INTERACTION OF THE CD5 CYTOPLASMIC DOMAIN WITH THE CA2+ CALMODULIN-DEPENDENT KINASE II-DELTA/

CD5 is a type I transmembrane protein expressed on the surface of T ce lls and of B1 B cells. The analysis of CDS-deficient mice suggests tha t CD5 can down-regulate positive signals from the antigen receptors on T and B cells but the mechanism is not known at present. In contrast to the extracellular domain the 93 amino acid long cytoplasmic domain of CD5 is highly conserved between CD5 proteins of different mammalian species. Using the yeast two-hybrid system, we identified two protein s which specifically bind to the N-terminal part of the CD5 cytoplasmi c sequence. These are the Ca2+/calmodulin-dependent kinase II delta an d Tctex-1, a light chain component of the dynein motor complex. The in teraction of CD5 with the Ca2+/calmodulin-dependent kinase II delta wa s reproduced in vitro using fusion proteins. The potential function of these proteins in CDS internalization and negative signaling is discu ssed.