Distinct and additive effects of elastase and endotoxin on expression of α₁ proteinase inhibitor in mononuclear phagocytes

Expression of α₁ proteinase inhibitor (α₁-PI) in human mononuclear phagocytes may provide a local mechanism for inactivation of serine proteases at sites of tissue injury, thereby preventing incidental damage to surrounding tissue and allowing for orderly initiation of repair. We have previously shown that serine (neutrophilic or pancreatic) elastase and lipopolysaccharide (LPS) each mediate an increase in the expression of α₁-PI in human peripheral blood monocytes and bronchoalveolar macrophages. In this study we demonstrate that elastase and LPS have an additive positive regulatory effect on α₁-PI expression. Distinct pretranslation and translational mechanisms of action for elastase and LPS, respectively, account for the additive effect. The possibility that translational regulation of α₂-PI by LPS involves a mechanism analogous to that of the yeast gene GCN4 during amino acid starvation and that of the human ferritin gene in response to iron is discussed.