Phosphotyrosine phosphatase activity in the macrophage is enhanced by lipopolysaccharide, tumor necrosis factor α, and granulocyte/macrophage-colony stimulating factor: correlation with priming of the respiratory burst

Abstract

Tyrosine phosphorylation is now recognised as a key event in the activation of the macrophage respiratory burst. Since vanadate, a phosphotyrosine phosphatase (PTP) inhibitor is able to enhance the respiratory burst, we proposed that agents which prime the macrophage for enhance respiratory burst activity may do so by suppressing cellular PTP activity. The level of PTP activity in murine bone marrow-derived macrophages (BMM) was assessed by the ability of cell lysates to dephosphorylate 32P-labelled RR- src peptide. In contrast to our hypothesis, pretreatment of BMM with bacterial lipopolysaccharide (LPS), tumor necrosis factor α (TNF α) or granulocyte/macrophage-colony stimulating factor (GMCSF), agents which prime for enhanced respiratory burst activity, was found to dramatically increase the level of cellular PTP activity. The time-course for this increase correlated well with the time course of priming by these agents. In addition, colony stimulating factor-1, a cytokine which does not prime the macrophage respiratory burst, did not enhance PTP levels. The physiological relevance of the increased PTP activity was further supported by confirming it was active against endogenous tyrosine phosphorylated substrates. Interestingly, phorbol myristate acetate and zymosan, agents which trigger the macrophage respiratory burst, were found to inhibit the PTP activity of BMM. Our results demonstrate the regulation of cellular PTP activity by priming agents and further highlight the importance of tyrosine phosphorylation and dephosphorylation events in the regulation of macrophage function.