Actin: a target of lipopolysaccharide-induced phosphorylation in human monocytes.

We have previously reported that lipopolysaccharide (LPS) causes altered phosphate labelling of cytosolic proteins of 36 kDa and 38 kDa (p36/38) and that inhibition of phosphorylation is accompanied by a loss of cytokine production. Here we have purified the two phosphorylated proteins via two-dimensional polyacrylamide gel electrophoresis. P 36 was found to consist of two proteins p36a and p36b. The proteins were analysed by matrix-assisted laser desorption ionization (MALDI) mass spectrometry and p36b was identified as gamma-actin, p36a as beta/gamma-actin. The ability of LPS to cause altered phosphate labelling of beta/gamma-actin suggests a participation of the microfilament network in LPS-induced monocyte activation.