Expression of placental leucine aminopeptidase is associated with a poor outcome in endometrial endometrioid adenocarcinoma

The emerging role of dipeptidyl peptidase 3 in pathophysiology

Dipeptidyl peptidase 3 (DPP3), a zinc-dependent aminopeptidase, is a highly conserved enzyme among higher animals. The enzyme cleaves dipeptides from the N-terminus of tetra- to decapeptides, thereby taking part in activation as well as degradation of signalling peptides critical in physiological and pathological processes such as blood pressure regulation, nociception, inflammation and cancer. Besides its catalytic activity, DPP3 moonlights as a regulator of the cellular oxidative stress response pathway, e.g., the Keap1-Nrf2 mediated antioxidative response. The enzyme is also recognized as a key modulator of the renin-angiotensin system. Recently, DPP3 has been attracting growing attention within the scientific community, which has significantly augmented our knowledge of its physiological relevance. Herein, we review recent advances in our understanding of the structure and catalytic activity of DPP3, with a focus on attributing its molecular architecture and catalytic mechanism to its wide-ranging biological functions. We further highlight recent intriguing reports that implicate a broader role for DPP3 as a valuable biomarker in cardiovascular and renal pathologies and furthermore discuss its potential as a promising drug target.

Placental Leucine Aminopeptidase as a Potential Specific Urine Biomarker for Invasive Ovarian Cancer

BACKGROUND

A non-invasive and sensitive biomarker for the detection of ovarian cancer (OvCa) is lacking. We aim to investigate if urinary placental leucine aminopeptidase (P-LAP) can serve as a reliable biomarker for OvCa.

METHODS

P-LAP activity was measured using a LAP assay kit (Serotech Co., Ltd., Sapporo, Japan) in the urine of 22 patients with benign or borderline malignant ovarian tumors and 18 patients with OvCa. In this assay, L-methionine was added at 20 mM because P-LAP is functional, but other aminopeptidases are inhibited at this dose of L-methionine.

RESULTS

The mean urinary P-LAP activity was significantly higher in the OvCa group than in the benign or borderline malignant tumor group. When the cut-off value of P-LAP was determined as 11.00 U/L, its sensitivity and specificity for differentiating invasive cancer were 77.8% and 95.5%, respectively.

CONCLUSION

Although the usefulness of this test should be confirmed in a larger cohort of cases and controls, our study is the first to highlight the importance of urinary P-LAP as a biomarker for OvCa.

Prognostic Value of Preoperative Serum Leucine Aminopeptidases in Hepatocellular Carcinoma Patients Who Underwent Liver Transplantation

Background

Leucine aminopeptidases (LAPs) have been reported to be involved in tumor cell proliferation, invasion and angiogenesis. However, the relationship between serum leucine aminopeptidases and prognosis of hepatocellular carcinoma (HCC) patients who underwent liver transplantation (LT) was not yet reported. We aimed to evaluate the prognostic value of preoperative serum leucine aminopeptidases in these patients.

Methods

Clinical data of 106 HCC patients who underwent LT were retrospectively analyzed. The sex ratio, age, HBV infection, Child-Pugh stage, preoperative tumor therapy, AFP, the largest tumor size, tumor number, Edmondson grading, macro- and micro-vascular invasion of patients with different serum LAP level and compositions of patients who met the criteria of Milan, UCSF or Hangzhou were compared using the chi-square test. The Kaplan-Meier method was performed in survival analysis and the log rank test was used in survival comparison.

Results

Serum LAPs were correlated with alpha-fetoprotein (AFP), the largest tumor size, tumor number and macro-vascular invasion. Patients with serum LAPs > 87 U/L showed significantly poorer disease-free survival (DFS) and overall survival (OS) than those with serum LAPs ≤ 87 U/L. Univariate analysis indicated that serum LAPs, AFP, the largest tumor size, tumor number, and macro- and micro-vascular invasion were all associated with DFS and OS. Multivariate analysis showed that serum LAPs, macro-vascular invasion and the largest tumor size were independently correlated with DFS and OS. Serum LAPs could also distinguish prognosis between patients with different status of AFP, the largest tumor size, tumor number, and macro- and micro-vascular invasion, as well as patients within and beyond selection criteria, such as Milan, University of California, San Francisco and Hangzhou criteria.

Conclusion

Elevated preoperative serum LAPs were associated with advanced tumor stage and aggressive biological behavior, and thus a poor outcome, which could be a prognostic marker for HCC patients who underwent LT.

The impact of peptidase activity on clear cell renal cell carcinoma survival

Several studies have proposed that protease expression and activity may have a predictive value in the survival of clear cell renal cell carcinoma (CCRCC). Most efforts on this issue have been focused on the analysis of matrix metalloproteinases (MMP) and very little on the role of other proteases, such as peptidases. The catalytic activity of 9 peptidases (APN, APB, ASP, CAP, DPP-IV, NEP/CD10, PEP, PGI, and PSA) was quantified by fluorometric methods in a series of 79 CCRCC patients, and the results obtained were analyzed for survival (Kaplan-Meier curves, log-rank test, and Cox multivariate analysis). CCRCC patients with higher activity levels of membrane-bound APN and soluble APN, DPP-IV, and CAP had significantly shorter 5-yr survival rates than those with lower levels. By contrast, higher soluble APB activity significantly correlated with longer survival. Our data suggest the involvement of peptidases in the biological aggressiveness of CCRCC and support the usefulness of measuring these proteases to assess the prognosis of patients with CCRCC.

Ablation of angiotensin IV receptor attenuates hypofibrinolysis via PAI-1 downregulation and reduces occlusive arterial thrombosis

OBJECTIVE

Reduced fibrinolytic activity is associated with adverse cardiovascular events. Although insulin-regulated aminopeptidase (IRAP) was recently identified as the angiotensin (Ang) IV receptor (AT4R), the impact of AngIV-AT4R signaling distal to AngII on the activation of type-1 plasminogen activator inhibitor (PAI-1) in the fibrinolytic process and subsequent formation of thrombosis remains unclarified.

METHODS AND RESULTS

To determine whether AngIV would inhibit fibrinolysis via PAI-1 activation and promote thrombosis, we evaluated the degree of fibrinolysis in thrombosis models and investigated the roles of AT4R after vascular injury using IRAP knockout mice (IRAP(-/-)). In endothelial cells from control mice (WT; C57Bl6/J), both AngII and AngIV treatments increased PAI-1 mRNA expression in a dose-dependent manner, whereas the response was blunted in endothelial cells from IRAP(-/-) mice. FeCl(3)-induced thrombosis was suppressed in the carotid arteries of IRAP(-/-) mice when compared with WT mice. Similarly, in a model of carotid artery ligation and cuff placement, IRAP(-/-) mice demonstrated accelerated fibrinolysis 7 days after surgery and reduced occlusive thrombosis with negative remodeling at 28 days.

CONCLUSIONS

AngIV-AT4R signaling has a key role in fibrinolysis and the subsequent formation of arterial thrombosis after vascular injury. AT4R may be a novel therapeutic target against cardiovascular disease.

Cystinyl aminopeptidase activity is decreased in renal cell carcinomas

The involvement of peptidases in carcinogenetic processes of several tumor types has been researched in recent years. Although kidney is one of the major tissues known to express cystinyl-aminopeptidase (CAP), little is known about its role in renal neoplasia. This study analyzes fluorimetrically membrane-bound and soluble CAP activity in the three main renal cancers: clear cell (CCRCC), papillary (PRCC), and chromophobe (ChRCC) renal cell carcinomas. Overall, a marked decrease of membrane-bound CAP activity in all the three renal cell carcinomas was detected when compared with their respective surrounding non-tumor tissues. So, the tumor vs. non-tumor CAP ratios (units of peptidase per mg of protein) was as follows: 926+/-111 vs. 3778+/-276 for CCRCCs, 737+/-181 vs. 4351+/-950 for PRCCs, and 592+/-118 vs. 4905+/-935 for ChRCCs. In contrast, the soluble fraction of this enzyme displayed minor and non-significant changes when comparing tumor and non-tumor CAP activities in the whole series. After stratification by stage and grade, CCRCCs displayed significant differences: pT3 category had significantly higher levels of membrane-bound activity than pT1, and high grade cases (G3-4) had higher soluble CAP activity than low grade ones (G1-2). These data may open additional possibilities in the study of renal cell carcinoma with regard to the prognosis of patients.

Essential role of placental leucine aminopeptidase in gynecologic malignancy

The M1 aminopeptidase family is important for the maturation or degradation of bioactive peptides by hydrolyzing their N-terminal amino acids. Some investigators have studied aminopeptidase in the maintenance of homeostasis including maintenance of normal pregnancy, memory retention, blood pressure regulation and antigen presentation. However, there are a few reports on the relation between the M1 aminopeptidase family and carcinoma. In addition to its capacity to degrade a range of peptides, placental-leucine aminopeptidase (P-LAP) has novel functions that impact on normal cells and neoplastic cells. P-LAP is the focus of this review.

P-LAP/IRAP-induced cell proliferation and glucose uptake in endometrial carcinoma cells via insulin receptor signaling

Background

Hyperglycemia or hyperinsulinemia contributes to poorer endometrial cancer survival. It was shown that P-LAP/IRAP translocates to the plasma membrane in response to insulin stimulation. Recently, we demonstrated that P-LAP/IRAP is associated with a poor prognosis in endometrial adenocarcinoma patients. The aim of this study was to examine whether the malignant potential of endometrial cancer enhanced by P-LAP/IRAP is due to increased glucose uptake via the P-LAP/IRAP-mediated activation of insulin signaling.

Methods

We transfected P-LAP/IRAP cDNA into A-MEC cells (endometrial adenocarcinoma cell line), and A-MEC-LAP cells expressed a remarkably high level of GLUT4 proteins.

Results

³H-2-deoxyglucose uptake which responds to insulin in A-MEC-LAP cells was significantly higher than that of A-MEC-pc cells. A-MEC-LAP cells exhibited a significant growth-stimulatory effect compared to A-MEC-pc cells. A-MEC-LAP cells expressed a remarkably high level of p85PI3K protein compared to A-MEC-pc cells, and showed a higher degree of AKT phosphorylation by insulin stimulation.

Conclusion

In summary, P-LAP/IRAP was involved in the increasing malignant potential of endometrial cancer mediated by insulin. P-LAP/IRAP was suggested to be a potential new target of molecular-targeted therapy for endometrial cancer.

Indoleamine 2,3-dioxygenase is a novel prognostic indicator for endometrial cancer

Indoleamine 2,3-dioxygenase (IDO) is a tryptophan-catabolising enzyme inducing immune tolerance. The present study aimed to investigate IDO expression and its prognostic significance in endometrial cancer. Indoleamine 2,3-dioxygenase expression in endometrial cancer tissues (n = 80) was immunohistochemically scored as four groups (IDO-, 1+, 2+, and 3+). The high IDO expression (IDO2+ or 3+) in tumour cells was found in 37 (46.3%) of the 80 cases, and was positively correlated with surgical stage, myometrial invasion, lymph-vascular space involvement, and lymph node metastasis, but not with the histological grade. Patients with high IDO expression had significantly impaired overall survival and progression-free survival (PFS) (P = 0.002 and P = 0.001, respectively) compared to patients with no or weak expression of IDO (IDO- or 1+). The 5-year PFS for IDO-/1+, 2+, and 3+ were 97.7, 72.9, and 36.4%, respectively. Even in patients with early-stage disease (International Federation of Gynecology and Obstetrics I/II, n = 64), the PFS for IDO2+/3+ was significantly poor (P = 0.001) compared to that for IDO-/1+. On multivariate analysis, IDO expression was an independent prognostic factor for PFS (P = 0.020). These results indicated that the high IDO expression was involved in the progression of endometrial cancer and correlated with the impaired clinical outcome, suggesting that IDO is a novel and reliable prognostic indicator for endometrial cancer.

A novel role for placental leucine aminopeptidase (P-LAP) as a determinant of chemoresistance in endometrial carcinoma cells

In several recent studies, we have shown that P-LAP can be a poor prognostic factor and a factor of chemoresistance in endometrial carcinoma, especially in the advanced patients. In our study, we investigated whether P-LAP alters the expression of apoptosis regulatory proteins as a mechanism of drug resistance. We transfected P-LAP cDNA into A-MEC cells (endometrial adenocarcinoma cell line), and A-MEC-LAP cells displayed a 1.8-fold, 2.0-fold and 1.7-fold increase in IC(50) against paclitaxel, carboplatin and cisplatin respectively. Translational downregulation by siRNA2 to P-LAP on A-MEC-LAP cells demonstrated 60%, 51% and 58% decrease in IC(50). To investigate the mechanism of P-LAP-induced chemoresistance, we also assessed whether P-LAP transfection had an effect on carboplatin-induced apoptotic death of A-MEC cells. A-MEC and A-MEC-pc (transfected with vector alone) cells exhibited a strong apoptotic response to carboplatin, while A-MEC-LAP cells exhibited a weak apoptotic response. In an attempt to identify the mechanism of the inhibitory effect on apoptotic response to carboplatin, we next assessed the expression of cleaved caspases and PARP cleavage. While treatment of A-MEC-pc cells with carboplatin exhibited increased levels of cleaved caspase 3, caspase 7 and caspase 9 compared to that after no treatment, A-MEC-LAP cells did not show any expression of these caspases. These results suggest that P-LAP reduces sensitivity to anticancer drugs via inhibition of mitochondria-mediated apoptosis, and may be a molecular target for conquering anticancer drug resistance.

Gene regulation and physiological function of placental leucine aminopeptidase/oxytocinase during pregnancy

Human pregnancy serum and placenta have the ability to degrade uterotonic peptide oxytocin (OT). Placental leucine aminopeptidase (P-LAP), which is also called cystine aminopeptidase, is the only membrane aminopeptidase known to functionally degrade OT as oxytocinase (OTase). P-LAP/OTase hydrolyzes several peptides other than OT including vasopressin and angiotensin III. P-LAP/OTase predicted from cDNA sequence is a type II integral membrane protein, which is converted to a soluble form existing in maternal serum by metalloproteases, possibly ADAM (a disintegrin and metalloproteinase) members. P-LAP/OTase activity increases with normal gestation, while decreases in the patients with preterm delivery and severe preeclampsia. In placenta, P-LAP/OTase is predominantly expressed in differentiated trophoblasts, syncytiotrophoblasts. Activator protein-2 (AP-2) and Ikaros transcription factors play significant roles in exerting high promoter activity of P-LAP/OTase in the trophoblastic cells. Moreover, P-LAP/OTase is transcriptionally regulated in a trophoblast-differentiation-dependent fashion via up-regulation of AP-2, putatively AP-2alpha. P-LAP/OTase may be involved in maintaining pregnancy homeostasis via metabolizing peptides such as OT and vasopressin.

Placental leucine aminopeptidase (P-LAP) and glucose transporter 4 (GLUT4) expression in benign, borderline, and malignant ovarian epithelia

OBJECTIVE

Increased glucose consumption is a characteristic of malignant cells. Glucose is transported into the cell via facilitative glucose transporters, which are known to be members of a supergene family. The insulin-responsive GLUT4 isoform is expressed almost exclusively in insulin target tissues. P-LAP is a cell surface aminopeptidase, and is a synonym for oxytocinase. P-LAP is also referred to as insulin-regulated membrane aminopeptidase (IRAP) associated with GLUT4-containing vesicle. The authors evaluated P-LAP and GLUT4 expression in benign, borderline, and malignant ovarian epithelia.

METHODS

Histologic sections of formalin-fixed, paraffin-embedded specimens from 11 patients with benign serous or mucinous cystadenomas, 14 patients with serous or mucinous borderline tumors, and 80 patients with epithelial-ovarian adenocarcinomas (29 serous, 17 endometrioid, 14 mucinous, and 20 clear cell adenocarcinomas) were stained for P-LAP and GLUT4 using each polyclonal antibody. Expressions of P-LAP and GLUT-4 in ovarian cancer cells were detected by Western blotting.

RESULTS

P-LAP immunoreactivity was detected in 2 of 11 benign cystadenomas. None of the 11 benign ovarian tumors showed any immunoreactivity for GLUT4. Seven of 14 borderline tumors demonstrated P-LAP immunoreactivity, while 5 of 14 borderline tumors demonstrated GLUT4 immunoreactivity. P-LAP was expressed in 23 of 29 in serous, 15 of 17 endometrioid, 13 of 14 mucinous, and all clear-cell adenocarcinomas. The tendency toward increased P-LAP expression with advancing grade was observed in serous adenocarcinomas. GLUT4 was expressed in 13 of 29 serous, 13 of 17 endometrioid, 13 of 14 mucinous, and 18 of 20 clear-cell adenocarcinomas. In invasive carcinomas, there was a direct correlation between P-LAP immunoreactivity and GLUT4 immunoreactivity (correlation coefficient [r] = 0.58; P < 0.01). Furthermore, P-LAP overexpression in SKOV3 cells induced the GLUT4 expression.

CONCLUSIONS

P-LAP and GLUT4 are available not only for the evaluation of ovarian epithelial malignancy, but also as targets for molecular therapy. Further study to investigate the roles of P-LAP and GLUT4 in ovarian carcinoma is needed.

Regulatory role of membrane-bound peptidases in the progression of gynecologic malignancies

Membrane-bound peptidases play a key role in the control of growth, differentiation, and signal transduction of many cellular systems by degrading bioactive peptides. Thus, abnormal changes in their expression pattern and catalytic function result in altered peptide activation, which contributes to neoplastic transformation or progression. In this review, we describe our recent findings along with work from other groups on the expression and biological functions of membrane-bound peptidases in cancer, focusing on the regulatory roles of three peptidases, aminopeptidase A (APA), neutral endopeptidase (NEP) and placental leucine aminopeptidase (P-LAP), in the progression of gynecologic malignancies. APA, NEP and P-LAP are differentially expressed and localized in various gynecologic malignancies including cervical cancer, endometrial cancer, ovarian cancer and choriocarcinoma in a tumor-type specific pattern. The expression levels are up- or down-regulated depending on histological grade or disease progression. These peptidases play regulatory roles in tumor cell proliferation, invasion or angiogenesis via degradation/inactivation of target peptides such as angiotensin II, endothelin-1 and oxytocin, which act on cancer cells as stimulatory or inhibitory factors. Thus, membrane-bound peptidases may become not only a new diagnostic/prognostic marker, but also a novel molecular target for the treatment of gynecologic malignancies.