Human endothelial cells selectively express large amounts of pancreatic‐type ribonuclease (RNase 1)

Abstract

Pyrimidine-specific ribonucleases are a superfamily of structurally related enzymes with distinct catalytic and biological properties. We used a combination of enzymatic and non-enzymatic assays to investigate the release of such enzymes by isolated cells in serum-free and serum-containing media. We found that human endothelial cells typically expressed large amounts of a pancreatic-type RNase that is related to, if not identical to, human pancreatic RNase. This enzyme exhibits pyrimidine-specific catalytic activity, with a marked preference for poly(C) substrate over poly(U) substrate. It was potently inhibited by placental RNase inhibitor, the selective pancreatic-type RNase inhibitor Inhibit-Ace, and a polyclonal antibody against human pancreatic RNase. The enzyme isolated from medium conditioned by immortalized umbilical vein endothelial cells (EA.hy926) possesses an amino-terminal sequence identical to that of pancreatic RNase, and shows molecular heterogeneity (molecular weights 18,000-26,000) due to different degrees of N-glycosylation. Endothelial cells from arteries, veins, and capillaries secreted up to 100 ng of this RNase daily per million cells, whereas levels were low or undetectable in media conditioned by other cell types examined. The corresponding messenger RNA was detected by RT-PCR in most cell types tested so far, and level of its expression was in keeping with the amounts of protein. The selective strong release of pancreatic-type RNase by endothelial cells suggests that it is endowed with non-digestive functions and involved in vascular homeostasis.

Extracellular RNA is a natural cofactor for the (auto-)activation of Factor VII-activating protease (FSAP)

“…Yet, we were unable so far to relate the content of extracellular RNA in these plasma samples with an increased potential for FSAP activation, possibly due to the excess of RNases or the presence of several as yet unidentified RNA-binding proteins. Interestingly, endothelial cells, in particular, were recently shown to produce and secrete RNase A homologue (RNase 1) in appreciable amounts, whereas a series of other cell types in culture do not [21]. Although speculative at the moment, the endothelial cell-specific expression and secretion of RNase may very well contribute to vascular homoeostasis in general, and be a strong counter-player for the putative cofactor role of cell-derived extracellular RNA in haemostatic reactions described here.…”

Human Ribonuclease A Superfamily Members, Eosinophil-Derived Neurotoxin and Pancreatic Ribonuclease, Induce Dendritic Cell Maturation and Activation

“…The observation that hPR is also an activator of DCs was unexpected. However, hPR is known to be expressed by tissues other than the pancreas (19), including activated monocytes (39), ␣-galactosylceramide-stimulated monocyte-derived DCs (42), and human endothelial cells from arteries, veins, and capillaries (43). Thus, hPR may have nondigestive biological roles that have not been previously appreciated.…”

Bovine Brain Ribonuclease Is the Functional Homolog of Human Ribonuclease 1

“…RNase 1 is secreted profusely from endothelial cells (6,9,51). Based on our findings that human RNase 1 and BRB can readily degrade dsRNA, we hypothesized that extracellular dsRNA in the blood might act as an agonist that promotes RNase 1 secretion.…”