Key peptide processing enzymes are expressed by a variant form of small-cell carcinoma of the lung

Carboxypeptidase E mRNA: Overexpression predicts recurrence and death in lung adenocarcinoma cancer patients

BACKGROUND

Effective biomarkers for prediction of recurrence of lung adenocarcinoma cancer (LADC) patients are needed to determine treatment strategies post-surgery to improve outcome.

OBJECTIVE

This study evaluates the efficacy of carboxypeptidase E (CPE) mRNA including its splice isoforms, CPE-ΔN, as a biomarker for predicting recurrence in adenocarcinoma patients.

METHODS

RNA was extracted from resected tumors from 86 patients with different stages of non-small cell LADC. cDNA was synthesized and qRT-PCR carried out to determine the copy numbers of CPE/CPE-ΔN mRNA. Patients were followed for 7 years post-tumor resection to determine recurrence and death.

RESULTS

ROC curve analysis showed the overall AUC for CPE/CPE-ΔN copy number was 0.563 in predicting recurrence and 0.563 in predicting death. Kaplan-Meier survival analysis showed statistical difference (p= 0.018), indicating that patients with high CPE/CPE-ΔN copy numbers had a shorter time of disease-free survival and also shorter time to death (p= 0.035). Subgroup analyses showed that association of disease-free survival time with CPE/CPE-ΔN copy number was stronger among stage I and II LADC patients (p= 0.047).

CONCLUSIONS

CPE/CPE-ΔN mRNA is a potentially useful biomarker for predicting recurrence and death in LADC patients, especially in identifying patients at high risk of recurrence at early stages I and II.

Biochemical and cell biological properties of the human prohormone convertase 1/3 Ser357Gly mutation: a PC1/3 hypermorph

Satiety and appetite signaling are accomplished by circulating peptide hormones. These peptide hormones require processing from larger precursors to become bioactive, often by the proprotein convertase 1/3 (PC1/3). Several subcellular maturation steps are necessary for PC1/3 to achieve its optimal enzymatic activity. Certain PC1/3 variants found in the general population slightly attenuate its enzymatic activity and are associated with obesity and diabetes. However, mutations that increase PC1/3 activity and/or affect its specificity could also have physiological consequences. We here present data showing that the known human Ser357Gly PC1/3 mutant (PC1/3(S357G)) represents a PC1/3 hypermorph. Conditioned media from human embryonic kidney-293 cells transfected with PC1/3(WT) and PC1/3(S357G) were collected and enzymatic activity characterized. PC1/3(S357G) exhibited a lower calcium dependence; a higher pH optimum (neutral); and a higher resistance to peptide inhibitors than the wild-type enzyme. PC1/3(S357G) exhibited increased cleavage to the C-terminally truncated form, and kinetic parameters of the full-length and truncated mutant enzymes were also altered. Lastly, the S357G mutation broadened the specificity of the enzyme; we detected PC2-like specificity on the substrate proCART, the precursor of the cocaine- and amphetamine regulated transcript neuropeptide known to be associated with obesity. The production of another anorexigenic peptide normally synthesized only by PC2, αMSH, was increased when proopiomelanocortin was coexpressed with PC1/3(S357G). Considering the aberrant enzymatic profile of PC1/3(S357G), we hypothesize that this enzyme possesses unusual processing activity that may significantly change the profile of circulating peptide hormones.

Carboxypeptidase E promotes cancer cell survival, but inhibits migration and invasion

Carboxypeptidase E (CPE), a prohormone processing enzyme is highly expressed and secreted from (neuro)endocrine tumors and gliomas, and has been implicated in cancer progression by promoting tumor growth. Our study demonstrates that secreted or exogenously applied CPE promotes survival of pheochromocytoma (PC12) and hepatocellular carcinoma (MHCC97H) cells under nutrient starvation and hypoxic conditions, but had no effect on their proliferation. CPE also reduced migration and invasion of fibrosarcoma (HT1080) cells. We show that CPE treatment mediates survival of MHCC97H cells during metabolic stress by up-regulating the expression of anti-apoptotic protein BCL-2, and other pro-survival genes, via activation of the ERK1/2 pathway.

New roles of carboxypeptidase E in endocrine and neural function and cancer

Carboxypeptidase E (CPE) or carboxypeptidase H was first discovered in 1982 as an enkephalin-convertase that cleaved a C-terminal basic residue from enkephalin precursors to generate enkephalin. Since then, CPE has been shown to be a multifunctional protein that subserves many essential nonenzymatic roles in the endocrine and nervous systems. Here, we review the phylogeny, structure, and function of CPE in hormone and neuropeptide sorting and vesicle transport for secretion, alternative splicing of the CPE transcript, and single nucleotide polymorphisms in humans. With this and the analysis of mutant and knockout mice, the data collectively support important roles for CPE in the modulation of metabolic and glucose homeostasis, bone remodeling, obesity, fertility, neuroprotection, stress, sexual behavior, mood and emotional responses, learning, and memory. Recently, a splice variant form of CPE has been found to be an inducer of tumor growth and metastasis and a prognostic biomarker for metastasis in endocrine and nonendocrine tumors.

Carboxypeptidase E: elevated expression correlated with tumor growth and metastasis in pheochromocytomas and other cancers

Expression of carboxypeptidase E (CPE), a prohormone processing enzyme in different cancer types, was analyzed from data in the GEO profile database (http://www.ncbi.nlm.nih.gov/geo/) and experimentally in pheochromocytomas. Analysis of microarray data demonstrated that significantly elevated levels of CPE mRNA was found in many metastatic non-endocrine cancers: cervical, colon rectal, renal cancers, Ewing sarcomas (bone cancer), and various types of astrocytomas and oligodendrogliomas, whereas expression of CPE mRNA was virtually absent in their respective counterpart normal tissues. Moreover, there was higher CPE mRNA expression in cells from the metastatic tumor compared to those from the primary tumor in colorectal cancer. Elevated CPE mRNA expression was found in neuroendocrine tumors in lung and pituitary adenomas, although the significance is unclear since endocrine and neuroendocrine cells normally express CPE. However, studies of neuroendocrine tumors, pheochromocytomas, revealed expression of not only wild-type CPE, but a variant which was correlated with tumor behavior. Extremely high CPE mRNA copy numbers of the variant were found in very large or invasive tumors, both of which usually indicate poor prognosis. Thus, collectively the data suggest that CPE may play a role in promoting tumor growth and invasion. CPE could potentially serve as a diagnostic and prognostic biomarker for metastasis in different cancer types.

Possible relevance between prohormone convertase 2 expression and tumor growth in human adrenocorticotropin-producing pituitary adenoma

CONTEXT

Methods for preoperative diagnosis of prohormone convertase 2 (PC2)-positive ACTH-producing pituitary adenomas (APPAs) have not been established. Also, their characteristics are not evident.

OBJECTIVE

This study was designed to understand the meaning of plasma alphaMSH levels and the role of cell proliferation-signaling molecules in PC2-positive APPAs.

PATIENTS AND MAIN OUTCOME MEASURES

Nineteen human APPAs (four males and 15 females) were examined for the expression of PC2, phosphorylated ERK1/2, phosphorylated Akt1/2/3 (p-Akt) and receptor tyrosine kinases. alphaMSH was measured in extracted plasma from 17 APPA patients and 30 healthy volunteers.

RESULTS

Nine adenomas (47.4%) were immunopositive for PC2 and were large and invasive in nature. In all normal controls and eight PC2-negative cases, plasma alphaMSH was undetectable, whereas in four PC2-positive cases, it was detected at abnormally higher levels. Eight adenomas (42.1%) were immunopositive for both PC2 and p-Akt, and seven others (36.8%) were immunonegative for both, suggesting significant coexpression of PC2 and p-Akt in tumors. Quantitative RT-PCR revealed that PC2 expression is associated with phosphorylation of Akt but not with its gene expression. Most APPAs expressed receptor tyrosine kinases, but membrane-bound receptors could not be identified.

CONCLUSIONS

Our study suggests that PC2 expression and Akt phosphorylation are related at the molecular level, resulting in a change in cell cycle and an increase in pituitary adenoma size. An elevation of plasma alphaMSH could conjecture the activation of the phosphatidylinositol 3/Akt cascade in PC2-positive APPAs and may become a valuable clinical marker of tumor growth in Cushing's disease.

Enkephalin, its precursor, processing enzymes, and receptor as part of a local opioid network throughout the respiratory system of lung cancer patients

Evidence is accumulating regarding the local opioid regulation of physiologic respiratory functions. However, anatomical evidence for a local opioid network of the respiratory system is scarce. In this study, tissue samples from 12 lung cancer patients undergoing lobectomy or pneumonectomy were examined immunohistochemically for the expression of the opioid network components met-enkephalin, the respective precursor proenkephalin, the key processing enzymes prohormone convertases 1 and 2, carboxypeptidase E, and the delta opioid receptor in different areas of human lung. Colocalization of proenkephalin with met-enkephalin, prohormone convertase 1, prohormone convertase 2, and carboxypeptidase E was demonstrated by double-immunofluorescence confocal microscopy in alveolar macrophages, submucosal glands, cancerous cells, and pulmonary neuroendocrine cells of bronchial epithelium. Corresponding delta opioid receptor was identified on cells of all these functionally relevant anatomical structures and on substance P-immunoreactive sensory nerve fibers arborizing within bronchial epithelium. Our findings provide evidence of a local opioid network, that is, the exact anatomical localization of proenkephalin, its functionally active peptide met-enkephalin, and the key processing enzymes as well as corresponding delta opioid receptor, linked to functionally important structures of the respiratory system. These findings encourage future studies to examine the functional role of local opioid peptides within the respiratory system.

SCG3 transcript in peripheral blood is a prognostic biomarker for REST-deficient small cell lung cancer

PURPOSE

Specific markers of circulating tumor cells may be informative in managing lung cancer. Because the RE-1 silencing transcription factor (REST/NRSF) is a transcriptional repressor that is inactivated in neuroendocrine lung cancer, we identified REST-regulated transcripts (CHGA, CHGB, SCG3, VGF, and PCSK1) for evaluation as biomarkers in peripheral blood.

EXPERIMENTAL DESIGN

Transcripts were screened across lung cancer and normal cell lines. Candidates were assessed by reverse transcription-PCR and hybridization of RNA extracted from the peripheral blood of 111 lung cancer patients obtained at clinical presentation and from 27 cancer-free individuals.

RESULTS

Expression profiling revealed multiple chromogranin transcripts were readily induced on REST depletion, most notably SCG3 was induced >500-fold. The SCG3 transcript was also overexpressed by 12,000-fold in neuroendocrine compared with nonneuroendocrine lung cancer cells. In peripheral blood of lung cancer patients and cancer-free individuals, we found that SCG3 was more tumor-specific and more sensitive than other chromogranin transcripts as a biomarker of circulating tumor cells. Overall, 36% of small cell lung cancer (SCLC) and 16% of non-SCLC patients scored positively for normalized SCG3 transcript. This correlated with worse survival among SCLC patients with limited disease (n = 33; P = 0.022) but not extensive disease (n = 29; P = 0.459). Interestingly, the subcohort of 6 SCLC patients with resistance to platinum/etoposide chemotherapy all scored positively for peripheral blood SCG3 transcript (P = 0.022).

CONCLUSIONS

SCG3 mRNA, a component of the REST-dependent neurosecretory transcriptional profile, provides a sensitive prognostic biomarker for noninvasive monitoring of neuroendocrine lung cancer.

Substituted hippurates and hippurate analogs as substrates and inhibitors of peptidylglycine alpha-hydroxylating monooxygenase (PHM)

Peptidyl alpha-hydroxylating monooxygenase (PHM) functions in vivo towards the biosynthesis of alpha-amidated peptide hormones in mammals and insects. PHM is a potential target for the development of inhibitors as drugs for the treatment of human disease and as insecticides for the management of insect pests. We show here that relatively simple ground state analogs of the PHM substrate hippuric acid (C(6)H(5)-CO-NH-CH(2)-COOH) inhibit the enzyme with K(i) values as low as 0.5microM. Substitution of sulfur atom(s) into the hippuric acid analog increases the affinity of PHM for the inhibitor. Replacement of the acetylglycine moiety, -CO-NH-CH(2)-COOH with an S-(thioacetyl)thioglycolic acid moiety, -CS-S-CH(2)-COOH, yields compounds with the highest PHM affinity. Both S-(2-phenylthioacetyl)thioglycolate and S-(4-ethylthiobenzoyl)thioglycolic acid inhibit the proliferation of cultured human prostate cancer cells at concentrations >100-fold excess of their respective K(i) values. Comparison of K(i) values between mammalian PHM and insect PHM shows differences in potency suggesting that a PHM-based insecticide with limited human toxicity can be developed.

Membrane-bound carboxypeptidase E facilitates the entry of eosinophil cationic protein into neuroendocrine cells

ECP (eosinophil cationic protein) is a major component of eosinophil granule proteins, and is used as a clinical biomarker for asthma and allergic inflammatory disease. ECP has been implicated in damage to the cell membrane of many tissue types, but the mechanism is not well known. In the present study, mECP-eGFP-6H, a recombinant fusion protein containing mature ECP (mECP), enhanced green fluorescence protein (eGFP) and a His(6) tag (6H), has been expressed, purified and added to GH3 neuroendocrine cells to study the internalization ability of ECP. We found that mECP-eGFP-6H entered into GH3 neuroendocrine cells and inhibited the growth of the cells with an IC(50) of 0.8 microM. By yeast two-hybrid screening and immunoprecipitation, we have identified a specific protein-protein interaction between mECP and CPE (carboxypeptidase E), a well characterized metalloprotease. Further in vivo yeast two-hybrid screening has also revealed that residues 318-387 located in a region of unknown function in mature CPE are indispensable for association with mECP. In addition, the uptake of mECP-eGFP-6H is suppressed by dominant-negative expression of the recycling defect mutant pre-pro-HA-CPE(S471A,E472A) in GH3 cells, suggesting that the entry of mECP-eGFP-6H is associated with the recycling of CPE in GH3 cells. Taken together, we have demonstrated that CPE possesses a novel function to facilitate the entry of ECP to neuroendocrine cells, and such an endocytotic process allows the cytotoxic ECP to inhibit growth of the target cells.

Overexpression of dopa decarboxylase in peritoneal dissemination of gastric cancer and its potential as a novel marker for the detection of peritoneal micrometastases with real-time RT-PCR

We previously performed a global analysis of the gene expression of gastric cancer cell lines established from metastases to the peritoneal cavity with the cDNA microarray method, which made it possible to analyse the expression of approximately 21 168 genes for the identification of novel markers for the detection of micrometastases in the peritoneal cavity. One of the upregulated genes is dopa decarboxylase (DDC), which is responsible for the synthesis of the key neurotransmitters dopamine and serotonine. We have examined its potential as a novel marker for the detection of peritoneal micrometastases of gastric cancer.

DDC mRNA in the peritoneal wash from 112 gastric cancer patients was quantified for comparison of carcinoembryonic antigen (CEA) mRNA by means of real-time reverse transcriptase–polymerase chain reaction (RT–PCR) with a fluorescently labelled probe to predict peritoneal recurrence. The quantity of DDC and CEA correlated with wall penetration. Real-time RT–PCR could quantitate 10–10⁶ DDC-expressing gastric cancer cells per 10⁷ mesothelial cells. The cutoff value was set at the upper limit of the quantitative value for noncancer patients, and those above this cutoff value constituted the micrometastasis (MM+) group. Of 15 cases with peritoneal dissemination, 13 were MM+DDC (87% sensitivity), and one of 48 t1 cases was MM+ (98% specificity). DDC levels in peritoneal washes from patients with synchronous peritoneal metastases were more than 50 times higher than in those from patients without metastasis (P<0.01). For 15 cases of peritoneal dissemination (seven cases were cytologically positive), DDC was positive in 13 cases (87% sensitivity), but CEA failed to detect micrometastases in four cases (73% sensitivity), indicating that DDC is in some cases superior to CEA for the detection of peritoneal micrometastases of gastric cancer in terms of sensitivity as well as specificity, especially for poorly differentiated adenocarcinomas. A combination of CEA and DDC improved the accuracy of diagnosis up to 94%.

These results suggest that DDC is potentially a novel marker for peritoneal dissemination of gastric cancer and that quantitative RT–PCR of DDC is reliable and efficient for the selection of patients for adjuvant intraperitoneal chemotherapy to prevent peritoneal recurrence.

Curbing activation: proprotein convertases in homeostasis and pathology

The proprotein convertases (PCs) are a seven-member family of endoproteases that activate proproteins by cleavage at basic motifs. Expression patterns for individual PCs vary widely, and all cells express several members. The list of substrates activated by PCs has grown to include neuropeptides, peptide hormones, growth and differentiation factors, receptors, enzymes, adhesion molecules, blood coagulation factors, plasma proteins, viral coat proteins, and bacterial toxins. It has become clear that the PC family plays a crucial role in a variety of physiological processes and is involved in the pathology of diseases such as cancer, viral infection, and Alzheimer's disease. Recent studies using PC inhibitors have demonstrated their potential as therapeutic targets. Despite the avalanche of in vitro data, the physiological role of individual PCs has remained largely elusive. Recently, however, knockout mouse models have been developed for furin, PC1, PC2, PC4, PC6B, LPC, and PACE4, and human patients with PC1 deficiency have been identified. The phenotypes range from undetectable to early embryonic lethality. The major lesson learned from these studies is that specific PC-substrate pairs do exist, but that there is substantial redundancy for the majority of substrates. To some extent, redundancy may be cell type and even species dependent.

Differential gene expression profiles of gastric cancer cells established from primary tumour and malignant ascites

Advanced gastric cancer is often accompanied by metastasis to the peritoneum, resulting in a high mortality rate. Mechanisms involved in gastric cancer metastasis have not been fully clarified because metastasis involves multiple steps and requires a combination of altered expressions of many different genes. Thus, independent analysis of any single gene would be insufficient to understand all of the aspects of gastric cancer peritoneal dissemination. In this study, we performed a global analysis of the differential gene expression of a gastric cancer cell line established from a primary main tumour (SNU-1) and of other cell lines established from the metastasis to the peritoneal cavity (SNU-5, SNU-16, SNU-620, KATO-III and GT3TKB). The application of a high-density cDNA microarray method made it possible to analyse the expression of approximately 21 168 genes. Our examinations of SNU-5, SNU-16, SNU-620, KATO-III and GT3TKB showed that 24 genes were up-regulated and 17 genes down-regulated besides expression sequence tags. The analysis revealed the following altered expression such as: (a) up-regulation of CD44 (cell adhesion), keratins 7, 8, and 14 (epitherial marker), aldehyde dehydrogenase (drug metabolism), CD9 and IP3 receptor type3 (signal transduction); (b) down-regulation of IL2 receptor gamma, IL4-Stat (immune response), p27 (cell cycle) and integrin beta4 (adhesion) in gastric cancer cells from malignant ascites. We then analysed eight gastric cancer cell lines with Northern blot and observed preferential up-regulation and down-regulation of these selected genes in cells prone to peritoneal dissemination. Reverse transcriptase-polymerase chain reaction confirmed that several genes selected by DNA microarray were also overexpressed in clinical samples of malignant ascites. It is therefore considered that these genes may be related to the peritoneal dissemination of gastric cancers. The results of this global gene expression analysis of gastric cancer cells with peritoneal dissemination, promise to provide a new insight into the study of human gastric cancer peritoneal dissemination.

Key peptide processing enzymes are expressed by breast cancer cells

The expression of the three key peptide processing enzyme families, represented by CPE, PAM, and PC1/3 plus PC2, were examined in MCF-7 and ZR-75-1 breast cancer cell lines. Both of these cell lines express vasopressin receptors as well as the vasopressin gene, but the processing of vasopressin gene-related proteins appears to be limited. Products of the expected size for, CPE, PAM and PC1/PC3 could be amplified by reverse transcription-polymerase chain reaction (RT-PCR) from both cell lines. Cloning and sequencing of these RT-PCR products revealed that each enzyme mRNA had a structure identical to that published for the human form of the respective enzyme. Western analysis provided evidence that mRNAs for these enzymes are translated into proteins. Alternatively, PC2 mRNA was identified to be present in MCF-7 cells both by RT-PCR and Western blot analysis, but could not be demonstrated for ZR-75-1 cells. Our findings suggest that the key processing enzymes needed to generate active vasopressin and other neuropeptide growth factors are present in breast cancer cells.

Gene regulation of vasopressin and vasopressin receptors in cancer

It is proposed that neuropeptide production by tumours is an important part of a special process of oncogenic transformation rather than a pre-existing condition of progenitor cells; this concept is called Selective Tumour gene Expression of Peptides essential for Survival (STEPS). All small-cell lung cancers and breast cancers evidently express the vasopressin gene, and this gene seems to be structurally normal in all but exceptional cases. Vasopressin gene expression in cancer cells leads to the production of both normal and abnormal forms of tumour vasopressin mRNA and proteins. Although the necessary post-translational processing enzymes are expressed in these cells, most processing seems to be extragranular, and most of the protein products become components of the plasma membrane. Small-cell lung cancer and breast cancer cells also express normal genes for all vasopressin receptors and produce normal vasopressin receptor mRNAs and V1a and V1b receptor proteins, and the vasopressin-activated calcium mobilising (VACM) protein; plus both normal and abnormal forms of the V2 receptor. Through these receptors, vasopressin exercises multifaceted effects on tumour growth and metabolism. A normal protein vasopressin gene promoter seems to be present in small-cell lung cancer cells, and this promoter contains all of the transcriptional elements known to be involved in gene regulation within hypothalamic neurones. Since these elements largely account for regulation of tumour gene expression observed in vitro, it is likely that as yet unknown factors are selectively produced by tumours in vivo to account for the observed seemingly autonomous or unregulated production of hormone in tumour patients. Promoter elements thought to be responsible for selective vasopressin gene expression in small-cell lung cancer probably include an E-box and a neurone restrictive silencer element close to the transcription start site. It is possible that transcription factors acting at these same elements can explain selective vasopressin expression, not only in small-cell tumours, but also in all other tumours such as breast cancer. By extrapolation, similar mechanisms might also be responsible for the expression of additional features that characterize the 'neuroendocrine' profile of these cancers.