THE CYTOPLASMIC DOMAINS OF COMPLEMENT REGULATORY PROTEIN CD46 INTERACT WITH MULTIPLE KINASES IN MACROPHAGES

Membrane cofactor protein (CD46), which normally protects autologous c ells from complement lysis, is the human cell receptor for measles vir us (MV). Interaction between MV and CD46 on monocytes can lead to supp ression of monocyte activation. We hare investigated the interaction b etween the cytoplasmic sequences of CD46 and kinases in a mouse macrop hage cell line. Glutathione-S-transferase (GST) fusion proteins bearin g tile Cyt1 or Cyt2 alternative cytoplasmic domain of CD46 associate w ith macrophage kinase activity, which phosphorylates multiple proteins co-purified with the GST fusion protein, Association with the macroph age kinase activity correlates with tyrosine phosphorylation of the CD 46 cytoplasmic domains, Removing the CD46 sequences of introducing a f rame-shift mutation abrogates the association with macrophage kinase a ctivity. Renaturation studies reveal multiple kinases with apparent mo lecular mass of 82, 79, 58, and 50/49 kDa, which associate specificall y with both CD46 cytoplasmic domains, Alanine substitutions at a juxta membrane Tyr-X-X-Leu motif in the Cyt1 domain completely abrogate the association with macrophage kinases and tyrosine phosphorylation of Cy t1; but similar substitutions in the Cyt2 domain only partially reduce the association with kinases and tyrosine phosphorylation of Cyt2. Th ese results reveal a specific interaction between complement regulator y protein CD46 and macrophage kinases, These findings may provide an i mportant clue for understanding immune modulation by MV.