The truncated somatostatin receptor sst5TMD4 stimulates the angiogenic process and is associated to lymphatic metastasis and disease-free survival in breast cancer patients

Somatostatin and Somatostatin Receptors in Tumour Biology

Somatostatin (SST), a growth hormone inhibitory peptide, is expressed in endocrine and non-endocrine tissues, immune cells and the central nervous system (CNS). Post-release from secretory or immune cells, the first most appreciated role that SST exhibits is the antiproliferative effect in target tissue that served as a potential therapeutic intervention in various tumours of different origins. The SST-mediated in vivo and/or in vitro antiproliferative effect in the tumour is considered direct via activation of five different somatostatin receptor subtypes (SSTR1-5), which are well expressed in most tumours and often more than one receptor in a single cell. Second, the indirect effect is associated with the regulation of growth factors. SSTR subtypes are crucial in tumour diagnosis and prognosis. In this review, with the recent development of new SST analogues and receptor-specific agonists with emerging functional consequences of signaling pathways are promising therapeutic avenues in tumours of different origins that are discussed.

Dysregulation of splicing variants and spliceosome components in breast cancer

The dysregulation of the splicing process has emerged as a novel hallmark of metabolic and tumor pathologies. In breast cancer (BCa), which represents the most diagnosed cancer type among women worldwide, the generation and/or dysregulation of several oncogenic splicing variants have been described. This is the case of the splicing variants of HER2, ER, BRCA1, or the recently identified by our group, In1-ghrelin and SST5TMD4, which exhibit oncogenic roles, increasing the malignancy, poor prognosis, and resistance to treatment of BCa. This altered expression of oncogenic splicing variants has been closely linked with the dysregulation of the elements belonging to the macromolecular machinery that controls the splicing process (spliceosome components and the associated splicing factors). In this review, we compile the current knowledge demonstrating the altered expression of splicing variants and spliceosomal components in BCa, showing the existence of a growing body of evidence supporting the close implication of the alteration in the splicing process in mammary tumorigenesis.

Somatostatin Receptor Splicing Variant sst5TMD4 Overexpression in Glioblastoma Is Associated with Poor Survival, Increased Aggressiveness Features, and Somatostatin Analogs Resistance

Glioblastoma (GBM) is the most malignant and lethal brain tumor. Current standard treatment consists of surgery followed by radiotherapy/chemotherapy; however, this is only a palliative approach with a mean post-operative survival of scarcely ~12-15 months. Thus, the identification of novel therapeutic targets to treat this devastating pathology is urgently needed. In this context, the truncated splicing variant of the somatostatin receptor subtype 5 (sst5TMD4), which is produced by aberrant alternative splicing, has been demonstrated to be overexpressed and associated with increased aggressiveness features in several tumors. However, the presence, functional role, and associated molecular mechanisms of sst5TMD4 in GBM have not been yet explored. Therefore, we performed a comprehensive analysis to characterize the expression and pathophysiological role of sst5TMD4 in human GBM. sst5TMD4 was significantly overexpressed (at mRNA and protein levels) in human GBM tissue compared to non-tumor (control) brain tissue. Remarkably, sst5TMD4 expression was significantly associated with poor overall survival and recurrent tumors in GBM patients. Moreover, in vitro sst5TMD4 overexpression (by specific plasmid) increased, whereas sst5TMD4 silencing (by specific siRNA) decreased, key malignant features (i.e., proliferation and migration capacity) of GBM cells (U-87 MG/U-118 MG models). Furthermore, sst5TMD4 overexpression in GBM cells altered the activity of multiple key signaling pathways associated with tumor aggressiveness/progression (AKT/JAK-STAT/NF-κB/TGF-β), and its silencing sensitized GBM cells to the antitumor effect of pasireotide (a somatostatin analog). Altogether, these results demonstrate that sst5TMD4 is overexpressed and associated with enhanced malignancy features in human GBMs and reveal its potential utility as a novel diagnostic/prognostic biomarker and putative therapeutic target in GBMs.

Splicing Machinery is Dysregulated in Pituitary Neuroendocrine Tumors and is Associated with Aggressiveness Features

Pituitary neuroendocrine tumors (PitNETs) constitute approximately 15% of all brain tumors, and most have a sporadic origin. Recent studies suggest that altered alternative splicing and, consequently, appearance of aberrant splicing variants, is a common feature of most tumor pathologies. Moreover, spliceosome is considered an attractive therapeutic target in tumor pathologies, and the inhibition of SF3B1 (e.g., using pladienolide-B) has been shown to exert antitumor effects. Therefore, we aimed to analyze the expression levels of selected splicing-machinery components in 261 PitNETs (somatotropinomas/non-functioning PitNETS/corticotropinomas/prolactinomas) and evaluated the direct effects of pladienolide-B in cell proliferation/viability/hormone secretion in human PitNETs cell cultures and pituitary cell lines (AtT-20/GH3). Results revealed a severe dysregulation of splicing-machinery components in all the PitNET subtypes compared to normal pituitaries and a unique fingerprint of splicing-machinery components that accurately discriminate between normal and tumor tissue in each PitNET subtype. Moreover, expression of specific components was associated with key clinical parameters. Interestingly, certain components were commonly dysregulated throughout all PitNET subtypes. Finally, pladienolide-B reduced cell proliferation/viability/hormone secretion in PitNET cell cultures and cell lines. Altogether, our data demonstrate a drastic dysregulation of the splicing-machinery in PitNETs that might be associated to their tumorigenesis, paving the way to explore the use of specific splicing-machinery components as novel diagnostic/prognostic and therapeutic targets in PitNETs.

Peptides derived from the extracellular domain of the somatostatin receptor splicing variant SST5TMD4 increase malignancy in multiple cancer cell types

Extracellular fragments derived from plasma membrane receptors can play relevant roles in the development/progression of tumor pathologies, thereby offering novel diagnostic or therapeutic opportunities. The truncated variant of somatostatin receptor subtype-5, SST5TMD4, is an aberrantly spliced receptor with 4 transmembrane domains, highly overexpressed in several tumor types, whose C-terminal tail is exposed towards the extracellular matrix, and could therefore be the substrate for proteolytic enzymes. In silico analysis implemented herein predicted 2 possible cleavage sites for metalloproteases MMP2, 9, 14, and 16 in its sequence, which could generate 3 releasable peptides. Of note, expression of those MMPs was directly correlated with SST5TMD4 in several cancer-derived cell lines (ie neuroendocrine tumors and prostate, breast, and liver cancers). Moreover, incubation with SST5TMD4-derived peptides enhanced malignancy features in all cancer cell types tested (ie proliferation, migration, etc.) and blunted the antiproliferative response to somatostatin in QGP-1 cells, acting probably through PI3K/AKT and/or MEK/ERK signaling pathways and the modulation of key cancer-associated genes (eg MMPs, MKI67, ACTR2/3, CD24/44). These results suggest that SST5TMD4-derived peptides could contribute to the strong oncogenic role of SST5TMD4 observed in multiple tumor pathologies, and, therefore, represent potential candidates to identify novel diagnostic, prognostic, or therapeutic targets in cancer.

Biological and Biochemical Basis of the Differential Efficacy of First and Second Generation Somatostatin Receptor Ligands in Neuroendocrine Neoplasms

Endogenous somatostatin shows anti-secretory effects in both physiological and pathological settings, as well as inhibitory activity on cell growth. Since somatostatin is not suitable for clinical practice, researchers developed synthetic somatostatin receptor ligands (SRLs) to overcome this limitation. Currently, SRLs represent pivotal tools in the treatment algorithm of neuroendocrine tumors (NETs). Octreotide and lanreotide are the first-generation SRLs developed and show a preferential binding affinity to somatostatin receptor (SST) subtype 2, while pasireotide, which is a second-generation SRL, has high affinity for multiple SSTs (SST₅ > SST₂ > SST₃ > SST₁). A number of studies demonstrated that first-generation and second-generation SRLs show distinct functional properties, besides the mere receptor affinity. Therefore, the aim of the present review is to critically review the current evidence on the biological effects of SRLs in pituitary adenomas and neuroendocrine tumors, by mainly focusing on the differences between first-generation and second-generation ligands.

International Union of Basic and Clinical Pharmacology. CV. Somatostatin Receptors: Structure, Function, Ligands, and New Nomenclature

Somatostatin, also known as somatotropin-release inhibitory factor, is a cyclopeptide that exerts potent inhibitory actions on hormone secretion and neuronal excitability. Its physiologic functions are mediated by five G protein-coupled receptors (GPCRs) called somatostatin receptor (SST)1-5. These five receptors share common structural features and signaling mechanisms but differ in their cellular and subcellular localization and mode of regulation. SST₂ and SST₅ receptors have evolved as primary targets for pharmacological treatment of pituitary adenomas and neuroendocrine tumors. In addition, SST₂ is a prototypical GPCR for the development of peptide-based radiopharmaceuticals for diagnostic and therapeutic interventions. This review article summarizes findings published in the last 25 years on the physiology, pharmacology, and clinical applications related to SSTs. We also discuss potential future developments and propose a new nomenclature.

Ghrelin-O-Acyltransferase (GOAT) Enzyme as a Novel Potential Biomarker in Gastroenteropancreatic Neuroendocrine Tumors

OBJECTIVES

The association between the presence and alterations of the components of the ghrelin system and the development and progression of neuroendocrine tumors (NETs) is still controversial and remains unclear.

METHODS

Here, we systematically evaluated the expression levels (by quantitative-PCR) of key ghrelin system components of in gastroenteropancreatic (GEP)-NETs, as compared to non-tumor adjacent (NTA; n = 42) and normal tissues (NT; n = 14). Then, we analyzed their putative associations with clinical-histological characteristics.

RESULTS

The results indicate that ghrelin and its receptor GHSR1a are present in a high proportion of normal tissues, while the enzyme ghrelin-O-acyltransferase (GOAT) and the splicing variants In1-ghrelin and GHSR1b were present in a lower proportion of normal tissues. In contrast, all ghrelin system components were present in a high proportion of tumor and NTA tissues. GOAT was significantly overexpressed (by quantitative-PCR (qPCR)) in tumor samples compared to NTA, while a trend was found for ghrelin, In1-ghrelin and GHSR1a. In addition, expression of these components displayed significant correlations with key clinical parameters. The marked overexpression of GOAT in tumor samples compared to NTA regions was confirmed by IHC, revealing that this enzyme is particularly overexpressed in gastrointestinal NETs, where it is directly correlated with tumor diameter.

CONCLUSIONS

These results provide novel information on the presence and potential pathophysiological implications of the ghrelin system components in GEP-NETs, wherein GOAT might represent a novel diagnostic biomarker.

Prognostic and predictive biomarkers for somatostatin analogs, peptide receptor radionuclide therapy and serotonin pathway targets in neuroendocrine tumours

Neuroendocrine tumours (NETs) are a heterogeneous group of neoplasms regarding their molecular biology, clinical behaviour, prognosis and response to therapy. Several attempts to establish robust predictive biomarkers have failed. Neither tissue markers nor blood borne ones have proven to be successful yet. Circulating tumour cells (CTCs) as "liquid biopsies" could provide prognostic information at the time a therapeutic decision needs to be made and could be an attractive tool for tumour monitoring throughout the treatment period. However, "liquid biopsies" are far from becoming the standard biomarker in NETs. Promising results have been presented over the last few years using a novel biomarker candidate, a multianalyte algorithm analysis PCR-based test (NETest). New technologies will open the field to different ways of approaching the biomarker conundrum in NETs. However, the complications derived from being a heterogeneous group of malignancies will remain with us forever. In summary, there is an unmet need to incorporate new biomarker candidates into clinical research trials to obtain a robust prospective validation under the most demanding scenario.

The Role of Midkine in Arteriogenesis, Involving Mechanosensing, Endothelial Cell Proliferation, and Vasodilation

Mechanical forces in blood circulation such as shear stress play a predominant role in many physiological and pathophysiological processes related to vascular responses or vessel remodeling. Arteriogenesis, defined as the growth of pre-existing arterioles into functional collateral arteries compensating for stenosed or occluded arteries, is such a process. Midkine, a pleiotropic protein and growth factor, has originally been identified to orchestrate embryonic development. In the adult organism its expression is restricted to distinct tissues (including tumors), whereby midkine is strongly expressed in inflamed tissue and has been shown to promote inflammation. Recent investigations conferred midkine an important function in vascular remodeling and growth. In this review, we introduce the midkine gene and protein along with its cognate receptors, and highlight its role in inflammation and the vascular system with special emphasis on arteriogenesis, particularly focusing on shear stress-mediated vascular cell proliferation and vasodilatation.

Structural and functional analysis of two novel somatostatin receptors identified from topmouth culter (Erythroculter ilishaeformis)

In the present study, we cloned and characterized two somatostatin (SS) receptors (SSTRs) from topmouth culter (Erythroculter ilishaeformis) designated as EISSTR6 and EISSTR7. Analysis of EISSTR6 and EISSTR7 signature motifs, 3D structures, and homology with the known members of the SSTR family indicated that the novel receptors had high similarity to the SSTRs of other vertebrates. EISSTR6 and EISSTR7 mRNA expression was detected in 17 topmouth culter tissues, and the highest level was observed in the pituitary. Luciferase reporter assay revealed that SS14 significantly inhibited forskolin-stimulated pCRE-luc promoter activity in HEK293 cells transiently expressing EISSTR6 and EISSTR7, indicating that the receptors can be activated by SS14. We also identified phosphorylation sites important for the functional activity of EISSTR6 and EISSTR7 by mutating Ser^{23, 43, 107, 196, 311} and Ser^{7, 29, 61, 222, 225} residues, respectively, to Ala, which significantly reduced the inhibitory effects of SS14 on the CRE promoter mediated by EISSTR6 and EISSTR7. Furthermore, treatment of juvenile topmouth culters with microcystin-LR or 17β-estradiol significantly affected EISSTR6 and EISSTR7 transcription in the brain, liver and spleen, suggesting that these receptors may be involved in the pathogenic mechanisms induced by endocrine disruptors. Our findings should contribute to the understanding of the structure-function relationship and evolution of the SSTR family.

In1-ghrelin splicing variant is associated with reduced disease-free survival of breast cancer patients and increases malignancy of breast cancer cells lines

Ghrelin gene generates several variants that regulate multiple pathophysiological functions, including tumor-related processes. In1-ghrelin is a splicing variant that was previously shown to be overexpressed in breast cancer (BCa), where it correlated with proliferation markers; however, its possible association with clinical outcome of BCa patients and underlying mechanisms are still unknown. To address this issue, expression levels and clinical associations of In1-ghrelin were analyzed in a cohort of 117 BCa samples. Additionally, a battery of cellular and molecular assays was implemented using two BCa cell lines (MCF-7 and MDA-MB-231), wherein the role of In1-ghrelin on proliferation, migration, dedifferentiation and signaling pathways was explored. The results generated revealed that high expression of In1-ghrelin in BCa samples was associated with lymph node metastasis and reduced disease-free survival. Indeed, In1-ghrelin overexpression stimulated proliferation and migration in MCF-7 and MDA-MB-231 cells. Similar results were found by treating MDA-MB-231 and MCF-7 with In1-ghrelin-derived peptides. Conversely, In1-ghrelin silencing decreased proliferation and migration capacities of MDA-MB-231. Furthermore, In1-ghrelin (but not ghrelin) overexpression increased the capacity to form mammospheres in both cell lines. These effects could be associated with activation of MAPK-ERK, Jag1/Notch, Wnt/β-catenin and/or TGF-β1 pathways. Altogether, our data indicate that In1-ghrelin could play relevant functional roles in the regulation of BCa development and progression and may provide insights to identify novel biomarkers and new therapeutic approaches for this pathology.

Metformin Reduces Prostate Tumor Growth, in a Diet-Dependent Manner, by Modulating Multiple Signaling Pathways

Prostate-cancer is strongly influenced by obesity, wherein metformin could represent a promising treatment; however, the endocrine metabolic/cellular/molecular mechanisms underlying these associations and effects are still unclear. To determine the beneficial antitumoral effects of metformin on prostate cancer progression/aggressiveness and the relative contribution of high-fat diet (HFD; independently of obesity), we used HFD-fed immunosuppressed mice inoculated with PC3 cells (which exhibited partial resistance to diet-induced obesity) compared with low-fat diet (LFD)-fed control mice. Moreover, gene expression analysis was performed on cancer-associated genes in the xenografted tumors, and the antitumorigenic role of metformin on tumoral (PC3/22Rv1/LNCaP) and normal (RWPE1) prostate cells was evaluated. The results demonstrate that HFD is associated with enhanced prostate cancer growth irrespective of body weight gain and endocrine metabolic dysregulations and that metformin can reduce prostate cancer growth under LFD but more prominently under HFD, acting through the modulation of several tumoral-associated processes (e.g., cell cycle, apoptosis, and/or necrosis). Moreover, the actions observed in vivo could be mediated by the modulation of the local expression of GH/IGF1 axis components. Finally, it was demonstrated that metformin had disparate effects on proliferation, migration, and prostate-specific antigen secretion from different cell lines. Altogether, these data reveal that metformin inhibits prostate cancer growth under LFD and, specially, under HFD conditions through multiple metabolic/tumoral signaling pathways.Implications: The current study linking dietary influence on metformin-regulated signaling pathways and antitumoral response provides new and critical insight on environment-host interactions in cancer and therapy. Mol Cancer Res; 15(7); 862-74. ©2017 AACR.

Obesity and metabolic dysfunction severely influence prostate cell function: role of insulin and IGF1

Obesity is a major health problem that courses with severe comorbidities and a drastic impairment of homeostasis and function of several organs, including the prostate gland (PG). The endocrine–metabolic regulatory axis comprising growth hormone (GH), insulin and IGF1, which is drastically altered under extreme metabolic conditions such as obesity, also plays relevant roles in the development, modulation and homeostasis of the PG. However, its implication in the pathophysiological interplay between obesity and prostate function is still to be elucidated. To explore this association, we used a high fat–diet obese mouse model, as well as in vitro primary cultures of normal‐mouse PG cells and human prostate cancer cell lines. This approach revealed that most of the components of the GH/insulin/IGF1 regulatory axis are present in PGs, where their expression pattern is altered under obesity conditions and after an acute insulin treatment (e.g. Igfbp3), which might have some pathophysiological implications. Moreover, our results demonstrate, for the first time, that the PG becomes severely insulin resistant under diet‐induced obesity in mice. Finally, use of in vitro approaches served to confirm and expand the conception that insulin and IGF1 play a direct, relevant role in the control of normal and pathological PG cell function. Altogether, these results uncover a fine, germane crosstalk between the endocrine–metabolic status and the development and homeostasis of the PG, wherein key components of the GH, insulin and IGF1 axes could play a relevant pathophysiological role.

Management of aggressive growth hormone secreting pituitary adenomas

Aggressive GH-secreting pituitary adenomas (GHPAs) represent an important clinical problem in patients with acromegaly. Surgical therapy, although often the mainstay of treatment for GHPAs, is less effective in aggressive GHPAs due to their invasive and destructive growth patterns, and their proclivity for infrasellar invasion. Medical therapies for GHPAs, including somatostatin analogues and GH receptor antagonists, are becoming increasingly important adjuncts to surgical intervention. Stereotactic radiosurgery serves as an important fallback therapy for tumors that cannot be cured with surgery and medications. Data suggests that patients with aggressive and refractory GHPAs are best treated at dedicated tertiary pituitary centers with multidisciplinary teams of neuroendocrinologists, neurosurgeons, radiation oncologists and other specialists who routinely provide advanced care to GHPA patients. Future research will help clarify the defining features of "aggressive" and "atypical" PAs, likely based on tumor behavior, preoperative imaging characteristics, histopathological characteristics, and molecular markers.