Modulation of G Protein-Coupled Receptor Intracellular Trafficking and Signal Transduction

The seven transmembrane-spanning G Protein-coupled Receptor (GPCR) super family is the largest family of cell-surface receptors, comprising greater than 650 members. GPCRs represent the primary targets of most therapeutic drugs. Desensitization, endocytosis and recycling are major mechanisms of receptor regulation and intracellular trafficking of GPCRs is linked to the Rab family of small G proteins. In the present study, we examined whether multiple Rab GTPase regulate receptor trafficking through endosomal cellular compartments as a consequence of their direct association with GPCRs. We find that Rab4, Rab7 and Rab11 all bind to the last 10 amino acid residues of the angiotensin II Type 1 (AT1R) carboxyl-terminal tail. We show that the Rab GTPases compete with one another for receptor binding and that Rab4 effectively displaces Rab11 from the receptor. In contrast, Rab11 overexpression does not prevent Rab4 binding to the AT1R. Overexpression of wild-type Rab4, but not Rab11, facilitates AT1R dephosphorylation, and a constitutively active Rab4-Q67L mutant reduces AT1R desensitization and promotes AT1R resensitization. We also find that Rab8, a RabGTPase involved in the regulation of secretory/recycling vesicles, modulation of the actin cytoskeleton and cell polarity, interacts with the carboxyl-terminal tail of metabotropic glutamate receptor 1 (mGluR1a) and attenuates mGluR1a signalling and endocytosis in a protein kinase C-dependent manner. Finally, we have examined several previously uncharacterised but naturally occurring single nucleotide polymorphisms (SNPs) in mGluR1a that have been associated with cancer that may alter mGluR1a signalling. We find that SNPs found within the ligand binding domain of mGluR1a result in both decreased cell surface expression and basal inositol 1,4,5, trisphosphate formation and bias mGluR1a signalling via the ERK1/2 pathway. Additional mGluR1a SNPs localized to the mGluR1a glutamate binding site, intracellular regulatory domains and Homer binding site also result in changes in mGluR1a subcellular localization, signalling and cell morphology. Taken together, these results indicate that GPCR signalling is significantly modulated by the association of intracellular regulatory proteins that can be influenced by receptor structure

Pannexin 1 Influences Lineage Specification of Human iPSCs

Every single cell in the body communicates with nearby cells to locally organize activities with their neighbors and dysfunctional cell-cell communication can be detrimental during cell lineage commitment, tissue patterning and organ development. Pannexin channels (PANX1, PANX2, and PANX3) facilitate purinergic paracrine signaling through the passage of messenger molecules out of cells. PANX1 is widely expressed throughout the body and has recently been identified in human oocytes as well as 2 and 4-cell stage human embryos. Given its abundance across multiple adult tissues and its expression at the earliest stages of human development, we sought to understand whether PANX1 impacts human induced pluripotent stem cells (iPSCs) or plays a role in cell fate decisions. Western blot, immunofluorescence and flow cytometry reveal that PANX1 is expressed in iPSCs as well as all three germ lineages derived from these cells: ectoderm, endoderm, and mesoderm. PANX1 demonstrates differential glycosylation patterns and subcellular localization across the germ lineages. Using CRISPR-Cas9 gene ablation, we find that loss of PANX1 has no obvious impact on iPSC morphology, survival, or pluripotency gene expression. However, PANX1 gene knockout iPSCs exhibit apparent lineage specification bias under 3-dimensional spontaneous differentiation into the three germ lineages. Indeed, loss of PANX1 increases representation of endodermal and mesodermal populations in PANX1 knockout cells. Importantly, PANX1 knockout iPSCs are fully capable of differentiating toward each specific lineage when exposed to the appropriate external signaling pressures, suggesting that although PANX1 influences germ lineage specification, it is not essential to this process

Pharmacokinetics and safety of ixazomib plus lenalidomide–dexamethasone in Asian patients with relapsed/refractory myeloma: a phase 1 study

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A Phase 2 Study of Bortezomib in Relapsed, Refractory Myeloma

BACKGROUND Bortezomib, a boronic acid dipeptide, is a novel proteasome inhibitor that has been shown in preclinical and phase 1 studies to have antimyeloma activity. METHODS In this multicenter, open-label, nonrandomized, phase 2 trial, we enrolled 202 patients with relapsed myeloma that was refractory to the therapy they had received most recently. Patients received 1.3 mg of bortezomib per square meter of body-surface area twice weekly for 2 weeks, followed by 1 week without treatment, for up to eight cycles (24 weeks). In patients with a suboptimal response, oral dexamethasone (20 mg daily, on the day of and the day after bortezomib administration) was added to the regimen. The response was evaluated according to the criteria ofthe European Group for Blood and Marrow Transplantation and confirmed by an independent review committee. RESULTS Of 193 patients who could be evaluated, 92 percent had been treated with three or more ofthe major classes of agents for myeloma, and in 91 percent, the myeloma was refractory to the therapy received most recently. The rate of response to bortezomib was 35 percent, and those with a response included 7 patients in whom myeloma protein became undetectable and 12 in whom myeloma protein was detectable only by immuno-fixation. The median overall survival was 16 months, with a median duration of response of 12 months. Grade 3 adverse events included thrombocytopenia (in 28 percent of patients), fatigue (in 12 percent), peripheral neuropathy (in 12 percent), and neutropenia (in 11 percent). Grade 4 events occurred in 14 percent of patients. CONCLUSIONS Bortezomib, a member of a new class of anticancer drugs, is active in patients with relapsed multiple myeloma that is refractory to conventional chemotherapy

Local protein kinase A action proceeds through intact holoenzymes

Hormones can transmit signals through adenosine 3’,5’-monophosphate (cAMP) to precise intracellular locations. The fidelity of these responses relies on the activation of localized protein kinase A (PKA) holoenzymes. Association of PKA regulatory (RII) subunits with A-kinase anchoring proteins (AKAPs) confers location, and catalytic (C) subunits phosphorylate substrates. Single-particle electron microscopy demonstrated that AKAP79 constrains RII-C sub-assemblies within 150 to 250Å of its targets. Native mass spectrometry established that these macromolecular assemblies incorporated stoichiometric amounts of cAMP. Chemical-biology and live-cell imaging techniques revealed that catalytically active PKA holoenzymes remained intact within the cytoplasm. In contrast, little, if any PKA activity was detected in the nucleus. Hence the parameters of anchored PKA holoenzyme action are much more restricted than originally anticipated

A phase I and pharmacologic study of the combination of bortezomib and pegylated liposomal doxorubicin in patients with refractory solid tumors

Pre-clinical studies combining the proteasome inhibitor bortezomib with anthracyclines have shown enhanced anti-tumor activity. We therefore conducted a phase I trial of bortezomib and pegylated liposomal doxorubicin (PLD) in patients with refractory solid tumors

Bortezomib plus melphalan and prednisone in elderly untreated patients with multiple myeloma: updated time-to-events results and prognostic factors for time to progression

New treatment options offering enhanced activity in elderly, newly diagnosed patients with multiple myeloma are required. One strategy is to combine melphalan and prednisone with novel agents. We previously reported an 89% response rate, including 32% complete responses and 11% near complete responses, in our phase 1/2 study of bortezomib plus melphalan and prednisone (VMP) in 60 newly diagnosed multiple myeloma patients with a median age of 75 years. Here, we report updated time-to-events data and the impact of poor prognosis factors on outcome

Design and Characterization of a Human Monoclonal Antibody that Modulates Mutant Connexin 26 Hemichannels Implicated in Deafness and Skin Disorders

Background: Mutations leading to changes in properties, regulation, or expression of connexin-made channels have been implicated in 28 distinct human hereditary diseases. Eight of these result from variants of connexin 26 (Cx26), a protein critically involved in cell-cell signaling in the inner ear and skin. Lack of non-toxic drugs with defined mechanisms of action poses a serious obstacle to therapeutic interventions for diseases caused by mutant connexins. In particular, molecules that specifically modulate connexin hemichannel function without affecting gap junction channels are considered of primary importance for the study of connexin hemichannel role in physiological as well as pathological conditions. Monoclonal antibodies developed in the last three decades have become the most important class of therapeutic biologicals. Recombinant methods permit rapid selection and improvement of monoclonal antibodies from libraries with large diversity.Methods: By screening a combinatorial library of human single-chain fragment variable (scFv) antibodies expressed in phage, we identified a candidate that binds an extracellular epitope of Cx26. We characterized antibody action using a variety of biochemical and biophysical assays in HeLa cells, organotypic cultures of mouse cochlea and human keratinocyte-derived cells.Results: We determined that the antibody is a remarkably efficient, non-toxic, and completely reversible inhibitor of hemichannels formed by connexin 26 and does not affect direct cell-cell communication via gap junction channels. Importantly, we also demonstrate that the antibody efficiently inhibits hyperative mutant Cx26 hemichannels implicated in autosomal dominant non-syndromic hearing impairment accompanied by keratitis and hystrix-like ichthyosis-deafness (KID/HID) syndrome. We solved the crystal structure of the antibody, identified residues that are critical for binding and used molecular dynamics to uncover its mechanism of action.Conclusions: Although further studies will be necessary to validate the effect of the antibody in vivo, the methodology described here can be extended to select antibodies against hemichannels composed by other connexin isoforms and, consequently, to target other pathologies associated with hyperactive hemichannels. Our study highlights the potential of this approach and identifies connexins as therapeutic targets addressable by screening phage display libraries expressing human randomized antibodies