ERBB4 (HER4) is a member of the ERBB family of receptor tyrosine kinases, a family that includes the epidermal growth factor receptor (EGFR/ERBB1/HER1), ERBB2 (Neu/HER2), and ERBB3 (HER3). EGFR and ERBB2 are oncoproteins and validated targets for therapeutic intervention in a variety of solid tumors. In contrast, the role that ERBB4 plays in human malignancies is ambiguous. Thus, here we review the literature regarding ERBB4 function in human malignancies. We review the mechanisms of ERBB4 signaling with an emphasis on mechanisms of signaling specificity. In the context of this signaling specificity, we discuss the hypothesis that ERBB4 appears to function as a tumor suppressor protein and as an oncoprotein. Next, we review the literature that describes the role of ERBB4 in tumors of the bladder, liver, prostate, brain, colon, stomach, lung, bone, ovary, thyroid, hematopoietic tissues, pancreas, breast, skin, head, and neck. Whenever possible, we discuss the possibility that ERBB4 mutants function as biomarkers in these tumors. Finally, we discuss the potential roles of ERBB4 mutants in the staging of human tumors and how ERBB4 function may dictate the treatment of human tumors. Significance Statement This articles reviews ERBB4 function in the context of the mechanistic model that ERBB4 homodimers function as tumor suppressors, whereas ERBB4-EGFR or ERBB4-ERBB2 heterodimers act as oncogenes. Thus, this review serves as a mechanistic framework for clinicians and scientists to consider the role of ERBB4 and ERBB4 mutants in staging and treating human tumors.

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Alzheimer’s disease (AD) poses a critical public health challenge, and there is an urgent need for novel treatment options. Glutamate, the principal excitatory neurotransmitter in the human brain, plays a critical role in mediating cognitive and behavioral functions; and clinical symptoms in AD patients are highly correlated with the loss of glutamatergic synapses. In this review, we highlight how dysregulated glutamatergic mechanisms can underpin cognitive and behavioral impairments and contribute to the progression of AD via complex interactions with neuronal and neural network hyperactivity, Aβ, tau, glial dysfunction, and other disease-associated factors. We focus on the tripartite synapse, where glutamatergic neurotransmission occurs, and evidence elucidating how the tripartite synapse can be pathologically altered in AD. We also discuss promising therapeutic approaches that have the potential to rescue these deficits. These emerging data support the development of novel glutamatergic drug candidates as compelling approaches for treating AD.

Whereas recent clinical studies report metastatic melanoma survival rates high as 30–50%, many tumors remain nonresponsive or become resistant to current therapeutic strategies. Analyses of The Cancer Genome Atlas (TCGA) skin cutaneous melanoma (SKCM) data set suggests that a significant fraction of melanomas potentially harbor gain-of-function mutations in the gene that encodes for the ErbB4 receptor tyrosine kinase. In this work, a drug discovery strategy was developed that is based on the observation that the Q43L mutant of the naturally occurring ErbB4 agonist Neuregulin-2beta (NRG2β) functions as a partial agonist at ErbB4. NRG2β/Q43L stimulates tyrosine phosphorylation, fails to stimulate ErbB4-dependent cell proliferation, and inhibits agonist-induced ErbB4-dependent cell proliferation. Compounds that exhibit these characteristics likely function as ErbB4 partial agonists, and as such hold promise as therapies for ErbB4-dependent melanomas. Consequently, three highly sensitive and reproducible (Z’ > 0.5) screening assays were developed and deployed for the identification of small-molecule ErbB4 partial agonists. Six compounds were identified that stimulate ErbB4 phosphorylation, fail to stimulate ErbB4-dependent cell proliferation, and appear to selectively inhibit ErbB4-dependent cell proliferation. Whereas further characterization is needed to evaluate the full therapeutic potential of these molecules, this drug discovery platform establishes reliable and scalable approaches for the discovery of ErbB4 inhibitors.

It is known that deletion of the ectonucleotidase CD39 leads to liver insulin resistance in mice; however, it remains unknown whether this phenotype is due to a lack of extracellular adenosine generation or an excessive nucleotides accumulation and signaling. We hypothesized that the nucleotide P2Y2 receptor mediates insulin resistance in human hepatocytes. RT‐PCR showed that among the eight known P2Y receptors, only the P2Y2, P2Y6 and P2Y11 mRNAs were detected in cultured HepG2 cells, a human hepatocytes model; however, stimulation of the cells with P2Y6‐ and P2Y11‐selective agonists all failed to induce intracellular Ca2+ mobilization, whereas both ATP and UTP induced significant Ca2+ signaling in a dose‐dependent manner, which was abolished by pretreatment of the cells with ARC‐118925XX, a selective and competitive P2Y2 receptor antagonist, suggesting that the P2Y2 receptor is the only functional P2Y receptor expressed in HepG2 cells. In addition, we found that stimulation of the P2Y2 receptor induced MAPK signaling including phosphorylated ERK1/2, JNK and p38, but not the AKT pathway. Interestingly, stimulation of the cells with ATP or UTP dose‐dependently blocked insulin‐induced AKT phosphorylation, but potentiated ERK1/2 signaling, indicating a selective disruption of the insulin‐AKT signaling axis by P2Y2 receptor. Furthermore, we found that a notable release of ATP into the extracellular space was observed when exposing HepG2 cells to high glucose concentrations (25mM) as compared with normal glucose (6.1 mM). Consistent with this, we also found that extracellular nucleotides signaling through P2Y2 receptor induced a dose‐dependent reduction in hepatocyte glucose uptake. We conclude that the P2Y2 receptor mediates liver insulin resistance in response to hyperglycemia, possibly through activation of the JNK pathway and inhibition of insulin signaling to the AKT pathway, highlighting that P2Y2 receptor may be a new drug target for type‐2 diabetes. Support or Funding Information Supported in part by NIH funding 1R01HL125279‐01A1 (JS)

Lipids play an essential role in physiology. In addition to serving as an energy source, bioactive lipids, also known as lipokines, function as signaling molecules regulating metabolism and inflammation. A major source of lipokines, brown adipose tissue (BAT) has been shown to have beneficial effects on cardiometabolic health by increasing energy expenditure and improving glucose tolerance, thus providing a potential target for therapeutic interventions. Recent studies have identified 12,13-dihydroxy-9Z-octadecenoic acid (12,13-diHOME, produced by cytochrome P450-epoxide hydrolase metabolism of linoleic acid (C18:2n-6), as a lipokine produced by BAT that modulates fatty acid uptake (FAU) into brown adipocytes and skeletal muscle cells in response to cold stimulation or exercising, respectively. Here, we characterized the molecular mechanism and structure-activity relationship (SAR) of 12,13-diHOME in BAT fatty acid uptake. Conversion of the terminal carboxylic acid of 12,13-diHOME to ethyl acetate and changes in saturation results in decreased stimulated FAU indicating 12,13-diHOME's activity is structurally dependent. In addition, we provide insight into a novel protein target responsible for enhancing FAU in BAT, in part, by enhancing intracellular calcium mobilization and influencing the expression of lipolytic genes. Furthermore, we have determined that the 12,13-diHOME-stimulated FAU is, in part, dependent on Gq-mediated calcium mobilization as determined by the utilization of Gq inhibitor YM-254890. Thus, the receptor of 12,13-diHOME could represent a target to augment BAT activity by modulating fatty acid metabolism, which could contribute to increased energy expenditure and, consequently, to the prevention of cardiometabolic diseases. Disclosure J.I.Senfeld: None. M.Lynes: None. S.Kodani: None. K.Lee: None. Y.Tseng: Consultant; Cellarity, LyGenesis.

Metformin, created in 1922, has been the first-line medication treating type 2 diabetes mellitus for almost 70 years; however, its mechanism of action has been heavily debated, partly because most prior studies used supratherapeutic concentrations exceeding 1mM. Here we report that at a clinically relevant concentration of 10 μM, metformin blocks high glucose-stimulated ATP secretion from hepatocytes mediating its antihyperglycemic action. Following glucose administration, mice demonstrate increased circulating ATP concentrations, which are prevented by metformin. Extracellular ATP through P2Y2 receptors (P2Y2R) compromises insulin-induced AKT activation and increases hepatic glucose production. In addition, metformin-dependent improvement in glucose tolerance is abolished in P2Y2R-null mice. Thus, removing the target of extracellular ATP, P2Y2R, mimics the effects of metformin, revealing a novel purinergic antidiabetic mechanism for metformin.

Introduction: Gain-of-function mutations in the ErbB4 receptor tyrosine kinase have been found in a significant fraction of melanoma cell lines that are dependent on ErbB4 for proliferation. However, there is a scarcity of therapeutics for treating these ErbB4-dependent tumors. Consequently, we have developed high-throughput screening assays to identify small molecule ErbB4 antagonists that may hold promise as targeted melanoma therapeutics. Our approach is based on the observation that the Q43L mutant of the ErbB4 agonist Neuregulin 2beta (NRG2b) functions as a partial agonist at ErbB4. NRG2b/Q43L stimulates ErbB4 tyrosine phosphorylation, fails to stimulate ErbB4-dependent cell proliferation, and competitively antagonizes agonist stimulation of ErbB4-dependent cell proliferation. Experimental procedures: Therefore, we have developed three high-throughput screening assays to identify ErbB4 partial agonists that function as antagonists. The primary screen identifies molecules that stimulate ErbB4 tyrosine phosphorylation. The secondary screen identifies molecules that stimulate or fail to stimulate ErbB4-dependent cell proliferation. The tertiary screen identifies molecules that antagonize agonist stimulation of ErbB4-dependent cell proliferation. Results: A phospho-ErbB4 sandwich ELISA assay identifies molecules that stimulate ErbB4 tyrosine phosphorylation with high sensitivity and fidelity (Z’ >0.5). IL3-independence assays in conjunction with MTT assays using a cell line that displays ErbB4-dependent cell proliferation distinguish between molecules that stimulate and fail to stimulate ErbB4-dependent proliferation (Z’>0.5) and identify molecules that antagonize agonist stimulation of ErbB4 dependent proliferation. These assays have been used to identify small molecules that stimulate ErbB4 tyrosine phosphorylation. Efforts to determine whether these hits function as ErbB4 full agonists or partial agonists (antagonists) are underway and will be reported. Structures of these small molecule ErbB4 full and partial agonists may be reported, pending submission of a provisional patent application. Conclusions: We have validated an HTS strategy for identifying ErbB4 partial agonists that function as ErbB4 antagonists and deployment of that strategy has led to the identification of several hits (~20 from the primary screen). Such molecules may hold promise as targeted therapeutics for melanoma and other ErbB4-dependent tumors. Citation Format: Richard L. Cullum, John T. Piazza, Jared I. Senfeld, Logan T. Neel, Ram B. Gupta, Allan E. David, David J. Riese. Screening methodologies for the discovery of small molecule melanoma therapeutics targeted at the ErbB4 receptor tyrosine kinase [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1245. doi:10.1158/1538-7445.AM2017-1245