Structural basis for activation of somatostatin receptor 5 by cyclic neuropeptide agonists.

Somatostatin receptor 5 (SSTR5) is an important G protein-coupled receptor and drug target for neuroendocrine tumors and pituitary disorders. This study presents two high-resolution cryogenicelectron microscope structures of the SSTR5-Gi complexes bound to the cyclic neuropeptide agonists, cortistatin-17 (CST17) and octreotide, with resolutions of 2.7 Å and 2.9 Å, respectively. The structures reveal that binding of these peptides causes rearrangement of a "hydrophobic lock", consisting of residues from transmembrane helices TM3 and TM6. This rearrangement triggers outward movement of TM6, enabling Gαi protein engagement and receptor activation. In addition to hydrophobic interactions, CST17 forms conserved polar contacts similar to somatostatin-14 binding to SSTR2, while further structural and functional analysis shows that extracellular loops differently recognize CST17 and octreotide. These insights elucidate agonist selectivity and activation mechanisms of SSTR5, providing valuable guidance for structure-based drug development targeting this therapeutically relevant receptor.

Pituitary Adenoma: SSTR2 rs2236750, SSTR5 rs34037914, and AIP rs267606574 Genetic Variants, Serum Levels, and Ki-67 Labeling Index Associations.

Background and Objectives: This study explores the complex pathogenesis of pituitary adenomas (PAs), prevalent intracranial tumors in the pituitary gland. Despite their generally benign nature, PAs exhibit a diverse clinical spectrum involving hormone hypersecretion and varying invasiveness, hinting at multifaceted molecular mechanisms and abnormalities in tumorigenesis and gene regulation. Materials and Methods: The investigation focuses on the Ki-67 labeling index, SSTR2 rs2236750, SSTR5 rs34037914, and AIP rs267606574 polymorphisms, alongside serum levels of SSTR2, SSTR5, and AIP, to discern their association with PAs. The Ki-67 labeling index was assessed using immunohistochemical analysis with the monoclonal antibody clone SP6, representing the percentage of tumor cells showing positive staining. Genotyping was performed via real-time polymerase chain reaction, and serum levels were analyzed using ELISA. The study included 128 PA patients and 272 reference group subjects. Results: The results derived from binary logistic regression analysis revealed an intriguing correlation between the SSTR2 rs2236750 AG genotype and approximately a 1.6-fold increased likelihood of PA occurrence. When analyzing SSTR5 rs34037914, statistically significant differences were found between Micro-PA and the reference group (p = 0.022). Additionally, the SSTR5 rs34037914 TT genotype, compared with CC + CT, under the most robust genetic model (selected based on the lowest AIC value), was associated with a 12-fold increased odds of Micro-PA occurrence. However, it is noteworthy that after applying Bonferroni correction, these findings did not retain statistical significance. Conclusions: Consequently, while this study hinted at a potential link between SSTR2 rs2236750 and pituitary adenoma development, as well as a potential link between SSTR5 rs34037914 and Micro-PA development, it underscored the need for further analysis involving a larger cohort to robustly validate these findings.

Candidate Genes in Testing Strategies for Linkage Analysis and Bioinformatic Sorting of Whole Genome Sequencing Data in Three Small Japanese Families with Idiopathic Superior Oblique Muscle Palsy.

Idiopathic superior oblique muscle palsy is a major type of paralytic, non-comitant strabismus and presents vertical and cyclo-torsional deviation of one eye against the other eye, with a large vertical fusion range and abnormal head posture such as head tilt. Genetic background is considered to play a role in its development, as patients with idiopathic superior oblique muscle palsy have varying degrees of muscle hypoplasia and, rarely, the complete absence of the muscle, that is, aplasia. In this study, whole genome sequencing was performed, and single nucleotide variations and short insertions/deletions (SNVs/InDels) were annotated in two patients each in three small families (six patients in total) with idiopathic superior oblique muscle palsy, in addition to three normal individuals in one family. At first, linkage analysis was carried out in the three families and SNVs/InDels in chromosomal loci with negative LOD scores were excluded. Next, SNVs/InDels shared by the six patients, but not by the three normal individuals, were chosen. SNVs/InDels were further narrowed down by choosing low-frequency (<1%) or non-registered SNVs/InDels in four databases for the Japanese population, and then by choosing SNVs/InDels with functional influence, leading to one candidate gene, SSTR5-AS1 in chromosome 16. The six patients were heterozygous for 13-nucleotide deletion in SSTR5-AS1, except for one homozygous patient, while the three normal individuals were wild type. Targeted polymerase chain reaction (PCR) and direct sequencing of PCR products confirmed the 13-nucleotide deletion in SSTR5-AS1. In the face of newly-registered SSTR5-AS1 13-nucleotide deletion at a higher frequency in a latest released database for the Japanese population, the skipping of low-frequency and non-registration sorting still resulted in only 13 candidate genes including SSTR5-AS1 as common variants. The skipping of linkage analysis also led to the same set of 13 candidate genes. Different testing strategies that consisted of linkage analysis and simple unintentional bioinformatics could reach candidate genes in three small families with idiopathic superior oblique muscle palsy.

Long non-coding RNA SSTR5-AS1 facilitates gemcitabine resistance via stabilizing NONO in gallbladder carcinoma.

Gallbladder carcinoma (GBC) is the most aggressive carcinoma of the biliary tract, effective chemotherapy was critical for the patients with unresectable GBC. However, chemotherapy resistance is still problematic for clinicians. Here, we identified a specific long non-coding RNA, SSTR5-AS1, in GBC patient that facilitates gemcitabine resistance. SSTR5-AS1 is significantly increased in GBC samples and cell lines, especially in gemcitabine-resistant cell lines, and higher SSTR5-AS1 expression was correlated with poorer overall survival rate in GBC patients. Our data revealed that upregulated SSTR5-AS1 facilitates gemcitabine resistance via inhibiting apoptosis. Knockdown of SSTR5-AS1 sensitized drug resistant GBC cells to gemcitabine in vitro and strongly inhibited xenografts formed by drug resistant GBC cells in vivo. Moreover, we found via streptavidin pull down assay that NONO specifically binds to sense sequence of SSTR5-AS1 and prevented proteasome mediated NONO degradation, which resulted in increased NONO protein level without affecting the transcription of NONO. NONO functions as the downstream effector of SSTR5-AS1 and is required for SSTR5-AS1 mediated gemcitabine resistance. Collectively, our data provided novel insights into lncRNA-mediated chemotherapy resistance and suggested a novel therapeutic target to improve chemotherapy strategies for unresectable GBC patients.

Discovery of novel 5-oxa-2,6-diazaspiro[3.4]oct-6-ene derivatives as potent, selective, and orally available somatostatin receptor subtype 5 (SSTR5) antagonists for treatment of type 2 diabetes mellitus.

Somatostatin receptor subtype 5 (SSTR5) has emerged as a novel attractive drug target for type 2 diabetes mellitus. Starting from N-benzyl azetidine derivatives 1 and 2 as in-house hit compounds, we explored the introduction of a carboxyl group into the terminal benzene of 1 to enhance SSTR5 antagonistic activity by the combination of the substituents at the 3-position of the isoxazoline. Incorporation of a carboxyl group at the 4-position of the benzene ring resulted in a significant enhancement in potency, however, the 4-benzoic acid derivative 10c exhibited moderate human ether-a-go-go related gene (hERG) inhibitory activity. A subsequent optimization study revealed that replacement of the 4-benzoic acid with an isonipecotic acid dramatically reduced hERG inhibition (5.6% inhibition at 30µM) by eliminating π-related interaction with hERG K+ channel, which resulted in the identification of 1-(2-((2,6-diethoxy-4'-fluorobiphenyl-4-yl)methyl)-5-oxa-2,6-diazaspiro[3.4]oct-6-en-7-yl)piperidin-4-carboxylic acid 25a (hSSTR5/mSSTR5 IC50=9.6/57nM). Oral administration of 25a in high-fat diet fed C57BL/6J mice augmented insulin secretion in a glucose-dependent manner and lowered blood glucose concentration.

Discovery of novel somatostatin receptor subtype 5 (SSTR5) antagonists: Pharmacological studies and design to improve pharmacokinetic profiles and human Ether-a-go-go-related gene (hERG) inhibition.

Somatostatin (SST) is a peptide hormone comprising 14 or 28 amino acids that inhibits endocrine and exocrine secretion via five distinct G-protein-coupled receptors (SSTR1-5). SSTR5 has an important role in inhibiting the secretion of pancreatic and gastrointestinal hormones (e.g., insulin, GLP-1, PYY) through the binding of SSTs; hence, SSTR5 antagonists are expected to be novel anti-diabetic drugs. In the course of our lead generation program of SSTR5 antagonists, we have discovered a novel spiroazetidine derivative 3a. However, pharmacological evaluation of 3a revealed that it had to be administered at a high dose (100mg/kg) to show a persistent glucose-lowering effect in an oral glucose tolerance test (OGTT). We therefore initiated an optimization study based on 3a aimed at improving the antagonistic activity and mean residence time (MRT), resulting in the identification of 2-cyclopropyl-5-methoxybiphenyl derivative 3k. However, 3k did not show a sufficient persistent glucose-lowering effect in an OGTT; moreover, hERG inhibition was observed. Hence, further optimization study of the biphenyl moiety of compound 3k, focused on improving the pharmacokinetic (PK) profile and hERG inhibition, was conducted. Consequently, the introduction of a chlorine atom at the 6-position on the biphenyl moiety addressed a putative metabolic soft spot and increased the dihedral angle of the biphenyl moiety, leading to the discovery of 3p with an improved PK profile and hERG inhibition. Furthermore, 3p successfully exhibited a persistent glucose-lowering effect in an OGTT at a dose of 3mg/kg.

Theoretical analysis of somatostatin receptor 5 with antagonists and agonists for the treatment of neuroendocrine tumors.

We report on SSTR5 receptor modeling and its interaction with reported antagonist and agonist molecules. Modeling of the SSTR5 receptor was carried out using multiple templates with the aim of improving the precision of the generated models. The selective SSTR5 antagonists, agonists and native somatostatin SRIF-14 were employed to propose the binding site of SSTR5 and to identify the critical residues involved in the interaction of the receptor with other molecules. Residues Q2.63, D3.32, Q3.36, C186, Y7.34 and Y7.42 were found to be highly significant for their strong interaction with the receptor. SSTR5 antagonists were utilized to perform a 3D quantitative structure-activity relationship study. A comparative molecular field analysis (CoMFA) was conducted using two different alignment schemes, namely the ligand-based and receptor-based alignment methods. The best statistical results were obtained for ligand-based ([Formula: see text], [Formula: see text] = 0.988, noc = 4) and receptor-guided methods (docked mode 1:[Formula: see text], [Formula: see text], noc = 5), (docked mode 2:[Formula: see text] = 0.555, [Formula: see text], noc = 5). Based on CoMFA contour maps, an electropositive substitution at [Formula: see text], [Formula: see text] and [Formula: see text] position and bulky group at [Formula: see text] position are important in enhancing molecular activity.

Somatostatin regulates NHE8 protein expression via the ERK1/2 MAPK pathway in DSS-induced colitis mice.

Previous studies reported that administration of somatostatin (SST) to human patients mitigated their diarrheal symptoms. Octreotide (an analog of SST) treatment in animals resulted in upregulation of sodium/hydrogen exchanger 8 (NHE8). NHE8 is important for water/sodium absorption in the intestine, and loss of NHE8 function results in mucosal injury. Thus we hypothesized that NHE8 expression is inhibited during colitis and that SST treatment during pathological conditions can restore NHE8 expression. Our data showed for the first time that NHE8 is expressed in the human colonic tissue and that NHE8 expression is decreased in ulcerative colitis (UC) patients. We also found that octreotide could stimulate colonic NHE8 expression in colitic mice. Furthermore, the somatostatin receptor 2 (SSTR2) agonist seglitide and the somatostatin receptor 5 (SSTR5) agonist L-817,818 could restore NHE8 expression via its role in suppressing ERK1/2 phosphorylation. Our study uncovered a novel mechanism of SST stimulation of NHE8 expression in colitis.

Octreotide in combination with AT-101 induces cytotoxicity and apoptosis through up-regulation of somatostatin receptors 2 and 5 in DU-145 prostate cancer cells.

Prostate cancer (PCa) is the most common type of cancer among males. Although survival rate of early-stage PCa is high, treatment options are very limited for recurrent disease. In this study, the possible synergistic cytotoxic and apoptotic effect of octreotide in combination with AT-101 was investigated in DU-145 hormone and drug refractory prostate cancer cell line. To enlighten the action mechanisms of the combination treatment, expression levels of somatostatin receptors 2 and 5 (SSTR2 and SSTR5) were also investigated. Cell viability was measured by XTT assay. Apoptosis was assessed through DNA fragmentation analysis and caspase 3/7 assay. mRNA and protein levels of SSTR2 and SSTR5 were evaluated by qRT-PCR and western blot analysis, respectively. Octreotide in combination with AT-101 inhibited cell viability and induced apoptosis synergistically in DU-145 cells as compared to any agent alone. Combination treatment increased both SSTR2 and SSTR5 mRNA and protein levels in DU-145 cells. The data suggest that this combination therapy may be a good candidate for patients with advanced metastatic PCa do not respond to androgen deprivation.

Discovery and exploration of novel somatostatin receptor subtype 5 (SSTR5) antagonists for the treatment of cholesterol gallstones.

The shortage of cholesterol gallstones treatment intensifies the need to discover of effective small molecule drugs. Clinical follow-up and studies have found that activation of somatostatin receptor subtype 5 (SSTR5) reduce gallbladder contraction and thus increase the risk of cholesterol gallstones, implying that antagonizing SSTR5 may promote gallbladder emptying and reduce the formation of gallstones. Herein, we discovered novel SSTR5 antagonists and firstly investigated its effects on cholesterol gallstone. From loperamide, a reported seed structure with micromole activity, we identified optimal compound 23 as an SSTR5 antagonist exhibiting single-digit nanomolar potency, low hERG inhibition and oral availability. Further in vivo evaluation revealed that 23 significantly promoted gallbladder emptying. Moreover, in a mouse cholesterol gallstone model, 23 (3 mg/kg) effectively reduced the cholesterol gallstones formation, showing better efficacy than the clinical first-line drug UDCA (60 mg/kg), providing a new insight into the development of anti-gallstone drugs.

Efficacy of pasireotide LAR for acromegaly: a prolonged real-world monocentric study.

Background: Acromegaly is caused by excessive growth hormone (GH) and insulin-like growth factor 1 (IGF1). Medical therapy plays a role as a treatment option for persistent disease after non-curative surgery or as a first-line therapy when surgery is not feasible. Pasireotide-LAR (Pas-LAR) is recommended for patients with acromegaly as second-line treatment. Aim: To evaluate the patients characteristics predictive of an adequate response to Pas-LAR and the long-term efficacy and safety of the Pas-LAR treatment. Methods: Data from 19 patients with active acromegaly, who were and resistant or intolerant to first-line medical therapy and were switched to pas-LAR have been retrospectively collected. We compared the baseline clinical and biochemical characteristics of patients who were found to respond to Pas-LAR therapy (responders, n=14) with those of patients who did not respond (non-responders, n=5). We then evaluated the Pas-LAR efficacy and safety during long-term follow-up in responders. Results: IGF1 normalization occurred in 71.4% of responders after one injection. IGF1 levels, [median(interquartile range) of the upper limit of the normal range (ULN) fold increase] were higher in non-responders compared to responders within the initial month of therapy [1.40(1.30-2.34) vs 0.70(0.55-1.25), respectively, p=0.009] and after three [1.77(1.74-2.29) vs 0.94(0.82-1.13), respectively, p=0.029] and six months [1.68(1.33-1.72) vs 1.00(0.65 -1.28), respectively, p=0.002]. Out of 6 patients with symptomatic headache (all in responder group), 5 and 1 reported the resolution and improvement of headache, respectively, already after the first injection. Median HbA1c levels tended to increase from baseline to 6 months both in responder (36 mMol/Mol to 42 mMol/Mol) and non-responder patients (45 mMol/Mol to 48 mMol/Mol). During long term follow up, in the responder group 2 new patients developed diabetes. Tumor shrinkage was observed in 6 out of 7 evaluated responders, with no cases of size increase during the long-term follow-up. Conclusion: Pas-LAR is effective and safe and the early identification of responders is possible just after the first administration.

LncRNA SSTR5-AS1 promotes esophageal carcinoma through regulating ITGB6/JAK1/STAT3 signaling.

Aim: To investigate function of somatostatin receptor 5 antisense RNA 1 (SSTR5-AS1) in esophageal carcinoma (ESCA).Materials & methods: The cellular function was assessed using EdU staining and Transwell assay. The localization of SSTR5-AS1 was measured using fluorescence in situ hybridization staining.Results: SSTR5-AS1 shRNA repressed invasion and migration and induced apoptosis in ESCA cells. SSTR5-AS1 was distributed in cytoplasm, and it regulated its subunit integrin beta 6 (ITGB6) via eukaryotic translation initiation factor 4A3 (EIF4A3). SSTR5-AS1 shRNA inactivated ITGB6 and JAK1/STAT3 signaling. SSTR5-AS1 silencing attenuated the malignant behavior of ESCA cells through the ITGB6-mediated JAK1/STAT3 axis.Conclusion: SSTR5-AS1 promotes tumorigenesis of ESCA by interacting with EIF4A3 to regulate ITGB6/JAK1/STAT3 axis, which serves a basis for discovering strategies against ESCA.

The development of esophageal carcinoma (ESCA) seriously affects the health of people. Although great efforts have been made for curing ESCA, the outcomes remain limited. In this research, we used large amounts of experiments about the molecular biology. As expected, we found knockdown of lncRNA SSTR5-AS1 could inhibit the tumorigenesis of ESCA through mediation of its subunit integrin beta 6 /JAK1/STAT3 axis. Thus, our research provided new molecular targets for ESCA treatment.

Selective somatostatin receptor 5 inhibition improves hepatic insulin sensitivity.

Diabetes is a metabolic disorder with an increasing global prevalence. Somatostatin (SST), a peptide hormone, regulates hormone secretion via five SST receptor (SSTR) subtypes (SSTR1-5) in a tissue-specific manner. As SSTR5 is expressed in pancreatic ß-cells and intestinal L-cells, studies have suggested that SSTR5 regulates glucose tolerance through insulin and incretin secretion, thereby having a prominent role in diabetes. Moreover, SSTR5 knockout (KO) mice display enhanced insulin sensitivity; however, the underlying mechanism has not been clarified. Therefore, in this study, we investigate the effect of SSTR5 blockade on insulin resistance and the target organ using SSTR5 KO mice and a selective SSTR5 antagonist (compound-1). High-fat diet (HFD)-fed SSTR5 KO mice exhibited significantly lower homeostasis model assessment of insulin resistance (HOMA-IR) than HFD-fed wild-type mice. Two-week oral administration of compound-1 dose-dependently and significantly reduced changes in the levels of glycosylated hemoglobin (GHb), plasma glucose, plasma insulin, and HOMA-IR in male KK-Ay /Ta Jcl mice (KK-Ay mice), a model of obese type 2 diabetes with severe insulin resistance. Additionally, compound-1 significantly increased the glucose infusion rate while decreasing hepatic glucose production in male KK-Ay mice, as evidenced by hyperinsulinemic-euglycemic clamp analyses. In addition, compound-1 ameliorated the insulin-induced Akt phosphorylation suppression by octreotide in the liver of male C57BL/6J mice. Collectively, our results demonstrate that selective SSTR5 inhibition can improve insulin sensitivity by enhancing liver insulin action; thus, selective SSTR5 antagonists represent potentially novel therapeutic agents for type 2 diabetes.

Identification of SSTR5 Gene Polymorphisms and Their Association With Growth Traits in Hulun Buir Sheep.

The aim of this study was to locate SSTR5 polymorphisms and evaluate their association with growth traits in Hulun Buir sheep. The study followed up 884 Hulun Buir sheep from birth to 16 months of age, which were born in the same pasture and the same year, and a consistent grazing management strategy was maintained. The birth weight (BRW) was recorded at birth, and body weight (BW), body height (BH), body length (BL), chest circumference (ChC), chest depth (ChD), chest width (ChW), hip width (HW), and cannon circumference (CaC) were measured at 4 and 9 months of age. BW, BH, BL, ChD, HW, and CaC were also recorded at 16 months of age. Based on the growth traits, 233 sheep were selected as experimental animals. Sanger sequencing was performed, and seven single-nucleotide polymorphisms (SNPs) were identified. Association analyses of the SNPs and the growth traits were then conducted. Seven SNPs of the SSTR5 exhibited moderate polymorphism (0.25

Characterization of agonist-dependent somatostatin receptor subtype 2 trafficking in neuroendocrine cells.

BACKGROUND: Somatostatin (SOM) receptor subtype 2 (SSTR2) is the major receptor subtype mediating SOM effects throughout the neuraxis. We previously demonstrated that the non-selective agonist [D-Trp8]-SOM induces intracellular sequestration of SSTR2, whereas this receptor is maintained at the cell surface after treatment with the SSTR2-selective agonist L-779,976 in cells co-expressing SSTR2 and SSTR5. METHODS AND RESULTS: In this study, we knocked-out SSTR5 in AtT20 cells endogenously expressing both SSTR2 and SSTR5 and used immuno-labeling and confocal microscopy to investigate the effect of SSTR5 on regulation of SSTR2 trafficking. Our results indicate that unlike [D-Trp8]-SOM-induced intracellular sequestration, L-779,976 stimulation results in the maintenance of SSTR2 at the cell surface regardless of whether SSTR5 is present or not. We then examined the trafficking pathways of SSTR2 upon stimulation by either agonist. We found that both [D-Trp8]-SOM and L-779,976 induce SSTR2 internalization via transferrin-positive vesicles. However, SSTR2 internalized upon L-779,976 treatment undergoes rapid recycling to the plasma membrane, whereas receptors internalized by [D-Trp8]-SOM recycle slowly after washout of the agonist. Furthermore, [D-Trp8]-SOM stimulation induces degradation of a fraction of internalized SSTR2 whereas L-779,976-dependent, rapid SSTR2 recycling appears to protect internalized SSTR2 from degradation. In addition, Octreotide which has preferential SSTR2 affinity, induced differential effects on both SSTR2 trafficking and degradation. CONCLUSION: Our results indicate that the biased agonistic property of L-779,976 protects against SSTR2 surface depletion by rapidly initiating SSTR2 recycling while SSTR5 does not regulate L-779-976-dependent SSTR2 trafficking.

TSC2/PKD1 contiguous gene syndrome, with emphasis on a case with an atypical mild polycystic kidney phenotype and a novel genetic variant.

About 80% of patients with tuberous sclerosis complex (TSC) present renal involvement, usually as angiomyolipomas followed by cystic disease. An early diagnosis of polycystic kidney disease (PKD) in such patients is frequently related to the TSC2/PKD1 contiguous gene syndrome (PKDTS). Molecular confirmation of PKDTS is important for a prompt diagnosis, which can be complicated by the phenotypic heterogeneity of PKD and the absence of a clear phenotype-genotype correlation. Herein, we report three PKDTS pediatric patients. The case 3 did not present a classic PKDTS phenotype, having only one observable cyst on renal ultrasound at age 4 and multiple small cysts on magnetic resonance imaging at age 15. In this patient, chromosomal microarray analysis showed a gross deletion of 230.8kb that involved TSC2, PKD1 and 13 other protein-coding genes, plus a heterozygous duplication of a previously undescribed copy number variant of 242.9kb that involved six protein-coding genes, including SSTR5, in the 16p13.3 region. Given the observations that the case 3 presented the mildest renal phenotype, harbored three copies of SSTR5, and the reported inhibition of cystogenesis (specially in liver) observed with somatostatin analogs in some patients with autosomal dominant PKD, it can be hypothesized that other genetic factors as the gene dosage of SSTR5 may influence the PKD phenotype and the progression of the disease; however, future work is needed to examine this possibility.

Aberrant methylation-mediated downregulation of lncRNA SSTR5-AS1 promotes progression and metastasis of laryngeal squamous cell carcinoma.

BACKGROUND: Laryngeal squamous cell carcinoma (LSCC) is among the most common malignant tumors with poor prognosis. Accumulating evidences have identified the important roles of long noncoding RNAs (lncRNAs) in the initiation and progression of various cancer types; however, the global lncRNAs expression profile for metastatic LSCC is limited. RESULTS: In the present study, we screen expression profiles of lncRNAs in advanced LSCC patients with paired tumor tissues and corresponding normal tissues by microarrays. We identify numerous differentially expressed transcripts, and after the necessary verification of the transcripts expression in expanded samples, we experimentally validate the expression patterns of the remarkable low expressed gene, SSTR5, and its antisense lncRNA, SSTR5-AS1. Downregulation of SSTR5 is detected in LSCC tissues and laryngeal carcinoma cells. Aberrant DNA hypermethylation of the CpG sites clustered in the exon 1 and accumulation of inactive histone modifications at SSTR5 promoter region may be epigenetic mechanisms for its inactivation in LSCC. SSTR5-AS1 may play antitumor role in LSCC and may be regulated by the hypermethylation of the same CpG sites with SSTR5. SSTR5-AS1 inhibits laryngeal carcinoma cells proliferation, migration, and invasion. SSTR5-AS1 increases the enrichment of MLL3 and H3K4me3 at the promoter region of SSTR5 by interacting with MLL3 and further induces the transcription of SSTR5. Furthermore, SSTR5-AS1 interacts with and recruits TET1 to its target gene E-cadherin to activate its expression. CONCLUSION: These findings suggest that the identified lncRNAs and mRNAs may be potential biomarkers in metastatic LSCC, and SSTR5-AS1 may act as a tumor suppressor as well as a potential biomarker for antitumor therapy.

Frequent expression of somatostatin receptor 2a in olfactory neuroblastomas: a new and distinctive feature.

Olfactory neuroblastoma (ONB) is a malignant neuroendocrine neoplasm with a usually slow course, but with considerable recurrence rate. Many neuroendocrine tumors have shown good response to the treatment with somatostatin analogs and somatostatin radioreceptor therapy. In ONBs, there are scarce data on somatostatin-based treatment and the cellular expression of somatostatin receptors (SSTR), the prerequisite for binding and effect of somatostatin on normal and tumor cells. The aim of our study was to investigate the immunohistochemical expression of SSTR2A and SSTR5 in a cohort of 40 ONBs. In addition, tissue microarrays containing 40 high-grade sinonasal carcinomas as well as 6 sinonasal lymphomas, 3 rhabdomyosarcomas, and 3 Ewing sarcomas were evaluated. Volante system was applied for staining evaluation. Thirty cases (75%) were immunopositive for SSTR2A and 3 (7.5%) for SSTR5. Among the 30 SSTR2A-positive ONBs, 19 tumors (63.3%) scored 2+ and 11 (36.7%) scored 3+. All SSTR5-positive ONBs scored 2+. Neither sinonasal carcinomas nor sinonasal small round blue cell neoplasms expressed SSTR2A or SSTR5. The frequent expression of SSTR2A provides a rationale for radioreceptor diagnosis and therapy with SST analogs in ONBs. SSTR2A expression in ONBs is a helpful adjunct in the differential diagnosis of ONBs.

The predicted ensemble of low-energy conformations of human somatostatin receptor subtype 5 and the binding of antagonists.

Human somatostatin receptor subtype 5 (hSSTR5) regulates cell proliferation and hormone secretion. However, the identification of effective therapeutic small-molecule ligands is impeded because experimental structures are not available for any SSTR subtypes. Here, we predict the ensemble of low-energy 3D structures of hSSTR5 using a modified GPCR Ensemble of Structures in Membrane BiLayer Environment (GEnSeMBLE) complete sampling computational method. We find that this conformational ensemble displays most interhelical interactions conserved in class A G protein-coupled receptors (GPCRs) plus seven additional interactions (e.g., Y2.43-D3.49, T3.38-S4.53, K5.64-Y3.51) likely conserved among SSTRs. We then predicted the binding sites for a series of five known antagonists, leading to predicted binding energies consistent with experimental results reported in the literature. Molecular dynamics (MD) simulation of 50 ns in explicit water and lipid retained the predicted ligand-bound structure and formed new interaction patterns (e.g. R3.50-T6.34) consistent with the inactive µ-opioid receptor X-ray structure. We suggest more than six mutations for experimental validation of our prediction. The final predicted receptor conformations and antagonist binding sites provide valuable insights for designing new small-molecule drugs targeting SSTRs.