CD44 signaling through p56lck involves lateral association with CD4 in human CD4+ T cells.
CD44 is a family of mucin-like membrane proteins generated by alternative splicing of several exons, and participate in T cell adhesion and activation. CD44-mediated signaling involves activation of p56(lck) and leads to ZAP-70 phosphorylation. The aim of the present study was to identify the signaling pathways that follow CD44-triggered ZAP-70 phosphorylation and the molecular mechanisms underlying the CD44 interaction with p56(lck). We found that CD44 cross-linking by mAb in CD4(+) peripheral blood T cells promotes formation of a trimeric complex of Grb2, phospholipase (PLC)-gamma1 and a 36-38 kDa phosphoprotein, and the activation of PLC-gamma1. The amount of inositol triphosphate and the time kinetics of its generation were comparable to those following CD3 cross-linking. Co-capping, co-immunoprecipitation and fluorescence resonance energy transfer experiments showed that CD44 associates with CD4 and CD3 on the cell surface. This association suggests functional interplay between the CD4-TCR complex and CD44. In line with this possibility, we found that CD4 triggering by gp120, a natural ligand of CD4, potentiates CD44-mediated adhesion to hyaluronic acid. Moreover, Ca2+ mobilization induced by CD44 cross-linking by mAb was higher in a subclone of the HUT78 cell line expressing CD4 than in a non-expressing subclone.
Dianzani
U
U
Dipartimento di Scienze Mediche, University A. Avogadro of Eastern Piedmont, via Solaroli 17, 28100 Novara, Italy.
Bragardo
M
M
Tosti
A
A
Ruggeri
L
L
Volpi
I
I
Casucci
M
M
Bottarel
F
F
Feito
M J
MJ
Bonissoni
S
S
Velardi
A
A
D015704:CD4 Antigens / Q000378:metabolism / Q000502:physiology*; D015496:CD4-Positive T-Lymphocytes / Q000201:enzymology / Q000276:immunology* / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D018960:Hyaluronan Receptors / Q000378:metabolism / Q000502:physiology*; D007527:Isoenzymes / Q000378:metabolism; D008213:Lymphocyte Activation / Q000276:immunology; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / Q000502:physiology*; D051966:Phospholipase C gamma; D010766:Phosphorylation; D010835:Phytohemagglutinins / Q000494:pharmacology; D011233:Precipitin Tests; D011505:Protein-Tyrosine Kinases / Q000378:metabolism / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology*; D010738:Type C Phospholipases / Q000378:metabolism; D051746:ZAP-70 Protein-Tyrosine Kinase
D015704:CD4 Antigens; D018960:Hyaluronan Receptors; D007527:Isoenzymes; D010835:Phytohemagglutinins; D011505:Protein-Tyrosine Kinases; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D051746:ZAP-70 Protein-Tyrosine Kinase; C497261:ZAP70 protein, human; D010738:Type C Phospholipases; D051966:Phospholipase C gamma