The ric-8b protein (resistance to inhibitors of cholinesterase 8b) is key to preserving contractile function in the adult heart.

Resistance to inhibitors of cholinesterases (ric-8 proteins) are involved in modulating G-protein function, but little is known of their potential physiological importance in the heart. In the present study, we assessed the role of resistance to inhibitors of cholinesterase 8b (Ric-8b) in determining cardiac contractile function. We developed a murine model in which it was possible to conditionally delete ric-8b in cardiac tissue in the adult animal after the addition of tamoxifen. Deletion of ric-8b led to severely reduced contractility as measured using echocardiography days after administration of tamoxifen. Histological analysis of the ventricular tissue showed highly variable myocyte size, prominent fibrosis, and an increase in cellular apoptosis. RNA sequencing revealed transcriptional remodeling in response to cardiac ric-8b deletion involving the extracellular matrix and inflammation. Phosphoproteomic analysis revealed substantial downregulation of phosphopeptides related to myosin light chain 2. At the cellular level, the deletion of ric-8b led to loss of activation of the L-type calcium channel through the ß-adrenergic pathways. Using fluorescence resonance energy transfer-based assays, we showed ric-8b protein selectively interacts with the stimulatory G-protein, Gαs. We explored if deletion of Gnas (the gene encoding Gαs) in cardiac tissue using a similar approach in the mouse led to an equivalent phenotype. The conditional deletion of the Gαs gene in the ventricle led to comparable effects on contractile function and cardiac histology. We conclude that ric-8b is essential to preserve cardiac contractile function likely through an interaction with the stimulatory G-protein and downstream phosphorylation of myosin light chain 2.

c-MET inhibition: novel treatment for sporadic and MEN1-associated GEP NETs.

Gastroenteropancreatic neuroendocrine tumors (GEP NETs) comprise a heterogenous and diverse group of neoplasms arising from a common neuroendocrine cell origin. The majority of these tumors occur sporadically while ~20% manifest within the context of hereditary syndromes. Germline MEN1 mutations cause a syndrome with an increased susceptibility to multifocal primary GEP NETs. In addition, somatic MEN1 mutations also occur in these sporadic lesions. MEN1 alterations are the most frequent somatic mutation found in pancreatic neuroendocrine tumors. In this review, we explore the implication of the loss of the MEN1-encoded protein menin as a key pathogenic driver in subsets of GEP NETs with downstream consequences including upregulation of the oncogenic receptor c-MET (hepatocyte growth factor receptor). Furthermore, the review will summarize the data related to the clinical presentation, therapeutic standards, and outcomes of these tumors in both sporadic and germline MEN1 mutation-associated contexts. Finally, we present the data on c-MET expression in GEP NETs, clinical trials using c-MET inhibitors and provide an overview of the molecular mechanisms by which c-MET inhibition in these lesions represents a potential precision-medicine targeted approach.

Distinct DNA Methylation Signatures in Neuroendocrine Tumors Specific for Primary Site and Inherited Predisposition.

PURPOSE: To compare the deoxyribonucleic acid (DNA) methylation signature of neuroendocrine tumors (NETs) by primary tumor site and inherited predisposition syndromes von Hippel-Lindau disease (VHL) and multiple endocrine neoplasia type 1 (MEN1). METHODS: Genome-wide DNA methylation (835 424 CpGs) of 96 NET samples. Principal components analysis (PCA) and unsupervised hierarchical clustering analyses were used to determine DNA methylome signatures. RESULTS: Hypomethylated CpGs were significantly more common in VHL-related versus sporadic and MEN1-related NETs (P < .001 for both comparisons). Small-intestinal NETs (SINETs) had the most differentially methylated CpGs, either hyper- or hypomethylated, followed by duodenal NETs (DNETs) and pancreatic NETs (PNETs, P < .001 for all comparisons). There was complete separation of SINETs on PCA, and 3 NETs of unknown origin clustered with the SINET samples. Sporadic, VHL-related, and MEN1-related PNETs formed distinct groups on PCA, and VHL clustered separately, showing pronounced DNA hypomethylation, while sporadic and MEN1-related NETs clustered together. MEN1-related PNETs, DNETs, and gastric NETs each had a distinct DNA methylome signature, with complete separation by PCA and unsupervised clustering. Finally, we identified 12 hypermethylated CpGs in the 1A promoter of the APC (adenomatous polyposis coli) gene, with higher methylation levels in MEN1-related NETs versus VHL-related and sporadic NETs (P < .001 for both comparisons). CONCLUSIONS: DNA CpG methylation profiles are unique in different primary NET types even when occurring in MEN1-related NETs. This tumor DNA methylome signature may be utilized for noninvasive molecular characterization of NETs, through DNA methylation profiling of biopsy samples or even circulating tumor DNA in the near future.