Overexpression of membrane proteins in primary and metastatic gastrointestinal neuroendocrine tumors

Characterization of the Cancer-Associated Meprin Βeta Variants G45R and G89R

Meprin β is a metalloprotease associated with neurodegeneration, inflammation, extracellular matrix homeostasis, transendothelial cell migration, and cancer. In this study, we investigated two melanoma-associated variants of meprin β, both exhibiting a single amino acid exchange, namely, meprin β G45R and G89R. Based on the structural data of meprin β and with regard to the position of the amino acid exchanges, we hypothesized an increase in proteolytic activity in the case of the G45R variant due to the induction of a potential new activation site and a decrease in proteolytic activity from the G89R variant due to structural instability. Indeed, the G89R variant showed, overall, a reduced expression level compared to wild-type meprin β, accompanied by decreased activity and lower cell surface expression but strong accumulation in the endoplasmic reticulum. This was further supported by the analysis of the shedding of the interleukin-6 receptor (IL-6R) by meprin β and its variants. In transfected HEK cells, the G89R variant was found to generate less soluble IL-6R, whereas the expression of meprin β G45R resulted in increased shedding of the IL-6R compared to wild-type meprin β and the G89R variant. A similar tendency of the induced shedding capacity of G45R was seen for the well-described meprin β substrate CD99. Furthermore, employing an assay for cell migration in a collagen IV matrix, we observed that the transfection of wild-type meprin β and the G45R variant resulted in increased migration of HeLa cells, while the G89R variant led to diminished mobility.

Role of meprin metalloproteases in metastasis and tumor microenvironment

A crucial step for tumor cell extravasation and metastasis is the migration through the extracellular matrix, which requires proteolytic activity. Hence, proteases, particularly matrix metalloproteases (MMPs), have been discussed as therapeutic targets and their inhibition should diminish tumor growth and metastasis. The metalloproteases meprin α and meprin β are highly abundant on intestinal enterocytes and their expression was associated with different stages of colorectal cancer. Due to their ability to cleave extracellular matrix (ECM) components, they were suggested as pro-tumorigenic enzymes. Additionally, both meprins were shown to have pro-inflammatory activity by cleaving cytokines and their receptors, which correlates with chronic intestinal inflammation and associated conditions. On the other hand, meprin β was identified as an essential enzyme for the detachment and renewal of the intestinal mucus, important to prevent bacterial overgrowth and infection. Considering this, it is hard to estimate whether high activity of meprins is generally detrimental or if these enzymes have also protective functions in certain cancer types. For instance, for colorectal cancer, patients with high meprin β expression in tumor tissue exhibit a better survival prognosis, which is completely different to prostate cancer. This demonstrates that the very same enzyme may have contrary effects on tumor initiation and growth, depending on its tissue and subcellular localization. Hence, precise knowledge about proteolytic enzymes is required to design the most efficient therapeutic options for cancer treatment. In this review, we summarize the current findings on meprins' functions, expression, and cancer-associated variants with possible implications for tumor progression and metastasis.

The Emerging Role of Adhesion GPCRs in Cancer

Aberrant expression, function, and mutation of G protein-coupled receptors (GPCRs) and their signaling partners, G proteins, have been well documented in many forms of cancer. These cell surface receptors and their endogenous ligands are implicated in all aspects of cancer including proliferation, angiogenesis, invasion, and metastasis. Adhesion GPCRs (aGPCRs) form the second largest family of GPCRs, most of which are orphan receptors with unknown physiological functions. This is mainly due to our limited insight into their structure, natural ligands, signaling pathways, and tissue expression profiles. Nevertheless, recent studies show that aGPCRs play important roles in cell adhesion to the extracellular matrix and cell-cell communication, processes that are dysregulated in cancer. Emerging evidence suggests that aGPCRs are implicated in migration, proliferation, and survival of tumor cells. We here review the role of aGPCRs in the five most common types of cancer (lung, breast, colorectal, prostate, and gastric) and emphasize the importance of further translational studies in this field.

Oxytocin Inhibition of Metastatic Colorectal Cancer by Suppressing the Expression of Fibroblast Activation Protein-α

Oxytocin (OXT) and its receptor (OXTR) are present in the gastrointestinal system and are involved in gastrointestinal tumorigenesis. However, the effect of OXTR signaling on the development of colorectal cancer (CRC) and its underlying mechanisms remain unexplored. To address these issues, we first examined the expressions of OXT, OXTR, and several cancer-associated proteins using colon “tissue chips” from a spectrum of malignant progression of the colon, which included normal colon tissue, chronic colitis, colorectal adenoma, and colorectal adenocarcinoma (CAC). The results showed that the expressions of OXT and OXTR decreased gradually with the malignant progression of the disease. Stimulation of CAC tissues with OXT increased OXTR expression while down-regulated FAPα and CCL-2 protein expressions in a concentration- and time-dependent manner. Moreover, cell invasion experiment showed that OXT treatment reduced the invasion ability of colon cancer cells and blocking OXTR with atosiban blocked OXT-reduced invasion ability of human colon cancer cell lines Ls174T and SW480. The results indicate that OXT has the potential to inhibit CRC development via down-regulating the immunosuppressive proteins FAPα and CCL-2. When the OXTR signaling is weakened, colon tissues may transform to CRC. These findings also highlight the possibility of applying OXT to inhibit CRC development directly.

The Pancreas as a Site of Metastasis or Second Primary in Patients with Small Bowel Neuroendocrine Tumors

BACKGROUND

The small bowel and pancreas are the most common primary sites of neuroendocrine tumors (NETs) giving rise to metastatic disease. Some patients with small bowel NETs (SBNETs) present with synchronous or metachronous pancreatic NETs (PNETs), and it is unclear whether these are separate primaries or metastases from one site to the other.

METHODS

A surgical NET database including patients undergoing operations for SBNETs or PNETs was reviewed. Patients with synchronous or metachronous tumors in both the small bowel and pancreas were identified, and available tissues from primary tumors and metastases were examined using a 4-gene quantitative polymerase chain reaction (qPCR) and immunohistochemistry (IHC) panel developed for evaluating NETs of unknown primary.

RESULTS

Of 338 patients undergoing exploration, 11 had NETs in both the small bowel and pancreas. Tissues from 11 small bowel tumors, 9 pancreatic tumors, and 10 metastases were analyzed. qPCR and IHC data revealed that three patients had separate SBNET and PNET primaries, and five patients had SBNETs that metastasized to the pancreas. Pancreatic tissue was unavailable in two patients, and qPCR and IHC gave discrepant results in one patient.

CONCLUSIONS

NETs in both the small bowel and pancreas were found in 3% of our patients. In nearly two-thirds of evaluable patients, the pancreatic tumor was a metastasis from the SBNET primary, while in the remaining one-third of patients it represented a separate primary. Determining the origin of these tumors can help guide the choice of systemic therapy and surgical management.

Role of biomarker tests for diagnosis of neuroendocrine tumours

Neuroendocrine tumours (NETs) are neoplasms that arise from neuroendocrine cells. Neuroendocrine cells and their tumours can secrete a wide range of amines and polypeptide hormones into the systemic circulation. This feature has triggered widespread investigation into circulating biomarkers for the diagnosis of NETs as well as for the prediction of the biological behaviour of tumour cells. Classic examples of circulating biomarkers for gastroenteropancreatic NETs include chromogranin A, neuron-specific enolase and pancreatic polypeptide as well as hormones that elicit clinical syndromes, such as serotonin and its metabolites, insulin, glucagon and gastrin. Biomarker metrics of general markers for diagnosing all gastroenteropancreatic NET subtypes are limited, but specific hormonal measurements can be of diagnostic value in select cases. In the past decade, methods for detecting circulating transcripts and tumour cells have been developed to improve the diagnosis of patients with NETs. Concurrently, modern scanning techniques and superior radiotracers for functional imaging have markedly expanded the options for clinicians dealing with NETs. Here, we review the latest research on biomarkers in the NET field to provide clinicians with a comprehensive overview of relevant diagnostic biomarkers that can be implemented in dedicated situations.

Cancer-associated mutations in the canonical cleavage site do not influence CD99 shedding by the metalloprotease meprin β but alter cell migration in vitro

Transendothelial cell migration (TEM) is crucial for inflammation and metastasis. The adhesion molecule CD99 was shown to be important for correct immune cell extravasation and is highly expressed on certain cancer cells. Recently, we demonstrated that ectodomain shedding of CD99 by the metalloprotease meprin β promotes TEM in vitro.

In this study, we employed an acute inflammation model (air pouch/carrageenan) and found significantly less infiltrated cells in meprin β knock-out animals validating the previously observed pro-inflammatory activity. To further analyze the impact of meprin β on CD99 shedding with regard to cell adhesion and proliferation we characterized two lung cancer associated CD99 variants (D92H, D92Y), carrying point mutations at the main cleavage site. Interestingly, ectodomain shedding of these variants by meprin β was still detectable. However the cleavage site shifted to adjacent positions. Nevertheless, expression of CD99 variants D92H and D92Y revealed partial misfolding and proteasomal degradation. A previously observed influence of CD99 on Src activation and increased proliferation could not be confirmed in this study, independent of wild-type CD99 or the variants D92H and D92Y. However, we identified meprin β as a potent inducer of Src phosphorylation. Importantly, we found significantly increased cell migration when expressing the cancer-associated CD99 variant D92H compared to the wild-type protein.

Weighted gene co-expression network analysis in identification of metastasis-related genes of lung squamous cell carcinoma based on the Cancer Genome Atlas database

BACKGROUND

Lung squamous cell carcinoma (lung SCC) is a common type of malignancy. Its pathogenesis mechanism of tumor development is unclear. The aim of this study was to identify key genes for diagnosis biomarkers in lung SCC metastasis.

METHODS

We searched and downloaded mRNA expression data and clinical data from The Cancer Genome Atlas (TCGA) database to identify differences in mRNA expression of primary tumor tissues from lung SCC with and without metastasis. Gene co-expression network analysis, protein-protein interaction (PPI) network, Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis and quantitative real-time polymerase chain reactions (qRT-PCR) were used to explore the biological functions of the identified dysregulated genes.

RESULTS

Four hundred and eighty-two differentially expressed genes (DEGs) were identified between lung SCC with and without metastasis. Nineteen modules were identified in lung SCC through weighted gene co-expression network analysis (WGCNA). Twenty-three DEGs and 26 DEGs were significantly enriched in the respective pink and black module. KEGG pathway analysis displayed that 26 DEGs in the black module were significantly enriched in bile secretion pathway. Forty-nine DEGs in the two gene co-expression module were used to construct PPI network. CFTR in the black module was the hub protein, had the connectivity with 182 genes. The results of qRT-PCR displayed that FIGF, SFTPD, DYNLRB2 were significantly down-regulated in the tumor samples of lung SCC with metastasis and CFTR, SCGB3A2, SSTR1, SCTR, ROPN1L had the down-regulation tendency in lung SCC with metastasis compared to lung SCC without metastasis.

CONCLUSIONS

The dysregulated genes including CFTR, SCTR and FIGF might be involved in the pathology of lung SCC metastasis and could be used as potential diagnosis biomarkers or therapeutic targets for lung SCC.

A practical method to determine the site of unknown primary in metastatic neuroendocrine tumors

INTRODUCTION

The site of a primary neuroendocrine tumor (NET) tumor is unknown before treatment in approximately 20% of small bowel (SBNET) and pancreatic (PNET) cases despite extensive workup. It can be difficult to discern a PNET from an SBNET on hematoxylin and eosin stains, and thus, more focused diagnostic tests are required. Immunohistochemistry (IHC) and gene expression profiling are two methods used to identify the tissue of origin from biopsied metastases.

METHODS

Tissue microarrays were created from operative specimens and stained with up to seven antibodies used in the NET-specific IHC algorithm. Expression of four genes for differentiating between PNETs and SBNETs was determined by quantitative polymerase chain reaction and then used in a previously validated gene expression classifier (GEC) algorithm designed to determine the primary site from gastrointestinal NET metastases.

RESULTS

The accuracy of the IHC algorithm in identifying the primary tumor site from a set of 37 metastases was 89%, with only one incorrect call. Three other samples were indeterminate as the result of pan-negative staining. The GEC's accuracy in a set of 136 metastases was 94%. The algorithm identified the primary tumor site in all cases in which IHC failed.

CONCLUSION

Performing IHC, followed by GEC for indeterminate cases, identifies accurately the primary site in SBNET and PNET metastases in virtually all patients.

Gene expression accurately distinguishes liver metastases of small bowel and pancreas neuroendocrine tumors

Small bowel (SBNETs) and pancreatic neuroendocrine tumors (PNETs) often present with liver metastases. Although liver biopsy establishes a neuroendocrine diagnosis, the primary tumor site is frequently unknown without exploratory surgery. Gene expression differences in metastases may distinguish primary SBNETs and PNETs. This study sought to determine expression differences of four genes in neuroendocrine metastases and to create a gene expression algorithm to distinguish the primary site. Nodal and liver metastases from SBNETs and PNETs (n = 136) were collected at surgery under an Institutional Review Board-approved protocol. Quantitative PCR measured expression of bombesin-like receptor-3, opioid receptor kappa-1, oxytocin receptor, and secretin receptor in metastases. Logistic regression models defined an algorithm predicting the primary tumor site. Models were developed on a training set of 21 nodal metastases and performance was validated on an independent set of nodal and liver metastases. Expression of all four genes was significantly different in SBNET compared to PNET metastases. The optimal model employed expression of bombesin-like receptor-3 and opioid receptor kappa-1. When these genes did not amplify, the algorithm used oxytocin receptor and secretin receptor expression, which allowed classification of all 136 metastases with 94.1 % accuracy. In the independent liver metastasis validation set, 52/56 (92.9 %) were correctly classified. Positive predictive values were 92.5 % for SBNETs and 93.8 % for PNETs. This validated algorithm accurately distinguishes SBNET and PNET metastases based on their expression of four genes. High accuracy in liver metastases demonstrates applicability to the clinical setting. Studies assessing this algorithm's utility in prospective clinical decision-making are warranted.

Pancreastatin predicts survival in neuroendocrine tumors

BACKGROUND

Serum neurokinin A, chromogranin A, serotonin, and pancreastatin reflect tumor burden in neuroendocrine tumors. We sought to determine whether their levels correlate with survival in surgically managed small bowel (SBNETs) and pancreatic neuroendocrine tumors (PNETs).

METHODS

Clinical data were collected with Institutional Review Board approval for patients undergoing surgery at one center. Progression-free (PFS) and overall (OS) survival were from the time of surgery. Event times were estimated by the Kaplan-Meier method. Preoperative and postoperative laboratory values were tested for correlation with outcomes. A multivariate Cox model adjusted for confounders.

RESULTS

Included were 98 SBNETs and 78 PNETs. Median follow-up was 3.8 years; 62 % had metastatic disease. SBNETs had lower median PFS than PNETs (2.0 vs. 5.6 years; p < 0.01). Median OS was 10.5 years for PNETs and was not reached for SBNETs. Preoperative neurokinin A did not correlate with PFS or OS. Preoperative serotonin correlated with PFS but not OS. Higher levels of preoperative chromogranin A and pancreastatin showed significant correlation with worse PFS and OS (p < 0.05). After multivariate adjustment for confounders, preoperative and postoperative pancreastatin remained independently predictive of worse PFS and OS (p < 0.05). Whether pancreastatin normalized postoperatively further discriminated outcomes. Median PFS was 1.7 years in patients with elevated preoperative pancreastatin versus 6.5 years in patients with normal levels (p < 0.001).

CONCLUSIONS

Higher pancreastatin levels are significantly associated with worse PFS and OS in SBNETs and PNETs. This effect is independent of age, primary tumor site, and presence of nodal or metastatic disease. Pancreastatin provides valuable prognostic information and identifies surgical patients at high risk of recurrence who could benefit most from novel therapies.

GIPR expression in gastric and duodenal neuroendocrine tumors

BACKGROUND

Compounds targeting somatostatin-receptor-type-2 (SSTR2) are useful for small bowel neuroendocrine tumor (SBNET) and pancreatic neuroendocrine tumor (PNET) imaging and treatment. We recently characterized expression of 13 cell surface receptor genes in SBNETs and PNETs, identifying three drug targets (GIPR, OXTR, and OPRK1). This study set out to characterize expression of this gene panel in the less common neuroendocrine tumors of the stomach and duodenum (gastric and duodenal neuroendocrine tumors [GDNETs]).

METHODS

Primary tumors and adjacent normal tissue were collected at surgery, RNA was extracted, and expression of 13 target genes was determined by quantitative polymerase chain reaction. Expression was normalized to GAPDH and POLR2A internal control genes. Expression relative to normal tissue (ddCT) and absolute expression (dCT) were calculated. Wilcoxon tests compared median expression with false discovery rate correction for multiple comparisons.

RESULTS

Gene expression was similar in two gastric and seven duodenal tumors, and these were analyzed together. Like SBNETs (n = 63) and PNETs (n = 51), GDNETs showed significant overexpression compared with normal tissue of BRS3, GIPR, GRM1, GPR113, OPRK1, and SSTR2 (P < 0.05 for all). Of these, SSTR2 had the highest absolute expression in GDNETs (median dCT 4.0). Absolute expression of BRS3, GRM1, GPR113, and OPRK1 was significantly lower than SSTR2 in GDNETs (P < 0.05 for all), whereas expression of GIPR was similar to SSTR2 (median 4.3, P = 0.4).

CONCLUSIONS

As in SBNETs and PNETs, GIPR shows absolute expression close to SSTR2 but has greater overexpression relative to normal tissue (21.1 versus 3.5-fold overexpression). We conclude that GIPR could provide an improved signal-to-noise ratio for imaging versus SSTR2 and represents a promising novel therapeutic target in GDNETs.

Gastric inhibitory polypeptide receptor (GIPR) is a promising target for imaging and therapy in neuroendocrine tumors

BACKGROUND

Ligands binding the somatostatin receptor type 2 (SSTR2) are useful for imaging and treatment of neuroendocrine tumors (NETs), but not all tumors express high levels of these receptors. The aim of this study was to evaluate gene expression of new therapeutic targets in NETs relative to SSTR2.

METHODS

RNA was extracted from 103 primary small bowel and pancreatic NETs, matched normal tissue, and 123 metastases. Expression of 12 candidate genes was measured by quantitative polymerase chain reaction normalized to internal controls; candidate gene expression was compared with SSTR2.

RESULTS

Relative to normal tissue, primary NET expression of SSTR2, GPR98, BRS3, GIPR, GRM1, and OPRK1 were increased by 3, 8, 13, 13, 17, and 20-fold, respectively. Similar changes were found in metastases. Although most candidate genes showed lesser absolute expressions than SSTR2, absolute GIPR expression was closest to SSTR2 (mean dCT 3.6 vs. 2.7, P = .01). Absolute OPRK1 and OXTR expression varied greatly by primary tumor type and was close to SSTR2 in small bowel NETs but not pancreatic NETs.

CONCLUSION

Compared with the current treatment standard SSTR2, GIPR has only somewhat lesser absolute gene expression in tumor tissue but much lesser expression in normal tissue, making it a promising new target for NET imaging and therapy.

Translational research in endocrine surgery

This article reviews translational research in endocrine surgery, with a focus on disorders of the thyroid, parathyroids, adrenals, and endocrine pancreas. Discovery of genes responsible for heritable endocrine cancer syndromes has increased knowledge of the causes and mechanisms of endocrine cancer and has refined surgical treatment options. Knowledge of mutations in sporadic cancer has led to rapid progress in small-molecule kinase inhibitor strategies. These breakthroughs and their influence on current therapy are discussed to provide surgeons with an overview of the basic science research currently creating new clinical treatments and improving patient care.