Signal transduction triggered by lipid A-like molecules in 70Z/3 pre-B lymphocyte tumor cells

The lipid A (endotoxin) moiety of lipopolysaccharide (LPS) elicits rapid ce llular responses from many cell types, including macrophages, lymphocytes, and monocytes. In CD14 transfected 70Z/3 pre-B lymphocyte tumor cells, thes e responses include activation of the MAP kinase homolog, p38, activation o f NF-kappa B, and transcription of kappa light chains, leading to the assem bly of surface IgM. In this work, we explored the specificity of the respon se with regard to lipid structure, and the requirement for p38 kinase activ ity prior to NF-kappa B activation in control and CD14 transfected 70Z/3 (C D14-70Z/3) cells. A p38-specific inhibitor, SB203580, was used to block p38 kinase activity in cells. CD14-70Z/3 cells were incubated with 1-50 mu M S B203580, and then stimulated with LPS. Nuclear extracts were prepared, and NF-kappa B activation was measured using an electrophoretic mobility shift assay. SB203580 did not inhibit LPS induced NF-kappa B activation. In addit ion, LPS failed to activate p38 tyrosine phosphorylation in 70Z/3 cells lac king CD14, in spite of rapid NF-kappa B activation and robust surface IgM p roduction with appropriate higher doses of LPS. LPS stimulation of p38 phos phorylation, NF-kappa B activation, and surface IgM expression were all blo cked completely by lipid A-like endotoxin antagonists whether or not CD14 w as present. Acidic glycerophospholipids and ceramides did not mimic lipid A -like molecules either as agonists or antagonists in this system. Our data support the hypothesis that lipid A-mediated activation of cells requires s timulation of a putative lipid A sensor that is downstream of CD14, but ups tream of p38 and NF-kappa B. (C) 1999 Published by Elsevier Science B.V. Al l rights reserved.