PKCβII acts downstream of chemoattractant receptors and mTORC2 to regulate cAMP production and myosin II activity in neutrophils

Quantitative Monitoring of GPCR-Mediated Spatiotemporal IP3 Dynamics Using Confocal Fluorescence Microscopy

Activation of G protein-coupled receptors upon chemoattractant stimulation induces activation of multiple signaling pathways. To fully understand how these signaling pathway coordinates to achieve directional migration of neutrophils, it is essential to determine the dynamics of the spatiotemporal activation profile of signaling components at the level of single living cells. Here, we describe a detailed methodology for monitoring and quantitatively analyzing the spatiotemporal dynamics of 1,4,5-inositol trisphosphate (IP3) in neutrophil-like HL60 cells in response to various chemoattractant fields by applying Förster resonance energy transfer (FRET) fluorescence microscopy.

The mTOR signalling in corneal diseases: A recent update

Corneal diseases affect 4.2 million people worldwide and are a leading cause of vision impairment and blindness. Current treatments for corneal diseases, such as antibiotics, steroids, and surgical interventions, have numerous disadvantages and challenges. Thus, there is an urgent need for more effective therapies. Although the pathogenesis of corneal diseases is not fully understood, it is known that injury caused by various stresses and postinjury healing, such as epithelial renewal, inflammation, stromal fibrosis, and neovascularization, are highly involved. Mammalian target of rapamycin (mTOR) is a key regulator of cell growth, metabolism, and the immune response. Recent studies have revealed that activation of mTOR signalling extensively contributes to the pathogenesis of various corneal diseases, and inhibition of mTOR with rapamycin achieves promising outcomes, supporting the potential of mTOR as a therapeutic target. In this review, we detail the function of mTOR in corneal diseases and how these characteristics contribute to disease treatment using mTOR-targeted drugs.

Metabolic reprogramming in cancer: Mechanisms and therapeutics

Cancer cells characterized by uncontrolled growth and proliferation require altered metabolic processes to maintain this characteristic. Metabolic reprogramming is a process mediated by various factors, including oncogenes, tumor suppressor genes, changes in growth factors, and tumor-host cell interactions, which help to meet the needs of cancer cell anabolism and promote tumor development. Metabolic reprogramming in tumor cells is dynamically variable, depending on the tumor type and microenvironment, and reprogramming involves multiple metabolic pathways. These metabolic pathways have complex mechanisms and involve the coordination of various signaling molecules, proteins, and enzymes, which increases the resistance of tumor cells to traditional antitumor therapies. With the development of cancer therapies, metabolic reprogramming has been recognized as a new therapeutic target for metabolic changes in tumor cells. Therefore, understanding how multiple metabolic pathways in cancer cells change can provide a reference for the development of new therapies for tumor treatment. Here, we systemically reviewed the metabolic changes and their alteration factors, together with the current tumor regulation treatments and other possible treatments that are still under investigation. Continuous efforts are needed to further explore the mechanism of cancer metabolism reprogramming and corresponding metabolic treatments.

Functional implications of neutrophil metabolism during ischemic tissue repair

Immune cell mobilization and their accumulation in the extravascular space is a key consequence of tissue injury. Maladaptive trafficking and immune activation following reperfusion of ischemic tissue can exacerbate tissue repair. After ischemic injury such as myocardial infarction (MI), PMNs are the first cells to arrive at the sites of insult and their response is critical for the sequential progression of ischemia from inflammation to resolution and finally to tissue repair. However, PMN-induced inflammation can also be detrimental to cardiac function and ultimately lead to heart failure. In this review, we highlight the role of PMNs during key cellular and molecular events of ischemic heart failure. We address new research on PMN metabolism, and how this orchestrates diverse functions such as PMN chemotaxis, degranulation, and phagocytosis. Particular focus is given to PMN metabolism regulation by mitochondrial function and mTOR kinase activity.

Physiological roles of mammalian transmembrane adenylyl cyclase isoforms

Adenylyl cyclases (ACs) catalyze the conversion of ATP to the ubiquitous second messenger cAMP. Mammals possess nine isoforms of transmembrane ACs, dubbed AC1-9, that serve as major effector enzymes of G protein-coupled receptors (GPCRs). The transmembrane ACs display varying expression patterns across tissues, giving the potential for them to have a wide array of physiological roles. Cells express multiple AC isoforms, implying that ACs have redundant functions. Furthermore, all transmembrane ACs are activated by Gαs, so it was long assumed that all ACs are activated by Gαs-coupled GPCRs. AC isoforms partition to different microdomains of the plasma membrane and form prearranged signaling complexes with specific GPCRs that contribute to cAMP signaling compartments. This compartmentation allows for a diversity of cellular and physiological responses by enabling unique signaling events to be triggered by different pools of cAMP. Isoform-specific pharmacological activators or inhibitors are lacking for most ACs, making knockdown and overexpression the primary tools for examining the physiological roles of a given isoform. Much progress has been made in understanding the physiological effects mediated through individual transmembrane ACs. GPCR-AC-cAMP signaling pathways play significant roles in regulating functions of every cell and tissue, so understanding each AC isoform's role holds potential for uncovering new approaches for treating a vast array of pathophysiological conditions.

Cross-Talk Between the Adenylyl Cyclase/cAMP Pathway and Ca2+ Homeostasis

Cyclic AMP and Ca²⁺ are the first second or intracellular messengers identified, unveiling the cellular mechanisms activated by a plethora of extracellular signals, including hormones. Cyclic AMP generation is catalyzed by adenylyl cyclases (ACs), which convert ATP into cAMP and pyrophosphate. By the way, Ca²⁺, as energy, can neither be created nor be destroyed; Ca²⁺ can only be transported, from one compartment to another, or chelated by a variety of Ca²⁺-binding molecules. The fine regulation of cytosolic concentrations of cAMP and free Ca²⁺ is crucial in cell function and there is an intimate cross-talk between both messengers to fine-tune the cellular responses. Cancer is a multifactorial disease resulting from a combination of genetic and environmental factors. Frequent cases of cAMP and/or Ca²⁺ homeostasis remodeling have been described in cancer cells. In those tumoral cells, cAMP and Ca²⁺ signaling plays a crucial role in the development of hallmarks of cancer, including enhanced proliferation and migration, invasion, apoptosis resistance, or angiogenesis. This review summarizes the cross-talk between the ACs/cAMP and Ca²⁺ intracellular pathways with special attention to the functional and reciprocal regulation between Orai1 and AC8 in normal and cancer cells.

Nanometric targeting of type 9 adenylyl cyclase in heart

Adenylyl cyclases (ACs) convert ATP into the classical second messenger cyclic adenosine monophosphate (cAMP). Cardiac ACs, specifically AC5, AC6, and AC9, regulate cAMP signaling controlling functional outcomes such as heart rate, contractility and relaxation, gene regulation, stress responses, and glucose and lipid metabolism. With so many distinct functional outcomes for a single second messenger, the cell creates local domains of cAMP signaling to correctly relay signals. Targeting of ACs to A-kinase anchoring proteins (AKAPs) not only localizes ACs, but also places them within signaling nanodomains, where cAMP levels and effects can be highly regulated. Here we will discuss the recent work on the structure, regulation and physiological functions of AC9 in the heart, where it accounts for <3% of total AC activity. Despite the small contribution of AC9 to total cardiac cAMP production, AC9 binds and regulates local PKA phosphorylation of Yotiao-IKs and Hsp20, demonstrating a role for nanometric targeting of AC9.

The chilling of adenylyl cyclase 9 and its translational potential

A recent break-through paper has revealed for the first time the high-resolution, three-dimensional structure of a mammalian trans-membrane adenylyl cyclase (tmAC) obtained by cryo-electronmicroscopy (cryo-EM). Reporting the structure of adenylyl cyclase 9 (AC9) in complex with activated Gsα, the cryo-EM study revealed that AC9 has three functionally interlinked, yet structurally distinct domains. The array of the twelve transmembrane helices is connected to the cytosolic catalytic core by two helical segments that are stabilized through the formation of a parallel coiled-coil. Surprisingly, in the presence of Gsα, the isoform-specific carboxyl-terminal tail of AC9 occludes the forskolin- as well as the active substrate-sites, resulting in marked autoinhibition of the enzyme. As AC9 has the lowest primary sequence homology with the eight further mammalian tmAC paralogues, it appears to be the best candidate for selective pharmacologic targeting. This is now closer to reality as the structural insight provided by the cryo-EM study indicates that all of the three structural domains are potential targets for bioactive agents. The present paper summarizes for molecular physiologists and pharmacologists what is known about the biological role of AC9, considers the potential modes of physiologic regulation, as well as pharmacologic targeting on the basis of the high-resolution cryo-EM structure. The translational potential of AC9 is considered upon highlighting the current state of genome-wide association screens, and the corresponding experimental evidence. Overall, whilst the high- resolution structure presents unique opportunities for the full understanding of the control of AC9, the data on the biological role of the enzyme and its translational potential are far from complete, and require extensive further study.

ADCY9 (Adenylate Cyclase Type 9) Inactivation Protects From Atherosclerosis Only in the Absence of CETP (Cholesteryl Ester Transfer Protein)

BACKGROUND

Pharmacogenomic studies have shown that ADCY9 genotype determines the effects of the CETP (cholesteryl ester transfer protein) inhibitor dalcetrapib on cardiovascular events and atherosclerosis imaging. The underlying mechanisms responsible for the interactions between ADCY9 and CETP activity have not yet been determined.

METHODS

Adcy9-inactivated ( Adcy9^Gt/Gt) and wild-type (WT) mice, that were or not transgenic for the CETP gene (CETPtg Adcy9^Gt/Gt and CETPtg Adcy9^WT), were submitted to an atherogenic protocol (injection of an AAV8 [adeno-associated virus serotype 8] expressing a PCSK9 [proprotein convertase subtilisin/kexin type 9] gain-of-function variant and 0.75% cholesterol diet for 16 weeks). Atherosclerosis, vasorelaxation, telemetry, and adipose tissue magnetic resonance imaging were evaluated.

RESULTS

Adcy9^Gt/Gt mice had a 65% reduction in aortic atherosclerosis compared to WT ( P<0.01). CD68 (cluster of differentiation 68)-positive macrophage accumulation and proliferation in plaques were reduced in Adcy9^Gt/Gt mice compared to WT animals ( P<0.05 for both). Femoral artery endothelial-dependent vasorelaxation was improved in Adcy9^Gt/Gt mice (versus WT, P<0.01). Selective pharmacological blockade showed that the nitric oxide, cyclooxygenase, and endothelial-dependent hyperpolarization pathways were all responsible for the improvement of vasodilatation in Adcy9^Gt/Gt ( P<0.01 for all). Aortic endothelium from Adcy9^Gt/Gt mice allowed significantly less adhesion of splenocytes compared to WT ( P<0.05). Adcy9^Gt/Gt mice gained more weight than WT with the atherogenic diet; this was associated with an increase in whole body adipose tissue volume ( P<0.01 for both). Feed efficiency was increased in Adcy9^Gt/Gt compared to WT mice ( P<0.01), which was accompanied by prolonged cardiac RR interval ( P<0.05) and improved nocturnal heart rate variability ( P=0.0572). Adcy9 inactivation-induced effects on atherosclerosis, endothelial function, weight gain, adipose tissue volume, and feed efficiency were lost in CETPtg Adcy9^Gt/Gt mice ( P>0.05 versus CETPtg Adcy9^WT).

CONCLUSIONS

Adcy9 inactivation protects against atherosclerosis, but only in the absence of CETP activity. This atheroprotection may be explained by decreased macrophage accumulation and proliferation in the arterial wall, and improved endothelial function and autonomic tone.

Insights into the Regulatory Properties of Human Adenylyl Cyclase Type 9

Membrane-bound adenylyl cyclase (AC) isoforms have distinct regulatory mechanisms that contribute to their signaling specificity and physiologic roles. Although insight into the physiologic relevance of AC9 has progressed, the understanding of AC9 regulation is muddled with conflicting studies. Currently, modes of AC9 regulation include stimulation by Gαs, protein kinase C (PKC) βII, or calcium-calmodulin kinase II (CaMKII) and inhibition by Gαi/o, novel PKC isoforms, or calcium-calcineurin. Conversely, the original cloning of human AC9 reported that AC9 is insensitive to Gαi inhibition. The purpose of our study was to clarify which proposed regulators of AC9 act directly or indirectly, particularly with respect to Gαi/o. The proposed regulators, including G proteins (Gαs, Gαi, Gαo, Gβγ), protein kinases (PKCβII, CaMKII), and forskolin, were systematically evaluated using classic in vitro AC assays and cell-based cAMP accumulation assays in COS-7 cells. Our studies show that AC9 is directly regulated by Gαs with weak conditional activation by forskolin; other modes of proposed regulation either occur indirectly or possibly require additional scaffolding proteins to facilitate regulation. We also show that AC9 contributes to basal cAMP production; knockdown or knockout of endogenous AC9 reduces basal AC activity in COS-7 cells and splenocytes. Importantly, although AC9 is not directly inhibited by Gαi/o, it can heterodimerize with Gαi/o-regulated isoforms, AC5 and AC6.

Biomarkers from circulating neutrophil transcriptomes have potential to detect unruptured intracranial aneurysms

BACKGROUND

Intracranial aneurysms (IAs) are dangerous because of their potential to rupture and cause deadly subarachnoid hemorrhages. Previously, we found significant RNA expression differences in circulating neutrophils between patients with unruptured IAs and aneurysm-free controls. Searching for circulating biomarkers for unruptured IAs, we tested the feasibility of developing classification algorithms that use neutrophil RNA expression levels from blood samples to predict the presence of an IA.

METHODS

Neutrophil RNA extracted from blood samples from 40 patients (20 with angiography-confirmed unruptured IA, 20 angiography-confirmed IA-free controls) was subjected to next-generation RNA sequencing to obtain neutrophil transcriptomes. In a randomly-selected training cohort of 30 of the 40 samples (15 with IA, 15 controls), we performed differential expression analysis. Significantly differentially expressed transcripts (false discovery rate < 0.05, fold change ≥ 1.5) were used to construct prediction models for IA using four well-known supervised machine-learning approaches (diagonal linear discriminant analysis, cosine nearest neighbors, nearest shrunken centroids, and support vector machines). These models were tested in a testing cohort of the remaining 10 neutrophil samples from the 40 patients (5 with IA, 5 controls), and model performance was assessed by receiver-operating-characteristic (ROC) curves. Real-time quantitative polymerase chain reaction (PCR) was used to corroborate expression differences of a subset of model transcripts in neutrophil samples from a new, separate validation cohort of 10 patients (5 with IA, 5 controls).

RESULTS

The training cohort yielded 26 highly significantly differentially expressed neutrophil transcripts. Models using these transcripts identified IA patients in the testing cohort with accuracy ranging from 0.60 to 0.90. The best performing model was the diagonal linear discriminant analysis classifier (area under the ROC curve = 0.80 and accuracy = 0.90). Six of seven differentially expressed genes we tested were confirmed by quantitative PCR using isolated neutrophils from the separate validation cohort.

CONCLUSIONS

Our findings demonstrate the potential of machine-learning methods to classify IA cases and create predictive models for unruptured IAs using circulating neutrophil transcriptome data. Future studies are needed to replicate these findings in larger cohorts.

Testosterone regulates myosin II isoforms expression and functional activity in the rat prostate

BACKGROUND

Benign prostatic hyperplasia (BPH) is mainly caused by increased prostatic smooth muscle (SM) tone and prostatic volume. At the molecular level, SM myosin II (SMM II) and non-muscle myosin II (NMM II) mediate SM tone and cell proliferation while testosterone (T) plays a permissive role in the development of BPH.

AIMS

The novel objective of this study was to elucidate the effects of T on the proliferation and apoptosis of rat prostatic cells and SM contractility as well as related regulatory signaling pathways.

MATERIALS AND METHODS

Briefly, 36 male rats were divided into three groups (sham-operated, surgically castrated, and castrated with T supplementation). In vitro organ bath studies, competitive RT-PCR, Western-blotting analysis, Masson's trichrome staining, and immunofluorescence staining were performed.

RESULTS

Our data showed that castration dramatically increased prostatic SM contractility and SM MHC immunostaining revealed a relatively increased SM cell numbers in the stroma. T deprivation altered prostate SMM II isoform composition with upregulation of SM-B and SM2 but downregulation of LC17a, favoring a faster more phasic-type contraction. Moreover, protein expressions of MLCK, p-MLCP, RhoB, ROCK1, and ROCK2 increased in castrated rats. Meanwhile NMM II heavy chain isoforms A, B, and C (NMMHC-A, B, and C isoforms) were altered by castration which may be linked to decreased cell proliferation and increased apoptosis.

CONCLUSION

Our novel data demonstrated T regulates SMM II and NMM II and their functional activities in rat prostate and T ablation not only decreases prostate size (static component) but also changes the prostatic SM tone (dynamic component).

The role of mTOR-mediated signals during haemopoiesis and lineage commitment

The serine/threonine protein kinase mechanistic target of rapamycin (mTOR) has been implicated in the regulation of an array of cellular functions including protein and lipid synthesis, proliferation, cell size and survival. Here, we describe the role of mTOR during haemopoiesis within the context of mTORC1 and mTORC2, the distinct complexes in which it functions. The use of conditional transgenic mouse models specifically targeting individual mTOR signalling components, together with selective inhibitors, have generated a significant body of research emphasising the critical roles played by mTOR, and individual mTOR complexes, in haemopoietic lineage commitment and development. This review will describe the profound role of mTOR in embryogenesis and haemopoiesis, underscoring the importance of mTORC1 at the early stages of haemopoietic cell development, through modulation of stem cell potentiation and self-renewal, and erythroid and B cell lineage commitment. Furthermore, the relatively discrete role of mTORC2 in haemopoiesis will be explored during T cell development and B cell maturation. Collectively, this review aims to highlight the functional diversity of mTOR signalling and underline the importance of this pathway in haemopoiesis.

Function of Adenylyl Cyclase in Heart: the AKAP Connection

Cyclic adenosine monophosphate (cAMP), synthesized by adenylyl cyclase (AC), is a universal second messenger that regulates various aspects of cardiac physiology from contraction rate to the initiation of cardioprotective stress response pathways. Local pools of cAMP are maintained by macromolecular complexes formed by A-kinase anchoring proteins (AKAPs). AKAPs facilitate control by bringing together regulators of the cAMP pathway including G-protein-coupled receptors, ACs, and downstream effectors of cAMP to finely tune signaling. This review will summarize the distinct roles of AC isoforms in cardiac function and how interactions with AKAPs facilitate AC function, highlighting newly appreciated roles for lesser abundant AC isoforms.

Two independent but synchronized Gβγ subunit-controlled pathways are essential for trailing-edge retraction during macrophage migration

Chemokine-induced directional cell migration is a universal cellular mechanism and plays crucial roles in numerous biological processes, including embryonic development, immune system function, and tissue remodeling and regeneration. During the migration of a stationary cell, the cell polarizes, forms lamellipodia at the leading edge (LE), and triggers the concurrent retraction of the trailing edge (TE). During cell migration governed by inhibitory G protein (G_i)-coupled receptors (GPCRs), G protein βγ (Gβγ) subunits control the LE signaling. Interestingly, TE retraction has been linked to the activation of the small GTPase Ras homolog family member A (RhoA) by the Gα_12/13 pathway. However, it is not clear how the activation of G_i-coupled GPCRs at the LE orchestrates the TE retraction in RAW264.7 macrophages. Here, using an optogenetic approach involving an opsin to activate the G_i pathway in defined subcellular regions of RAW cells, we show that in addition to their LE activities, free Gβγ subunits also govern TE retraction by operating two independent, yet synchronized, pathways. The first pathway involves RhoA activation, which prevents dephosphorylation of the myosin light chain, allowing actomyosin contractility to proceed. The second pathway activates phospholipase Cβ and induces myosin light chain phosphorylation to enhance actomyosin contractility through increasing cytosolic calcium. We further show that both of these pathways are essential, and inhibition of either one is sufficient to abolish the G_i-coupled GPCR-governed TE retraction and subsequent migration of RAW cells.

CRISPR Knockout of the HuR Gene Causes a Xenograft Lethal Phenotype

Pancreatic ductal adenocarcinoma (PDA) is the third leading cause of cancer-related deaths in the United States, whereas colorectal cancer is the third most common cancer. The RNA-binding protein HuR (ELAVL1) supports a pro-oncogenic network in gastrointestinal (GI) cancer cells through enhanced HuR expression. Using a publically available database, HuR expression levels were determined to be increased in primary PDA and colorectal cancer tumor cohorts as compared with normal pancreas and colon tissues, respectively. CRISPR/Cas9 technology was successfully used to delete the HuR gene in both PDA (MIA PaCa-2 and Hs 766T) and colorectal cancer (HCT116) cell lines. HuR deficiency has a mild phenotype, in vitro, as HuR-deficient MIA PaCa-2 (MIA.HuR-KO(-/-)) cells had increased apoptosis when compared with isogenic wild-type (MIA.HuR-WT(+/+)) cells. Using this isogenic system, mRNAs were identified that specifically bound to HuR and were required for transforming a two-dimensional culture into three dimensional (i.e., organoids). Importantly, HuR-deficient MIA PaCa-2 and Hs 766T cells were unable to engraft tumors in vivo compared with control HuR-proficient cells, demonstrating a unique xenograft lethal phenotype. Although not as a dramatic phenotype, CRISPR knockout HuR HCT116 colon cancer cells (HCT.HuR-KO(-/-)) showed significantly reduced in vivo tumor growth compared with controls (HCT.HuR-WT(+/+)). Finally, HuR deletion affects KRAS activity and controls a subset of pro-oncogenic genes.Implications: The work reported here supports the notion that targeting HuR is a promising therapeutic strategy to treat GI malignancies. Mol Cancer Res; 15(6); 696-707. ©2017 AACR.

Gβγ Pathways in Cell Polarity and Migration Linked to Oncogenic GPCR Signaling: Potential Relevance in Tumor Microenvironment

Cancer cells and stroma cells in tumors secrete chemotactic agonists that exacerbate invasive behavior, promote tumor-induced angiogenesis, and recruit protumoral bone marrow-derived cells. In response to shallow gradients of chemotactic stimuli recognized by G protein-coupled receptors (GPCRs), Gβγ-dependent signaling cascades contribute to specifying the spatiotemporal assembly of cytoskeletal structures that can dynamically alter cell morphology. This sophisticated process is intrinsically linked to the activation of Rho GTPases and their cytoskeletal-remodeling effectors. Thus, Rho guanine nucleotide exchange factors, the activators of these molecular switches, and their upstream signaling partners are considered participants of tumor progression. Specifically, phosphoinositide-3 kinases (class I PI3Ks, β and γ) and P-Rex1, a Rac-specific guanine nucleotide exchange factor, are fundamental Gβγ effectors in the pathways controlling directionally persistent motility. In addition, GPCR-dependent chemotactic responses often involve endosomal trafficking of signaling proteins; coincidently, endosomes serve as signaling platforms for Gβγ In preclinical murine models of cancer, inhibition of Gβγ attenuates tumor growth, whereas in cancer patients, aberrant overexpression of chemotactic Gβγ effectors and recently identified mutations in Gβ correlate with poor clinical outcome. Here we discuss emerging paradigms of Gβγ signaling in cancer, which are essential for chemotactic cell migration and represent novel opportunities to develop pathway-specific pharmacologic treatments.

Roles of mTOR complexes in the kidney: implications for renal disease and transplantation

The mTOR pathway has a central role in the regulation of cell metabolism, growth and proliferation. Studies involving selective gene targeting of mTOR complexes (mTORC1 and mTORC2) in renal cell populations and/or pharmacologic mTOR inhibition have revealed important roles of mTOR in podocyte homeostasis and tubular transport. Important advances have also been made in understanding the role of mTOR in renal injury, polycystic kidney disease and glomerular diseases, including diabetic nephropathy. Novel insights into the roles of mTORC1 and mTORC2 in the regulation of immune cell homeostasis and function are helping to improve understanding of the complex effects of mTOR targeting on immune responses, including those that impact both de novo renal disease and renal allograft outcomes. Extensive experience in clinical renal transplantation has resulted in successful conversion of patients from calcineurin inhibitors to mTOR inhibitors at various times post-transplantation, with excellent long-term graft function. Widespread use of this practice has, however, been limited owing to mTOR-inhibitor- related toxicities. Unique attributes of mTOR inhibitors include reduced rates of squamous cell carcinoma and cytomegalovirus infection compared to other regimens. As understanding of the mechanisms by which mTORC1 and mTORC2 drive the pathogenesis of renal disease progresses, clinical studies of mTOR pathway targeting will enable testing of evolving hypotheses.

Dynamic regulation of neutrophil polarity and migration by the heterotrimeric G protein subunits Gαi-GTP and Gβγ

Activation of the Gi family of heterotrimeric guanine nucleotide-binding proteins (G proteins) releases βγ subunits, which are the major transducers of chemotactic G protein-coupled receptor (GPCR)-dependent cell migration. The small molecule 12155 binds directly to Gβγ and activates Gβγ signaling without activating the Gαi subunit in the Gi heterotrimer. We used 12155 to examine the relative roles of Gαi and Gβγ activation in the migration of neutrophils on surfaces coated with the integrin ligand intercellular adhesion molecule-1 (ICAM-1). We found that 12155 suppressed basal migration by inhibiting the polarization of neutrophils and increasing their adhesion to ICAM-1-coated surfaces. GPCR-independent activation of endogenous Gαi and Gβγ with the mastoparan analog Mas7 resulted in normal migration. Furthermore, 12155-treated cells expressing a constitutively active form of Gαi1 became polarized and migrated. The extent and duration of signaling by the second messenger cyclic adenosine monophosphate (cAMP) were enhanced by 12155. Inhibiting the activity of cAMP-dependent protein kinase (PKA) restored the polarity of 12155-treated cells but did not decrease their adhesion to ICAM-1 and failed to restore migration. Together, these data provide evidence for a direct role of activated Gαi in promoting cell polarization through a cAMP-dependent mechanism and in inhibiting adhesion through a cAMP-independent mechanism.

mTOR and differential activation of mitochondria orchestrate neutrophil chemotaxis

Neutrophil chemotaxis is regulated by opposing autocrine purinergic signaling mechanisms, which are stimulated by mitochondrial ATP formation that is up-regulated via mTOR and P2Y2 receptors at the front and down-regulated via A2a receptors and cAMP/PKA signaling at the back of cells.

Neutrophils use chemotaxis to locate invading bacteria. Adenosine triphosphate (ATP) release and autocrine purinergic signaling via P2Y2 receptors at the front and A2a receptors at the back of cells regulate chemotaxis. Here, we examined the intracellular mechanisms that control these opposing signaling mechanisms. We found that mitochondria deliver ATP that stimulates P2Y2 receptors in response to chemotactic cues, and that P2Y2 receptors promote mTOR signaling, which augments mitochondrial activity near the front of cells. Blocking mTOR signaling with rapamycin or PP242 or mitochondrial ATP production (e.g., with CCCP) reduced mitochondrial Ca²⁺ uptake and membrane potential, and impaired cellular ATP release and neutrophil chemotaxis. Autocrine stimulation of A2a receptors causes cyclic adenosine monophosphate accumulation at the back of cells, which inhibits mTOR signaling and mitochondrial activity, resulting in uropod retraction. We conclude that mitochondrial, purinergic, and mTOR signaling regulates neutrophil chemotaxis and may be a pharmacological target in inflammatory diseases.

Osthol attenuates neutrophilic oxidative stress and hemorrhagic shock-induced lung injury via inhibition of phosphodiesterase 4

Oxidative stress caused by neutrophils is an important pathogenic factor in trauma/hemorrhagic (T/H)-induced acute lung injury (ALI). Osthol, a natural coumarin found in traditional medicinal plants, has therapeutic potential in various diseases. However, the pharmacological effects of osthol in human neutrophils and its molecular mechanism of action remain elusive. In this study, our data showed that osthol potently inhibited the production of superoxide anion (O2(•-)) and reactive oxidants derived therefrom as well as expression of CD11b in N-formylmethionylleucylphenylalanine (FMLP)-activated human neutrophils. However, osthol inhibited neutrophil degranulation only slightly and it failed to inhibit the activity of subcellular NADPH oxidase. FMLP-induced phosphorylation of extracellular signal-regulated kinase (ERK) and protein kinase B (Akt) was inhibited by osthol. Notably, osthol increased the cAMP concentration and protein kinase A (PKA) activity in activated neutrophils. PKA inhibitors reversed the inhibitory effects of osthol, suggesting that these are mediated through cAMP/PKA-dependent inhibition of ERK and Akt activation. Furthermore, the activity of cAMP-specific phosphodiesterase (PDE) 4, but not PDE3 or PDE7, was significantly reduced by osthol. In addition, osthol reduced myeloperoxidase activity and pulmonary edema in rats subjected to T/H shock. In conclusion, our data suggest that osthol has effective anti-inflammatory activity in human neutrophils through the suppression of PDE4 and protects significantly against T/H shock-induced ALI in rats. Osthol may have potential for future clinical application as a novel adjunct therapy to treat lung inflammation caused by adverse circulatory conditions.

Non-muscle myosin II in disease: mechanisms and therapeutic opportunities

The actin motor protein non-muscle myosin II (NMII) acts as a master regulator of cell morphology, with a role in several essential cellular processes, including cell migration and post-synaptic dendritic spine plasticity in neurons. NMII also generates forces that alter biochemical signaling, by driving changes in interactions between actin-associated proteins that can ultimately regulate gene transcription. In addition to its roles in normal cellular physiology, NMII has recently emerged as a critical regulator of diverse, genetically complex diseases, including neuronal disorders, cancers and vascular disease. In the context of these disorders, NMII regulatory pathways can be directly mutated or indirectly altered by disease-causing mutations. NMII regulatory pathway genes are also increasingly found in disease-associated copy-number variants, particularly in neuronal disorders such as autism and schizophrenia. Furthermore, manipulation of NMII-mediated contractility regulates stem cell pluripotency and differentiation, thus highlighting the key role of NMII-based pharmaceuticals in the clinical success of stem cell therapies. In this Review, we discuss the emerging role of NMII activity and its regulation by kinases and microRNAs in the pathogenesis and prognosis of a diverse range of diseases, including neuronal disorders, cancer and vascular disease. We also address promising clinical applications and limitations of NMII-based inhibitors in the treatment of these diseases and the development of stem-cell-based therapies.

The Novel Functions of the PLC/PKC/PKD Signaling Axis in G Protein-Coupled Receptor-Mediated Chemotaxis of Neutrophils

Chemotaxis, a directional cell migration guided by extracellular chemoattractant gradients, plays an essential role in the recruitment of neutrophils to sites of inflammation. Chemotaxis is mediated by the G protein-coupled receptor (GPCR) signaling pathway. Extracellular stimuli trigger activation of the PLC/PKC/PKD signaling axis, which controls several signaling pathways. Here, we concentrate on the novel functions of PLC/PKC/PKD signaling in GPCR-mediated chemotaxis of neutrophils.

Regulation of innate immune cell function by mTOR

The innate immune system is central for the maintenance of tissue homeostasis and quickly responds to local or systemic perturbations by pathogenic or sterile insults. This rapid response must be metabolically supported to allow cell migration and proliferation and to enable efficient production of cytokines and lipid mediators. This Review focuses on the role of mammalian target of rapamycin (mTOR) in controlling and shaping the effector responses of innate immune cells. mTOR reconfigures cellular metabolism and regulates translation, cytokine responses, antigen presentation, macrophage polarization and cell migration. The mTOR network emerges as an integrative rheostat that couples cellular activation to the environmental and intracellular nutritional status to dictate and optimize the inflammatory response. A detailed understanding of how mTOR metabolically coordinates effector responses by myeloid cells will provide important insights into immunity in health and disease.

Evolving perspectives of mTOR complexes in immunity and transplantation

Since the discovery of Rapamycin (RAPA) and its immunosuppressive properties, enormous progress has been made in characterizing the mechanistic target of rapamycin (mTOR). Use of RAPA and its analogues (rapalogs) as anti-rejection agents has been accompanied by extensive investigation of how targeting of mTOR complex 1 (mTORC1), the principal target of RAPA, and more recently mTORC2, affects the function of immune cells, as well as vascular endothelial cells, that play crucial roles in regulation of allograft rejection. While considerable knowledge has accumulated on the function of mTORC1 and 2 in T cells, understanding of the differential roles of these complexes in antigen-presenting cells, NK cells and B cells/plasma cells is only beginning to emerge. Immune cell-specific targeting of mTORC1 or mTORC2, together with use of novel, second generation, dual mTORC kinase inhibitors (TORKinibs) have started to play an important role in elucidating the roles of these complexes and their potential for targeting in transplantation. Much remains unknown about the role of mTOR complexes and the consequences of mTOR targeting on immune reactivity in clinical transplantation. Here we address recent advances in understanding and evolving perspectives of the role of mTOR complexes and mTOR targeting in immunity, with extrapolation to transplantation.

Genetics and pathogenesis of systemic lupus erythematosus and lupus nephritis

Systemic lupus erythematosus (SLE) is a multisystem autoimmune disorder that has a broad spectrum of effects on the majority of organs, including the kidneys. Approximately 40-70% of patients with SLE will develop lupus nephritis. Renal assault during SLE is initiated by genes that breach immune tolerance and promote autoantibody production. These genes might act in concert with other genetic factors that augment innate immune signalling and IFN-I production, which in turn can generate an influx of effector leucocytes, inflammatory mediators and autoantibodies into end organs, such as the kidneys. The presence of cognate antigens in the glomerular matrix, together with intrinsic molecular abnormalities in resident renal cells, might further accentuate disease progression. This Review discusses the genetic insights and molecular mechanisms for key pathogenic contributors in SLE and lupus nephritis. We have categorized the genes identified in human studies of SLE into one of four pathogenic events that lead to lupus nephritis. We selected these categories on the basis of the cell types in which these genes are expressed, and the emerging paradigms of SLE pathogenesis arising from murine models. Deciphering the molecular basis of SLE and/or lupus nephritis in each patient will help physicians to tailor specific therapies.