High concentration of neutral endopeptidase (enkephalinase E.C. 3.4.24.11) in a malignant tumor: rat hepatoma 3924A

Carboxypeptidase M in apoptosis, adipogenesis and cancer

This review covers carboxypeptidase M (CPM) research that appeared in the literature since 2009. The focus is on aspects that are new or interesting from a clinical perspective. Available research tools are discussed as well as their pitfalls and limitations. Evidence is provided to suggest the potential involvement of CPM in apoptosis, adipogenesis and cancer. This evidence derives from the expression pattern of CPM and its putative substrates in cells and tissues. In recent years CPM emerged as a potential cancer biomarker, in well differentiated liposarcoma where the CPM gene is co-amplified with the oncogene MDM2; and in lung adenocarcinoma where coexpression with EGFR correlates with poor prognosis. The available data call for extended investigation of the function of CPM in tumor cells, tumor-associated macrophages, stromal cells and tumor neovascularisation. Such experiments could be instrumental to validate CPM as a therapeutic target.

Subcellular distribution of membrane-bound aminopeptidases in the human and rat brain

We evaluated the subcellular distribution of four membrane-bound aminopeptidases in the human and rat brain cortex. The particulate enzymes under study--puromycin-sensitive aminopeptidase (PSA), aminopeptidase N (APN), pyroglutamyl-peptidase I (PG I) and aspartyl-aminopeptidase (Asp-AP)--were fluorometrically measured using beta-naphthylamide derivatives. Membrane-bound aminopeptidase activity was found in all the studied subcellular fractions (myelinic, synaptosomal, mitochondrial, microsomal and nuclear fractions), although not homogenously. Human PSA showed highest activity in the microsomal fraction. APN was significantly higher in the nuclear fraction of both species, while PG I showed highest activity in the synaptosomal and myelinic fractions of the human and rat brain. The present results suggest that in addition to inactivating neuropeptides at the synaptic cleft, these enzymes may participate in other physiological processes. Moreover, these peptidases may play specific roles depending on their activity levels at the different subcellular structures where they are localized.

Molecular structure and alternative splicing of the human carboxypeptidase M gene

Using RACE technology the 5' and 3' ends of human carboxypeptidase M (CPM) mRNA were determined and found to be divergent from the published sequence. With these results the complete structure of the human CPM gene was established based on the human genome sequence in the GenBank database. The gene was shown to contain 9 exons comprising at least 75 kb of genomic sequence. A novel first exon of 30 bp was identified and an upstream promoter sequence containing several transcription factor binding sites was found by computer analysis. Furthermore, the ATG starting codon was detected defining an open reading frame of 1329 bp that codes for a protein of 443 residues. Additionally, the polyadenylation site was discovered, determining a 3' noncoding region of 2000 nucleotides. The exon-intron boundaries diverged substantially compared to those of the other basic carboxypeptidases, CPD, CPE, CPN, and AEBP1. Cloning and sequencing of RT-PCR products from different tissues revealed alternative splicing of exons 3 and 5, which results in the generation of four different mRNA isoforms. RNA extracted from tumor tissues contained more CPM mRNA than control tissue, suggesting an upregulation of CPM expression in tumors and raising the question of the role of this enzyme in cancer.

Relationship of serum neutral endopeptidase E.C.3.4.24.11 activity to alcohol consumption

Neutral endopeptidase (NEP) is an ubiquitous enzyme that inactivates numerous endogenous peptides in the brain, kidney, and lung in vivo. The origin of the circulating soluble form and its determinants are largely unknown. The relationships of smoking habits and alcohol consumption to serum NEP activity have been explored in a longitudinal epidemiological study conducted in 204 Lorraine coal miners. At both surveys, 4 years apart, NEP activity was significantly related to alcohol consumption (in grams/day) reported by questionnaire, with correlation coefficients of 0.26 (p = 0.001) in 1990 and 0.23 (p = 0.001) in 1994. The correlations of gamma-glutamyltransferase to NEP activity were even stronger with correlation coefficients of 0.71 (p = 0.0001) in 1990 and 0.79 (p = 0.0001) in 1994. Longitudinally, the change in NEP activity between the first and the second surveys was significantly correlated with change in alcohol consumption (r = to 0.18, p = 0.02) and with change in gamma-glutamyltransferase level (r = 0.60, p = 0.0001). Serum NEP activity was unrelated to smoking habits. Results support the hypothesis of a causal role of alcohol on serum NEP activity.

Enkephalinase-blocking agent thiorphan affects cell growth and differentiation in long term culture of mouse bone marrow

Enkephalinase-blocking agent thiorphan was added to long-term cultures of mouse bone marrow cells at the time of culture initiation (time 0) or 2 weeks thereafter, when the stromal layer appears. Cellularity, cell morphology (in cytospin smears) and the yield of granulocyte-macrophage progenitor cells (GM-CFC assay in agar) were recorded. Low concentrations of thiorphan accelerated recovery of the cultures after an initial drop of the cell count. Expansion and maturation of the granulocytic lineage was promoted, with parallel decline of the GM-CFC yield. Thiorphan probably interfered with the activity of enkephalinase (endopeptidase 24.11) in the cultures. That enzyme is the CD10 surface marker (CALLA) of lymphoid, myeloid and stromal elements.