Abnormal expression and processing of the proprotein convertases PC1 and PC2 in human colorectal liver metastases

The Role of Proprotein Convertases in Upper Airway Remodeling

Chronic rhinosinusitis (CRS) is a multifactorial, heterogeneous disease characterized by persistent inflammation of the sinonasal mucosa and tissue remodeling, which can include basal/progenitor cell hyperplasia, goblet cell hyperplasia, squamous cell metaplasia, loss or dysfunction of ciliated cells, and increased matrix deposition. Repeated injuries can stimulate airway epithelial cells to produce inflammatory mediators that activate epithelial cells, immune cells, or the epithelial-mesenchymal trophic unit. This persistent inflammation can consequently induce aberrant tissue remodeling. However, the molecular mechanisms driving disease within the different molecular CRS subtypes remain inadequately characterized. Numerous secreted and cell surface proteins relevant to airway inflammation and remodeling are initially synthesized as inactive precursor proteins, including growth/differentiation factors and their associated receptors, enzymes, adhesion molecules, neuropeptides, and peptide hormones. Therefore, these precursor proteins require post-translational cleavage by proprotein convertases (PCs) to become fully functional. In this review, we summarize the roles of PCs in CRS-associated tissue remodeling and discuss the therapeutic potential of targeting PCs for CRS treatment.

Synergistic Effects of Genetic Variants of Glucose Homeostasis and Lifelong Exposures to Cigarette Smoking, Female Hormones, and Dietary Fat Intake on Primary Colorectal Cancer Development in African and Hispanic/Latino American Women

BACKGROUND

Disparities in cancer genomic science exist among racial/ethnic minorities. Particularly, African American (AA) and Hispanic/Latino American (HA) women, the 2 largest minorities, are underrepresented in genetic/genome-wide studies for cancers and their risk factors. We conducted on AA and HA postmenopausal women a genomic study for insulin resistance (IR), the main biologic mechanism underlying colorectal cancer (CRC) carcinogenesis owing to obesity.

METHODS

With 780 genome-wide IR-specific single-nucleotide polymorphisms (SNPs) among 4,692 AA and 1,986 HA women, we constructed a CRC-risk prediction model. Along with these SNPs, we incorporated CRC-associated lifestyles in the model of each group and detected the topmost influential genetic and lifestyle factors. Further, we estimated the attributable risk of the topmost risk factors shared by the groups to explore potential factors that differentiate CRC risk between these groups.

RESULTS

In both groups, we detected IR-SNPs in PCSK1 (in AA) and IFT172, GCKR, and NRBP1 (in HA) and risk lifestyles, including long lifetime exposures to cigarette smoking and endogenous female hormones and daily intake of polyunsaturated fatty acids (PFA), as the topmost predictive variables for CRC risk. Combinations of those top genetic- and lifestyle-markers synergistically increased CRC risk. Of those risk factors, dietary PFA intake and long lifetime exposure to female hormones may play a key role in mediating racial disparity of CRC incidence between AA and HA women.

CONCLUSIONS

Our results may improve CRC risk prediction performance in those medically/scientifically underrepresented groups and lead to the development of genetically informed interventions for cancer prevention and therapeutic effort, thus contributing to reduced cancer disparities in those minority subpopulations.

Genetic Signatures of Glucose Homeostasis: Synergistic Interplay With Long-Term Exposure to Cigarette Smoking in Development of Primary Colorectal Cancer Among African American Women

INTRODUCTION

Insulin resistance (IR)/glucose intolerance is a critical biologic mechanism for the development of colorectal cancer (CRC) in postmenopausal women. Whereas IR and excessive adiposity are more prevalent in African American (AA) women than in White women, AA women are underrepresented in genome-wide studies for systemic regulation of IR and the association with CRC risk.

METHODS

With 780 genome-wide IR single-nucleotide polymorphisms (SNPs) among 4,692 AA women, we tested for a causal inference between genetically elevated IR and CRC risk. Furthermore, by incorporating CRC-associated lifestyle factors, we established a prediction model on the basis of gene-environment interactions to generate risk profiles for CRC with the most influential genetic and lifestyle factors.

RESUTLS

In the pooled Mendelian randomization analysis, the genetically elevated IR was associated with 9 times increased risk of CRC, but with lack of analytic power. By addressing the variation of individual SNPs in CRC in the prediction model, we detected 4 fasting glucose-specific SNPs in GCK, PCSK1, and MTNR1B and 4 lifestyles, including smoking, aging, prolonged lifetime exposure to endogenous estrogen, and high fat intake, as the most predictive markers of CRC risk. Our joint test for those risk genotypes and lifestyles with smoking revealed the synergistically increased CRC risk, more substantially in women with longer-term exposure to cigarette smoking.

DISCUSSION

Our findings may improve CRC prediction ability among medically underrepresented AA women and highlight genetically informed preventive interventions (e.g., smoking cessation; CRC screening to longer-term smokers) for those women at high risk with risk genotypes and behavioral patterns.

PCSK2 expression in neuroendocrine tumors points to a midgut, pulmonary, or pheochromocytoma-paraganglioma origin

Neuroendocrine tumors (NETs) are often diagnosed from the metastases of an unknown primary tumor. Specific immunohistochemical (IHC) markers indicating the location of a primary tumor are needed. The proprotein convertase subtilisin/kexin type 2 (PCSK2) is found in normal neural and neuroendocrine cells, and known to express in NETs. We investigated the tissue microarray (TMA) of 86 primary tumors from 13 different organs and 9 metastatic NETs, including primary tumor‐metastasis pairs, for PCSK2 expression with polymer‐based IHC. PCSK2 was strongly positive in all small intestine and appendiceal NETs, the so‐called midgut NETs, in most pheochromocytomas and paragangliomas, and in some of the typical and atypical pulmonary carcinoid tumors. NETs showing strong positivity were re‐evaluated in larger tumor cohorts confirming the primary observation. In the metastases, the expression of PCSK2 mirrored that of the corresponding primary tumors. We found negative or weak staining in NETs from the thymus, gastric mucosa, pancreas, rectum, thyroid, and parathyroid. PCSK2 expression did not correlate with Ki‐67 in well‐differentiated NETs. Our data suggest that PCSK2 positivity can indicate the location of the primary tumor. Thus, PCSK2 could function in the IHC panel determined from screening metastatic NET biopsies of unknown primary origins.

PCSK1 Overexpression in Rectal Cancer Correlates with Poor Response to Preoperative Chemoradiotherapy and Prognosis

Background

In a data mining search for potential therapeutic targets to improve the outcome of rectal cancer, we identified PCSK1 as the cell-cell signaling gene most significantly associated with poor response to concurrent chemoradiotherapy (CCRT). This study aims to investigate the prognostic value of PCSK1 expression in rectal cancer patients who underwent neoadjuvant CCRT.

Methods

Endoscopic biopsy specimens from 172 rectal cancer patients receiving neoadjuvant CCRT followed by curative surgery were assessed immunohistochemically for PCSK1 expression, and H-scores were determined. Expression levels of PCSK1 were further analyzed for correlations with clinicopathologic features, tumor regression grade, metastasis-free survival, disease-specific survival, and recurrence-free survival.

Results

PCKS1 overexpression was significantly associated with pretreatment tumor status (T3-4; p = 0.009), pretreatment nodal status (N1-2; p < 0.001), posttreatment tumor status (T3-4; p < 0.001), posttreatment nodal status (N1-2; p < 0.001), vascular invasion (p = 0.003), and perineurial invasion (p = 0.023). PCKS1 overexpression was also found to be significantly associated with a lower degree of tumor regression (p < 0.001). In the univariate analysis, PCSK1 overexpression was significantly associated with lower disease-specific survival, metastasis-free survival, and recurrence-free survival (p < 0.005). PCSK1 overexpression remained an independent prognostic factor of lower disease-specific survival (p = 0.003; hazard ratio, 5.478) in the multivariate analysis.

Conclusion

Determination of PCSK1 overexpression may be useful for identifying rectal cancer patients at risk for a poor response and worse survival after CCRT.

Hypothalamic γ-melanocyte stimulating hormone gene delivery reduces fat mass in male mice

γ-Melanocyte stimulating hormone (γ-MSH) is an endogenous agonist of the melanocortin 3-receptor (MC3R). Genetic disruption of MC3Rs increases adiposity and blunts responses to fasting, suggesting that increased MC3R signaling could be physiologically beneficial in the long term. Interestingly, several studies have concluded that activation of MC3Rs is orexigenic in the short term. Therefore, we aimed to examine the short- and long-term effects of γ-MSH in the hypothalamic arcuate nucleus (ARC) on energy homeostasis and hypothesized that the effect of MC3R agonism is dependent on the state of energy balance and nutrition. Lentiviral gene delivery was used to induce a continuous expression of γ-Msh only in the ARC of male C57Bl/6N mice. Parameters of body energy homeostasis were monitored as food was changed from chow (6 weeks) to Western diet (13 weeks) and back to chow (7 weeks). The γ-MSH treatment decreased the fat mass to lean mass ratio on chow, but the effect was attenuated on Western diet. After the switch back to chow, an enhanced loss in weight (−15% vs −6%) and fat mass (−37% vs −12%) and reduced cumulative food intake were observed in γ-MSH-treated animals. Fasting-induced feeding was increased on chow diet only; however, voluntary running wheel activity on Western diet was increased. The γ-MSH treatment also modulated the expression of key neuropeptides in the ARC favoring weight loss. We have shown that a chronic treatment intended to target ARC MC3Rs modulates energy balance in nutritional state-dependent manner. Enhancement of diet-induced weight loss could be beneficial in treatment of obesity.

PACE4 inhibitors and their peptidomimetic analogs block prostate cancer tumor progression through quiescence induction, increased apoptosis and impaired neovascularisation

Prostate cancer is the leading cancer in North American men. Current pharmacological treatments are limited to anti-androgen strategies and the development of new therapeutic approaches remains a challenge. As a fundamentally new approach, we propose the inhibition of PACE4, a member of the proprotein convertases family of enzymes, as a therapeutic target in prostate cancer. We developed an inhibitor named the Multi-Leu peptide, with potent in vitro anti-proliferative effects. However, the Multi-Leu peptide has not been tested under in vivo conditions and its potency under such conditions is most likely limited, due to the labile characteristics of peptides in general. Using a peptidomimetic approach, we modified the initial scaffold, generating the analog Ac-[DLeu]LLLRVK-Amba, which demonstrates increased inhibitory potency and stability. The systemic administration of this peptidomimetic significantly inhibits tumor progression in the LNCaP xenograft model of prostate cancer by inducing tumor cell quiescence, increased apoptosis and neovascularization impairment. Pharmacokinetic and biodistribution profiles of this inhibitor confirm adequate tumor delivery properties of the compound. We conclude that PACE4 peptidomimetic inhibitors could result in stable and potent drugs for a novel therapeutic strategy for prostate cancer.

Repression of liver colorectal metastasis by the serpin Spn4A a naturally occurring inhibitor of the constitutive secretory proprotein convertases

Liver is the most common site of metastasis from colorectal cancers, and liver of patients with liver colorectal metastasis have abnormal levels of the proprotein convertases (PCs). These proteases are involved in the activation and/or expression of various colon cancer-related mediators, making them promising targets in colorectal liver metastasis therapy. Here, we revealed that the serpin Spn4 from Drosophila melanogaster inhibits the activity of all the PCs found in the constitutive secretory pathway and represses the metastatic potential of the colon cancer cells HT-29 and CT-26. In these cells, Spn4A inhibited the processing of the PCs substrates IGF-1R and PDGF-A that associated their reduced anchorage-independent growth, invasiveness and survival in response to apoptotic agents. In vivo, Spn4A-expressing tumor cells showed repressed subcutaneous tumor development and liver metastases formation in response to their intrasplenic inoculation. In these cells Spn4A induced the expression of molecules with anti-metastatic functions and inhibited expression of pro-tumorigenic molecules. Taken together, our findings identify Spn4A as the only endogenous inhibitor of all the constitutive secretory pathway PCs, which is able to repress the metastatic potential of colon cancer cells. These results suggest the potential use of Spn4A and/or derivates as a useful adduct colorectal liver metastasis prevention.

Differential processing of neuropeptide proprotein in human breast adenocarcinoma

BACKGROUND

The processing of proprotein convertase (PC)-mediated neuropeptide plays a very important role in carcinogenesis and tumor proliferation.

AIM

To investigate proneuropeptide processing mechanism in tumorigenesis and tumor proliferation.

MATERIALS AND METHODS

The expression and processing profiles of PC1, carboxypeptidase E (CPE), PC2, GHRH, or neuropeptide Y (NPY) gene and protein level were investigated between 42 human breast tumor tissues and 21 tumor-adjacent normal tissues.

RESULTS

Gene analyses indicated that the proPC1, CPE, or preproNPY gene had higher expression in the breast tumor tissues, whereas the proPC2 or preproGHRH gene showed lower expression in the tissues. Protein analyses showed that the proPC1, PC1, CPE, GHRH, and preproNPY proteins were upregulated in the tumor tissues, whereas the proPC2, PC2, preproGHRH, and NPY proteins were down-regulated in them. The tissue results were highly corroborated with the serum data from the tumor patients and healthy women.

CONCLUSIONS

The higher PC1 and CPE expressions as well as the transformation of more proGHRH into active GHRH peptide suggest stronger PC1/CPE-mediated neuropeptide processing in the tumor, whereas the lower PC2 expression as well as the transformation of less proNPY into active NPY peptide suggests a weak PC2-mediated processing in it. The alterations of the convertase expressions and processing show that there is a differential proprotein processing system in the tumor, which leads to the abnormal distributions of species, ratio, and concentration of (pro)peptide(s) in the microenvironment of cells. The latter may contribute to cancer progression.

Pituitary protein 7B2 plasma levels in patients with liver disease: Comparisons with other hormones and neuropeptides

7B2, a protein initially isolated from the porcine pituitary gland, has been identified in numerous animal and human tissues, with the highest concentrations in the pituitary and hypothalamus. The 7B2 molecule is highly evolutionarily conserved and is considered to be indispensable in the function and regulation of proprotein convertase 2 (PC2). In the present study, the plasma 7B2 immunoreactivity (7B2-IR) of 18 patients with liver disease was studied. Of these patients, seven (three male and four female), aged 37–67 [54.6±13.5 (SD)] years, suffered from liver cirrhosis of cryptogenic (n=2) or alcoholic (n=5) aetiology. The remaining 11 patients (four male and seven female), aged 22–76 [56.1±17.6 (SD)] years, suffered from miscellaneous liver abnormalities. The clinical diagnosis was confirmed in the majority of patients by the histological examination of a percutaneous liver biopsy or by appropriate radiological investigations. Plasma bilirubin, alkaline phosphatase, aspartate aminotransferase, albumin, prothrombin time, electrolytes, urea and creatinine were measured. The plasma 7B2-IR levels were estimated using a sensitive radioimmunoassay (RIA), and the elution position of 7B2-IR was verified by gel chromatography. The mean plasma 7B2-IR concentration in patients with liver disease was 99.44±15.9 pmol/l. In the patients with hepatocellular damage due to metastatic tumours [Ca bronchus, carcinoid (n=6)], the 7B2-IR concentrations were significantly higher [185±36.9 pmol/l, (P<0.05)] compared with the overall subjects with liver damage. The results of the present study demonstrate that 7B2-IR is increased in liver disease, with the highest levels detected in patients with tumourous liver conditions.

Alterations in gene expression of proprotein convertases in human lung cancer have a limited number of scenarios

Proprotein convertases (PCs) is a protein family which includes nine highly specific subtilisin-like serine endopeptidases in mammals. The system of PCs is involved in carcinogenesis and levels of PC mRNAs alter in cancer, which suggests expression status of PCs as a possible marker for cancer typing and prognosis. The goal of this work was to assess the information value of expression profiling of PC genes. Quantitative polymerase chain reaction was used for the first time to analyze mRNA levels of all PC genes as well as matrix metalloproteinase genes MMP2 and MMP14, which are substrates of PCs, in 30 matched pairs of samples of human lung cancer tumor and adjacent tissues without pathology. Significant changes in the expression of PCs have been revealed in tumor tissues: increased FURIN mRNA level (p<0.00005) and decreased mRNA levels of PCSK2 (p<0.007), PCSK5 (p<0.0002), PCSK7 (p<0.002), PCSK9 (p<0.00008), and MBTPS1 (p<0.00004) as well as a tendency to increase in the level of PCSK1 mRNA. Four distinct groups of samples have been identified by cluster analysis of the expression patterns of PC genes in tumor vs. normal tissue. Three of these groups covering 80% of samples feature a strong elevation in the expression of a single gene in cancer: FURIN, PCSK1, or PCSK6. Thus, the changes in the expression of PC genes have a limited number of scenarios, which may reflect different pathways of tumor development and cryptic features of tumors. This finding allows to consider the mRNAs of PC genes as potentially important tumor markers.

Molecular Validation of PACE4 as a Target in Prostate Cancer

Prostate cancer remains the single most prevalent cancer in men. Standard therapies are still limited and include androgen ablation that initially causes tumor regression. However, tumor cells eventually relapse and develop into a hormone-refractory prostate cancer. One of the current challenges in this disease is to define new therapeutic targets, which have been virtually unchanged in the past 30 years. Recent studies have suggested that the family of enzymes known as the proprotein convertases (PCs) is involved in various types of cancers and their progression. The present study examined PC expression in prostate cancer and validates one PC, namely PACE4, as a target. The evidence includes the observed high expression of PACE4 in all different clinical stages of human prostate tumor tissues. Gene silencing studies targeting PACE4 in the DU145 prostate cancer cell line produced cells (cell line 4-2) with slower proliferation rates, reduced clonogenic activity, and inability to grow as xenografts in nude mice. Gene expression and proteomic profiling of the 4-2 cell line reveals an increased expression of known cancer-related genes (e.g., GJA1, CD44, IGFBP6) that are downregulated in prostate cancer. Similarly, cancer genes whose expression is decreased in the 4-2 cell line were upregulated in prostate cancer (e.g., MUC1, IL6). The direct role of PACE4 in prostate cancer is most likely through the upregulated processing of growth factors or through the aberrant processing of growth factors leading to sustained cancer progression, suggesting that PACE4 holds a central role in prostate cancer.

Identification of the myosin heavy polypeptide 9 as a downstream effector of the proprotein convertases in the human colon carcinoma HT-29 cells

In addition to the large spectrum of the protein precursors processed and activated by the proprotein convertases (PCs) that are crucial for the maintenance of the malignant phenotype of colon cancer cells such as matrix metalloproteases, adhesion molecules, growth factors, and growth factor receptors, the PCs also regulate the expression and the activity of other proteins that are not PC substrates and involved in the acquisition of the metastatic and tumorigenic potential of these tumor cells. The identification in colon cancer cells of such proteins is thereby crucial for the understanding of the cascade of molecular events regulated by the PCs leading to tumorigenesis and metastasis and thus may constitute potential candidates for new colon cancer-specific targets and/or biomarkers. Using the human colon cancer cells HT-29 and ProteinChip arrays analysis that apply the surface-enhanced laser desorption ionization time-of-flight mass spectrometry (SELDI-TOF-MS), we identified the myosin heavy polypeptide 9 as new downstream effector of PCs in these cells. This protein was reported to be involved in the processes of malignant epithelial transformation and its role in colon cancer is unknown.

Inhibition of the proprotein convertases represses the invasiveness of human primary melanoma cells with altered p53, CDKN2A and N-Ras genes

BACKGROUND

Altered tumor suppressor p53 and/or CDKN2A as well as Ras genes are frequently found in primary and metastatic melanomas. These alterations were found to be responsible for acquisition of invasive and metastatic potential through their defective regulatory control of metalloproteinases and urokinase genes.

METHODOLOGY/PRINCIPAL FINDINGS

Using primary human melanoma M10 cells with altered p53, CDKN2A and N-Ras genes, we found that inhibition of the proprotein convertases (PCs), enzymes involved in the proteolytic activation of various cancer-related protein precursors resulted in significantly reduced invasiveness. Analysis of M10 cells and their gastric and lymph node derived metastatic cells revealed the presence of all the PCs found in the secretory pathway. Expression of the general PCs inhibitor alpha1-PDX in these cells in a stable manner (M10/PDX) had no effect on the mRNA expression levels of these PCs. Whereas, in vitro digestion assays and cell transfection experiments, revealed that M10/PDX cells display reduced PCs activity and are unable to process the PCs substrates proIGF-1R and proPDGF-A. These cells showed reduced migration and invasion that paralleled decreased gelatinase MMP-2 activity and increased expression and secretion of tissue inhibitor of metalloproteinase-1 (TIMP-1) and TIMP-2. Furthermore, these cells showed decreased levels of urokinase-type plasminogen activator receptor (uPAR) and increased levels of plasminogen activator inhibitor-1 (PAI-1).

CONCLUSIONS

Taken together, these data suggest that inhibition of PCs activity results in decreased invasiveness of primary human melanoma cells despite their altered p53, CDKN2A and N-Ras genes, suggesting that PCs may serve as novel therapeutic targets in melanoma.

Candidate gene polymorphisms for diabetes mellitus, cardiovascular disease and cancer are associated with longevity in Koreans

Long-lived people may have a unique genetic makeup that makes them more resistant than the general population to prevalent age-related diseases; however, not much is known about genes involved in the longevity. To identify susceptibility variants controlling longevity, we performed a high-throughput candidate gene study using 137 Koreans over 90 yr old and 213 young healthy Koreans. We evaluated 463 informative markers located in 176 candidate genes mostly for diabetes mellitus, cardiovascular disease and cancer under five genetic models. We estimated the odds ratios for each allele, genotype, haplotype, and gene-gene interaction using logistic regression analysis. Associations between 13 genes and longevity were detected at a P-value less than 0.01. Particularly, the rs671 (A) allele of the aldehyde dehydrogenase 2 family (mitochondrial) (ALDH2) gene was associated with longevity only in men (OR 2.11, P =0.008). Four genes, proprotein convertase subtilisin/kexin type 1 (PCSK1, P=0.008), epidermal growth factor receptor (EGFR, P=0.003), paired box 4 (PAX4, P=0.008), and V-yes-1 Yamaguchi sarcoma viral related oncogene homolog (LYN, P=0.002) consistently yielded statistical evidence for association with longevity. The findings of the current study may provide a starting point for future studies to unravel genetic factors controlling longevity in Koreans.

Peptide processing and biology in human disease

PURPOSE OF REVIEW

To describe recent advances in the processing of gastrointestinal hormones, and the consequences for human disease of mutations in the enzymes involved.

RECENT FINDINGS

Although gastrointestinal prohormones were long regarded as devoid of biological activity, recent data indicate that the prohormones for both gastrin and gastrin-releasing peptide are bioactive, through different receptors from the mature hormones. Mutations in the family of prohormone convertases responsible for the initial steps in the processing of gastrointestinal hormones are associated with several different pathophysiological conditions in humans.

SUMMARY

Human mutational studies, when taken together with the phenotypes observed in mice deficient in the prohormone convertases, emphasize the crucial importance of the processing enzymes in mammalian biology. Although the phenotypes may often be ascribed to defective production of a mature hormone or growth factor, the recognition that the precursors are independently bioactive suggests that the increased precursor concentrations may also contribute to the symptoms. The observation that the precursors often act through different receptors from the mature hormones may permit the development of precursor-selective antagonists for therapeutic use.

Knockdown of Pdcd4 results in induction of proprotein convertase 1/3 and potent secretion of chromogranin A and secretogranin II in a neuroendocrine cell line

BACKGROUND INFORMATION

Pdcd4 (programmed cell death 4) is up-regulated during apoptosis and seems to play an important role as a tumour suppressor. To gain further insights into its biological functions, we suppressed Pdcd4 expression in the neuroendocrine cell line Bon-1 via siRNA (small interfering RNA) technology.

RESULTS

Using this cell line, we found that suppression of Pdcd4 resulted in an increased release of CgA (chromogranin A) and Sg II (secretogranin II), and was accompanied by an up-regulation of intracellular PC1 (proprotein convertase 1/3). The enhanced secretion of CgA and Sg II seemed to be mediated by an activation of protein kinase Akt via PI3K (phosphoinositide 3-kinase). In accordance with this, inhibition of PI3K activity and, thereby, reduced phosphorylation of Akt was shown to enhance Pdcd4 expression. Neither the PKC (protein kinase C) signal transduction cascade nor the MAPK (mitogen-activated protein kinase) pathway seemed to play a role in the regulation of CgA and Sg II secretion by Pdcd4.

CONCLUSIONS

CgA is considered to be a marker for neuroendocrine tumours, and up-regulation of PC1 has been reported in various types of cancers. The repression of PC1 by Pdcd4 may represent a novel mechanism for the function of Pdcd4 as a tumour suppressor. Our results are of particular interest, as we observed that pioglitazone, an oral medication used in the treatment of Type 2 diabetes, decreased Pdcd4 levels, activated Akt, increased CgA and Sg II secretion and augmented PC1 protein in Bon-1 cells. Enhanced PC1 levels, leading to improved processing of proinsulin and proglucagon, may contribute to the benefits of pioglitazone therapy. The in vivo relevance of our findings was highlighted by data indicating elevated CgA amounts in the sera of patients treated with pioglitazone. This is the first study connecting Pdcd4 levels, secretion behaviour of neuroendocrine cells and regulation of PI3K activity.

Colon-derived liver metastasis, colorectal carcinoma, and hepatocellular carcinoma can be discriminated by the Ca(2+)-binding proteins S100A6 and S100A11

BACKGROUND

It is unknown, on the proteomic level, whether the protein patterns of tumors change during metastasis or whether markers are present that allow metastases to be allocated to a specific tumor entity. The latter is of clinical interest if the primary tumor is not known.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, tissue from colon-derived liver metastases (n = 17) were classified, laser-microdissected, and analysed by ProteinChip arrays (SELDI). The resulting spectra were compared with data for primary colorectal (CRC) and hepatocellular carcinomas (HCC) from our former studies. Of 49 signals differentially expressed in primary HCC, primary CRC, and liver metastases, two were identified by immunodepletion as S100A6 and S100A11. Both proteins were precisely localized immunohistochemically in cells. S100A6 and S100A11 can discriminate significantly between the two primary tumor entities, CRC and HCC, whereas S100A6 allows the discrimination of metastases and HCC.

CONCLUSIONS

Both identified proteins can be used to discriminate different tumor entities. Specific markers or proteomic patterns for the metastases of different primary cancers will allow us to determine the biological characteristics of metastasis in general. It is unknown how the protein patterns of tumors change during metastasis or whether markers are present that allow metastases to be allocated to a specific tumor entity. The latter is of clinical interest if the primary tumor is not known.

Thyroid hormone promotes cell invasion through activation of furin expression in human hepatoma cell lines

The objective of this study was to identify genes regulated by thyroid hormone (T(3)) and associated with tumor invasion. The gene encoding furin, as previously identified by cDNA microarray, is known to be up-regulated by T(3) treatment, and stimulated furin production occurs in thyroidectomized rats after administration of T(3). Presently, by using serial deletion of the promoter and EMSAs, the T(3) response element on the furin promoter was localized to the -6317/-6302 region. T(3)-mediated furin up-regulation was cooperative with TGF-beta because T(3) induction increased after Smad3/4 addition. Furthermore, the invasiveness of HepG2-thyroid hormone receptor (TR) cells was significantly increased by T(3) treatment, perhaps due to furin processing of matrix metalloproteinase-2 and -9. In addition, furin up-regulation either by stable overexpression or T(3) and/or TGF-beta induction was evident in severe-combined immune-deficient mice inoculated with HepG2-TRalpha1 cells. The HepG2-furin mice displayed a higher metastasis index and tumor size than HepG2-neo mice. Notably, the increased liver and lung tumor number or size in the hyperthyroid severe-combined immune-deficient mice as well as TGF-beta mice was attributed specifically to furin overexpression in the HepG2-TRalpha1 cells. Furthermore, this study demonstrated that furin overexpression in some types of hepatocellular carcinomas is TR dependent and might play a crucial role in the development of hepatocellular carcinoma. Thus, T(3) regulates furin gene expression via a novel mechanism or in cooperation with TGF-beta to enhance tumor metastasis in vitro and in vivo.

Selective inhibition of proprotein convertases represses the metastatic potential of human colorectal tumor cells

The proprotein convertases (PCs) are implicated in the activation of various precursor proteins that play an important role in tumor cell metastasis. Here, we report their involvement in the regulation of the metastatic potential of colorectal tumor cells. PC function in the human and murine colon carcinoma cell lines HT-29 and CT-26, respectively, was inhibited using siRNA targeting the PCs furin, PACE4, PC5, and PC7 or by overexpression of the general PC inhibitor alpha1-antitrypsin Portland (alpha1-PDX). We found that overexpression of alpha1-PDX and knockdown of furin expression inhibited processing of IGF-1 receptor and its subsequent activation by IGF-1 to induce IRS-1 and Akt phosphorylation, all important in colon carcinoma metastasis. These data suggest that the PC furin is a major IGF-1 receptor convertase. Expression of alpha1-PDX reduced the production of TNF-alpha and IL-1alpha by human colon carcinoma cells, and incubation of murine liver endothelial cells with conditioned media derived from these cells failed to induce tumor cell adhesion to activated murine endothelial cells, a critical step in metastatic invasion. Furthermore, colon carcinoma cells in which PC activity was inhibited by overexpression of alpha1-PDX when injected into the portal vein of mice showed a significantly reduced ability to form liver metastases. This suggests that inhibition of PCs is a potentially promising strategy for the prevention of colorectal liver metastasis.

Integrated endoplasmic reticulum stress responses in cancer

The endoplasmic reticulum (ER) has emerged as a major site of cellular homeostasis regulation, particularly in the unfolded protein response, which is being found to play a major role in cancer and many other diseases. Here, we address ER-mediated signaling and regulations in the context of environmental challenges in cancer, such as hypoxia, angiogenesis, and chemotherapeutic resistance, and we discuss how ER-resident molecular machines become deregulated and involved in cancer-related pathology. Further exploration of how the ER senses, signals, and adapts to stress may redefine and deepen our understanding of its functions in cancer pathobiology.

Prohormone convertases 1/3, 2, furin and protein 7B2 (Secretogranin V) in endocrine cells of the human pancreas

Prohormone convertases (PCs) are proteinases that cleave inactive prohormones to biologically active peptides. Seven PCs have been identified; two of them, PC1/3 and PC2, have only been localized in neuroendocrine (NE) tissues; a third, furin, in both endocrine and exocrine tissues. We have studied the immunoreactivity of PC1/3, PC2 and furin in the four major NE cell types of the human pancreas by using double immunofluorescence techniques. The study also included the expression of NE secretory protein 7B2 (secretogranin V), a member of the granin family, which influences the function of PC2. The results showed that the three PCs and 7B2 were expressed only in endocrine pancreas, furin also in exocrine cells. Insulin (B) cells harboured PC1/3 and PC2, but not furin. Glucagon (A) cells were immunoreactive to all three PCs; all glucagon cells expressed PC2, but one subpopulation showed PC1/3 immunoreactivity and another furin. Only a few somatostatin (D) cells contained PC2, but no other proconvertase. Pancreatic polypeptide (PP) cells were non-reactive to all three PCs. 7B2 occurred only in insulin and glucagon cells. A varying co-localization pattern was observed between PCs and between PCs and 7B2, with the exception of PC1/3 and furin which were not co-localized. In conclusion, our study shows that PCs are localized in insulin and glucagon cells and do seem to be important in these cell types for processing of hormone and other protein precursors, especially chromogranins, but for the two other major cell types probably other enzymes are of importance.