Human corin isoforms with different cytoplasmic tails that alter cell surface targeting

USP11 plays a critical role in the onset and progression of acute graft-versus-host disease：Novel target for precision therapeutics

Acute graft-versus-host disease (aGvHD) is considered a result of "cytokine storm." Targeted therapeutic interventions on cytokines via ubiquitination regulatory pathways may provide a potential approach for aGvHD treatment. Ubiquitin-specific peptidase 11 (USP11) has been reported to play key roles in a variety of physiopathological processes by regulating the stability and function of several vital protein molecules. However, its role in aGvHD remains unclear. In this study, we identified USP11 was associated with aGvHD in patients. In the aGvHD mouse model, the colon and liver were more seriously affected in recipient mice who received USP11 wt bone marrow (BM) cells and eased after the donor was treated with a USP11 inhibitor or received USP11 ko BM cells. In mouse models, IL-6 was identified as a major effecter in accelerating aGvHD induced by USP11. In the cell model, IL-6 mRNA transcript was affected by USP11. In addition, USP11 also inhibited IL-6 degradation by affecting IL-6 ubiquitination. Furthermore, the positive correlation between USP11 and IL-6 was confirmed in the GvHD patients' samples. Collectively, all results indicated that USP11 played a critical role in the onset and progression of aGvHD. USP11 might be a potential target for aGvHD treatment.

H22954, a long non-coding RNA, inhibits glucose uptake in leukemia cells in a GLUT10-dependent manner

OBJECTIVES

To investigate the performance of H22954, a novel long non-coding RNA (lncRNA), in inhibiting glucose uptake in leukemia cells.

METHODS

¹⁸F-FDG uptake, RNA half-life quantitative real-time polymerase chain reaction (qRT-PCR) and luciferase assays were performed to detect the glucose uptake in the condition of leukemia. Microarrays and qRT-PCR analyses were used to identify the related genes or proteins and elucidate the underlying these processes.

RESULTS

H22954, a novel lncRNA, inhibited glucose uptake in leukemia cells. Using bioinformatics and microarray analyses, GLUT10 was identified as a possible target molecule of H22954. H22954 targeted the 3'untranslated region of GLUT10. In the luciferase assay, the luciferase activity of pGL3-GLUT10 was inhibited by H22954. Consistently, H22954 expression levels were inversely correlated with GLUT10 expression in cell lines and acute myeloid leukemia (AML) samples. Conversely, the degradation rate of GLUT10 mRNA was increased after H22954 overexpression. Moreover, glucose uptake was recovered when the GLUT10-interaction sites in H22954 were mutated.

CONCLUSION

The lncRNA H22954 regulated GLUT10 expression to inhibit glucose uptake in leukemia cells. Our findings provide potentially valuable data for designing new targeted strategies based on H22954.

CD320 expression and apical membrane targeting in renal and intestinal epithelial cells

Vitamin B12 is an essential nutrient acquired via dietary intake. Receptor-mediated endocytosis is a key mechanism in vitamin B12 absorption, cellular uptake, and reabsorption. CD320 is a type I transmembrane protein responsible for cellular uptake of vitamin B12 in peripheral tissues. In this study, we examined segmental distribution and cellular expression of CD320 in mouse kidneys and intestines. We show that CD320 is expressed on the luminal surface in the small intestine and in proximal tubules in the kidney, suggesting that, in addition to its role in vitamin B12 uptake in peripheral tissues, CD320 may participate in vitamin B12 absorption in the small intestine and reabsorption in the kidney. Moreover, we show that an amino acid motif, DSSDE, in the second low-density lipoprotein receptor class A domain of CD320 is a key apical membrane targeting signal in both renal and intestinal epithelial cells. Mutations or deletion of this motif abolish the specific apical membrane expression of CD320 in polarized Madin-Darby canine kidney cells and human colon cancer-derived Caco-2 cells. In short-hairpin RNA-based gene knockdown experiments, we show that the apical membrane targeting of CD320 is mediated by a Rab11a-dependent mechanism. These results extend our knowledge regarding the cell biology of CD320 and its role in vitamin B12 metabolism.

Function and regulation of corin in physiology and disease

Atrial natriuretic peptide (ANP) is of major importance in the maintenance of electrolyte balance and normal blood pressure. Reduced plasma ANP levels are associated with the increased risk of cardiovascular disease. Corin is a type II transmembrane serine protease that converts the ANP precursor to mature ANP. Corin deficiency prevents ANP generation and alters electrolyte and body fluid homeostasis. Corin is synthesized as a zymogen that is proteolytically activated on the cell surface. Factors that disrupt corin folding, intracellular trafficking, cell surface expression, and zymogen activation are expected to impair corin function. To date, CORIN variants that reduce corin activity have been identified in hypertensive patients. In addition to the heart, corin expression has been detected in non-cardiac tissues, where corin and ANP participate in diverse physiological processes. In this review, we summarize the current knowledge in corin biosynthesis and post-translational modifications. We also discuss tissue-specific corin expression and function in physiology and disease.

Therapeutic Prospects in Preeclampsia - A Mini-Review

BACKGROUND

Preeclapmsia (PE) is characterized by early onset symptoms such as elevated blood pressure, proteinuria and edema in the pregnant woman, and may result in seizures in the affected female. Currently, there are no therapeutic drugs available to treat this condition, but there are interventions to regulate the symptoms based on the gestational period of the fetus, although the largely favored option is delivery of the fetus and placenta.

OBJECTIVE

A search for biomolecules associated with PE was conducted so as to identify diagnostic markers and therapeutic leads.

RESULTS

The literature search resulted in the identification of biomolecules such as Corin and Placental Protein 13 (PP13), among others that are associated with PE. Thereby, giving an insight into the various mechanistic pathways involved in the causation of PE. However, it is also evident that PE cannot be solely attributed to any single mechanism but is due to an interplay of different factors that have led to the development of this disease condition.

CONCLUSION

The identified biomarkers would ultimately help in understanding this complex disease and perhaps lead to the discovery of potential effective molecular targets for clinical trials, thereby providing a valuable therapeutic option for affected pregnant women.

Ectopic expression of human airway trypsin-like protease 4 in acute myeloid leukemia promotes cancer cell invasion and tumor growth

Transmembrane serine proteases have been implicated in the development and progression of solid and hematological cancers. Human airway trypsin-like protease 4 (HAT-L4) is a transmembrane serine protease expressed in epithelial cells and exocrine glands. In the skin, HAT-L4 is important for normal epidermal barrier function. Here, we report an unexpected finding of ectopic HAT-L4 expression in neutrophils and monocytes from acute myeloid leukemia (AML) patients. Such expression was not detected in bone marrow cells from normal individuals or patients with chronic myeloid leukemia, acute lymphocytic leukemia and chronic lymphocytic leukemia. In AML patients who underwent chemotherapy, persistent HAT-L4 expression in bone marrow cells was associated with minimal residual disease and poor prognostic outcomes. In culture, silencing HAT-L4 expression in AML-derived THP-1 cells by short hairpin RNAs inhibited matrix metalloproteinase-2 activation and Matrigel invasion. In mouse xenograft models, inhibition of HAT-L4 expression reduced the proliferation and growth of THP-1 cell-derived tumors. Our results indicate that ectopic HAT-L4 expression is a pathological mechanism in AML and that HAT-L4 may be used as a cell surface marker for AML blast detection and targeting.

N-glycosylation in the protease domain of trypsin-like serine proteases mediates calnexin-assisted protein folding

Trypsin-like serine proteases are essential in physiological processes. Studies have shown that N-glycans are important for serine protease expression and secretion, but the underlying mechanisms are poorly understood. Here, we report a common mechanism of N-glycosylation in the protease domains of corin, enteropeptidase and prothrombin in calnexin-mediated glycoprotein folding and extracellular expression. This mechanism, which is independent of calreticulin and operates in a domain-autonomous manner, involves two steps: direct calnexin binding to target proteins and subsequent calnexin binding to monoglucosylated N-glycans. Elimination of N-glycosylation sites in the protease domains of corin, enteropeptidase and prothrombin inhibits corin and enteropeptidase cell surface expression and prothrombin secretion in transfected HEK293 cells. Similarly, knocking down calnexin expression in cultured cardiomyocytes and hepatocytes reduced corin cell surface expression and prothrombin secretion, respectively. Our results suggest that this may be a general mechanism in the trypsin-like serine proteases with N-glycosylation sites in their protease domains.

Identification and functional analysis of CORIN variants in hypertensive patients

Corin is a serine protease that activates atrial natriuretic peptide (ANP). CORIN gene variants have been reported in patients with hypertension. To date, however, the prevalence of CORIN variants in hypertensive patients remains unknown. To understand the prevalence and functional significance of CORIN variants in hypertension, we sequenced CORIN exons in 300 normal and 401 hypertensive individuals in a Chinese population and identified nine nonsynonymous variants, of which eight were not characterized previously. Among them, variants c.131A > G (p.Tyr13Cys), c.376G > T (p.Asp95Tyr), c.1094T > G (p.Leu334Trp), and c.1667G > A (p.Arg525His) occurred similarly in both normal and hypertensive individuals. Variants c1139G > A (p.Arg349His), c.2689C > T (p.Pro866Ser), and c.2864C > T (p.Thr924Met) were found once each in hypertensive individuals. Variant c.1683G > T (p.Arg530Ser) occurred preferentially in hypertensive individuals [10/401 (2.5%) vs. 1/300 (0.3%) in normal individuals; P = 0.023], which was confirmed in another independent cohort [9/368 (2.44%) in hypertensive and 2/377 (0.53%) in normal individuals; P = 0.033]. In biochemical and cell-based functional studies, variants p.Arg530Ser and p.Thr924Met, but not p.Tyr13Cys, p.Asp95Tyr, p.Leu334Trp, p.Arg349His, p.Arg525His, and p.Pro866Ser, exhibited reduced pro-ANP processing activity, which was caused by endoplasmic reticulum retention and poor zymogen activation, respectively. These results indicate that genetic variants impairing corin function are not uncommon in general populations and that such variants may be an important contributing factor in hypertension.

The Transmembrane Serine Protease HAT-like 4 Is Important for Epidermal Barrier Function to Prevent Body Fluid Loss

Membrane-bound proteases are essential for epidermal integrity. Human airway trypsin-like protease 4 (HAT-L4) is a type II transmembrane serine protease. Currently, its biochemical property, cellular distribution and physiological function remain unknown. Here we examined HAT-L4 expression and function in vitro and in vivo. In Western analysis, HAT-L4 expressed in transfected CHO cells appeared as a 48-kDa protein. Flow cytometry confirmed HAT-L4 expression on the cell surface with the expected membrane topology. RT-PCR and immunostaining experiments indicated that HAT-L4 was expressed in epithelial cells and exocrine glands in tissues including skin, esophagus, trachea, tongue, eye, bladder, testis and uterus. In the skin, HAT-L4 expression was abundant in keratinocytes and sebaceous glands. We generated HAT-L4 knockout mice by disrupting the Tmprss11f gene encoding HAT-L4. HAT-L4 knockout mice were viable and fertile. No defects were found in HAT-L4 knockout mice in hair growth, wound healing, water repulsion and body temperature regulation. Compared with wild-type controls, HAT-L4-deficient newborn mice had greater body fluid loss and higher mortality in a trans-epidermal body fluid loss test. In metabolic studies, HAT-L4-deficient adult mice drank water more frequently than wild-type controls did. These results indicate that HAT-L4 is important in epidermal barrier function to prevent body fluid loss.

Role of corin in the regulation of blood pressure

PURPOSE OF REVIEW

Corin is a transmembrane protease that activates atrial natriuretic peptide (ANP), an important hormone in regulating salt-water balance and blood pressure. This review focuses on the regulation of corin function and potential roles of corin defects in hypertensive, heart, and renal diseases.

RECENT FINDINGS

Proprotein convertase subtilisin/kexin-6 has been identified as a primary enzyme that converts zymogen corin to an active protease. Genetic variants that impair corin intracellular trafficking, cell surface expression, and zymogen activation have been found in patients with hypertension, cardiac hypertrophy, and pre-eclampsia. Reduced corin expression has been detected in animal models of cardiomyopathies and in human failing hearts. Low levels of circulating soluble corin have been reported in patients with heart disease and stroke. Corin, ANP and natriuretic peptide receptor-A mRNAs, and proteins have been colocalized in human renal segments, suggesting a corin-ANP autocrine function in the kidney.

SUMMARY

Corin is a key enzyme in the natriuretic peptide system. The latest findings indicate that corin-mediated ANP production may act in a tissue-specific manner to regulate cardiovascular and renal function. Corin defects may contribute to major diseases such as hypertension, heart failure, pre-eclampsia, and kidney disease.

Three molecular forms of atrial natriuretic peptides: quantitative analysis and biological characterization

Atrial natriuretic peptide (ANP) is primarily produced in the heart tissue and plays a pivotal role in maintaining cardiovascular homeostasis in endocrine and autocrine/paracrine systems and has clinical applications as a biomarker and a therapeutic agent for cardiac diseases. ANP is synthesized by atrial cardiomyocytes as a preprohormone that is processed by a signal peptidase and stored in secretory granules as a prohormone. Subsequent proteolytic processing of ANP by corin during the secretion process results in a bioactive form consisting of 28 amino acid residues. Mechanical stretch of the atrial wall and multiple humoral factors directly stimulates the transcription and secretion of ANP. Secreted ANP elicits natriuretic and diuretic effects via cyclic guanosine monophosphate produced through binding to the guanylyl cyclase-A/natriuretic peptide receptor-A. Circulating ANP is subjected to rapid clearance by a natriuretic peptide receptor-C-mediated mechanism and proteolytic degradation by neutral endopeptidase. In humans, ANP is present as three endogenous molecular forms: bioactive α-ANP, a homodimer of α-ANP designated as β-ANP, and an ANP precursor designated as proANP (also referred to as γ-ANP). The proANP and especially β-ANP, as minor forms in circulation, are notably increased in patients with cardiac diseases, suggesting the utility of monitoring the pathophysiological conditions that result in abnormal proANP processing that cannot be monitored by inactive N-terminal proANP-related fragments. Emerging plate-based sandwich immunoassays for individual quantitation of the three ANP forms enables evaluation of diagnostic implications and net ANP bioactivity. This new tool may provide further understanding in the pathophysiology of cardiac diseases. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

TMPRSS2 Isoform 1 Activates Respiratory Viruses and Is Expressed in Viral Target Cells

The cellular protease TMPRSS2 cleaves and activates the influenza virus hemagglutinin (HA) and TMPRSS2 expression is essential for viral spread and pathogenesis in mice. Moreover, severe acute respiratory syndrome coronavirus (SARS-CoV) and other respiratory viruses are activated by TMPRSS2. However, previous studies on viral activation by TMPRSS2 focused on a 492 amino acids comprising form of the protein (isoform 2) while other TMPRSS2 isoforms, generated upon alternative splicing of the tmprss2 mRNA, have not been characterized. Here, we show that the mRNA encoding a TMPRSS2 isoform with an extended N-terminal cytoplasmic domain (isoform 1) is expressed in lung-derived cell lines and tissues. Moreover, we demonstrate that TMPRSS2 isoform 1 colocalizes with HA and cleaves and activates HA. Finally, we show that isoform 1 activates the SARS-CoV spike protein for cathepsin L-independent entry into target cells. Our results indicate that TMPRSS2 isoform 1 is expressed in viral target cells and might contribute to viral activation in the host.

PCSK6-mediated corin activation is essential for normal blood pressure

Hypertension is the most common cardiovascular disease, afflicting >30% of adults. The cause of hypertension in most individuals remains unknown, suggesting that additional contributing factors have yet to be discovered. Corin is a serine protease that activates the natriuretic peptides, thereby regulating blood pressure. It is synthesized as a zymogen that is activated by proteolytic cleavage. CORIN variants and mutations impairing corin activation have been identified in people with hypertension and pre-eclampsia. To date, however, the identity of the protease that activates corin remains elusive. Here we show that proprotein convertase subtilisin/kexin-6 (PCSK6, also named PACE4; ref. 10) cleaves and activates corin. In cultured cells, we found that corin activation was inhibited by inhibitors of PCSK family proteases and by small interfering RNAs blocking PCSK6 expression. Conversely, PCSK6 overexpression enhanced corin activation. In addition, purified PCSK6 cleaved wild-type corin but not the R801A variant that lacks the conserved activation site. Pcsk6-knockout mice developed salt-sensitive hypertension, and corin activation and pro-atrial natriuretic peptide processing activity were undetectable in these mice. Moreover, we found that CORIN variants in individuals with hypertension and pre-eclampsia were defective in PCSK6-mediated activation. We also identified a PCSK6 mutation that impaired corin activation activity in a hypertensive patient. Our results indicate that PCSK6 is the long-sought corin activator and is important for sodium homeostasis and normal blood pressure.

A novel cytoplasmic tail motif regulates mouse corin expression on the cell surface

Type II transmembrane serine proteases (TTSPs) are important in many biological processes. Cell surface expression is critical for TTSP activation and function. To date, the mechanism underlying TTSP cell surface expression is poorly understood. Corin is a TTSP and acts as the pro-atrial natriuretic peptide convertase that is essential for sodium homeostasis and normal blood pressure. In this study, we investigated how cytoplasmic tail sequences may regulate corin expression and activation on the cell surface. By site-directed mutagenesis, we made mouse corin proteins with truncations or point-mutations in the cytoplasmic tail. We expressed the mutants in transfected HEK293 cells and analyzed corin cell surface expression and activation by Western blotting and flow cytometry. We found that corin truncation mutants lacking a Lys-Phe-Gln sequence at residues 71-73 had higher levels of cell surface expression and activation compared with that in wild-type corin. When Lys-71, Phe-72 and Gln-73 residues were mutated together, but not individually, in corin with the full-length cytoplasmic tail, increased levels of cell surface expression and zymogen activation were also observed. These results indicate that residues Lys-71, Phe-72 and Gln-73 serve as a novel retention motif in the intracellular pathway to regulate corin cell surface expression and activation.

A corin variant identified in hypertensive patients that alters cytoplasmic tail and reduces cell surface expression and activity

Corin is a membrane-bound protease that regulates blood pressure by activating the natriuretic peptides. CORIN variants have been associated with hypertension and heart disease in African Americans. In this study, we conducted targeted exome sequencing and identified an insertion variant, c.102_103insA, in exon 1 of the CORIN gene. Analysis of two independent cohorts showed that the variant was preferentially present in hypertensive patients (38/795 or 4.78% vs. 4/632 or 0.63% in normal individuals, p = 4.14E-6). The insertion shifted the reading frame, resulting in a corin variant with a truncated cytoplasmic tail. In cell-based studies, the corin variant exhibited poor trafficking in the Golgi, reduced cell surface expression and zymogen activation, and low natriuretic peptide processing activity. Compared with normal individuals with the wild-type allele, individuals with the variant allele had lower levels of plasma corin [0.59 ± 0.07 ng/mL (n = 25) vs. 0.91 ± 0.02 ng/mL (n = 215), p<0.001] and higher levels of plasma N-terminal pro-atrial natriuretic peptide (NT-pro-ANP) [2.39 ± 3.6 nmol/L (n = 21) vs. 0.87 ± 0.6 nmol/L (n = 48), p = 0.005]. These results indicate that the variant altered corin structure and impaired the natriuretic peptide processing activity in vivo. The results highlight corin defects as an important underlying mechanism in hypertension.

Distinct roles of N-glycosylation at different sites of corin in cell membrane targeting and ectodomain shedding

Corin is a membrane-bound protease essential for activating natriuretic peptides and regulating blood pressure. Human corin has 19 predicted N-glycosylation sites in its extracellular domains. It has been shown that N-glycans are required for corin cell surface expression and zymogen activation. It remains unknown, however, how N-glycans at different sites may regulate corin biosynthesis and processing. In this study, we examined corin mutants, in which each of the 19 predicted N-glycosylation sites was mutated individually. By Western analysis of corin proteins in cell lysate and conditioned medium from transfected HEK293 cells and HL-1 cardiomyocytes, we found that N-glycosylation at Asn-80 inhibited corin shedding in the juxtamembrane domain. Similarly, N-glycosylation at Asn-231 protected corin from autocleavage in the frizzled-1 domain. Moreover, N-glycosylation at Asn-697 in the scavenger receptor domain and at Asn-1022 in the protease domain is important for corin cell surface targeting and zymogen activation. We also found that the location of the N-glycosylation site in the protease domain was not critical. N-Glycosylation at Asn-1022 may be switched to different sites to promote corin zymogen activation. Together, our results show that N-glycans at different sites may play distinct roles in regulating the cell membrane targeting, zymogen activation, and ectodomain shedding of corin.

Corin in natriuretic peptide processing and hypertension

Corin is a serine protease originally isolated from the heart. Functional studies show that corin is the long-sought enzyme responsible for activating cardiac natriuretic peptides. In mice, lack of corin prevents natriuretic peptide processing, causing salt-sensitive hypertension. In humans, corin variants and mutations that reduce corin activity have been identified in patients with hypertension and heart failure. Decreased plasma levels of corin antigen and activity have been reported in patients with heart failure and coronary artery disease. Low levels of urinary corin also have been found in patients with chronic kidney disease. Most recent studies show that corin also acts in the uterus to promote spiral artery remodeling and prevent pregnancy-induced hypertension. Here, we review the role of corin in natriuretic peptide processing and cardiovascular diseases such as hypertension, heart disease, pre-eclampsia, and chronic kidney disease.

Bafilomycin A1 inhibits autophagy and induces apoptosis in MG63 osteosarcoma cells

The purpose of the present study was to investigate the effects of bafilomycin A1 (BafA1) on proliferation, apoptosis and autophagy in MG63 osteosarcoma cells. The growth rate of MG63 cells was determined using a Cell Counting Kit‑8 assay. The mitochondrial membrane potential (Δψ) was measured using a fluorescent probe, JC‑1, and the inhibition of autophagy and apoptosis was monitored by transmission electron microscopy. In addition, the inhibition of autophagy was monitored by western blot analysis of microtubule‑associated protein 1 light chain 3 (LC3), and the ratio of LC3‑II/LC3‑I protein levels was calculated as an indicator of the extent of autophagy. Furthermore, the expression levels of specific proteins associated with autophagy, including p53, Beclin1 and p62, were detected in cultured MG63 cells by western blotting. It was shown that the viability of MG63 cells was inhibited following the use of BafA1, and an induction in the expression levels of the apoptosis‑related protein p53 and the autophagic protein Beclin1 was detected. Furthermore, a collapse in Δψ was observed, together with an induction of apoptotic cell death, following treatment with BafA1. Therefore, following BafA1‑mediated inhibition of autophagy, the inhibition of MG63 cell proliferation and induction of apoptosis were observed.

N-glycosylation is required for matriptase-2 autoactivation and ectodomain shedding

Matriptase-2 is a hepatic membrane serine protease that regulates iron homeostasis. Defects in matriptase-2 cause iron deficiency anemia. In cells, matriptase-2 is synthesized as a zymogen. To date, how matriptase-2 expression and activation are regulated remains poorly understood. Here we expressed human matriptase-2 in HEK293 and hepatic BEL-7402, SMMC-7721, and QGY-7703 cells. By labeling cell surface proteins and Western analysis, we examined matriptase-2 cell surface expression, zymogen activation, and ectodomain shedding. Our results show that matriptase-2 was activated on the cell surface but not intracellularly. Activated matriptase-2 underwent ectodomain shedding, producing soluble fragments in the conditioned medium. By testing inactive mutants, R576A and S762A, we found that matriptase-2 activation and shedding were mediated by its own catalytic activity and that the one-chain form of matriptase-2 had little activity in ectodomain shedding. We made additional matriptase-2 mutants, N136Q, N184Q, N216Q, N338Q, N433Q, N453Q, and N518Q, in which each of the predicted N-glycosylation sites was mutated. All of these mutants were expressed on the cell surface. However, mutants N216Q, N453Q, and N518Q, but not the other mutants, had impaired zymogen activation and ectodomain shedding. Our results indicate that N-glycans at specific sites are critical for matriptase-2 activation. Together, these data provide new insights into the cell surface expression, zymogen activation, and ectodomain shedding of matriptase-2.

Corin mutations K317E and S472G from preeclamptic patients alter zymogen activation and cell surface targeting. [Corrected]

Corin is a membrane-bound serine protease that acts as the atrial natriuretic peptide (ANP) convertase in the heart. Recent studies show that corin also activates ANP in the pregnant uterus to promote spiral artery remodeling and prevent pregnancy-induced hypertension. Two CORIN gene mutations, K317E and S472G, were identified in preeclamptic patients and shown to have reduced activity in vitro. In this study, we carried out molecular modeling and biochemical experiments to understand how these mutations impair corin function. By molecular modeling, the mutation K317E was predicted to alter corin LDL receptor-2 module conformation. Western blot analysis of K317E mutant in HEK293 cells showed that the mutation did not block corin expression on the cell surface but inhibited corin zymogen activation. In contrast, the mutation S472G was predicted to abolish a β-sheet critical for corin frizzled-2 module structure. In Western blot analysis and flow cytometry, S472G mutant was not detected on the cell surface in transfected HEK293 cells. By immunostaining, the S472G mutant was found in the ER, indicating that the mutation S472G disrupted the β-sheet, causing corin misfolding and ER retention. Thus, these results show that mutations in the CORIN gene may impair corin function by entirely different mechanisms. Together, our data provide important insights into the molecular basis underlying corin mutations that may contribute to preeclampsia in patients.

Pulsatilla saponin A, an active molecule from Pulsatilla chinensis, induces cancer cell death and inhibits tumor growth in mouse xenograft models

BACKGROUND

Many natural compounds possess antitumor growth activities. Pulsatilla chinensis is an herb used in traditional Chinese medicine to treat infectious diseases. More recently, extracts from P chinensis have been shown to contain antitumor activities.

MATERIALS AND METHODS

In this study, we isolated Pulsatilla saponin A as an active compound from P chinensis extracts and tested its anticancer activity in vitro and in vivo.

RESULTS

In cell culture, Pulsatilla saponin A significantly inhibited the growth of human hepatocellular carcinoma SMCC-7721 cells and pancreatic BXPC3 and SW1990 cancer cells. Similar inhibitory activities were observed when the compound was tested in mouse xenograft tumor models using human hepatocellular carcinoma Bel-7402 and pancreatic cancer SW1990 cells. In Comet assay and flow cytometric analysis of cell cycle distribution and annexin V expression, DNA damage, G2 arrest, and apoptosis were identified in Pulsatilla saponin A-treated cancer cells. Based on the results of Western blotting, p53 and cyclin B protein levels were higher, whereas Bcl-2 protein levels were lower in Pulsatilla saponin A-treated cancer cells than in vehicle-treated cells.

CONCLUSIONS

Pulsatilla saponin A may exert its antitumor effect by inducing DNA damage and causing G2 arrest and apoptosis in cancer cells. Pulsatilla saponin A and its derivatives may be developed as a new class of anticancer agents.

Reduced urinary corin levels in patients with chronic kidney disease

Corin is a cardiac protease that regulates BP (blood pressure) by activating natriuretic peptides. Recent animal studies identified corin expression in the kidney where it may regulate renal function. In the present study, we tested the hypothesis that corin may be present in human urine and that urinary corin levels may be altered in patients with kidney disease. We obtained urine and kidney tissue samples from normal individuals and CKD (chronic kidney disease) patients. Using ELISA, we detected corin protein in human urine. In normal individuals, urinary corin levels did not correlate with that of plasma, indicating that urinary corin is probably of kidney origin. Compared with normal controls, CKD patients had markedly reduced urinary corin levels and this reduction correlated with disease severity. By immunostaining, human corin protein was identified on the epithelial cell surface in renal tubules. The renal corin mRNA and protein levels were significantly lower in CKD patients than non-CKD controls. The results indicate that renal tubular corin may be shed into urine and that urinary and renal corin levels were reduced in CKD patients. These data suggest that reduced corin levels in the kidney may reflect the underlying pathology in CKD.

Corin mutation R539C from hypertensive patients impairs zymogen activation and generates an inactive alternative ectodomain fragment

Corin is a cardiac transmembrane serine protease that regulates blood pressure by activating natriuretic peptides. Corin variants have been associated with African Americans with hypertension and heart disease. Here, we report a new mutation in exon 12 of the CORIN gene identified in a family of patients with hypertension. The mutation resulted in R539C substitution in the Fz2 (Frizzled-2) domain of the corin propeptide region. We expressed and characterized the corin R539C mutant in HEK293 cells. As determined by Western blot analysis, the R539C mutation did not alter corin expression in transfected cells but impaired corin zymogen activation. In a pro-atrial natriuretic peptide processing assay, the corin mutant had reduced activity and exhibited a dominant-negative effect on wild-type corin. In addition, the R539C mutation altered corin ectodomain shedding, producing an alternative ~75-kDa fragment that was biologically inactive. Using protease inhibitors and the catalytically inactive corin mutant S985A, we showed that the ~75-kDa fragment was generated by corin autocleavage. We constructed a series of mutants by replacing single or double Arg residues in the corin propeptide and identified Arg-530 in the Fz2 domain as the alternative autocleavage site. Our results show that the corin mutation R539C identified in hypertensive patients impairs corin zymogen activation and causes an alternative autocleavage that reduces corin activity. These data support that human CORIN gene mutations causing impaired corin activity may be an underlying mechanism in hypertension.

Role of corin and atrial natriuretic peptide in preeclampsia

In pregnancy, uterine spiral artery remodeling is an adaptive morphological change at the maternal and fetal interface, which is critical for dilating the artery and promoting blood flow to the fetus. Incompletely remodeled spiral arteries have been recognized as a common pathological feature in preeclamptic patients. To date, the molecular mechanism that controls spiral artery remodeling is not well defined. Corin is a transmembrane serine protease discovered in the heart, where it converts pro-atrial natriuretic peptide (pro-ANP) to active ANP, a cardiac hormone that regulates salt-water balance and blood pressure. Recent studies show that corin is up-regulated in the decidua of the pregnant uterus, suggesting a potential role of corin in pregnancy. In mice lacking corin or ANP, high blood pressure and proteinuria were found at late gestational stages. Histological analysis indicated delayed trophoblast invasion and impaired spiral artery remodeling in the uterus. In humans, CORIN gene mutations were identified in patients with preeclampsia. In this review, we discuss the function of corin and ANP in regulating blood pressure and their potential role in preeclampsia.

Salt-sensitive hypertension and cardiac hypertrophy in transgenic mice expressing a corin variant identified in blacks

Blacks represent a high-risk population for salt-sensitive hypertension and heart disease, but the underlying mechanism remains unclear. Corin is a cardiac protease that regulates blood pressure by activating natriuretic peptides. A corin gene variant (T555I/Q568P) was identified in blacks with hypertension and cardiac hypertrophy. In this study, we tested the hypothesis that the corin variant contributes to the hypertensive and cardiac hypertrophic phenotype in vivo. Transgenic mice were generated to express wild-type (WT) or T555I/Q568P variant corin in the heart under the control of α-myosin heavy chain promoter. The mice were crossed into a corin knockout (KO) background to create KO/TgWT and KO/TgV mice that expressed WT or variant corin, respectively, in the heart. Functional studies showed that KO/TgV mice had significantly higher levels of proatrial natriuretic peptide in the heart compared with that in control KO/TgWT mice, indicating that the corin variant was defective in processing natriuretic peptides in vivo. By radiotelemetry, corin KO/TgV mice were found to have hypertension that was sensitive to dietary salt loading. The mice also developed cardiac hypertrophy at 12 to 14 months of age when fed a normal salt diet or at a younger age when fed a high-salt diet. The phenotype of salt-sensitive hypertension and cardiac hypertrophy in KO/TgV mice closely resembles the pathological findings in blacks who carry the corin variant. The results indicate that corin defects may represent an important mechanism in salt-sensitive hypertension and cardiac hypertrophy in blacks.

Role of corin in trophoblast invasion and uterine spiral artery remodelling in pregnancy

In pregnancy, trophoblast invasion and uterine spiral artery remodelling are important for lowering maternal vascular resistance and increasing uteroplacental blood flow. Impaired spiral artery remodelling has been implicated in pre-eclampsia, a major complication of pregnancy, for a long time but the underlying mechanisms remain unclear. Corin (also known as atrial natriuretic peptide-converting enzyme) is a cardiac protease that activates atrial natriuretic peptide (ANP), a cardiac hormone that is important in regulating blood pressure. Unexpectedly, corin expression was detected in the pregnant uterus. Here we identify a new function of corin and ANP in promoting trophoblast invasion and spiral artery remodelling. We show that pregnant corin- or ANP-deficient mice developed high blood pressure and proteinuria, characteristics of pre-eclampsia. In these mice, trophoblast invasion and uterine spiral artery remodelling were markedly impaired. Consistent with this, the ANP potently stimulated human trophoblasts in invading Matrigels. In patients with pre-eclampsia, uterine Corin messenger RNA and protein levels were significantly lower than that in normal pregnancies. Moreover, we have identified Corin gene mutations in pre-eclamptic patients, which decreased corin activity in processing pro-ANP. These results indicate that corin and ANP are essential for physiological changes at the maternal-fetal interface, suggesting that defects in corin and ANP function may contribute to pre-eclampsia.

Corin in clinical laboratory diagnostics

Corin is a transmembrane serine protease identified in the heart, where it converts natriuretic peptides from inactive precursors to mature active forms. Studies in animal models and patients with hypertension and heart disease demonstrate that corin is critical in maintaining normal blood pressure and cardiac function. Like many proteolytic enzymes, corin expression and activity are regulated. Cell biology experiments indicate that transcriptional control, intracellular protein trafficking, cell surface targeting, zymogen activation and ectodomain shedding are important mechanisms in regulating corin expression and activity in the heart. More recently, soluble corin was detected in human blood and its levels were found to be reduced in patients with heart failure (HF). These findings indicate that corin deficiency may be involved in the pathogenesis of HF and suggest that soluble corin may be used as a biomarker for the disease. In this review, we describe the function and regulation of corin and discuss recent studies of soluble corin in human blood and its potential use as a biomarker for HF.