SRC family tyrosine kinases and cytokine‐induced arginase expression in pulmonary microvascular endothelial cells

Abstract

L-arginine can be metabolized by arginase to urea and L-ornithine, which can then form proline and polyamines in pulmonary endothelial cells. Proline and polyamines are central to the vascular remodeling seen in pulmonary hypertension. We have shown that pharmacological inhibition of the SRC family tyrosine kinases (STK) attenuates lipopolysaccharide (LPS)/tumor necrosis factor (TNF) induced arginase expression and urea production in pulmonary arterial endothelial cells. Of the STKs fyn, yes and src are widely expressed in the body. We hypothesized that specific STKs are involved in cytokine-mediated arginase up-regulation. To test this hypothesis, human pulmonary microvascular endothelial cells (hPMVEC) were treated with an siRNA against fyn, an siRNA against src, or scramble siRNA. After 48 hours the cells were treated with cytomix (LPS, TNF, interleukin-1β, and interferon-γ), and harvested after 24 hours to determine fyn, src, and arginase II protein levels. Treatment with the siRNA against fyn prevented the cytomix-induced up-regulation of arginase II expression in hPMVEC. Although treatment with an siRNA against src resulted in substantially less src expression, it did not prevent the cytomix-induced up-regulation of arginase II expression in hPMVEC. Treatment with a scramble siRNA had no effect on fyn or src expression, or arginase II expression following treatment with cytomix. Our results suggest that fyn is involved in cytokine-induced arginase II expression in hPMVEC. We speculate that fyn may represent a unique pathway regulating arginase II expression in pulmonary hypertension associated with inflammatory lung diseases.