Expression of the third complement component (C3) and carboxypeptidase N small subunit (CPN1) during mouse embryonic development

Complement regulatory proteins prevent excessive complement system activation and deposition, which can lead to host tissue damage, including fetal loss during pregnancy. To further understand the regulation of complement during development, we examined the expression of the complement protein, C3, and the active subunit of carboxypeptidase N (CPN1), the complement anaphylatoxin regulator. RNA and protein analyses indicated that CPN1 expression occurred as early as 8.5 days post coitus (dpc) and continued through birth. At 10.5 and 13.5 dpc, in situ hybridization revealed CPN1 RNA in erythroid progenitor cells. At 16.5 dpc, expression of CPN1 was also detected in hepatocytes. In comparison to CPN1, C3 RNA expression occurred later (after 13.5 dpc). Moreover, C3 expression was limited to the liver erythroid progenitor cells at 16.5 dpc. These results demonstrated that mouse embryos contain RNA and protein for both C3 and CPN1, and CPN1 expression precedes that of C3 by several days.

Pro-carboxypeptidase R is an acute phase protein in the mouse, whereas carboxypeptidase N is not

Carboxypeptidase R (EC 3.4.17.20; CPR) and carboxypeptidase N (EC 3. 4.17.3; CPN) cleave carboxyl-terminal arginine and lysine residues from biologically active peptides such as kinins and anaphylatoxins, resulting in regulation of their biological activity. Human proCPR, also known as thrombin-activatable fibrinolysis inhibitor, plasma pro-carboxypeptidase B, and pro-carboxypeptidase U, is a plasma zymogen activated during coagulation. CPN, however, previously termed kininase I and anaphylatoxin inactivator, is present in a stable active form in plasma. We report here the isolation of mouse proCPR and CPN cDNA clones that can induce their respective enzymatic activities in culture supernatants of transiently transfected cells. Potato carboxypeptidase inhibitor can inhibit carboxypeptidase activity in culture medium of mouse proCPR-transfected cells. The expression of proCPR mRNA in murine liver is greatly enhanced following LPS injection, whereas CPN mRNA expression remains unaffected. Furthermore, the CPR activity in plasma increased 2-fold at 24 h after LPS treatment. Therefore, proCPR can be considered a type of acute phase protein, whereas CPN is not. An increase in CPR activity may facilitate rapid inactivation of inflammatory mediators generated at the site of Gram-negative bacterial infection and may consequently prevent septic shock. In view of the ability of proCPR to also inhibit fibrinolysis, an excess of proCPR induced by LPS may contribute to hypofibrinolysis in patients suffering from disseminated intravascular coagulation caused by sepsis.

An arginine carboxypeptidase generated during coagulation is diminished or absent in patients with rheumatoid arthritis

A novel arginine carboxypeptidase that is generated during blood coagulation is diminished in sera obtained from patients with rheumatoid arthritis. The enzyme, which is unrelated to carboxypeptidase N, is more effective than lysine in removing terminal arginine from small synthetic substrates and may function in vivo in the removal of terminal arginine from inflammatory peptides such as C3a and C5a. Either diminished levels of this enzyme or an inability to generate it may be an important consideration in the mechanisms involved in the local inflammation that is observed in patients with rheumatoid arthritis.

Rat aortic smooth muscle cells in culture express kallikrein, kininogen, and bradykininase activity

We have studied rat vascular smooth muscle (VSM) cells in culture for the presence of key elements of the glandular kallikrein-kinin system. Direct radioimmunoassay (RIA) using antiserum against rat urinary kallikrein detected a glandular kallikrein-like enzyme (GKLE) in VSM cells and in media. VSM homogenates and culture media had kininogenase activity, generating kinins from dog kininogen. About half of the GKLE was enzymatically inactive which could be activated with trypsin. Kininogenase activity was inhibited completely by aprotinin but only 20% by soybean trypsin inhibitor (SBTI). Trypsin liberated kinins from homogenates and media, demonstrating that VSM cells contain kininogen. Homogenates and media rapidly degrade bradykinin. GKLE, kininogen, and bradykininase activity were all present in VSM cells grown in defined media that contain no serum, thus eliminating any contamination or artefacts from fetal calf serum in standard culture media. Blood vessels of the rat have been reported to contain GKLE. Our observations indicate that GKLE is synthesized by VSM cells, not deposited from plasma. Furthermore, VSM cells synthesize kininogen and bradykininase(s), the other key elements of the glandular kallikrein-kinin system. Thus it is possible that the system functions as an autocoid mechanism that regulates local vascular tone.

Decreased synthesis of serum carboxypeptidase N (SCPN) in familial SCPN deficiency

Serum carboxypeptidase N (SCPN) is the primary inactivator of the C3a, C4a, and C5a anaphylatoxins as well as an inactivator of bradykinin. Thus SCPN deficiency potentially could result in significant pathophysiologic consequences. Previous studies identified a deficient subject afflicted with frequent episodes of angioedema, and other family members also had SCPN deficiency. To delineate this abnormality further, the fractional catabolic rate (FRC) and enzyme synthesis were determined in three members of the afflicted kindred as well as in five normal persons following the infusion of homogeneous 125I-SCPN. The mean FCR and synthesis rates for SCPN in the normal subjects were 1.3%/hr and 20,793 U/kg/hr, respectively. Reduced synthesis was concluded to be primarily responsible for the low SCPN levels in the afflicted kindred. The high FRC of SCPN discourages attempted maintenance therapy with infusions of enriched SCPN preparations.

Angiotensin-producing enzyme I of serum: formation by immunization with renin

Immunization with renin from the kidneys of hog, beef, dog, rabbit and man induced the formation of a highly active enzyme (enzyme I) in the serum of dogs, guinea pigs, rabbits and rats. Enzyme I produces angiotensin I maximally at pH 4.7, up to 2900 ng/ml serum/h, i.e. at a rate 2500 times higher than the endogenous renin of normal serum. At pH 7.2 the angiotensin I production by enzyme I is about 16 to 28 times higher than that of plasma renin. Enzyme I is produced by immunization with renin and not by other kidney proteins. Enzymatically-active renin is required and separate mechanisms are involved in the formation of enzyme I and antirenin. Enzyme I is not identical to renin, pepsin, cathepsin D, plasmin, tonin or cathepsin G and it is inhibited by pepstatin, but not by diisopropyl fluorophosphate.