D002352:Carrier Proteins / Q000502:physiology*; D002448:Cell Adhesion / Q000187:drug effects / Q000502:physiology*; D002465:Cell Movement / Q000187:drug effects / Q000502:physiology; D006801:Humans; D039041:Integrin alpha4beta1 / Q000502:physiology*; D039302:Integrin alphaVbeta3 / Q000502:physiology*; D019169:Jurkat Cells; D007700:Kinetics; D008545:Melanoma; D010446:Peptide Fragments / Q000737:chemistry / Q000494:pharmacology; D013601:T-Lymphocytes / Q000276:immunology; D019700:Thrombospondin 1 / Q000502:physiology; D019699:Thrombospondins / Q000502:physiology; D014407:Tumor Cells, Cultured; D019010:Vascular Cell Adhesion Molecule-1 / Q000502:physiology; D000099262:Thrombospondin 2
D015703:Antigens, CD; D051928:CD47 Antigen; D002352:Carrier Proteins; D039041:Integrin alpha4beta1; D039302:Integrin alphaVbeta3; D010446:Peptide Fragments; D019700:Thrombospondin 1; D019699:Thrombospondins; D019010:Vascular Cell Adhesion Molecule-1; D000099262:Thrombospondin 2; C497894:CD47 protein, human