LIPOPROTEINS INDUCE TYROSINE PHOSPHORYLATION IN A MURINE MACROPHAGE CELL-LINE

Lipoproteins, chylomicrons (CM), very low density lipoprotein (VLDL), low density lipoprotein (LDL), high density lipoprotein (HDL) and acet yl modified LDL (AcLDL) are able to stimulate macrophages upon binding to specific receptors. Using flow cytometry and a specific monoclonal antibody against phosphotyrosine, we assessed the effect of lipoprote ins on total intracellular expression of immunoreactive phosphotyrosin e. Tyrosine phosphorylation increased when lipoproteins were added to a macrophage cell line, which was previously cultured in RPM-0.5% fatt y acid free bovine serum albumin. The optimal effect occurred at 15 mi n for all the lipoproteins used. The concentrations of lipoprotein wer e 10 mu g of protein/ml of CM, and 20 mu g of protein/ml for the other lipoproteins. The effect of lipoproteins on phosphotyrosine positiven ess was as follows: AcLDL > HDL > CM > VLDL > LDL. Thus lipoproteins m ay activate macrophages through tyrosine phosphorylation and this sign al transduction pathway seems to be enhanced when these cells are acti vated with AcLDL. Med Sci Res 26:535-537 (C) 1998 Lippincott Williams & Wilkins.