Plasma ghrelin O-acyltransferase (GOAT) enzyme levels: A novel non-invasive diagnosis tool for patients with significant prostate cancer

Cellular Uptake of a Fluorescent Ligand Reveals Ghrelin O-Acyltransferase Interacts with Extracellular Peptides and Exhibits Unexpected Localization for a Secretory Pathway Enzyme

Ghrelin O-acyltransferase (GOAT) plays a central role in the maturation and activation of the peptide hormone ghrelin, which performs a wide range of endocrinological signaling roles. Using a tight-binding fluorescent ghrelin-derived peptide designed for high selectivity for GOAT over the ghrelin receptor GHSR, we demonstrate that GOAT interacts with extracellular ghrelin and facilitates ligand cell internalization in both transfected cells and prostate cancer cells endogenously expressing GOAT. Coupled with enzyme mutagenesis, ligand uptake studies support the interaction of the putative histidine general base within GOAT with the ghrelin peptide acylation site. Our work provides a new understanding of GOAT's catalytic mechanism, establishes that GOAT can interact with ghrelin and other peptides located outside the cell, and raises the possibility that other peptide hormones may exhibit similar complexity in their intercellular and organismal-level signaling pathways.

Ghrelin system in Alzheimer's disease

Alzheimer's disease (AD) is the most common type of dementia in seniors. Current efforts to understand the etiopathogenesis of this neurodegenerative disorder have brought forth questions about systemic factors in the development of AD. Ghrelin is a brain-gut peptide that is activated by ghrelin O-acyltransferase (GOAT) and signals via its receptor, growth hormone secretagogue receptor (GHSR). With increasing recognition of the neurotropic effects of ghrelin, the role of ghrelin system deregulation in the development of AD has been accentuated in recent years. In this review, we summarized recent research progress regarding the mechanisms of ghrelin signaling dysregulation and its contribution to AD brain pathology. In addition, we also discussed the therapeutic potential of strategies targeting ghrelin signaling for the treatment of this neurological disease.

Ghrelin and Cancer: Examining the Roles of the Ghrelin Axis in Tumor Growth and Progression

Ghrelin, a hormone produced and secreted from the stomach, is prim arily known as an appetite stimulant. Recently, it has emerged as a potential regulator/biomarker of cancer progression. Inconsistent results on this subject make this body of literature difficult to interpret. Here, we attempt to identify commonalities in the relationships between ghrelin and various cancers, and summarize important considerations for future research. The main players in the ghrelin family axis are unacylated ghrelin (UAG), acylated ghrelin (AG), the enzyme ghrelin O-acyltransferase (GOAT), and the growth hormone secretagogue receptor (GHSR). GOAT is responsible for the acylation of ghrelin, after which ghrelin can bind to the functional ghrelin receptor GHSR-1a to initiate the activation cascade. Splice variants of ghrelin also exist, with the most prominent being In1-ghrelin. In this review, we focus primarily on the potential of In1-ghrelin as a biomarker for cancer progression, the unique characteristics of UAG and AG, the importance of the two known receptor variants GHSR-1a and 1b, as well as the possible mechanisms through which the ghrelin axis acts. Further understanding of the role of the ghrelin axis in tumor cell proliferation could lead to the development of novel therapeutic approaches for various cancers.

Dysregulation of the miRNome unveils a crosstalk between obesity and prostate cancer: miR-107 asa personalized diagnostic and therapeutic tool

Prostate-specific antigen (PSA) is the gold-standard marker to screen prostate cancer (PCa) nowadays. Unfortunately, its lack of specificity and sensitivity makes the identification of novel tools to diagnose PCa an urgent medical need. In this context, microRNAs (miRNAs) have emerged as potential sources of non-invasive diagnostic biomarkers in several pathologies. Therefore, this study was aimed at assessing for the first time the dysregulation of the whole plasma miRNome in PCa patients and its putative implication in PCa from a personalized perspective (i.e., obesity condition). Plasma miRNome from a discovery cohort (18 controls and 19 PCa patients) was determined using an Affymetrix-miRNA array, showing that the expression of 104 miRNAs was significantly altered, wherein six exhibited a significant receiver operating characteristic (ROC) curve to distinguish between control and PCa patients (area under the curve [AUC] = 1). Then, a systematic validation using an independent cohort (135 controls and 160 PCa patients) demonstrated that miR-107 was the most profoundly altered miRNA in PCa (AUC = 0.75). Moreover, miR-107 levels significantly outperformed the ability of PSA to distinguish between control and PCa patients and correlated with relevant clinical parameters (i.e., PSA). These differences were more pronounced when considering only obese patients (BMI > 30). Interestingly, miR-107 levels were reduced in PCa tissues versus non-tumor tissues (n = 84) and in PCa cell lines versus non-tumor cells. In vitro miR-107 overexpression altered key aggressiveness features in PCa cells (i.e., proliferation, migration, and tumorospheres formation) and modulated the expression of important genes involved in PCa pathophysiology (i.e., lipid metabolism [i.e., FASN] and splicing process). Altogether, miR-107 might represent a novel and useful personalized diagnostic and prognostic biomarker and a potential therapeutic tool in PCa, especially in obese patients.

In1-Ghrelin Splicing Variant as a Key Element in the Pathophysiological Association Between Obesity and Prostate Cancer

CONTEXT

Recent studies emphasize the importance of considering the metabolic status to develop personalized medicine approaches. This is especially relevant in prostate cancer (PCa), wherein the diagnostic capability of prostate-specific antigen (PSA) dramatically drops when considering patients with PSA levels ranging from 3 to 10 ng/mL, the so-called grey zone. Hence, additional noninvasive diagnostic and/or prognostic PCa biomarkers are urgently needed, especially in the metabolic-status context.

OBJECTIVE

To assess the potential relation of urine In1-ghrelin (a ghrelin-splicing variant) levels with metabolic-related/pathological conditions (eg, obesity, diabetes, body mass index, insulin and glucose levels) and to define its potential clinical value in PCa (diagnostic/prognostic capacity) and relationship with PCa risk in patients with PSA in the grey zone.

METHODS

Urine In1-ghrelin levels were measured by radioimmunoassay in a clinically, metabolically, pathologically well-characterized cohort of patients without (n = 397) and with (n = 213) PCa with PSA in the grey zone.

RESULTS

Key obesity-related factors associated with PCa risk (BMI, diabetes, glucose and insulin levels) were strongly correlated to In1-ghrelin levels. Importantly, In1-ghrelin levels were higher in PCa patients compared to control patients with suspect of PCa but negative biopsy). Moreover, high In1-ghrelin levels were associated with increased PCa risk and linked to PCa aggressiveness (eg, tumor stage, lymphovascular invasion). In1-ghrelin levels added significant diagnostic value to a clinical model consisting of age, suspicious digital rectal exam, previous biopsy, and PSA levels. Furthermore, a multivariate model consisting of clinical and metabolic variables, including In1-ghrelin levels, showed high specificity and sensitivity to diagnose PCa (area under the receiver operating characteristic curve = 0.740).

CONCLUSIONS

Urine In1-ghrelin levels are associated with obesity-related factors and PCa risk and aggressiveness and could represent a novel and valuable noninvasive PCa biomarker, as well as a potential link in the pathophysiological relationship between obesity and PCa.

GHSR methylation-dependent expression of a variant ligand and receptor of the ghrelin system induces thymoma tumorigenesis

Our previous study reported that the DNA methylation of growth hormone secretagogue receptor (GHSR) was significantly higher in thymoma or thymic carcinoma (TC) than in normal thymic tissue samples. Thymic epithelial tumors (TETs) with higher GHSR DNA methylation were associated with significantly worse prognosis than those with lower levels of DNA methylation. Diversified components of the ghrelin-GHSR axis may exert opposing effects in cancer progression, depending on the cancer type in question. However, the precise function of the axis remains unclear. In the present study, the mRNA expression of five key components of the ghrelin system [native ligand ghrelin, variant ligand In-1 ghrelin, native receptor GHSR1a, variant receptor GHSR1b and acylation enzyme ghrelin O-acyltransferase (GOAT)] were examined in 58 TET samples by reverse transcription-quantitative PCR, and protein expression of GHSR1a and GHSR1b was assessed in 20 TETs using immunohistochemistry. The results revealed that In-1 ghrelin, GHSR1b (variant forms) and GOAT were more strongly expressed in thymoma compared with thymic-adjacent tissue. By contrast, no significant differences were observed in the expression of ghrelin and GHSR1a (native forms) between thymoma and thymic tissue. The mRNA expression of In-1 ghrelin and GHSR1b (variant forms) was positively associated with GHSR methylation in thymoma tissue samples. However, a relationship was not found between ghrelin, GHSR1a or GOAT expression (native forms) and GHSR methylation in thymoma. Immunohistochemical analysis revealed that mRNA expression of GHSR1a and GHSR1b generally correlated with expression of the corresponding protein, and that the expression of GHSR1b was increased in advanced-stage TETs. These results indicate that the DNA methylation of GHSR is associated with a shift from native expression (ghrelin and GHSR1a) to variant expression (In-1 ghrelin and GHSR1b), which induces the tumorigenesis of thymoma, but not TC.

Influence of Obesity in the miRNome: miR-4454, a Key Regulator of Insulin Response Via Splicing Modulation in Prostate

CONTEXT

Obesity is a major health problem associated with severe comorbidities, including type 2 diabetes and cancer, wherein microRNAs (miRNAs) might be useful as diagnostic/prognostic tools or therapeutic targets.

OBJECTIVE

To explore the differential expression pattern of miRNAs in obesity and their putative role in obesity-related comorbidities such as insulin resistance.

METHODS

An Affymetrix-miRNA array was performed in plasma samples from normoweight (n = 4/body mass index < 25) and obese subjects (n = 4/body mass index > 30). The main changes were validated in 2 independent cohorts (n = 221/n = 18). Additionally, in silico approaches were performed and in vitro assays applied in tissue samples and prostate (RWPE-1) and liver (HepG2) cell-lines.

RESULTS

A total of 26 microRNAs were altered (P < 0.01) in plasma of obese subjects compared to controls using the Affymetrix-miRNA array. Validation in ampler cohorts revealed that miR-4454 levels were consistently higher in obesity, associated with insulin-resistance (Homeostatic Model Assessment of Insulin Resistance/insulin) and modulated by medical (metformin/statins) and surgical (bariatric surgery) strategies. miR-4454 was highly expressed in prostate and liver tissues and its expression was increased in prostate and liver cells by insulin. In vitro, overexpression of miR-4454 in prostate cells resulted in decreased expression levels of INSR, GLUT4, and phosphorylation of AMPK/AKT/ERK, as well as in altered expression of key spliceosome components (ESRP1/ESRP2/RBM45/RNU2) and insulin-receptor splicing variants.

CONCLUSIONS

Obesity was associated to an alteration of the plasmatic miRNA landscape, wherein miR-4454 levels were higher, associated with insulin-resistance and modulated by obesity-controlling interventions. Insulin regulated miR-4454, which, in turn may impair the cellular response to insulin, in a cell type-dependent manner (i.e., prostate gland), by modulating the splicing process.

Recent progress in the discovery of ghrelin O-acyltransferase (GOAT) inhibitors

Ghrelin is a stomach-derived peptide hormone which stimulates appetite. For ghrelin to exert its orexigenic effect, octanoylation on the serine-3 residue of this gut-brain peptide is essential. The octanoylation of ghrelin is mediated by a unique acyltransferase enzyme known as ghrelin O-acyltransferase (GOAT). Thus modulating this enzyme offers viable approaches to alter feeding behaviors. Over the past decade, several small-molecule based approaches have appeared dealing with the discovery of compounds able to modulate this enzyme for the treatment of obesity and type 2 diabetes. Drug discovery efforts from academic groups and several pharmaceutical companies have fielded compounds having efficacy in altering acylated ghrelin levels in animal models but to date, compounds modulating the activity of the GOAT enzyme do not yet represent clinical options. This mini-review covers the drug discovery approaches of the last decade since the discovery of the GOAT enzyme.

Appetite-regulating hormones-leptin, adiponectin and ghrelin-and the development of prostate cancer: a systematic review and exploratory meta-analysis

BACKGROUND

Obesity has been proposed as a risk factor for prostate cancer (PCa). In obesity, serum levels of the appetite-regulating hormones-leptin, adiponectin, and ghrelin-become deregulated.

OBJECTIVE

To explore whether serum levels of appetite-regulating hormones associate with the incidence of PCa, the incidence of advanced disease, or PCa-specific mortality.

METHODS

PRISMA guidelines were followed. A systematic search for relevant articles published until March 2019 was performed using the databases PubMed, EMBASE, and Web of Science. Observational studies with data on serum levels of leptin, adiponectin, or ghrelin and PCa outcome were included. Meta-analysis was used to combine risk estimates. Meta-relative risks (mRRs) were calculated using random effects models. When available, raw data was pooled. Publication bias was assessed by funnel plot and Begg's test.

RESULTS

Thirty-five studies were eligible for inclusion. The qualitative analysis indicated that leptin was not consistently associated with any PCa outcome, although several cohorts reported decreased adiponectin levels in men who later developed advanced PCa. Based on the meta-analysis, there was no significant effect of leptin on PCa incidence (mRR = 0.93 (95% CI 0.75-1.16), p = 0.52) or advanced PCa (mRR = 0.90 (95% CI 0.74-1.10), p = 0.30). There were insufficient studies to estimate the mRR of PCa incidence for men with the highest levels of adiponectin. The combined risk of advanced PCa for men with the highest levels of adiponectin was reduced but did not reach significance (mRR = 0.81 (95% CI 0.61-1.08), p = 0.15).

CONCLUSIONS

The current evidence does not suggest an association between leptin and PCa outcome. However, there may be an inverse association between adiponectin and the incidence of advanced PCa that should be investigated by further studies. Serum ghrelin has not been largely investigated.

Clinical Utility of Ghrelin-O-Acyltransferase (GOAT) Enzyme as a Diagnostic Tool and Potential Therapeutic Target in Prostate Cancer

Recent data suggested that plasma Ghrelin O-Acyl Transferase enzyme (GOAT) levels could represent a new diagnostic biomarker for prostate cancer (PCa). In this study, we aimed to explore the diagnostic and prognostic/aggressiveness capacity of GOAT in urine, as well as to interrogate its putative pathophysiological role in PCa. We analysed urine/plasma levels of GOAT in a cohort of 993 patients. In vitro (i.e., cell-proliferation) and in vivo (tumor-growth in a xenograft-model) approaches were performed in response to the modulation of GOAT expression/activity in PCa cells. Our results demonstrate that plasma and urine GOAT levels were significantly elevated in PCa patients compared to controls. Remarkably, GOAT significantly outperformed PSA in the diagnosis of PCa and significant PCa in patients with PSA levels ranging from 3 to 10 ng/mL (the so-called PSA grey-zone). Additionally, urine GOAT levels were associated to clinical (e.g., Gleason-score, PSA levels) and molecular (e.g., CDK2/CDK6/CDKN2A expression) aggressiveness parameters. Indeed, GOAT overexpression increased, while its silencing/blockade decreased cell-proliferation in PCa cells. Moreover, xenograft tumors derived from GOAT-overexpressing PCa (DU145) cells were significantly higher than those derived from the mock-overexpressing cells. Altogether, our results demonstrate that GOAT could be used as a diagnostic and aggressiveness marker in urine and a therapeutic target in PCa.

Attribution of Ghrelin to Cancer; Attempts to Unravel an Apparent Controversy

Ghrelin is an endogenous peptide hormone mainly produced in the stomach. It has been known to regulate energy homeostasis, stimulate secretion of growth hormone, and mediate many other physiologic effects. Various effects attributed to ghrelin contribute to many aspects of cancer development and progression. Accordingly, a large body of evidence has emerged about the association of ghrelin with several types of cancer in scales of cell-line, animal, and human studies. However, existing data are controversial. This controversy occurs in two main domains: one is the controversial results in local effects of ghrelin on different types of human cancer cell-lines; the second is the apparent disagreement in the results of in-vitro and clinical studies that investigated ghrelin association to one type of cancer. These inconsistencies have hampered the indications to consider ghrelin as a potential tumor biomarker or therapeutic agent in cancer patients. Previous studies have reviewed different parts of current literature about the ghrelin-cancer relationship. Although they have highlighted these controversial results in various ways, no specific recommendations have been given to address it. In this study, we comprehensively reviewed in-vitro, in-vivo, and clinical studies and attempted to use the following approaches to unravel the inconsistencies detected: (a) to distinguish local and systemic effects of ghrelin in interpreting its summary clinical role in each cancer; (b) scrutinizing factors that regulate local effects of ghrelin and could justify different effects of ghrelin on different cancer cell-lines. These approaches could have notable implications for future in-vitro and clinical studies.

Oncogenic Role of Secreted Engrailed Homeobox 2 (EN2) in Prostate Cancer

Engrailed variant-2 (EN2) has been suggested as a potential diagnostic biomarker; however, its presence and functional role in prostate cancer (PCa) cells is still controversial or unknown. Here, we analyzed 1) the expression/secretion profile of EN2 in five independent samples cohorts from PCa patients and controls (prostate tissues and/or urine) to determine its utility as a PCa biomarker; and 2) the functional role of EN2 in normal (RWPE1) and tumor (LNCaP/22Rv1/PC3) prostate cells to explore its potential value as therapeutic target. EN2 was overexpressed in our two cohorts of PCa tissues compared to control and in tumor cell lines compared with normal-like prostate cells. This profile was corroborated in silico in three independent data sets [The Cancer Genome Atlas(TCGA)/Memorial Sloan Kettering Cancer Center (MSKCC)/Grasso]. Consistently, urine EN2 levels were elevated and enabled discrimination between PCa and control patients. EN2 treatment increased cell proliferation in LNCaP/22Rv1/PC3 cells, migration in RWPE1/PC3 cells, and PSA secretion in LNCaP cells. These effects were associated, at least in the androgen-sensitive LNCaP cells, with increased AKT and androgen-receptor phosphorylation levels and with modulation of key cancer-associated genes. Consistently, EN2 treatment also regulated androgen-receptor activity (full-length and splicing variants) in androgen-sensitive 22Rv1 cells. Altogether, this study demonstrates the potential utility of EN2 as a non-invasive diagnostic biomarker for PCa and provides novel and valuable information to further investigate its putative utility to develop new therapeutic tools in PCa.

Plasma ghrelin O-acyltransferase (GOAT) enzyme levels: A novel non-invasive diagnosis tool for patients with significant prostate cancer

Early detection of PCa faces severe limitations as PSA displays poor‐specificity/sensitivity. As we recently demonstrated that plasma ghrelin O‐acyltransferase (GOAT)‐enzyme is significantly elevated in PCa‐patients compared with healthy‐controls, using a limited patients‐cohort, we aimed to further explore the potential of GOAT to improve PCa diagnosis using an ample patients‐cohort (n = 312) and defining subgroups (i.e. significant PCa/metastatic patients, etc.) that could benefit from this biomarker. Plasma GOAT‐levels were evaluated by ELISA in patients with (n = 183) and without (n = 129) PCa. Gleason Score ≥ 7 was considered clinically significant PCa. GOAT‐levels were higher in PCa patients vs control patients, and in those with significant PCa vs non‐significant PCa. GOAT‐levels association with the diagnoses of significant PCa was independent from traditional clinical variables (i.e. PSA/age/DRE). Remarkably, GOAT outperformed PSA in patients with PSA‐levels ranging 3‐20 ng/mL for the significant PCa diagnosis [GOAT‐AUC = 0.612 (0.531‐0.693) vs PSA‐AUC = 0.494 (0.407‐0.580)]. A panel of key variables including GOAT/age/DRE/testosterone also outperformed the same panel but with PSA [AUC = 0.720 (0.710‐0.730) vs AUC = 0.705 (0.695‐0.716), respectively]. Notably, GOAT‐levels could also represent a novel predictive biomarker of aggressiveness, as its levels are positively associated with Gleason Score and the presence of metastasis at the time of diagnoses. Altogether, our data reveal that GOAT‐levels can be used as a non‐invasive biomarker for significant PCa diagnosis in patients at risk of PCa (with PSA: 3‐20 ng/mL).