Daple is a novel non-receptor GEF required for trimeric G protein activation in Wnt signaling

Going Rogue: Mechanisms, Regulation, and Roles of Mutationally Activated Gα in Human Cancer

G protein-coupled receptors (GPCRs) couple to heterotrimeric G proteins, comprised of α and βγ subunits, to convert extracellular signals into activation of intracellular signaling pathways. Canonically, GPCR-mediated activation results in the exchange of GDP for GTP on G protein α subunits (Gα) and the dissociation of Gα-GTP and G protein βγ subunits (Gβγ), both of which can regulate a variety of signaling pathways. Hydrolysis of bound GTP by Gα returns the protein to Gα-GDP and allows reassociation with Gβγ to reform the inactive heterotrimer. Naturally occurring mutations in Gα have been found at conserved glutamine and arginine amino acids that disrupt the canonical G protein cycle by inhibiting GTP hydrolysis, rendering these mutants constitutively active. Interestingly, these dysregulated Gα mutants are found in many different cancers due to their ability to sustain aberrant signaling without a need for activation by GPCRs. This review will highlight an increased recognition of the prevalence of such constitutively activating Gα mutations in cancers and the signaling pathways activated. In addition, we will discuss new knowledge regarding how these constitutively active Gα are regulated, how different mutations are biochemically distinct, and how mutationally activated Gα are unique compared with GPCR-activated Gα Lastly, we will discuss recent progress in developing inhibitors directly targeting constitutively active Gα mutants. SIGNIFICANCE STATEMENT: Constitutively activating mutations in G protein α subunits (Gα) widely occur in and contribute to the development of many human cancers. To develop ways to inhibit dysregulated, oncogenic signaling by these mutant Gα, it is crucial to better understand mechanisms that lead to constitutive Gα activation and unique mechanisms that regulate mutationally activated Gα in cells. The prevalence of activating mutations in Gα in various cancers makes Gα proteins compelling targets for the development of therapeutics.

International Union of Basic and Clinical Pharmacology CXV: The Class F of G Protein-Coupled Receptors

The class F of G protein-coupled receptors (GPCRs) consists of 10 Frizzleds (FZD1-10) and Smoothened (SMO). FZDs bind and are activated by secreted lipoglycoproteins of the Wingless/Int-1 (WNT) family, and SMO is indirectly activated by the Hedgehog (Hh) family of morphogens acting on the transmembrane protein Patched. The advance of our understanding of FZDs and SMO as dynamic transmembrane receptors and molecular machines, which emerged during the past 14 years since the first-class F GPCR IUPHAR nomenclature report, justifies an update. This article focuses on the advances in molecular pharmacology and structural biology providing new mechanistic insight into ligand recognition, receptor activation mechanisms, signal initiation, and signal specification. Furthermore, class F GPCRs continue to develop as drug targets, and novel technologies and tools such as genetically encoded biosensors and CRISP/Cas9 edited cell systems have contributed to refined functional analysis of these receptors. Also, advances in crystal structure analysis and cryogenic electron microscopy contribute to the rapid development of our knowledge about structure-function relationships, providing a great starting point for drug development. Despite the progress, questions and challenges remain to fully understand the complexity of the WNT/FZD and Hh/SMO signaling systems. SIGNIFICANCE STATEMENT: The recent years of research have brought about substantial functional and structural insight into mechanisms of activation of Frizzleds and Smoothened. While the advance furthers our mechanistic understanding of ligand recognition, receptor activation, signal specification, and initiation, broader opportunities emerge that allow targeting class F GPCRs for therapy and regenerative medicine employing both biologics and small molecule compounds.

Wnt7b acts in concert with Wnt5a to regulate tissue elongation and planar cell polarity via noncanonical Wnt signaling

Intercellular signaling mediated by evolutionarily conserved planar cell polarity (PCP) proteins aligns cell polarity along the tissue plane and drives polarized cell behaviors during tissue morphogenesis. Accumulating evidence indicates that the vertebrate PCP pathway is regulated by noncanonical, β-catenin-independent Wnt signaling; however, the signaling components and mechanisms are incompletely understood. In the mouse hearing organ, both PCP and noncanonical Wnt (ncWnt) signaling are required in the developing auditory sensory epithelium to control cochlear duct elongation and planar polarity of resident sensory hair cells (HCs), including the shape and orientation of the stereociliary hair bundle essential for sound detection. We have recently discovered a Wnt/G-protein/PI3K pathway that coordinates HC planar polarity and intercellular PCP signaling. Here, we identify Wnt7b as a ncWnt ligand acting in concert with Wnt5a to promote tissue elongation in diverse developmental processes. In the cochlea, Wnt5a and Wnt7b are redundantly required for cochlear duct coiling and elongation, HC planar polarity, and asymmetric localization of core PCP proteins Fzd6 and Dvl2. Mechanistically, Wnt5a/Wnt7b-mediated ncWnt signaling promotes membrane recruitment of Daple, a nonreceptor guanine nucleotide exchange factor for Gαi, and activates PI3K/AKT and ERK signaling, which promote asymmetric Fzd6 localization. Thus, ncWnt and PCP signaling pathways have distinct mutant phenotypes and signaling components, suggesting that they act as separate, parallel pathways with nonoverlapping functions in cochlear morphogenesis. NcWnt signaling drives tissue elongation and reinforces intercellular PCP signaling by regulating the trafficking of PCP-specific Frizzled receptors.

CCDC88C, an O-GalNAc glycosylation substrate of GALNT6, drives breast cancer metastasis by promoting c-JUN-mediated CEMIP transcription

Coiled-coil domain containing 88C (CCDC88C) is a component of non-canonical Wnt signaling, and its dysregulation causes colorectal cancer metastasis. Dysregulated expression of CCDC88C was observed in lymph node metastatic tumor tissues of breast cancer. However, the role of CCDC88C in breast cancer metastasis remains unclear. To address this, the stable BT549 and SKBR3 cell lines with CCDC88C overexpression or knockdown were developed. Loss/gain-of-function experiments suggested that CCDC88C drove breast cancer cell motility in vitro and lung and liver metastasis in vivo. We found that CCDC88C led to c-JUN-induced transcription activation. Overlapping genes were identified from the genes modulated by CCDC88C and c-JUN. CEMIP, one of these overlapping genes, has been confirmed to confer breast cancer metastasis. We found that CCDC88C regulated CEMIP mRNA levels via c-JUN and it exerted pro-metastatic capabilities in a CEMIP-dependent manner. Moreover, we identified the CCDC88C as a substrate of polypeptide N-acetylgalactosaminyltransferase 6 (GALNT6). GALNT6 was positively correlated with CCDC88C protein abundance in the normal breast and breast cancer tissues, indicating that GALNT6 might be associated with expression patterns of CCDC88C in breast cancer. Our data demonstrated that GALNT6 maintained CCDC88C stability by promoting its O-linked glycosylation, and the modification was critical for the pro-metastatic potential of CCDC88C. CCDC88C also could mediate the pro-metastatic potential of GALNT6 in breast cancer. Collectively, our findings uncover that CCDC88C may increase the risk of breast cancer metastasis and elucidate the underlying molecular mechanisms.

Mechanistic insights into G-protein activation via phosphorylation mediated non-canonical pathway

Activation of heterotrimeric G-proteins (Gαβγ) downstream to receptor tyrosine kinases (RTKs) is a well-established crosstalk between the signaling pathways mediated by G-protein coupled receptors (GPCRs) and RTKs. While GPCR serves as a guanine exchange factor (GEF) in the canonical activation of Gα that facilitates the exchange of GDP for GTP, the mechanism through which RTK phosphorylations induce Gα activation remains unclear. Recent experimental studies revealed that the epidermal growth factor receptor (EGFR), a well-known RTK, phosphorylates the helical domain tyrosine residues Y154 and Y155 and accelerates the GDP release from the Gαi3, a subtype of Gα-protein. Using well-tempered metadynamics and extensive unbiased molecular dynamics simulations, we captured the GDP release event and identified the intermediates between bound and unbound states through Markov state models. In addition to weakened salt bridges at the domain interface, phosphorylations induced the unfolding of helix αF, which contributed to increased flexibility near the hinge region, facilitating a greater distance between domains in the phosphorylated Gαi3. Although the larger domain separation in the phosphorylated system provided an unobstructed path for the nucleotide, the accelerated release of GDP was attributed to increased fluctuations in several conserved regions like P-loop, switch 1, and switch 2. Overall, this study provides atomistic insights into the activation of G-proteins induced by RTK phosphorylations and identifies the specific structural motifs involved in the process. The knowledge gained from the study could establish a foundation for targeting non-canonical signaling pathways and developing therapeutic strategies against the ailments associated with dysregulated G-protein signaling.

Prognostic value of CD8+T cells related genes and exhaustion regulation of Notch signaling pathway in hepatocellular carcinoma

Immunotherapy has emerged as the primary treatment modality for patients with advanced Hepatocellular carcinoma (HCC). However, its clinical efficacy remains limited, benefiting only a subset of patients, while most exhibit immune tolerance and face a grim prognosis. The infiltration of immune cells plays a pivotal role in tumor initiation and progression. In this study, we conducted an analysis of immune cell infiltration patterns in HCC patients and observed a substantial proportion of CD8+T cells. Leveraging the weighted gene co-expression network analysis (WGCNA), we identified 235 genes associated with CD8+T cell and constructed a risk prediction model. In this model, HCC patients were stratified into a high-risk and low-risk group. Patients in the high-risk group exhibited a lower survival rate, predominantly presented with intermediate to advanced stages of cancer, displayed compromised immune function, showed limited responsiveness to immunotherapy, and demonstrated elevated expression levels of the Notch signaling pathway. Further examination of clinical samples demonstrated an upregulation of the Notch1+CD8+T cell exhaustion phenotype accompanied by impaired cytotoxicity and cytokine secretion functions that worsened with increasing Notch activation levels. Our study not only presents a prognostic model but also highlights the crucial involvement of the Notch pathway in CD8+T cell exhaustion-a potential target for future immunotherapeutic interventions.

Non-canonical G protein signaling

The original paradigm of classical - also referred to as canonical - cellular signal transduction of heterotrimeric G proteins (G protein) is defined by a hierarchical, orthograde interaction of three players: the agonist-activated G protein-coupled receptor (GPCR), which activates the transducing G protein, that in turn regulates its intracellular effectors. This receptor-transducer-effector concept was extended by the identification of regulators and adapters such as the regulators of G protein signaling (RGS), receptor kinases like βARK, or GPCR-interacting arrestin adapters that are integrated into this canonical signaling process at different levels to enable fine-tuning. Finally, the identification of atypical signaling mechanisms of classical regulators, together with the discovery of novel modulators, added a new and fascinating dimension to the cellular G protein signal transduction. This heterogeneous group of accessory G protein modulators was coined "activators of G protein signaling" (AGS) proteins and plays distinct roles in canonical and non-canonical G protein signaling pathways. AGS proteins contribute to the control of essential cellular functions such as cell development and division, intracellular transport processes, secretion, autophagy or cell movements. As such, they are involved in numerous biological processes that are crucial for diseases, like diabetes mellitus, cancer, and stroke, which represent major health burdens. Although the identification of a large number of non-canonical G protein signaling pathways has broadened the spectrum of this cellular communication system, their underlying mechanisms, functions, and biological effects are poorly understood. In this review, we highlight and discuss atypical G protein-dependent signaling mechanisms with a focus on inhibitory G proteins (Gi) involved in canonical and non-canonical signal transduction, review recent developments and open questions, address the potential of new approaches for targeted pharmacological interventions.

Heterotrimeric G protein signaling without GPCRs: The Gα-binding-and-activating (GBA) motif

Heterotrimeric G proteins (Gαβγ) are molecular switches that relay signals from 7-transmembrane receptors located at the cell surface to the cytoplasm. The function of these receptors is so intimately linked to heterotrimeric G proteins that they are named G protein-coupled receptors (GPCRs), showcasing the interdependent nature of this archetypical receptor-transducer axis of transmembrane signaling in eukaryotes. It is generally assumed that activation of heterotrimeric G protein signaling occurs exclusively by the action of GPCRs, but this idea has been challenged by the discovery of alternative mechanisms by which G proteins can propagate signals in the cell. This review will focus on a general principle of G protein signaling that operates without the direct involvement of GPCRs. The mechanism of G protein signaling reviewed here is mediated by a class of G protein regulators defined by containing an evolutionarily conserved sequence named the Gα-binding-and-activating (GBA) motif. Using the best characterized proteins with a GBA motif as examples, Gα-interacting vesicle-associated protein (GIV)/Girdin and dishevelled-associating protein with a high frequency of leucine residues (DAPLE), this review will cover (i) the mechanisms by which extracellular cues not relayed by GPCRs promote the coupling of GBA motif-containing regulators with G proteins, (ii) the structural and molecular basis for how GBA motifs interact with Gα subunits to facilitate signaling, (iii) the relevance of this mechanism in different cellular and pathological processes, including cancer and birth defects, and (iv) strategies to manipulate GBA-G protein coupling for experimental therapeutics purposes, including the development of rationally engineered proteins and chemical probes.

Synaptic plasticity via receptor tyrosine kinase/G-protein-coupled receptor crosstalk

Cellular signaling involves a large repertoire of membrane receptors operating in overlapping spatiotemporal regimes and targeting many common intracellular effectors. However, both the molecular mechanisms and the physiological roles of crosstalk between receptors, especially those from different superfamilies, are poorly understood. We find that the receptor tyrosine kinase (RTK) TrkB and the G-protein-coupled receptor (GPCR) metabotropic glutamate receptor 5 (mGluR5) together mediate hippocampal synaptic plasticity in response to brain-derived neurotrophic factor (BDNF). Activated TrkB enhances constitutive mGluR5 activity to initiate a mode switch that drives BDNF-dependent sustained, oscillatory Ca2+ signaling and enhanced MAP kinase activation. This crosstalk is mediated, in part, by synergy between Gβγ, released by TrkB, and Gαq-GTP, released by mGluR5, to enable physiologically relevant RTK/GPCR crosstalk.

Rapamycin as a Potential Alternative Drug for Squamous Cell Gingiva Carcinoma (Ca9-22): A Focus on Cell Cycle, Apoptosis and Autophagy Genetic Profile

Oral cancer is considered as one of the most common malignancies worldwide. Its conventional treatment primarily involves surgery with or without postoperative adjuvant therapy. The targeting of signaling pathways implicated in tumorigenesis is becoming increasingly prevalent in the development of new anticancer drug candidates. Based on our recently published data, Rapamycin, an inhibitor of the mTOR pathway, exhibits selective antitumor activity in oral cancer by inhibiting cell proliferation and inducing cancer cell apoptosis, autophagy, and cellular stress. In the present study, our focus is on elucidating the genetic determinants of Rapamycin's action and the interaction networks accountable for tumorigenesis suppression. To achieve this, gingival carcinoma cell lines (Ca9-22) were exposed to Rapamycin at IC50 (10 µM) for 24 h. Subsequently, we investigated the genetic profiles related to the cell cycle, apoptosis, and autophagy, as well as gene-gene interactions, using QPCR arrays and the Gene MANIA website. Overall, our results showed that Rapamycin at 10 µM significantly inhibits the growth of Ca9-22 cells after 24 h of treatment by around 50% by suppression of key modulators in the G2/M transition, namely, Survivin and CDK5RAP1. The combination of Rapamycin with Cisplatin potentializes the inhibition of Ca9-22 cell proliferation. A P1/Annexin-V assay was performed to evaluate the effect of Rapamycin on cell apoptosis. The results obtained confirm our previous findings in which Rapamycin at 10 μM induces a strong apoptosis of Ca9-22 cells. The live cells decreased, and the late apoptotic cells increased when the cells were treated by Rapamycin. To identify the genes responsible for cell apoptosis induced by Rapamycin, we performed the RT2 Profiler PCR Arrays for 84 apoptotic genes. The blocked cells were believed to be directed towards cell death, confirmed by the downregulation of apoptosis inhibitors involved in both the extrinsic and intrinsic pathways, including BIRC5, BNIP3, CD40LG, DAPK1, LTA, TNFRSF21 and TP73. The observed effects of Rapamycin on tumor suppression are likely to involve the autophagy process, evidenced by the inhibition of autophagy modulators (TGFβ1, RGS19 and AKT1), autophagosome biogenesis components (AMBRA1, ATG9B and TMEM74) and autophagy byproducts (APP). Identifying gene-gene interaction (GGI) networks provided a comprehensive view of the drug's mechanism and connected the studied tumorigenesis processes to potential functional interactions of various kinds (physical interaction, co-expression, genetic interactions etc.). In conclusion, Rapamycin shows promise as a clinical agent for managing Ca9-22 gingiva carcinoma cells.

BTB protein family and human breast cancer: signaling pathways and clinical progress

BACKGROUND

Breast cancer is considered the number one killer of women both in China and abroad, and the leading cause of cancer death. It severely affects female health-related quality of life. Broad-complex, tramtrack, bric à brac (BTB) protein family was first discovered in drosophila as early as in 1993 by Godt D and peers, since then, more family members and their critical biological functions were uncovered. Moreover, researchers around the world have recently demonstrated that numerous signaling pathways connect BTB family members and human breast cancer.

PURPOSE

In this review, we critically discuss these findings regarding the essential mechanisms and functions of the BTB protein family in mediating the organic processes of human breast cancer. Meanwhile, we summarize the signaling pathways the BTB protein family participates in. And we address that BTB proteins regulate the growth, apoptosis, and other behaviors of breast cancer cells. We also point out the future directions for further studies in this field.

METHODS

The relevant online literatures have been reviewed for this article.

CONCLUSION

This review could offer an update on novel molecular targets for treating human breast cancer and new insights into BTB protein family research.

Synaptic plasticity via receptor tyrosine kinase/G protein-coupled receptor crosstalk

Cellular signaling involves a large repertoire of membrane receptors operating in overlapping spatiotemporal regimes and targeting many common intracellular effectors. However, both the molecular mechanisms and physiological roles of crosstalk between receptors, especially those from different superfamilies, are poorly understood. We find that the receptor tyrosine kinase (RTK), TrkB, and the G protein-coupled receptor (GPCR), metabotropic glutamate receptor 5 (mGluR5), together mediate a novel form of hippocampal synaptic plasticity in response to brain-derived neurotrophic factor (BDNF). Activated TrkB enhances constitutive mGluR5 activity to initiate a mode-switch that drives BDNF-dependent sustained, oscillatory Ca 2+ signaling and enhanced MAP kinase activation. This crosstalk is mediated, in part, by synergy between Gβγ, released by TrkB, and Gα q -GTP, released by mGluR5, to enable a previously unidentified form of physiologically relevant RTK/GPCR crosstalk.

Fine-tuning GPCR-mediated neuromodulation by biasing signaling through different G protein subunits

G-protein-coupled receptors (GPCRs) mediate neuromodulation through the activation of heterotrimeric G proteins (Gαβγ). Classical models depict that G protein activation leads to a one-to-one formation of Gα-GTP and Gβγ species. Each of these species propagates signaling by independently acting on effectors, but the mechanisms by which response fidelity is ensured by coordinating Gα and Gβγ responses remain unknown. Here, we reveal a paradigm of G protein regulation whereby the neuronal protein GINIP (Gα inhibitory interacting protein) biases inhibitory GPCR responses to favor Gβγ over Gα signaling. Tight binding of GINIP to Gαi-GTP precludes its association with effectors (adenylyl cyclase) and, simultaneously, with regulator-of-G-protein-signaling (RGS) proteins that accelerate deactivation. As a consequence, Gαi-GTP signaling is dampened, whereas Gβγ signaling is enhanced. We show that this mechanism is essential to prevent the imbalances of neurotransmission that underlie increased seizure susceptibility in mice. Our findings reveal an additional layer of regulation within a quintessential mechanism of signal transduction that sets the tone of neurotransmission.

Gβγ signaling regulates microtubule-dependent control of Golgi integrity

Gβγ subunits regulate several non-canonical functions at distinct intracellular organelles. Previous studies have shown that Gβγ signaling at the Golgi is necessary to mediate vesicular protein transport function and to regulate mitotic Golgi fragmentation. Disruption of Golgi structure also occurs in response to microtubule depolymerizing agents, such as nocodazole. In this study, we use siRNA against Gβ1/2 or specific Gγ subunits to deplete their expression, and show that their knockdown causes a significant reduction in nocodazole-induced Golgi fragmentation. We establish that knockdown of Gβγ or inhibition of Gβγ with gallein resulted in decreased activation of protein kinase D (PKD) in response to nocodazole treatment. We demonstrate that restricting the amount of free Gβγ available for signaling by either inhibiting Gαi activation using pertussis toxin or by knockdown of the non-GPCR GEF, Girdin/GIV protein, results in a substantial decrease in nocodazole-induced Golgi fragmentation and PKD phosphorylation. Our results also indicate that depletion of Gβγ or inhibition with gallein or pertussis toxin significantly reduces the microtubule disruption-dependent Golgi fragmentation phenotype observed in cells transfected with mutant SOD1, a major causative protein in familial amyotrophic lateral sclerosis (ALS). These results provide compelling evidence that Gβγ signaling is critical for the regulation of Golgi integrity.

Regulation of DNA damage response by trimeric G-proteins

Upon sensing DNA double-strand breaks (DSBs), eukaryotic cells either die or repair DSBs via one of the two competing pathways, i.e., non-homologous end-joining (NHEJ) or homologous recombination (HR). We show that cell fate after DSBs hinges on GIV/Girdin, a guanine nucleotide-exchange modulator of heterotrimeric Giα•βγ protein. GIV suppresses HR by binding and sequestering BRCA1, a key coordinator of multiple steps within the HR pathway, away from DSBs; it does so using a C-terminal motif that binds BRCA1's BRCT-modules via both phospho-dependent and -independent mechanisms. Using another non-overlapping C-terminal motif GIV binds and activates Gi and enhances the "free" Gβγ→PI-3-kinase→Akt pathway, which promotes survival and is known to suppress HR, favor NHEJ. Absence of GIV, or loss of either of its C-terminal motifs enhanced cell death upon genotoxic stress. Because GIV selectively binds other BRCT-containing proteins suggests that G-proteins may fine-tune sensing, repair, and survival after diverse types of DNA damage.

Role of G-Proteins and GPCRs in Cardiovascular Pathologies

Cell signaling is a fundamental process that enables cells to survive under various ecological and environmental contexts and imparts tolerance towards stressful conditions. The basic machinery for cell signaling includes a receptor molecule that senses and receives the signal. The primary form of the signal might be a hormone, light, an antigen, an odorant, a neurotransmitter, etc. Similarly, heterotrimeric G-proteins principally provide communication from the plasma membrane G-protein-coupled receptors (GPCRs) to the inner compartments of the cells to control various biochemical activities. G-protein-coupled signaling regulates different physiological functions in the targeted cell types. This review article discusses G-proteins' signaling and regulation functions and their physiological relevance. In addition, we also elaborate on the role of G-proteins in several cardiovascular diseases, such as myocardial ischemia, hypertension, atherosclerosis, restenosis, stroke, and peripheral artery disease.

Polarity in respiratory development, homeostasis and disease

The respiratory system is composed of a multitude of cells that organize to form complex branched airways that end in alveoli, which respectively function to guide air flow and mediate gas exchange with the bloodstream. The organization of the respiratory sytem relies on distinct forms of cell polarity, which guide lung morphogenesis and patterning in development and provide homeostatic barrier protection from microbes and toxins. The stability of lung alveoli, the luminal secretion of surfactants and mucus in the airways, and the coordinated motion of multiciliated cells that generate proximal fluid flow, are all critical functions regulated by cell polarity, with defects in polarity contributing to respiratory disease etiology. Here, we summarize the current knowledge of cell polarity in lung development and homeostasis, highlighting key roles for polarity in alveolar and airway epithelial function and outlining relationships with microbial infections and diseases, such as cancer.

RGS12 polarizes the GPSM2-GNAI complex to organize and elongate stereocilia in sensory hair cells

Inhibitory G proteins (GNAI/Gαi) bind to the scaffold G protein signaling modulator 2 (GPSM2) to form a conserved polarity complex that regulates cytoskeleton organization. GPSM2 keeps GNAI in a guanosine diphosphate (GDP)-bound state, but how GPSM2-GNAI is generated or relates to heterotrimeric G protein signaling remains unclear. We find that RGS12, a GTPase-activating protein (GAP), is required to polarize GPSM2-GNAI at the hair cell apical membrane and to organize mechanosensory stereocilia in rows of graded heights. Accordingly, RGS12 and the guanine nucleotide exchange factor (GEF) DAPLE are asymmetrically co-enriched at the hair cell apical junction, and Rgs12 mouse mutants are deaf. GPSM2 and RGS12 share GoLoco motifs that stabilize GNAI(GDP), and GPSM2 outcompetes RGS12 to bind GNAI. Our results suggest that polarized GEF/GAP junctional activity might dissociate heterotrimeric G proteins, generating free GNAI(GDP) for GPSM2 at the adjacent apical membrane. GPSM2-GNAI(GDP), in turn, imparts asymmetry to the forming stereocilia to enable sensory function in hair cells.

DAPLE orchestrates apical actomyosin assembly from junctional polarity complexes

Establishment of apicobasal polarity and the organization of the cytoskeleton must operate coordinately to ensure proper epithelial cell shape and function. However, the precise molecular mechanisms by which polarity complexes directly instruct the cytoskeletal machinery to determine cell shape are poorly understood. Here, we define a mechanism by which the PAR polarity complex (PAR3–PAR6–aPKC) at apical cell junctions leads to efficient assembly of the apical actomyosin network to maintain epithelial cell morphology. We found that the PAR polarity complex recruits the protein DAPLE to apical cell junctions, which in turn triggers a two-pronged mechanism that converges upon assembly of apical actomyosin. More specifically, DAPLE directly recruits the actin-stabilizing protein CD2AP to apical junctions and, concomitantly, activates heterotrimeric G protein signaling in a GPCR-independent manner to favor RhoA-myosin activation. These observations establish DAPLE as a direct molecular link between junctional polarity complexes and the formation of apical cytoskeletal assemblies that support epithelial cell shape.

Interaction between TMEFF1 and AHNAK proteins in ovarian cancer cells: Implications for clinical prognosis

TMEFF1 is a newly discovered protein involved in the physiological functions of the central nervous system, embryonic development, and other biological processes. Our previous study revealed that TMEFF1 acts as a tumor-promoting gene in ovarian cancer. AHNAK, as a giant scaffolding protein, plays a role in the formation of the blood-brain barrier, cell architecture and the regulation of cardiac calcium channels. However, its role in ovarian cancer remains poorly researched. In this study, we detected the expression of AHNAK and TMEFF1 in 148 different ovarian cancer tissues, determined their relationship with pathological parameters and prognosis, clarified the interaction between the two proteins, and explored the related cancer-promoting mechanisms through immunohistochemistry, immunoprecipitation, immunofluorescence double staining, western blotting, and bioinformatics. The high expression of ANHAK and TMEFF1 in ovarian cancer indicated a higher degree of tumor malignancy and a worse prognosis. Furthermore, the expression of TMEFF1 and AHNAK was significantly positively correlated. The results also showed that AHNAK and TMEFF1 co-localized and interacted with each other in ovarian cancer tissues and cells. And knockdown of AHNAK promoted proliferation, migration and invasion of ovarian cancer cells in vitro. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway analyses showed that AHNAK and related genes were enriched during mitosis regulation, cytoskeleton formation, gene epigenetics, etc., whereas TMEFF1 and related genes are enriched during immune regulation and other processes. We also clarified the network of kinases, microRNA, and transcription factor targets, and the impact of genetic mutations on prognosis. Notably, AHNAK was regulated by the expression of TMEFF1 and can activate the MAPK pathways. Overall, high expression of AHNAK and TMEFF1 in ovarian cancer cells indicated a higher degree of tumor malignancy and a worse prognosis. Therefore, the interaction between AHNAK and TMEFF1 may become a potential anti-tumor target for ovarian cancer treatment.

Use of miRNA Sequencing to Reveal Hub miRNAs and the Effect of miR-582-3p/SMAD2 in the Progression of Hepatocellular Carcinoma

Hepatocellular carcinoma is a common tumor with a high fatality rate worldwide, and exploring its pathogenesis and deterioration mechanism is a focus for many researchers. Increasing evidence has shown that miRNAs are involved in the occurrence and progression of a variety of cancers, including hepatocellular carcinoma. Therefore, this study mainly aimed identify key miRNAs related to hepatocellular carcinoma and explore their potential functions and clinical significance. In this study, we performed miRNA sequencing on three pairs of hepatocellular carcinoma tissue samples and screened 26 differentially expressed miRNAs. Then 2 key miRNAs (miR-139-5p and miR-582-3p) were screened by Kaplan-Meier curve analysis, Cox multivariate analysis and qPCR methods. The expression of miR-582-3p was positively correlated with clinicopathological parameters in patients with hepatocellular carcinoma. Subsequently, miRwalk and starbase were used to predict the target genes of key miRNAs, and then the key pairs miR-582-3p/SMAD2 identified by WGCNA, PPI, qPCR and Pearson correlation analysis. Finally, a dual luciferase experiment, the rescue-of-function experiment and qPCR confirmed that miR-582-3p directly targets SMAD2 and regulates the proliferation, migration and invasion of HepG2 cells by targeting SMAD2. At the same time, interference with SMAD2 can influence the effect of miR-582-3p on HepG2 cells. In conclusion, our findings confirm that miR-582-3p is an independent factor for the prognosis of hepatocellular carcinoma patients, and can regulate the progression of hepatocellular carcinoma cells by targeting SMAD2.

The expression of ADAMTS14 is regulated by promoter DNA methylation and is associated with poor prognosis in colorectal cancer

Colorectal cancer (CRC) is one of the most common malignant tumors of digestive system, and its main cause of death is tumor metastasis. The occurrence of CRC is a polygenic and multi-step complex process involving genetic and epigenetic alterations. It has been demonstrated that ADAMTS14 (A disintegrin and metalloproteinase with thrombospondin motifs 14) was hypermethylated in esophageal cancer using whole-genome methylation microarray in our previous report. The present study revealed that ADAMTS14 was highly methylated accompanied with low expression in CRC. In addition, demethylation agent 5-Aza-dC could demethylate ADAMTS14 promoter region and reactivate ADAMTS14 expression effectively in vitro. Therefore, promoter hypermethylation was probably contributed to ADAMTS14 epigenetic silencing in CRC. Furthermore, ADAMTS14 protein expression was higher at invasive tumor front than at the tumor center or other areas of tumor. Kaplan-meier survival analysis indicated that the high ADAMTS14 expression was correlated with poor prognosis in CRC patients, suggesting the possibility that ADAMTS14 is a promising indicator in the evaluation of CRC prognosis.

Daple deficiency causes hearing loss in adult mice by inducing defects in cochlear stereocilia and apical microtubules

The V-shaped arrangement of hair bundles on cochlear hair cells is critical for auditory sensing. However, regulation of hair bundle arrangements has not been fully understood. Recently, defects in hair bundle arrangement were reported in postnatal Dishevelled-associating protein (ccdc88c, alias Daple)-deficient mice. In the present study, we found that adult Daple^−/− mice exhibited hearing disturbances over a broad frequency range through auditory brainstem response testing. Consistently, distorted patterns of hair bundles were detected in almost all regions, more typically in the basal region of the cochlear duct. In adult Daple^−/− mice, apical microtubules were irregularly aggregated, and the number of microtubules attached to plasma membranes was decreased. Similar phenotypes were manifested upon nocodazole treatment in a wild type cochlea culture without affecting the microtubule structure of the kinocilium. These results indicate critical role of Daple in hair bundle arrangement through the orchestration of apical microtubule distribution, and thereby in hearing, especially at high frequencies.

A protein network map of head and neck cancer reveals PIK3CA mutant drug sensitivity

[Figure: see text].

Identifying cancer drivers

[Figure: see text].

Identification of Key lncRNA-mRNA Pairs and Functional lncRNAs in Breast Cancer by Integrative Analysis of TCGA Data

Long non-coding RNAs (lncRNAs) play an important role in many diseases and are involved in the post-transcriptional regulatory network of tumors. The purpose of this study is to mine new lncRNA–mRNA regulatory pairs and analyze the new mechanism of lncRNA involvement in breast cancer progression. Using breast cancer miRNA and mRNA expression profiling from The Cancer Genome Atlas (TCGA), we identified 59 differentially expressed lncRNAs, 88 differentially expressed miRNAs, and 1,465 differentially expressed mRNAs between breast cancer tissue and adjacent normal breast cancer. Whereafter, four candidate lncRNAs (FGF14-AS2, LINC01235, AC055854.1, and AC124798.1) were identified by the Kaplan–Meier (K–M) plotter. Furthermore, we screened the hub lncRNA (LINC01235) through univariate Cox analysis, multivariate Cox analysis, and qPCR validation, which was significantly correlated with breast cancer stage, ER status, and pathological N. Subsequently, 107 LINC01235-related mRNAs were obtained by combining differentially expressed miRNAs, differentially expressed mRNAs, and LINC01235 targeting miRNAs and mRNAs. The protein–protein interaction (PPI) network was established by Cytoscape software, and 53 key genes were screened. Function and pathway enrichment showed that LINC01235-related key genes might be involved in the process of cell differentiation, cell proliferation, and p53 signal pathway. In addition, LINC01235 has been confirmed to regulate the proliferation, migration, and invasion of MCF-7 cells in in vitro experiments. Furthermore, we screened three mRNAs (ESR1, ADRA2A, and DTL) associated with breast cancer drug resistance from key genes. Through RNA interference experiments in vitro and correlation analysis, we found that there was a negative feedback mechanism between LINC01235 and ESR1/ADRA2A. In conclusion, our results suggest that LINC01235-ESR1 and LINC01235-ADRA2A could serve as important co-expression pairs in the progression of breast cancer, and LINC01235 plays a key role as an independent prognostic factor in patients with breast cancer. The findings of this work greatly increase our understanding of the molecular regulatory mechanisms of lncRNA in breast cancer.

Regulation of Dishevelled protein activity and stability by post-translational modifications and autophagy

As a key component of Wnt signaling, Dishevelled (Dvl/Dsh) plays essential roles in development processes and adult tissue homeostasis in multicellular organisms, and its deregulation results in human development disorders and other diseases. Dvl integrates and relays complex Wnt signals by acting as a branch-point of β-catenin-dependent canonical and β-catenin-independent noncanonical pathways. It dynamically interacts with multiple proteins to modulate Wnt signaling, while its activity and stability are tightly controlled by other proteins. This Review summarizes the current understanding of regulation of Dvl activity, localization, and stability by post-translational modifications, aggregation, and autophagy, and the impacts on Dvl function in both Wnt signaling and biological processes.

Regulation of DNA damage response by trimeric G-protein Signaling.. [DOI: 10.1101/2021.07.21.452842] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Upon sensing DNA double-strand breaks (DSBs), eukaryotic cells either die or repair DSBs via one of two competing pathways, i.e., non-homologous end-joining (NHEJ) or homologous recombination (HR). We show that cell fate after DNA damage hinges on the guanine nucleotide-exchange modulator of heterotrimeric G-protein, Giα•βγ, GIV/Girdin. GIV suppresses HR by binding and sequestering BRCA1, a key coordinator of multiple steps within the HR pathway, away from DSBs; it does so using a C-terminal motif that binds BRCA1’s BRCT-modules via both phospho-dependent and -independent mechanisms. GIV promotes NHEJ, and binds and activates Gi and enhances the ‘free’ Gβγ→PI-3-kinase→Akt pathway, thus revealing the enigmatic origin of prosurvival Akt signals during dsDNA repair. Absence of GIV, or the loss of either of its two functions impaired DNA repair, and induced cell death when challenged with numerous cytotoxic agents. That GIV selectively binds few other BRCT-containing proteins suggests convergent signaling such that heterotrimeric G-proteins may finetune sensing, repair, and outcome after DNA damage.

GRAPHIC ABSTRACT

HIGHLIGHTS

Non-receptor G protein modulator, GIV/Girdin binds BRCA1

Binding occurs in both canonical and non-canonical modes

GIV sequesters BRCA1 away from dsDNA breaks, suppresses HR

Activation of Gi by GIV enhances Akt signals, favors NHEJ

IN BRIEF

In this work, the authors show that heterotrimeric G protein signaling that is triggered by non-receptor GEF, GIV/Girdin, in response to double-stranded DNA breaks is critical for decisive signaling events which favor non-homologous end-joining (NHEJ) and inhibit homologous recombination (HR).

Neuropathological hallmarks of fetal hydrocephalus linked to CCDC88C pathogenic variants

The prevalence of congenital hydrocephalus has been estimated at 1.1 per 1000 infants when including cases diagnosed before 1 year of age after exclusion of neural tube defects. Classification criteria are based either on CSF dynamics, pathophysiological mechanisms or associated lesions. Whereas inherited syndromic hydrocephalus has been associated with more than 100 disease-causing genes, only four genes are currently known to be linked to congenital hydrocephalus either isolated or as a major clinical feature: L1CAM, AP1S2, MPDZ and CCDC88C. In the past 10 years, pathogenic variants in CCDC88C have been documented but the neuropathology remains virtually unknown. We report the neuropathology of two foetuses from one family harbouring two novel compound heterozygous pathogenic variants in the CCDC88C gene: a maternally inherited indel in exon 22, c.3807_3809delinsACCT;p.(Gly1270Profs*53) and a paternally inherited deletion of exon 23, c.3967-?_c.4112-?;p.(Leu1323Argfs*10). Medical termination of pregnancy was performed at 18 and 23 weeks of gestation for severe bilateral ventriculomegaly. In both fetuses, brain lesions consisted of multifocal atresia-forking along the aqueduct of Sylvius and the central canal of the medulla, periventricular neuronal heterotopias and choroid plexus hydrops. The second fetus also presented lumbar myelomeningocele, left diaphragmatic hernia and bilateral renal agenesis. CCDC88C encodes the protein DAPLE which contributes to ependymal cell planar polarity by inhibiting the non-canonical Wnt signaling pathway and interacts with MPDZ and PARD3. Interestingly, heterozygous variants in PARD3 result in neural tube defects by defective tight junction formation and polarization process of the neuroepithelium. Besides, during organ formation Wnt signalling is a prerequisite for planar cell polarity pathway activation, and mutations in planar cell polarity genes lead to heart, lung and kidney malformations. Hence, candidate variants in CCDC88C should be carefully considered whether brain lesions are isolated or associated with malformations suspected to result from disorders of planar cell polarity.

EMX2-GPR156-Gαi reverses hair cell orientation in mechanosensory epithelia

Hair cells detect sound, head position or water movements when their mechanosensory hair bundle is deflected. Each hair bundle has an asymmetric architecture that restricts stimulus detection to a single axis. Coordinated hair cell orientations within sensory epithelia further tune stimulus detection at the organ level. Here, we identify GPR156, an orphan GPCR of unknown function, as a critical regulator of hair cell orientation. We demonstrate that the transcription factor EMX2 polarizes GPR156 distribution, enabling it to signal through Gαi and trigger a 180° reversal in hair cell orientation. GPR156-Gαi mediated reversal is essential to establish hair cells with mirror-image orientations in mouse otolith organs in the vestibular system and in zebrafish lateral line. Remarkably, GPR156-Gαi also instructs hair cell reversal in the auditory epithelium, despite a lack of mirror-image organization. Overall, our work demonstrates that conserved GPR156-Gαi signaling is integral to the framework that builds directional responses into mechanosensory epithelia.

Building unconventional G protein-coupled receptors, one block at a time

The structure, function, and dynamics of canonical activation of heterotrimeric G proteins by the seven-transmembrane G protein-coupled receptors (GPCRs) have been illustrated in detail. However, emerging studies during the past decade have started to shed light on how the same G proteins may also be accessed and modulated by a diverse family of receptors that are not conventional GPCRs. Can we learn about common themes and variations in how cells assemble these atypical GPCRs?

Planar cell polarity induces local microtubule bundling for coordinated ciliary beating

Multiciliated cells (MCCs) in tracheas generate mucociliary clearance through coordinated ciliary beating. Apical microtubules (MTs) play a crucial role in this process by organizing the planar cell polarity (PCP)-dependent orientation of ciliary basal bodies (BBs), for which the underlying molecular basis remains elusive. Herein, we found that the deficiency of Daple, a dishevelled-associating protein, in tracheal MCCs impaired the planar polarized apical MTs without affecting the core PCP proteins, causing significant defects in the BB orientation at the cell level but not the tissue level. Using live-cell imaging and ultra-high voltage electron microscope tomography, we found that the apical MTs accumulated and were stabilized by side-by-side association with one side of the apical junctional complex, to which Daple was localized. In vitro binding and single-molecule imaging revealed that Daple directly bound to, bundled, and stabilized MTs through its dimerization. These features convey a PCP-related molecular basis for the polarization of apical MTs, which coordinate ciliary beating in tracheal MCCs.

Complementary biosensors reveal different G-protein signaling modes triggered by GPCRs and non-receptor activators

It has become evident that activation of heterotrimeric G-proteins by cytoplasmic proteins that are not G-protein-coupled receptors (GPCRs) plays a role in physiology and disease. Despite sharing the same biochemical guanine nucleotide exchange factor (GEF) activity as GPCRs in vitro, the mechanisms by which these cytoplasmic proteins trigger G-protein-dependent signaling in cells have not been elucidated. Heterotrimeric G-proteins can give rise to two active signaling species, Gα-GTP and dissociated Gβγ, with different downstream effectors, but how non-receptor GEFs affect the levels of these two species in cells is not known. Here, a systematic comparison of GPCRs and three unrelated non-receptor proteins with GEF activity in vitro (GIV/Girdin, AGS1/Dexras1, and Ric-8A) revealed high divergence in their contribution to generating Gα-GTP and free Gβγ in cells directly measured with live-cell biosensors. These findings demonstrate fundamental differences in how receptor and non-receptor G-protein activators promote signaling in cells despite sharing similar biochemical activities in vitro.

Wnts regulate planar cell polarity via heterotrimeric G protein and PI3K signaling

In the mammalian cochlea, the planar cell polarity (PCP) pathway aligns hair cell orientation along the plane of the sensory epithelium. Concurrently, multiple cell intrinsic planar polarity (referred to as iPCP) modules mediate planar polarization of the hair cell apical cytoskeleton, including the kinocilium and the V-shaped hair bundle essential for mechanotransduction. How PCP and iPCP are coordinated during development and the roles of Wnt ligands in this process remain unresolved. Here we show that genetic blockade of Wnt secretion in the cochlear epithelium resulted in a shortened cochlear duct and misoriented and misshapen hair bundles. Mechanistically, Wnts stimulate Gi activity by regulating the localization of Daple, a guanine nucleotide exchange factor (GEF) for Gαi. In turn, the Gβγ complex signals through phosphoinositide 3-kinase (PI3K) to regulate kinocilium positioning and asymmetric localizations of a subset of core PCP proteins, thereby coordinating PCP and iPCP. Thus, our results identify a putative Wnt/heterotrimeric G protein/PI3K pathway for PCP regulation.

Wnt5A-Mediated Actin Organization Regulates Host Response to Bacterial Pathogens and Non-Pathogens

Wnt5A signaling facilitates the killing of several bacterial pathogens, but not the non-pathogen E. coli DH5α. The basis of such pathogen vs. non-pathogen distinction is unclear. Accordingly, we analyzed the influence of Wnt5A signaling on pathogenic E. coli K1 in relation to non-pathogenic E. coli K12-MG1655 and E. coli DH5α eliminating interspecies variability from our study. Whereas cell internalized E. coli K1 disrupted cytoskeletal actin organization and multiplied during Wnt5A depletion, rWnt5A mediated activation revived cytoskeletal actin assembly facilitating K1 eradication. Cell internalized E. coli K12-MG1655 and E. coli DH5α, which did not perturb actin assembly appreciably, remained unaffected by rWnt5A treatment. Phagosomes prepared separately from Wnt5A conditioned medium treated K1 and K12-MG1655 infected macrophages revealed differences in the relative levels of actin and actin network promoting proteins, upholding that the Wnt5A-Actin axis operates differently for internalized pathogen and non-pathogen. Interestingly, exposure of rWnt5A treated K1 and K12-MG1655/DH5α infected macrophages to actin assembly inhibitors reversed the scenario, blocking killing of K1, yet promoting killing of both K12-MG1655 and DH5α. Taken together, our study illustrates that the state of activation of the Wnt5A/Actin axis in the context of the incumbent bacteria is crucial for directing host response to infection.

A long isoform of GIV/Girdin contains a PDZ-binding module that regulates localization and G-protein binding

PDZ domains are one of the most abundant protein domains in eukaryotes and are frequently found on junction-localized scaffold proteins. Various signaling molecules bind to PDZ proteins via PDZ-binding motifs (PBM) and fine-tune cellular signaling. However, how such interaction affects protein function is difficult to predict and must be solved empirically. Here we describe a long isoform of the guanine nucleotide exchange factor GIV/Girdin (CCDC88A) that we named GIV-L, which is conserved throughout evolution, from invertebrates to vertebrates, and contains a PBM. Unlike GIV, which lacks PBM and is cytosolic, GIV-L localizes onto cell junctions and has a PDZ interactome (as shown through annotating Human Cell Map and BioID-proximity labeling studies), which impacts GIV-L's ability to bind and activate trimeric G-protein, Gαi, through its guanine-nucleotide exchange modulator (GEM) module. This GEM module is found exclusively in vertebrates. We propose that the two functional modules in GIV may have evolved sequentially: the ability to bind PDZ proteins via the PBM evolved earlier in invertebrates, whereas G-protein binding and activation may have evolved later only among vertebrates. Phenotypic studies in Caco-2 cells revealed that GIV and GIV-L may have antagonistic effects on cell growth, proliferation (cell cycle), and survival. Immunohistochemical analysis in human colon tissues showed that GIV expression increases with a concomitant decrease in GIV-L during cancer initiation. Taken together, these findings reveal how regulation in GIV/CCDC88A transcript helps to achieve protein modularity, which allows the protein to play opposing roles either as a tumor suppressor (GIV-L) or as an oncogene (GIV).

Identification of a Ubiquitination-Related Gene Risk Model for Predicting Survival in Patients With Pancreatic Cancer

Pancreatic cancer is known as "the king of cancer," and ubiquitination/deubiquitination-related genes are key contributors to its development. Our study aimed to identify ubiquitination/deubiquitination-related genes associated with the prognosis of pancreatic cancer patients by the bioinformatics method and then construct a risk model. In this study, the gene expression profiles and clinical data of pancreatic cancer patients were downloaded from The Cancer Genome Atlas (TCGA) database and the Genotype-tissue Expression (GTEx) database. Ubiquitination/deubiquitination-related genes were obtained from the gene set enrichment analysis (GSEA). Univariate Cox regression analysis was used to identify differentially expressed ubiquitination-related genes selected from GSEA which were associated with the prognosis of pancreatic cancer patients. Using multivariate Cox regression analysis, we detected eight optimal ubiquitination-related genes (RNF7, NPEPPS, NCCRP1, BRCA1, TRIM37, RNF25, CDC27, and UBE2H) and then used them to construct a risk model to predict the prognosis of pancreatic cancer patients. Finally, the eight risk genes were validated by the Human Protein Atlas (HPA) database, the results showed that the protein expression level of the eight genes was generally consistent with those at the transcriptional level. Our findings suggest the risk model constructed from these eight ubiquitination-related genes can accurately and reliably predict the prognosis of pancreatic cancer patients. These eight genes have the potential to be further studied as new biomarkers or therapeutic targets for pancreatic cancer.

Autophagy and the Wnt signaling pathway: A focus on Wnt/β-catenin signaling

Cellular homeostasis and adaptation to various environmental conditions are importantly regulated by the sophisticated mechanism of autophagy and its crosstalk with Wnt signaling and other developmental pathways. Both autophagy and Wnt signaling are involved in embryogenesis and differentiation. Autophagy is responsible for degradation and recycling of cytosolic materials by directing them to lysosomes through the phagophore compartment. A dual feedback mechanism regulates the interface between autophagy and Wnt signaling pathways. During nutrient deprivation, β-catenin and Dishevelled (essential Wnt signaling proteins) are targeted for autophagic degradation by LC3. When Wnt signaling is activated, β-catenin acts as a corepressor of one of the autophagy proteins, p62. In contrast, another key Wnt signaling protein, GSK3β, negatively regulates the Wnt pathway and has been shown to induce autophagy by phosphorylation of the TSC complex. This article reviews the interplay between autophagy and Wnt signaling, describing how β-catenin functions as a key cellular integration point coordinating proliferation with autophagy, and it discusses the clinical importance of the crosstalk between these mechanisms.

Evolution of Modularity, Interactome and Functions of GIV/Girdin (CCDC88A) from Invertebrates to Vertebrates.. [DOI: 10.1101/2020.09.28.317172] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

PDZ domains are one of the most abundant protein domains in eukaryotes and frequently found on junction-localized scaffold proteins. Various signaling molecules bind to PDZ proteins via PDZ-binding motifs (PBM) and finetune cellular signaling. Here we describe the presence of a PBM on GIV/Girdin (CCDC88A) that is conserved throughout evolution, from invertebrates to vertebrates, and is generated as a long isoform-variant in humans, which we named GIV-L. Unlike GIV, which lacks PBM and is cytosolic, GIV-L localizes to the cell junctions, and has a unique PDZ-interactome, which impacts GIV-L’s ability to bind and activate trimeric G-protein, Gi through its guanine-nucleotide exchange modulator (GEM) module; the GEM module is found exclusively in vertebrates. Thus, the two functional modules in GIV evolved sequentially: the ability to bind PDZ proteins via the PBM evolved earlier in invertebrates, whereas G-protein binding and activation may have evolved later only among vertebrates. Phenotypic studies in Caco-2 cells revealed that GIV and GIV-L may have antagonistic effects on cell growth, proliferation (cell cycle), and survival. Immunohistochemical analyses in human colon tissues showed that GIV expression increases with a concomitant decrease in GIV-L during cancer initiation. Taken together, these findings reveal how GIV/CCDC88A in humans displays evolutionary flexibility in modularity, which allows the resultant isoforms to play opposing roles either as a tumor suppressor (GIV-L) or as an oncogene (GIV).

Optogenetic activation of heterotrimeric G-proteins by LOV2GIVe, a rationally engineered modular protein

Heterotrimeric G-proteins are signal transducers involved in mediating the action of many natural extracellular stimuli and many therapeutic agents. Non-invasive approaches to manipulate the activity of G-proteins with high precision are crucial to understand their regulation in space and time. Here, we developed LOV2GIVe, an engineered modular protein that allows the activation of heterotrimeric G-proteins with blue light. This optogenetic construct relies on a versatile design that differs from tools previously developed for similar purposes, that is metazoan opsins, which are light-activated G-protein-coupled receptors (GPCRs). Instead, LOV2GIVe consists of the fusion of a G-protein activating peptide derived from a non-GPCR regulator of G-proteins to a small plant protein domain, such that light uncages the G-protein activating module. Targeting LOV2GIVe to cell membranes allowed for light-dependent activation of Gi proteins in different experimental systems. In summary, LOV2GIVe expands the armamentarium and versatility of tools available to manipulate heterotrimeric G-protein activity.

Intersection of two key signal integrators in the cell: activator of G-protein signaling 3 and dishevelled-2

Activator of G-protein signaling 3 (AGS3, encoded by GPSM1) was discovered as a one of several receptor-independent activators of G-protein signaling, which are postulated to provide a platform for divergence between canonical and noncanonical G-protein signaling pathways. Similarly, Dishevelled (DVL) proteins serve as a point of divergence for β-catenin-dependent and -independent signaling pathways involving the family of Frizzled (FZD) ligands and cell-surface WNT receptors. We recently discovered the apparent regulated localization of dishevelled-2 (DVL2) and AGS3 to distinct cellular puncta, suggesting that the two proteins interact as part of various cell signaling systems. To address this hypothesis, we asked the following questions: (1) do AGS3 signaling pathways influence the activation of β-catenin (CTNNB1)-regulated transcription through the WNT-Frizzled-Dishevelled axis, and (2) is the AGS3 and DVL2 interaction regulated? The interaction of AGS3 and DVL2 was regulated by protein phosphorylation, subcellular distribution, and a cell-surface G-protein-coupled receptor. These data, and the commonality of functional system impacts observed for AGS3 and DVL2, suggest that the AGS3-DVL2 complex presents an unexpected path for functional integration within the cell.This article has an associated First Person interview with the first author of the paper.

The Daple-CK1ε complex regulates Dvl2 phosphorylation and canonical Wnt signaling

The canonical Wnt signaling pathway plays a crucial role in embryonic development, tissue homeostasis and cancer progression. The binding of Wnt ligands to their cognate receptors, the Frizzled (Fzd) family of proteins, recruits Dishevelled segment polarity protein (Dvl) to the plasma membrane and induces its phosphorylation via casein kinase 1 (CK1), which leads to the activation of β-catenin. Previous studies showed that Dishevelled-associating protein with a high frequency of leucine residues (Daple) is an important component of the Wnt signaling pathway and essential for Dvl phosphorylation. However, the mechanism by which Daple promotes CK1-mediated phosphorylation of Dvl is not fully understood. In this study, we found that Daple overexpression induced CK1ε-mediated Dvl2 phosphorylation at threonine 224 (Thr224). A Daple mutant (Daple ΔGCV) that lacks a carboxyl-terminal motif to associate with Dvl, retained the ability to interact with CK1ε, but did not induce Dvl phosphorylation, suggesting the importance of the Daple/Dvl/CK1ε trimeric protein complex. We further found that Thr224 phosphorylation of Dvl was required for full activation of β-catenin transcriptional activity. Consistent with this, wild-type Daple promoted β-catenin transcriptional activity, following dissociation of β-catenin and axin. Finally, Wnt3a stimulation increased the membrane localization of Daple and its association with Dvl, and Daple knockdown attenuated Wnt3a-mediated β-catenin transcriptional activity. Collectively, these data suggested a essential role of spatial Daple localization in CK1ε-mediated activation of Dvl in the canonical Wnt signaling pathway.

Many functionally connected loci foster adaptive diversification along a neotropical hybrid zone

Characterizing the genetic complexity of adaptation and trait evolution is a major emphasis of evolutionary biology and genetics. Incongruent findings from genetic studies have resulted in conceptual models ranging from a few large-effect loci to massively polygenic architectures. Here, we combine chromatin immunoprecipitation sequencing, Hi-C, RNA sequencing, and 40 whole-genome sequences from Heliconius butterflies to show that red color pattern diversification occurred via many genomic loci. We find that the red wing pattern master regulatory transcription factor Optix binds dozens of loci also under selection, which frequently form three-dimensional adaptive hubs with selection acting on multiple physically interacting genes. Many Optix-bound genes under selection are tied to pigmentation and wing development, and these loci collectively maintain separation between adaptive red color pattern phenotypes in natural populations. We propose a model of trait evolution where functional connections between loci may resolve much of the disparity between large-effect and polygenic evolutionary models.

The PI3K-AKT-mTOR Pathway and Prostate Cancer: At the Crossroads of AR, MAPK, and WNT Signaling

Oncogenic activation of the phosphatidylinositol-3-kinase (PI3K), protein kinase B (PKB/AKT), and mammalian target of rapamycin (mTOR) pathway is a frequent event in prostate cancer that facilitates tumor formation, disease progression and therapeutic resistance. Recent discoveries indicate that the complex crosstalk between the PI3K-AKT-mTOR pathway and multiple interacting cell signaling cascades can further promote prostate cancer progression and influence the sensitivity of prostate cancer cells to PI3K-AKT-mTOR-targeted therapies being explored in the clinic, as well as standard treatment approaches such as androgen-deprivation therapy (ADT). However, the full extent of the PI3K-AKT-mTOR signaling network during prostate tumorigenesis, invasive progression and disease recurrence remains to be determined. In this review, we outline the emerging diversity of the genetic alterations that lead to activated PI3K-AKT-mTOR signaling in prostate cancer, and discuss new mechanistic insights into the interplay between the PI3K-AKT-mTOR pathway and several key interacting oncogenic signaling cascades that can cooperate to facilitate prostate cancer growth and drug-resistance, specifically the androgen receptor (AR), mitogen-activated protein kinase (MAPK), and WNT signaling cascades. Ultimately, deepening our understanding of the broader PI3K-AKT-mTOR signaling network is crucial to aid patient stratification for PI3K-AKT-mTOR pathway-directed therapies, and to discover new therapeutic approaches for prostate cancer that improve patient outcome.

Cytoplasmic Dynein Functions in Planar Polarization of Basal Bodies within Ciliated Cells

Despite common consensus about the importance of planar cell polarity (PCP) proteins in tissue orientation, little is known about the mechanisms used by PCP proteins to promote planar polarization of cytoskeletons within individual cells. One PCP protein Fzd6 asymmetrically localizes to the apical cell membrane of multi-ciliated ependymal cells lining the lateral ventricular (LV) wall on the side that contacts cerebrospinal fluid flow. Individual ependymal cells have planar polarized microtubules that connect ciliary basal bodies (BBs) with the cell cortex of the Fzd side to coordinate cilia orientation. Here, we report that cytoplasmic dynein is anchored to the cell cortex of the Fzd side via an adapter protein Daple that regulates microtubule dynamics. Asymmetric localization of cortical dynein generates a pulling force on dynamic microtubules connected to BBs, which in turn orients BBs toward the Fzd side. This is required for coordinated cilia orientation on the LV wall.

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Daple anchors cytoplasmic dynein to the cell cortex of ependymal cells on LV wall

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Cytoplasmic dynein is anchored to the Fzd6/Dvl1/Daple side of the cell cortex

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Cytoplasmic dynein functions include BB positioning and orientation

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Cortex-anchored dynein generates a pulling force on microtubules connected to BBs

TRIM11 facilitates chemoresistance in nasopharyngeal carcinoma by activating the β-catenin/ABCC9 axis via p62-selective autophagic degradation of Daple

Chemotherapy resistance is the major cause of nasopharyngeal carcinoma (NPC) treatment failure. Tripartite motif-containing protein (TRIM) family members play important roles in tumor development and chemotherapy failure. Here, based on a screening analysis of 71 TRIM family members by qRT-PCR, we first confirmed that the TRIM11 levels were significantly higher in drug-resistant NPC cells than in non-drug-resistant NPC cells, and high TRIM11 expression predicted poor overall survival (OS) and progression-free survival (PFS). N(6)-Methyladenosine (m6A) was highly enriched in TRIM11 in NPC drug-resistant cells and enhanced its RNA stability. TRIM11 enhanced the multidrug resistance in NPC by inhibiting apoptosis in vitro and promoting cisplatin (DDP) resistance in vivo. TRIM11 associated with Daple and promoted Daple ubiquitin-mediated degradation in a p62-selective autophagic manner, further upregulating β-catenin expression to induce ABCC9 expression by directly binding to the ABCC9 promoter. TRIM11 may regulate NPC drug resistance by positively modulating the Daple/β-catenin/ABCC9 signaling pathway. Thus, TRIM11 may be a potential diagnostic marker and therapeutic target for chemoresistant NPC.

Regulating cellular cyclic adenosine monophosphate: "Sources," "sinks," and now, "tunable valves"

A number of hormones and growth factors stimulate target cells via the second messenger pathways, which in turn regulate cellular phenotypes. Cyclic adenosine monophosphate (cAMP) is a ubiquitous second messenger that facilitates numerous signal transduction pathways; its production in cells is tightly balanced by ligand-stimulated receptors that activate adenylate cyclases (ACs), that is, "source" and by phosphodiesterases (PDEs) that hydrolyze it, that is, "sinks." Because it regulates various cellular functions, including cell growth and differentiation, gene transcription and protein expression, the cAMP signaling pathway has been exploited for the treatment of numerous human diseases. Reduction in cAMP is achieved by blocking "sources"; however, elevation in cAMP is achieved by either stimulating "source" or blocking "sinks." Here we discuss an alternative paradigm for the regulation of cellular cAMP via GIV/Girdin, the prototypical member of a family of modulators of trimeric GTPases, Guanine nucleotide Exchange Modulators (GEMs). Cells upregulate or downregulate cellular levels of GIV-GEM, which modulates cellular cAMP via spatiotemporal mechanisms distinct from the two most often targeted classes of cAMP modulators, "sources" and "sinks." A network-based compartmental model for the paradigm of GEM-facilitated cAMP signaling has recently revealed that GEMs such as GIV serve much like a "tunable valve" that cells may employ to finetune cellular levels of cAMP. Because dysregulated signaling via GIV and other GEMs has been implicated in multiple disease states, GEMs constitute a hitherto untapped class of targets that could be exploited for modulating aberrant cAMP signaling in disease states. This article is categorized under: Models of Systems Properties and Processes > Mechanistic Models Biological Mechanisms > Cell Signaling.

Tyrosine-Based Signals Regulate the Assembly of Daple⋅PARD3 Complex at Cell-Cell Junctions

Polarized distribution of organelles and molecules inside a cell is vital for a range of cellular processes and its loss is frequently encountered in disease. Polarization during planar cell migration is a special condition in which cellular orientation is triggered by cell-cell contact. We demonstrate that the protein Daple (CCDC88C) is a component of cell junctions in epithelial cells which serves like a cellular “compass” for establishing and maintaining contact-triggered planar polarity. Furthermore, these processes may be mediated through interaction with the polarity regulator PARD3. This interaction, mediated by Daple's PDZ-binding motif (PBM) and the third PDZ domain of PARD3, is fine-tuned by tyrosine phosphorylation on Daple's PBM by receptor and non-receptor tyrosine kinases, such as Src. Hypophosphorylation strengthens the interaction, whereas hyperphosphorylation disrupts it, thereby revealing an unexpected role of Daple as a platform for signal integration and gradient sensing for tyrosine-based signals within the planar cell polarity pathway.

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Daple localizes to cell junction, regulates planar cell migration

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Localization requires Daple's C-terminal PDZ-binding motif (PBM)

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The PBM binds a PDZ module of the polarity determinant PARD3

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The Daple⋅PARD3 interaction is regulated by tyrosine-based signals

DAPLE protein inhibits nucleotide exchange on Gαs and Gαq via the same motif that activates Gαi

Besides being regulated by G-protein-coupled receptors, the activity of heterotrimeric G proteins is modulated by many cytoplasmic proteins. GIV/Girdin and DAPLE (Dvl-associating protein with a high frequency of leucine) are the best-characterized members of a group of cytoplasmic regulators that contain a Gα-binding and -activating (GBA) motif and whose dysregulation underlies human diseases, including cancer and birth defects. GBA motif-containing proteins were originally reported to modulate G proteins by binding Gα subunits of the G_i/o family (Gα_i) over other families (such as G_s, G_q/11, or G_12/13), and promoting nucleotide exchange in vitro However, some evidence suggests that this is not always the case, as phosphorylation of the GBA motif of GIV promotes its binding to Gα_s and inhibits nucleotide exchange. The G-protein specificity of DAPLE and how it might affect nucleotide exchange on G proteins besides Gα_i remain to be investigated. Here, we show that DAPLE's GBA motif, in addition to Gα_i, binds efficiently to members of the G_s and G_q/11 families (Gα_s and Gα_q, respectively), but not of the G_12/13 family (Gα₁₂) in the absence of post-translational phosphorylation. We pinpointed Met-1669 as the residue in the GBA motif of DAPLE that diverges from that in GIV and enables better binding to Gα_s and Gα_q Unlike the nucleotide-exchange acceleration observed for Gα_i, DAPLE inhibited nucleotide exchange on Gα_s and Gα_q These findings indicate that GBA motifs have versatility in their G-protein-modulating effect, i.e. they can bind to Gα subunits of different classes and either stimulate or inhibit nucleotide exchange depending on the G-protein subtype.

Wnt Signaling: Pathogen Incursion and Immune Defense

Wnt ligands interact with the transmembrane cell surface receptors Frizzled and ROR/RYK to initiate complex signaling cascades that are crucial for cell physiology and the proper functioning of the immune system. Wnt signaling is instrumental in maintaining immune surveillance and during infections by pathogenic microbes helps mount host resistance to infection. Some pathogens, however, utilize Wnt signaling to build a niche for their survival. The goal of this review is to summarize current and developing concepts about the tug of war between Wnt signaling and pathogens for deployment of host resources, focusing mostly on macrophages and cytoskeletal actin dynamics. An additional objective is to outline the interrelation between Wnt signaling and the host microbiota, which is vital for immune defense, discussing in the same perspective, how Wnt signaling could be differentiating pathogen from non-pathogen.