CELL ACTIVATION MEDIATED BY GLYCOSYLPHOSPHATIDYLINOSITOL-ANCHORED OR TRANSMEMBRANE FORMS OF CD14

CD14 is a glycosylphosphatidylinositol (GPI)-anchored membrane glycopr otein which functions as a receptor on myeloid cells for ligands deriv ed from microbial pathogens such as lipopolysaccharide (LPS). We have studied the importance of the GPI tail of CD14 in signalling with the promonocytic cell line THP-1 expressing recombinant CD14 in a GPI-anch ored form (THP1-wtCD14 cells) or in a transmembrane form (THP1-tmCD14) . We found that, like other GPI-anchored molecules, GPI-anchored CD14 was recovered mainly form a Triton X-100-insoluble fraction, whereas t ransmembrane CD14 was fully soluble in Triton X-100. LPS induced cell activation of THP1-wtCD14 and of THP1-tmCD14 (protein tyrosine kinase phosphorylation, NF-kappa B activation, and cytokine production) in a very similar manner. However, anti-CD14 antibody-induced cross-linking caused a rapid calcium mobilization signal only in GPI-anchored CD14 cells. Studies with pharmacologic inhibitors of intracellular signalli ng events implicate phospholipase C and protein tyrosine kinases in th e genesis of this antibody-induced calcium signal. Our results suggest that GPI anchoring and CD14 targeting to glycolipid-rich membrane mic rodomains are not required for LPS-mediated myeloid cell activation. G PI anchoring may however by important for other signalling functions, such as those events reflected by antibody cross-linking.