Elastase regulates the synthesis of its inhibitor, alpha 1-proteinase inhibitor, and exaggerates the defect in homozygous PiZZ alpha 1 PI deficiency

Abstract

The net balance of neutrophil elastase, an enzyme that degrades many components of the extracellular matrix, and its inhibitor, alpha-1-proteinase inhibitor (alpha 1 PI), is thought to be a critical determinant in the development of destructive lung disease, especially in individuals with homozygous alpha 1 PI deficiency. Synthesis and secretion of alpha 1 PI has been recently demonstrated in cells of mononuclear phagocyte lineage, including peripheral blood monocytes and tissue macrophages. In this study we show that alpha 1 PI gene expression in human monocytes and bronchoalveolar macrophages is affected by a novel mechanism, whereby elastase directly regulates the synthesis of its inhibitor. In nanomolar concentrations, neutrophil or pancreatic elastase mediates a dose- and time-dependent increase in steady state levels of alpha 1 PI mRNA and in the rate of synthesis of alpha 1 PI in human monocytes and bronchoalveolar macrophages. Antisera to neutrophil elastase or pretreatment of elastase with the serine proteinase inhibitor diisopropylfluorophosphate abrogates the effect of elastase on alpha 1 PI expression. Elastase also stimulates the synthesis of alpha 1 PI in monocytes from homozygous PiZZ alpha 1 PI-deficient individuals, but has no effect on the rate of secretion; hence, the enzyme mediates an effect on alpha 1 PI that increases the intracellular accumulation of inhibitor and exaggerates the intrinsic defect in secretion of alpha 1 PI that characterizes the homozygous PiZZ alpha 1 PI deficiency.