The hypofunctional effect of P335L single nucleotide polymorphism on SSTR5 function

Repositioning Lomitapide to block ZDHHC5-dependant palmitoylation on SSTR5 leads to anti-proliferation effect in preclinical pancreatic cancer models

Palmitoylation of proteins plays important roles in various physiological processes, such as cell proliferation, inflammation, cell differentiation etc. However, inhibition of protein palmitoylation has led to few new drugs to date. ZDHHC5 serves as a key enzyme to catalyze palmitoylation on SSTR5 (a proven anti-proliferation receptor in pancreatic cells). Herein, we compare single-cell transcriptome data between pancreatic cancer tissues and normal pancreas tissues and identify that ZDHHC5 is a potential target to inhibit proliferation of pancreatic cancer cells. In addition, we report the repositioning of an orphan drug (Lomitapide) as an inhibitor of ZDHHC5, and we speculate that this inhibitor may be able to block palmitylation on SSTR5. Pharmacological blockade of ZDHHC5 with Lomitapide results in attenuated cancer cell growth and proliferation which collectively contributes to antitumor responses in vitro and in vivo. This is the first study, to our knowledge, to demonstrate the utility of a pharmacological inhibitor of ZDHHC5 in pancreatic cancer, representing a new class of palmitoylation targeted therapy and laying a framework for paradigm-shifting therapies targeting cancer cell palmitoylation.

Undertreatment of Pancreatic Cancer: The Intersection of Bias, Biology, and Geography

Pancreatic cancer is the third leading cause of cancer deaths in the United States. Black patients with pancreatic cancer experience higher incidence and increased mortality. Although racial biologic differences exist, socioeconomic status, insurance type, physician bias, and patient beliefs contribute to the disparities in outcomes observed among patients who are Black, indigenous, and people of color.

The repertoire of family A-peptide GPCRs in archaic hominins

Given the importance of G-protein coupled receptors in the regulation of many physiological functions, deciphering the relationships between genotype and phenotype in past and present hominin GPCRs is of main interest to understand the evolutionary process that contributed to the present-day variability in human traits and health. Here, we carefully examined the publicly available genomic and protein sequence databases of the archaic hominins (Neanderthal and Denisova) to draw up the catalog of coding variations in GPCRs for peptide ligands, in comparison with living humans. We then searched in the literature the functional changes, phenotypes and risk of disease possibly associated with the detected variants. Our survey suggests that Neanderthal and Denisovan hominins were likely prone to lower risk of obesity, to enhanced platelet aggregation in response to thrombin, to better response to infection, to less anxiety and aggressiveness and to favorable sociability. While some archaic variants were likely advantageous in the past, they might be responsible for maladaptive disorders today in the context of modern life and/or specific regional distribution. For example, an archaic haplotype in the neuromedin receptor 2 is susceptible to confer risk of diabetic nephropathy in type 1 diabetes in present-day Europeans. Paying attention to the pharmacological properties of some of the archaic variants described in this study may be helpful to understand the variability of therapeutic efficacy between individuals or ethnic groups.

Closing the Disparity in Pancreatic Cancer Outcomes: A Closer Look at Nonmodifiable Factors and Their Potential Use in Treatment

OBJECTIVES

African Americans (AAs) have disproportionately higher incidence and lower survival rates from pancreatic cancer compared with whites. Historically, this disparity has been attributed to modifiable risk factors. Recent studies suggest that nonmodifiable aspects may also play an important role. We review these new contributions as potential targets for closing the disparity.

METHODS

A PubMed search was conducted to review studies of nonmodifiable elements contributing to pancreatic cancer disparities in AAs.

RESULTS

Several nonmodifiable risks are associated with the racial disparity in pancreatic cancer. SSTR5 P335L, Kaiso, and KDM4/JMJD2A demonstrate differential racial expression, increasing their potential as therapeutic targets. Many social determinants of health and their associations with diabetes, obesity, and the microbiome are partially modifiable risk factors that significantly contribute to outcomes in minorities. Barriers to progress include the low minority inclusion in research studies.

CONCLUSIONS

Genomics, epigenetics, the microbiome, and social determinants of health are components that contribute to the pancreatic cancer disparity in AAs. These factors can be researched, targeted, and modified to improve mortality rates. Closing the disparity in pancreatic cancer will require an integrated approach of personalized medicine, increased minority recruitment to studies, and advanced health care/education access.

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.

Irisin inhibits pancreatic cancer cell growth via the AMPK-mTOR pathway

Irisin, a recently identified myokine that is released from skeletal muscle following exercise, regulates body weight and influences various metabolic diseases such as obesity and diabetes. In this study, human recombinant nonglycosylated P-irisin (expressed in Escherichia coli prokaryote cell system) or glycosylated E-irisin (expressed in Pichia pastoris eukaryote cell system) were compared to examine the role of recombinant irisin against pancreatic cancer (PC) cells lines, MIA PaCa-2 and Panc03.27. MTT [3-(4, 5-dimethylthiazol-2-yl)-2, 5-di phenyltetrazolium bromide] and cell colony formation assays revealed that irisin significantly inhibited the growth of MIA PaCa-2 and Panc03.27 in a dose-dependent manner. Irisin also induced G1 arrest in both cell lines. Scratch wound healing and transwell assays revealed that irisin also inhibited the migration of PC cells. Irisin reversed the activity of epithelial–mesenchymal transition (EMT) while increasing E-cadherin expression and reducing vimentin expression. Irisin activated the adenosine monophosphate-activated protein kinase (AMPK) pathway and suppressed the mammalian target of rapamycin (mTOR) signaling. Besides, our results suggest that irisin receptors exist on the surface of human MIA PaCa-2 and Panc03.27 cells. Our results clearly demonstrate that irisin suppressed PC cell growth via the activation of AMPK, thereby downregulating the mTOR pathway and inhibiting EMT of PC cells.

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.

Metformin Restrains Pancreatic Duodenal Homeobox-1 (PDX-1) Function by Inhibiting ERK Signaling in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is one of the most potent and perilous diseases known, with a median survival rate of 3-5 months due to the combination of only advanced stage diagnosis and ineffective therapeutic options. Metformin (1,1-Dimethylbiguanide hydrochloride), the leading drug used for type 2 diabetes mellitus, emerges as a potential therapy for PDAC and other human cancers. Metformin exerts its anticancer action via a variety of adenosine monophosphate (AMP)-activated protein kinase (AMPK)- dependent and/or AMPK-independent mechanisms. We present data here showing that metformin downregulated pancreatic transcription factor pancreatic duodenal homeobox-1 (PDX-1), suggesting a potential novel mechanism by which metformin exerts its anticancer action. Metformin inhibited PDX-1 expression at both protein and mRNA levels and PDX-1 transactivity as well in PDAC cells. Extracellular signal-regulated kinase (ERK) was identified as a PDX-1-interacting protein by antibody array screening in GFP-PDX-1 stable HEK293 cells. Co-transfection of ERK1 with PDX-1 resulted in an enhanced PDX-1 expression in HEK293 cells in a dose-dependent manner. Immunoprecipitation/Western blotting analysis confirmed the ERK-PDX-1 interaction in PANC-1 cells stimulated by epidermal growth factor (EGF). EGF induced an enhanced PDX-1 expression in PANC-1 cells and this stimulation was inhibited by MEK inhibitor PD0325901. Metformin inhibited EGF-stimulated PDX-1 expression with an accompanied inhibition of ERK kinase activation in PANC- 1 cells. Taken together, our studies show that PDX-1 is a potential novel target for metformin in PDAC cells and that metformin may exert its anticancer action in PDAC by down-regulating PDX-1 via a mechanism involving inhibition of ERK signaling.

Down-regulation of pancreatic and duodenal homeobox-1 by somatostatin receptor subtype 5: a novel mechanism for inhibition of cellular proliferation and insulin secretion by somatostatin

Somatostatin (SST) is a regulatory peptide and acts as an endogenous inhibitory regulator of the secretory and proliferative responses of target cells. SST’s actions are mediated by a family of seven transmembrane domain G protein-coupled receptors that comprise five distinct subtypes (SSTR1-5). SSTR5 is one of the major SSTRs in the islets of Langerhans. Homeodomain-containing transcription factor pancreatic and duodenal homeobox-1 (PDX-1) is essential for pancreatic development, β cell differentiation, maintenance of normal β cell functions in adults and tumorigenesis. Recent studies show that SSTR5 acts as a negative regulator for PDX-1 expression and that SSTR5 mediates somatostatin’s inhibitory effect on cell proliferation and insulin expression/excretion through down-regulating PDX-1 expression. SSTR5 exerts its inhibitory effect on PDX-1 expression at both the transcriptional level by down-regulating PDX-1 mRNA and the post-translational level by enhancing PDX-1 ubiquitination. Identification of PDX-1 as a transcriptional target for SSTR5 may help in guiding the choice of therapeutic cancer treatments.

Scaffold architecture controls insulinoma clustering, viability, and insulin production

Recently, in vitro diagnostic tools have shifted focus toward personalized medicine by incorporating patient cells into traditional test beds. These cell-based platforms commonly utilize two-dimensional substrates that lack the ability to support three-dimensional cell structures seen in vivo. As monolayer cell cultures have previously been shown to function differently than cells in vivo, the results of such in vitro tests may not accurately reflect cell response in vivo. It is therefore of interest to determine the relationships between substrate architecture, cell structure, and cell function in 3D cell-based platforms. To investigate the effect of substrate architecture on insulinoma organization and function, insulinomas were seeded onto 2D gelatin substrates and 3D fibrous gelatin scaffolds with three distinct fiber diameters and fiber densities. Cell viability and clustering was assessed at culture days 3, 5, and 7 with baseline insulin secretion and glucose-stimulated insulin production measured at day 7. Small, closely spaced gelatin fibers promoted the formation of large, rounded insulinoma clusters, whereas monolayer organization and large fibers prevented cell clustering and reduced glucose-stimulated insulin production. Taken together, these data show that scaffold properties can be used to control the organization and function of insulin-producing cells and may be useful as a 3D test bed for diabetes drug development.

Notch1 activation up-regulates pancreatic and duodenal homeobox-1

Transcription factor pancreatic and duodenal homeobox-1 (PDX-1) plays an essential role in pancreatic development, β-cell differentiation, maintenance of normal β-cell function and tumorigenesis. PDX-1 expression is tightly controlled through a variety of mechanisms under different cellular contexts. We report here that overexpression of Notch1 intracellular domain (NICD), an activated form of Notch1, enhanced PDX-1 expression in both PDX-1 stable HEK293 cells and mouse insulinoma β-TC-6 cells, while NICD shRNA inhibited the enhancing effect. NICD-enhanced PDX-1 expression was accompanied by increased insulin expression/secretion and cell proliferation in β-TC-6 cells, which was reversed by NICD shRNA. Cre activation-induced specific expression of NICD in islet β cells of transgenic β^NICD+/+ mice induced increased expression of PDX-1, insulin and proliferating cell nuclear antigen (PCNA) and decreased expression of p27 with accompanied fasting hyperinsulinemia and hypoglycemia and altered responses to intraperitoneal glucose tolerance test. Systemically delivered NICD shRNA suppressed islet expression of PDX-1 and reversed the hypoglycemia and hyperinsulinemia. Moreover, expression levels of NICD were correlated with those of PDX-1 in human pancreatic neuroendocrine tumor. Thus, Notch1 acts as a positive regulator for PDX-1 expression, cooperates with PDX-1 in the development of insulin overexpression and islet cell neoplasia and represents a potential therapeutic target for islet neoplasia.

Negative regulation of pancreatic and duodenal homeobox-1 by somatostatin receptor subtype 5

Somatostatin receptor subtype 5 (SSTR5) mediates the inhibitory effect of somatostatin and its analogs on insulin expression/secretion and islet cell proliferation. We provide biochemical and genetic evidence that SSTR5 exerted its physiological actions via down-regulating pancreatic and duodenal homeobox-1 (PDX-1), a β-cell-specific homeodomain-containing transcription factor. Cotransfection of SSTR5 with PDX-1 resulted in dose-dependent inhibition of PDX-1 expression in human embryonic kidney 293 cells. SSTR5 agonist RPL-1980 inhibited PDX-1 expression and abolished glucagon-like peptide 1-stimulated PDX-1 expression in mouse insulinoma β-TC-6 cells. SSTR5 knockdown by short hairpin RNA led to increased PDX-1 expression that was accompanied by enhanced insulin secretion stimulated by high glucose in β-TC6 cells and alternated expressions of cell cycle proteins that favor cell proliferation in mouse insulinoma MIN6 cells. Quantitative RT-PCR analysis showed that cotransfected SSTR5 inhibited PDX-1 mRNA expression, whereas knockdown of SSTR5 increased PDX-1 mRNA expression. In addition, we found that cotransfected wild-type SSTR5 increased PDX-1 ubiquitination in human embryonic kidney 293 cells, whereas SSTR5 P335L, a hypofunctional single nucleotide polymorphism of SSTR5, inhibited PDX-1 ubiquitination. SSTR5 knockout resulted in increased expression of PDX-1, insulin, and proliferating cell nuclear antigen in the islets of sstr(-/-) mice. Immunohistochemistry analysis showed that SSTR5 P335L was associated with elevated expression of PDX-1 in human pancreatic neuroendocrine tumor. Taken together, our studies demonstrated that SSTR5 is a negative regulator for PDX-1 expression and that SSTR5 may mediate the inhibitory effects of somatostatin and its analogs on insulin expression/secretion and cell proliferation via down-regulating PDX-1 at both transcriptional and posttranslational levels.

SSTR5 P335L monoclonal antibody differentiates pancreatic neuroendocrine neuroplasms with different SSTR5 genotypes

BACKGROUND

Somatostatin receptor type 5 (SSTR5) P335L is a hypofunctional, single nucleotide polymorphism of SSTR5 with implications in the diagnostics and therapy of pancreatic neuroendocrine neoplasms. The purpose of this study is to determine whether a SSTR5 P335L-specific monoclonal antibody could sufficiently differentiate pancreatic neuroendocrine neoplasms (PNENs) with different SSTR5 genotypes.

METHODS

Cellular proliferation rate, SSTR5 mRNA level, and SSTR5 protein level were measured by performing MTS assay, a quantitative reverse transcription polymerase chain reaction study, Western blot analysis, and immunohistochemistry, respectively. SSTR5 genotype was determined with the TaqMan SNP Genotyping assay (Applied Biosystems, Foster City, CA).

RESULTS

We found that the SSTR5 analogue RPL-1980 inhibited cellular proliferation of CAPAN-1 cells more than that of PANC-1 cells. Only PANC-1 (TT) cells, but not CAPAN-1 (CC) cells expressed SSTR5 P335L. In 29 white patients with PNENs, 38% had a TT genotype for SSTR5 P335L, 24% had a CC genotype for WT SSTR5, and 38% hada CT genotype for both SSTR5 P335L and WT SSTR5. Immunohistochemistry using SSTR5 P335L monoclonal antibody detected immunostaining signals only from the neuroendocrine specimens with TT and CT genotypes, but not those with CC genotypes.

CONCLUSION

A SSTR5 P335L monoclonal antibody that specifically recognizes SSTR5 P335L but not WT SSTR5 could differentiate PNENs with different SSTR5 genotypes, thereby providing a potential tool for the clinical diagnosis of PNEN.

Identification of somatostatin receptor type 5 gene polymorphisms associated with acromegaly

OBJECTIVE

The aim of this study was to characterize the genetic variance of somatostatin receptor 5 (SSTR5) and investigate the possible correlation of such variants with acromegaly risk and different disease characteristics.

DESIGN AND METHODS

The SSTR5 gene coding region and 2000 bp upstream region was sequenced in 48 patients with acromegaly and 96 control subjects. Further, three single nucleotide polymorphisms (SNPs) were analyzed in the same group of acromegaly patients and in an additional group of 475 age- and sex-matched controls.

RESULTS

In total, 19 SNPs were identified in the SSTR5 gene locus by direct sequencing. Three SNPs (rs34037914, rs169068, and rs642249) were significantly associated with the presence of acromegaly using the initial controls. The allele frequencies were significantly (P<0.01) different between the acromegaly patients and the additional large control group. rs34037914 and rs642249 remained significantly associated with acromegaly after Bonferroni correction and permutation tests (odds ratio (OR)=3.38; 95% confidence interval (CI), 1.78-6.42; P=0.00016 and OR=2.41; 95% CI, 1.41-4.13; P=0.0014 respectively). Haplotype reconstruction revealed two possible risk haplotypes determined by rs34037914 (633T) and rs642249 (1044A) alleles. Both haplotypes were found in significantly higher frequency in acromegaly patients compared with controls (P<0.001). In addition, the 663T allele was significantly associated with a younger age of acromegaly diagnosis (unstandardized regression coefficient β=-10.4; P=0.002), increased body mass index (β=4.1; P=0.004), higher number of adenoma resection (P<0.001) and lack of observable tumor shrinkage after somatostatin analog treatment (P=0.014).

CONCLUSIONS

Our results demonstrate a previously undetected strong association of two SSTR5 SNPs with acromegaly. The data also suggest a possible involvement of SSTR5 variants in decreased suppression of GH production and increased tumor proliferation.