Dominant-negative effect of the lymphocyte function-associated antigen-1 beta (CD18) cytoplasmic domain on leukocyte adhesion to ICAM-1 and fibronectin.
The cytoplasmic domains of LFA-1 (CD11a/CD18) are thought to play an important role in the regulation of LFA-1 function. To further elucidate the role of the LFA-1 cytoplasmic domains, we transfected chimeric proteins consisting of the extracellular domain of CD4 fused with the transmembrane and cytoplasmic domains of LFA-1 into T and B cell lines, EL-4 and A20, respectively, and examined their effects on LFA-1-mediated cell adhesion. The CD4/18, but not CD4/11a, chimera profoundly inhibited LFA-1-mediated cell adhesion to ICAM-1, as well as cell spreading following cell adhesion. Unexpectedly, cell adhesion to fibronectin was also inhibited by the CD4/18 chimera. The CD4/18 chimera did not affect the expression of endogenous LFA-1 or the association of CD11a and CD18. Truncation of the carboxyl-terminal 13 amino acid residues of the CD18 cytoplasmic domain of the chimera completely abrogated the inhibitory effect on LFA-1. Among these amino acid residues, the carboxyl-terminal six residues were dispensable for the inhibitory effect in EL-4 cells, whereas it significantly reduced the inhibitory activity of CD4/18 in A20 cells. A larger truncation of the CD18 cytoplasmic domain was needed to fully abrogate the inhibitory effects of CD4/18 on the adhesion to fibronectin. These results show that 1) the CD4/18 chimera has dominant-negative effects on cell adhesion mediated by LFA-1 as well as fibronectin receptors, and 2) amino acid residues of the CD18 cytoplasmic domain involved in the inhibition of LFA-1 seem to be different from those for fibronectin receptors.
Rey-Ladino
J A
JA
The Terry Fox Laboratory, British Columbia Cancer Agency, Vancouver, Canada.
Pyszniak
A M
AM
Takei
F
F
D000595:Amino Acid Sequence; D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism / Q000502:physiology*; D018821:CD18 Antigens / Q000235:genetics / Q000502:physiology*; D015704:CD4 Antigens / Q000235:genetics / Q000502:physiology; D002448:Cell Adhesion / Q000276:immunology; D002460:Cell Line; D003593:Cytoplasm / Q000276:immunology*; D005353:Fibronectins / Q000502:physiology*; D006801:Humans; D018799:Intercellular Adhesion Molecule-1 / Q000502:physiology*; D008213:Lymphocyte Activation / Q000235:genetics; D016169:Lymphocyte Function-Associated Antigen-1 / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000502:physiology; D013601:T-Lymphocytes / Q000378:metabolism / Q000502:physiology*
D018821:CD18 Antigens; D015704:CD4 Antigens; D005353:Fibronectins; D016169:Lymphocyte Function-Associated Antigen-1; D011993:Recombinant Fusion Proteins; D018799:Intercellular Adhesion Molecule-1