p85 regulatory subunit of PI3K mediates cAMP-PKA and estrogens biological effects on growth and survival

The Role of PIK3R1 in Metabolic Function and Insulin Sensitivity

PIK3R1 (also known as p85α) is a regulatory subunit of phosphoinositide 3-kinases (PI3Ks). PI3K, a heterodimer of a regulatory subunit and a catalytic subunit, phosphorylates phosphatidylinositol into secondary signaling molecules involved in regulating metabolic homeostasis. PI3K converts phosphatidylinositol 4,5-bisphosphate (PIP2) to phosphatidylinositol 3,4,5-triphosphate (PIP3), which recruits protein kinase AKT to the inner leaflet of the cell membrane to be activated and to participate in various metabolic functions. PIK3R1 stabilizes and inhibits p110 catalytic activity and serves as an adaptor to interact with insulin receptor substrate (IRS) proteins and growth factor receptors. Thus, mutations in PIK3R1 or altered expression of PIK3R1 could modulate the activity of PI3K and result in significant metabolic outcomes. Interestingly, recent studies also found PI3K-independent functions of PIK3R1. Overall, in this article, we will provide an updated review of the metabolic functions of PIK3R1 that includes studies of PIK3R1 in various metabolic tissues using animal models, the mechanisms modulating PIK3R1 activity, and studies on the mutations of human PIK3R1 gene.

PDE4 inhibitor eliminates breast cancer stem cells via noncanonical activation of mTOR

Ineffective cancer treatment is implicated in metastasis, recurrence, resistance to chemotherapy and radiotherapy, and evasion of immune surveillance. All these failures occur due to the persistence of cancer stem cells (CSCs) even after rigorous therapy, thereby rendering them as essential targets for cancer management. Contrary to the quiescent nature of CSCs, a gene profiler array disclosed that phosphatidylinositol-3-kinase (PI3K), which is known to be crucial for cell proliferation, differentiation, and survival, was significantly upregulated in CSCs. Since PI3K is modulated by cyclic adenosine 3',5' monophosphate (cAMP), analyses of cAMP regulation revealed that breast CSCs expressed increased levels of phosphodiesterase 4 (PDE4) in contrast to normal stem cells. In accordance, the effects of rolipram, a PDE4 inhibitor, were evaluated on PI3K regulators and signaling. The efficacy of rolipram was compared with paclitaxel, an anticancer drug that is ineffective in obliterating breast CSCs. Analyses of downstream signaling components revealed a switch between cell survival and death, in response to rolipram, specifically of the CSCs. Rolipram-mediated downregulation of PDE4A levels in breast CSCs led to an increase in cAMP levels and protein kinase A (PKA) expression. Subsequently, PKA-mediated upregulation of phosphatase and tensin homolog antagonized the PI3K/AKT/mTOR pathway and led to cell cycle arrest. Interestingly, direct yet noncanonical activation of mTOR by PKA, circumventing the influence of PI3K and AKT, temporally shifted the fate of CSCs toward apoptosis. Rolipram in combination with paclitaxel indicated synergistic consequences, which effectively obliterated CSCs within a tumor, thereby suggesting combinatorial therapy as a sustainable and effective strategy to abrogate breast CSCs for better patient prognosis.

The Role of Curcumin in Prostate Cancer Cells and Derived Spheroids

A major challenge in the clinical management of prostate cancer (PC) is to inhibit tumor growth and prevent metastatic spreading. In recent years, considerable efforts have been made to discover new compounds useful for PC therapy, and promising advances in this field were reached. Drugs currently used in PC therapy frequently induce resistance and PC progresses toward metastatic castration-resistant forms (mCRPC), making it virtually incurable. Curcumin, a commercially available nutritional supplement, represents an attractive therapeutic agent for mCRPC patients. In the present study, we compared the effects of chemotherapeutic drugs such as docetaxel, paclitaxel, and cisplatin, to curcumin, on two PC cell lines displaying a different metastatic potential: DU145 (moderate metastatic potential) and PC-3 (high metastatic potential). Our results revealed a dose-dependent reduction of DU145 and PC-3 cell viability upon treatment with curcumin similar to chemotherapeutic agents (paclitaxel, cisplatin, and docetaxel). Furthermore, we explored the EGFR-mediated signaling effects on ERK activation in DU145 and PC-3 cells. Our results showed that DU145 and PC-3 cells overexpress EGFR, and the treatment with chemotherapeutic agents or curcumin reduced EGFR expression levels and ERK activation. Finally, chemotherapeutic agents and curcumin reduced the size of DU145 and PC-3 spheroids and have the potential to induce apoptosis and also in Matrigel. In conclusion, despite different studies being carried out to identify the potential synergistic curcumin combinations with chemopreventive/therapeutic efficacy for inhibiting PC growth, the results show the ability of curcumin used alone, or in combinatorial approaches, to impair the size and the viability of PC-derived spheroids.

Titanium Functionalized with Polylysine Homopolymers: In Vitro Enhancement of Cells Growth

In oral implantology, the success and persistence of dental implants over time are guaranteed by the bone formation around the implant fixture and by the integrity of the peri-implant mucosa seal, which adheres to the abutment and becomes a barrier that hinders bacterial penetration and colonization close to the outer parts of the implant. Research is constantly engaged in looking for substances to coat the titanium surface that guarantees the formation and persistence of the peri-implant bone, as well as the integrity of the mucous perimeter surrounding the implant crown. The present study aimed to evaluate in vitro the effects of a titanium surface coated with polylysine homopolymers on the cell growth of dental pulp stem cells and keratinocytes to establish the potential clinical application. The results reported an increase in cell growth for both cellular types cultured with polylysine-coated titanium compared to cultures without titanium and those without coating. These preliminary data suggest the usefulness of polylysine coating not only for enhancing osteoinduction but also to speed the post-surgery mucosal healings, guarantee appropriate peri-implant epithelial seals, and protect the fixture against bacterial penetration, which is responsible for compromising the implant survival.

The In Vitro Effect of Steroid Hormones, Arachidonic Acid, and Kinases Inhibitors on Aquaporin 1, 2, 5, and 7 Gene Expression in the Porcine Uterine Luminal Epithelial Cells during the Estrous Cycle

Aquaporins (AQPs) are integral membrane proteins, which play an important role in water homeostasis in the uterus. According to the literature, the expression of aquaporins in reproductive structures depends on the local hormonal milieu. The current study investigated the effect of selected PKA kinase inhibitor H89 and MAPK kinase inhibitor PD98059, on the expression of AQP1, 2, 5, and 7, and steroid hormones (E₂), progesterone (P₄), and arachidonic acid (AA) in the porcine endometrium on days 18–20 and 2–4 of the estrous cycle (the follicular phase where estrogen and follicle-stimulating hormone (FSH) are secreted increasingly in preparation for estrus and the luteal phase where the ovarian follicles begin the process of luteinization with the formation of the corpus luteum and progesterone secretion, respectively). The luminal epithelial cells were incubated in vitro in the presence of the aforementioned factors. The expression of mRNA was determined by the quantitative real-time PCR technique. In general, in Experiment 1, steroid hormones significantly increased expression of AQP1, 2, and 5 while arachidonic acid increased expression of AQP2 and AQP7. On the other hand, MAPK kinase inhibitor significantly decreased the expression of AQP1 and 5. In Experiment 2, E₂, P₄, or AA combined with kinase inhibitors differentially affected on AQPs expression. E₂ in combination with PKA inhibitor significantly decreased expression of AQP1 but E₂ or P₄ combined with this inhibitor increased the expression of AQP5 and 7. On the contrary, E₂ with PD98059 significantly increased AQP5 and AQP7 expression. Progesterone in combination with MAPK kinase inhibitor significantly downregulated the expression of AQP5 and upregulated AQP7. Arachidonic acid mixed with H89 or PD98059 caused a decrease in the expression of AQP5 and an increase of AQP7. The obtained results indicate that estradiol, progesterone, and arachidonic acid through PKA and MAPK signaling pathways regulate the expression of AQP1 and AQP5 in the porcine luminal epithelial cells in the periovulatory period.

MPPED2 is downregulated in glioblastoma, and its restoration inhibits proliferation and increases the sensitivity to temozolomide of glioblastoma cells

Glioblastoma (GBM) is the most aggressive and lethal neoplasia of the central nervous system in adults. Based on the molecular signature genes, GBM has been classified in proneural, neural, mesenchymal and classical subtypes. The Metallophosphoesterase-domain-containing protein 2 (MPPED2) gene encodes a metallophosphodiesterase protein highly conserved throughout the evolution. MPPED2 downregulation, likely due to its promoter hypermethylation, has been found in several malignant neoplasias and correlated with a poor prognosis. In this study, we aimed to investigate the expression and the functional role of MPPED2 in GBM. TCGA and Gravendeel databases were employed to explore the MPPED2 expression levels in this type of tumor. We have found that MPPED2 expression is downregulated in GBM patients, showing a positive correlation with survival. Moreover, TCGA and Gravendeel data also revealed that MPPED2 expression negatively correlates with the most aggressive mesenchymal subtype. Additionally, the restoration of MPPED2 expression in U251 and GLI36 GBM cell lines decreases cell growth, migration and enhanced the sensitivity to the temozolomide, inducing apoptotic cell death, of GBM cells. These findings suggest that the restoration of MPPED2 function can be taken into consideration for an innovative GBM therapy.

Glucagon-like peptide 1 treatment reverses vascular remodelling by downregulating matrix metalloproteinase 1 expression through inhibition of the ERK1/2/NF-κB signalling pathway

In addition to serving as an incretin-based treatment of type 2 diabetes mellitus (T2DM), glucagon-like peptide 1 (GLP-1) can also reverse cardiovascular diseases caused by vascular remodelling. However, a detailed mechanism underlying how GLP-1 reverses vascular remodelling remains unclear. Here, Spontaneous hypertension rats (SHR) were used as an in vivo model of vascular remodelling. Treatment with a GLP-1 receptor (GLP-1R) agonist Liraglutide or dipeptidyl peptidase 4 (DPP4) inhibitor Alogliptin decreased systolic blood pressure (SBP), diastolic blood pressure (DBP), thickness of vascular wall, and overall collagen levels in SHR. In vitro vascular remodelling can be induced by exposing rat aortic smooth muscle cells (RASMC) to angiotensin II (Ang II); GLP-1 treatment attenuated AngII induction of RASMC proliferation, migration, and excessive extracellular matrix (ECM) degradation. Downregulation of matrix metalloproteinase 1 (MMP1) enhanced the inhibitory effects of GLP-1, and extracellular regulated protein kinase 1/2 (ERK1/2) and nuclear factor kappa-B (NF-κB) signalling participated in these processes. These results provide a new mechanistic understanding of key therapeutic strategies for the treatment of vascular remodelling-related diseases.

The Crosstalk between Prostate Cancer and Microbiota Inflammation: Nutraceutical Products Are Useful to Balance This Interplay?

The human microbiota shows pivotal roles in urologic health and disease. Emerging studies indicate that gut and urinary microbiomes can impact several urological diseases, both benignant and malignant, acting particularly on prostate inflammation and prostate cancer. Indeed, the microbiota exerts its influence on prostate cancer initiation and/or progression mechanisms through the regulation of chronic inflammation, apoptotic processes, cytokines, and hormonal production in response to different pathogenic noxae. Additionally, therapies' and drugs' responses are influenced in their efficacy and tolerability by microbiota composition. Due to this complex potential interconnection between prostate cancer and microbiota, exploration and understanding of the involved relationships is pivotal to evaluate a potential therapeutic application in clinical practice. Several natural compounds, moreover, seem to have relevant effects, directly or mediated by microbiota, on urologic health, posing the human microbiota at the crossroad between prostatic inflammation and prostate cancer development. Here, we aim to analyze the most recent evidence regarding the possible crosstalk between prostate, microbiome, and inflammation.

Sex Hormones and Inflammation Role in Oral Cancer Progression: A Molecular and Biological Point of View

Oral cancers have been proven to arise from precursors lesions and to be related to risk behaviour such as alcohol consumption and smoke. However, the present paper focuses on the role of chronic inflammation, related to chronical oral infections and/or altered immune responses occurring during dysimmune and autoimmune diseases, in the oral cancerogenesis. Particularly, oral candidiasis and periodontal diseases introduce a vicious circle of nonhealing and perpetuation of the inflammatory processes, thus leading toward cancer occurrence via local and systemic inflammatory modulators and via genetic and epigenetic factors.

The Alzheimer's Disease-Associated Protein BACE1 Modulates T Cell Activation and Th17 Function

β-site amyloid precursor protein-cleaving enzyme 1 (BACE1) is best known for its role in Alzheimer's disease amyloid plaque formation but also contributes to neurodegenerative processes triggered by CNS injury. In this article, we report that BACE1 is expressed in murine CD4⁺ T cells and regulates signaling through the TCR. BACE1-deficient T cells have reduced IL-17A expression under Th17 conditions and reduced CD73 expression in Th17 and inducible T regulatory cells. However, induction of the Th17 and T regulatory transcription factors RORγt and Foxp3 was unaffected. BACE1-deficient T cells showed impaired pathogenic function in experimental autoimmune encephalomyelitis. These data identify BACE1 as a novel regulator of T cell signaling pathways that impact autoimmune inflammatory T cell function.

Endocrine disruption through membrane estrogen receptors and novel pathways leading to rapid toxicological and epigenetic effects

Estrogen binding to estrogen receptors (ESR) triggers signaling cascades within cells. Historically, a major emphasis has been characterizing estrogen-induced genomic actions resulting from binding to nuclear estrogen receptor 1 (nESR1). However, recent evidence indicates the first receptors estrogens encounter as they enter a cell, membrane ESR1 (mESR1), also play crucial roles. Membrane and nuclear ESR are derived from the same transcripts but the former are directed to the membrane via palmitoylation. Binding and activation of mESR1 leads to rapid fluctuations in cAMP and Ca+2 and stimulation of protein kinase pathways. Endocrine disrupting chemicals (EDC) that mimic 17β-estradiol can signal through mESR1 and elicit non-genomic effects. Most current EDC studies have focused on genomic actions via nESR1. However, increasing number of studies have begun to examine potential EDC effects mediated through mESR1, and some EDC might have higher potency for signaling through mESR1 than nESR1. The notion that such chemicals might also affect mESR1 signaling via palmitoylation and depalmitoylation pathways has also begun to gain currency. Recent development of transgenic mice that lack either mESR1 or nESR1, while retaining functional ESR1 in the other compartment, will allow more precise in vivo approaches to determine EDC effects through nESR1 and/or mESR1. It is increasingly becoming apparent in this quickly evolving field that EDC directly affect mESR and estrogen signaling, but such chemicals can also affect proportion of ESR reaching the membrane. Future EDC studies should be designed to consider the full range of effects through mESR alone and in combination with nESR.

M1 muscarinic receptors regulate the phosphorylation of AMPA receptor subunit GluA1 via a signaling pathway linking cAMP-PKA and PI3K-Akt

M1 muscarinic acetylcholine receptors are highly expressed in key areas that control cognition, such as the cortex and hippocampus, representing one potential therapeutic target for cognitive dysfunctions of Alzheimer's disease and schizophrenia. We have reported that M1 receptors facilitate cognition by promoting membrane insertion of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor AMPA receptor subunit 1 (GluA1) through phosphorylation at Ser845. However, the signaling pathway is still unclear. Here we showed that adenylyl cyclase inhibitor 2',5'-dideoxyadenosine and PKA inhibitor KT5720 inhibited enhancement of phosphorylation of Ser845 and membrane insertion of GluA1 induced by M1 receptor activation. Furthermore, PI3K inhibitor LY294002 and protein kinase B (Akt) inhibitor IV blocked the effects of M1 receptors as well. Remarkably, the increase of the activity of PI3K-Akt signaling induced by M1 receptor activation could be abolished by cAMP-PKA inhibitors. Moreover, inhibiting the mammalian target of rapamycin (mTOR) complex 1, an important downstream effector of PI3K-Akt, by short-term application of rapamycin attenuated the effects of M1 receptors on GluA1. Furthermore, such effect was unrelated to possible protein synthesis promoted by mTOR. Taken together, these data demonstrate that M1 receptor activation induces membrane insertion of GluA1 via a signaling linking cAMP-PKA and PI3K-Akt-mTOR pathways but is irrelevant to protein synthesis.-Zhao, L.-X., Ge, Y.-H., Li, J.-B., Xiong, C.-H., Law, P.-Y., Xu, J.-R., Qiu, Y., Chen, H.-Z. M1 muscarinic receptors regulate the phosphorylation of AMPA receptor subunit GluA1 via a signaling pathway linking cAMP-PKA and PI3K-Akt.

PKA at a Cross-Road of Signaling Pathways Involved in the Regulation of Glioblastoma Migration and Invasion by the Neuropeptides VIP and PACAP

Glioblastoma (GBM) remains an incurable disease, mainly due to the high migration and invasion potency of GBM cells inside the brain. PI3K/Akt, Sonic Hedgehog (SHH), and PKA pathways play major regulatory roles in the progression of GBM. The vasoactive intestinal peptide (VIP) family of neuropeptides and their receptors, referred in this article as the “VIP-receptor system”, has been reported to regulate proliferation, differentiation, and migration in a number of tumor cell types and more particularly in GBM cells. These neuropeptides are potent activators of the cAMP/PKA pathway. The present study aimed to investigate the cross-talks between the above cited signaling cascades. Regulation by VIP-related neuropeptides of GBM migration and invasion was evaluated ex vivo in rat brain slices explanted in culture. Effects of different combinations of VIP-related neuropeptides and of pharmacological and siRNA inhibitors of PKA, Akt, and of the SHH/GLI1 pathways were tested on GBM migration rat C6 and human U87 GBM cell lines using the wound-healing technique. Quantification of nuclear GLI1, phospho-Akt, and phospho-PTEN was assessed by western-immunoblotting. The VIP-receptor system agonists VIP and PACAP-38 significantly reduced C6 cells invasion in the rat brain parenchyma ex vivo, and C6 and U87 migration in vitro. A VIP-receptor system antagonist, VIP_10-28 increased C6 cell invasion in the rat brain parenchyma ex vivo, and C6 and migration in vitro. These effects on cell migration were abolished by selective inhibitors of the PI3K/Akt and of the SHH pathways. Furthermore, VIP and PACAP-38 reduced the expression of nuclear GLI1 while VIP_10-28 increased this expression. Selective inhibitors of Akt and PKA abolished VIP, PACAP-38, and VIP_10-28 effects on nuclear GLI1 expression in C6 cells. PACAP-38 induced a time-dependent inhibition of phospho-Akt expression and an increased phosphorylation of PTEN in C6 cells. All together, these data indicate that triggering the VIP-receptor system reduces migration and invasion in GBM cells through a PKA-dependent blockade of the PI3K/Akt and of the SHH/GLI1 pathways. Therefore, the VIP-receptor system displays anti-oncogenic properties in GBM cells and PKA is a central core in this process.

Cell penetrating peptides to dissect host-pathogen protein-protein interactions in Theileria-transformed leukocytes

One powerful application of cell penetrating peptides is the delivery into cells of molecules that function as specific competitors or inhibitors of protein-protein interactions. Ablating defined protein-protein interactions is a refined way to explore their contribution to a particular cellular phenotype in a given disease context. Cell-penetrating peptides can be synthetically constrained through various chemical modifications that stabilize a given structural fold with the potential to improve competitive binding to specific targets. Theileria-transformed leukocytes display high PKA activity, but PKA is an enzyme that plays key roles in multiple cellular processes; consequently genetic ablation of kinase activity gives rise to a myriad of confounding phenotypes. By contrast, ablation of a specific kinase-substrate interaction has the potential to give more refined information and we illustrate this here by describing how surgically ablating PKA interactions with BAD gives precise information on the type of glycolysis performed by Theileria-transformed leukocytes. In addition, we provide two other examples of how ablating specific protein-protein interactions in Theileria-infected leukocytes leads to precise phenotypes and argue that constrained penetrating peptides have great therapeutic potential to combat infectious diseases in general.

Estrogens in Male Physiology

Estrogens have historically been associated with female reproduction, but work over the last two decades established that estrogens and their main nuclear receptors (ESR1 and ESR2) and G protein-coupled estrogen receptor (GPER) also regulate male reproductive and nonreproductive organs. 17β-Estradiol (E2) is measureable in blood of men and males of other species, but in rete testis fluids, E2 reaches concentrations normally found only in females and in some species nanomolar concentrations of estrone sulfate are found in semen. Aromatase, which converts androgens to estrogens, is expressed in Leydig cells, seminiferous epithelium, and other male organs. Early studies showed E2 binding in numerous male tissues, and ESR1 and ESR2 each show unique distributions and actions in males. Exogenous estrogen treatment produced male reproductive pathologies in laboratory animals and men, especially during development, and studies with transgenic mice with compromised estrogen signaling demonstrated an E2 role in normal male physiology. Efferent ductules and epididymal functions are dependent on estrogen signaling through ESR1, whose loss impaired ion transport and water reabsorption, resulting in abnormal sperm. Loss of ESR1 or aromatase also produces effects on nonreproductive targets such as brain, adipose, skeletal muscle, bone, cardiovascular, and immune tissues. Expression of GPER is extensive in male tracts, suggesting a possible role for E2 signaling through this receptor in male reproduction. Recent evidence also indicates that membrane ESR1 has critical roles in male reproduction. Thus estrogens are important physiological regulators in males, and future studies may reveal additional roles for estrogen signaling in various target tissues.

PKA and Apicomplexan Parasite Diseases

The cAMP-dependent protein kinase PKA is a well-characterized member of the serine-threonine protein AGC kinase family and is the effector kinase of cAMP signaling. As such, PKA is involved in the control of a wide variety of cellular processes including metabolism, cell growth, gene expression and apoptosis. cAMP-dependent PKA signaling pathways play important roles during infection and virulence of various pathogens. Since fluxes in cAMP are involved in multiple intracellular functions, a variety of different pathological infectious processes can be affected by PKA signaling pathways. Here, we highlight some features of cAMP-PKA signaling that are relevant to Plasmodium falciparum-infection of erythrocytes and present an update on AKAP targeting of PKA in PGE2 signaling via EP4 in Theileria annulata-infection of leukocytes and discuss cAMP-PKA signling in Toxoplasma.

cAMP Signaling of Adenylate Cyclase Toxin Blocks the Oxidative Burst of Neutrophils through Epac-Mediated Inhibition of Phospholipase C Activity

The adenylate cyclase toxin-hemolysin (CyaA) plays a key role in immune evasion and virulence of the whooping cough agent Bordetella pertussis. CyaA penetrates the complement receptor 3-expressing phagocytes and ablates their bactericidal capacities by catalyzing unregulated conversion of cytosolic ATP to the key second messenger molecule cAMP. We show that signaling of CyaA-generated cAMP blocks the oxidative burst capacity of neutrophils by two converging mechanisms. One involves cAMP/protein kinase A-mediated activation of the Src homology region 2 domain-containing phosphatase-1 (SHP-1) and limits the activation of MAPK ERK and p38 that are required for assembly of the NADPH oxidase complex. In parallel, activation of the exchange protein directly activated by cAMP (Epac) provokes inhibition of the phospholipase C by an as yet unknown mechanism. Indeed, selective activation of Epac by the cell-permeable analog 8-(4-chlorophenylthio)-2'-O-methyladenosine-3',5'-cyclic monophosphate counteracted the direct activation of phospholipase C by 2,4,6-trimethyl-N-[3-(trifluoromethyl)phenyl]benzenesulfonamide. Hence, by inhibiting production of the protein kinase C-activating lipid, diacylglycerol, cAMP/Epac signaling blocks the bottleneck step of the converging pathways of oxidative burst triggering. Manipulation of neutrophil membrane composition by CyaA-produced signaling of cAMP thus enables B. pertussis to evade the key innate host defense mechanism of reactive oxygen species-mediated killing of bacteria by neutrophils.

Mitochondrial cAMP signaling

Cyclic adenosine 3, 5'-monophosphate (cAMP) is a ubiquitous second messenger regulating many biological processes, such as cell migration, differentiation, proliferation and apoptosis. cAMP signaling functions not only on the plasma membrane, but also in the nucleus and in organelles such as mitochondria. Mitochondrial cAMP signaling is an indispensable part of the cytoplasm-mitochondrion crosstalk that maintains mitochondrial homeostasis, regulates mitochondrial dynamics, and modulates cellular stress responses and other signaling pathways. Recently, the compartmentalization of mitochondrial cAMP signaling has attracted great attentions. This new input should be carefully taken into account when we interpret the findings of mitochondrial cAMP signaling. In this review, we summarize previous and recent progress in our understanding of mitochondrial cAMP signaling, including the components of the signaling cascade, and the function and regulation of this signaling pathway in different mitochondrial compartments.

TDRG1 functions in testicular seminoma are dependent on the PI3K/Akt/mTOR signaling pathway

Human testis development-related gene 1 (TDRG1) is a recently identified gene that is expressed exclusively in the testes and promotes the development of testicular germ cell tumors. In this study, the role of TDRG1 in the development of testicular seminoma, which is the most common testicular germ cell tumor, was further investigated. Based on polymerase chain reaction, Western blotting, and immunohistochemistry tests, both gene and protein expression levels of TDRG1 were significantly upregulated in testicular seminoma tissues compared with normal testicular tissues. Additionally, the levels of phosphoinositide-3 kinase (PI3K)/p110 and Akt phosphorylation were dramatically upregulated in testicular seminoma tissues. Accordingly, in our cell experiment, seminoma TCam-2 cells were subjected to different treatments: the TDRG1 knockout, TDRG1 overexpression, PI3K inhibition (LY294002 administration), or PI3K activation (insulin-like growth factor-1 administration). Cell proliferation, the proliferation index, apoptosis rate, cell adhesive capacity, and cell invasion capability were assessed. Cells with both TDRG1 knockout and PI3K inhibition exhibited decreased cell proliferation, proliferation indexes, cell adhesion capacity, and cell invasion capability and increased apoptosis rates. Most of these effects were reversed by TDRG1 overexpression or PI3K activation, indicating that both TDRG1- and PI3K-mediated signaling promote proliferation and invasion of testicular seminoma cells. The knockout of TDRG1 significantly decreased the phosphorylation levels of PI3K/p85, PI3K/p110, Akt, and mammalian target of rapamycin (mTOR; Ser²⁴⁴⁸). Except for PI3K/p110, TDRG1 overexpression had the opposite effects on phosphorylation levels. Phosphorylated mTOR at Ser²⁴⁸¹ and Thr²⁴⁴⁶ was not affected by TDRG1 or PI3K in our tests. Thus, these results indicate that TDRG1 promotes the development and migration of seminoma cells via the regulation of the PI3K/Akt/mTOR signaling pathway; this contributes to an understanding of the precise mechanisms underlying the development and migration of seminomas and lays a theoretical foundation for the development of appropriate therapies.

The p85 regulatory subunit of PI3K mediates cAMP-PKA and insulin biological effects on MCF-7 cell growth and motility

Recent studies have shown that hyperinsulinemia may increase the cancer risk. Moreover, many tumors demonstrate an increased activation of IR signaling pathways. Phosphatidylinositol 3-kinase (PI3K) is necessary for insulin action. In epithelial cells, which do not express GLUT4 and gluconeogenic enzymes, insulin-mediated PI3K activation regulates cell survival, growth, and motility. Although the involvement of the regulatory subunit of PI3K (p85α (PI3K)) in insulin signal transduction has been extensively studied, the function of its N-terminus remains elusive. It has been identified as a serine (S83) in the p85α (PI3K) that is phosphorylated by protein kinase A (PKA). To determine the molecular mechanism linking PKA to insulin-mediated PI3K activation, we used p85α (PI3K) mutated forms to prevent phosphorylation (p85A) or to mimic the phosphorylated residue (p85D). We demonstrated that phosphorylation of p85α (PI3K)S83 modulates the formation of the p85α (PI3K)/IRS-1 complex and its subcellular localization influencing the kinetics of the insulin signaling both on MAPK-ERK and AKT pathways. Furthermore, the p85α (PI3K)S83 phosphorylation plays a central role in the control of insulin-mediated cell proliferation, cell migration, and adhesion. This study highlights the p85α (PI3K)S83 role as a key regulator of cell proliferation and motility induced by insulin in MCF-7 cells breast cancer model.

cAMP signalling in the normal and tumorigenic pituitary gland

cAMP signalling plays a key role in the normal physiology of the pituitary gland, regulating cellular growth and proliferation, hormone production and release. Deregulation of the cAMP signalling pathway has been reported to be a common occurrence in pituitary tumorigenesis. Several mechanisms have been implicated including somatic mutations, gene-gene interactions and gene-environmental interactions. Somatic mutations in G-proteins and protein kinases directly alter cAMP signalling, while malfunctioning of other signalling pathways such as the Raf/MAPK/ERK, PI3K/Akt/mTOR and Wnt pathways which normally interact with the cAMP pathway may mediate indirect effects on cAMP and varying downstream effectors. The aryl hydrocarbon receptor signalling pathway has been implicated in pituitary tumorigenesis and we review its role in general and specifically in relation to cAMP de-regulation.

PKA and CaMKII mediate PI3K activation in bovine sperm by inhibition of the PKC/PP1 cascade

To enable fertilization, spermatozoa must undergo several biochemical processes in the female reproductive tract, collectively called capacitation. These processes involve protein kinase A (PKA)-dependent protein tyrosine phosphorylation including phosphatidylinositol-3-kinase (PI3K). It is not known how PKA, a serine/threonine (S/T) kinase, mediates tyrosine phosphorylation of proteins. We recently showed that inhibition of S/T phosphatase 1 (PP1) causes a significant increase in phospho-PI3K. In this study, we propose a mechanism by which PKA and PP1 mediate an increase in PI3K tyrosine phosphorylation and implicate calmodulin-dependent kinase II (CaMKII) in this process. Inhibition of sperm PP1 or PKC, stimulated CaMKII phosphorylation/activation, and inhibition of PKC enhanced PP1 phosphorylation/inactivation. Inhibition of CaMKII, using KN-93, caused significant reduction in phospho-PP1, indicating its activation. Moreover, KN-93 prevented the dephosphorylation/inactivation of PKC. We therefore suggest that CaMKII inhibits PKC, leading to PP1 inhibition and the reciprocal auto-activation of CaMKII. Thus, CaMKII can regulate its own activation by inhibiting the PKC/PP1 cascade. Inhibition of Src family kinases (SFK) caused significant inhibition of CaMKII and PP1 phosphorylation, suggesting that SFK activity results in PP1 inhibition and CaMKII activation. Activation of sperm PKA by 8Br-cAMP revealed an increase in phospho-CaMKII, which was inhibited by PKA inhibitor. Tyrosine phosphorylation of PI3K was stimulated by 8Br-cAMP and by PKC or PP1 inhibition and was abrogated by CaMKII inhibition. Furthermore, phosphorylation/activation of the tyrosine kinase Pyk2 was enhanced by PP1 inhibition, and this activation is blocked by CaMKII inhibition. Thus, PKA activates Src, which inhibits PP1, leading to CaMKII and Pyk2 activation, resulting in PI3K tyrosine phosphorylation/activation.

Mechanisms for luteinizing hormone induction of growth hormone gene transcription in fish model: crosstalk of the cAMP/PKA pathway with MAPK-and PI3K-dependent cascades

In our previous studies in grass carp pituitary cells, local production of luteinizing hormone (LH) was shown to induce growth hormone (GH) production and gene expression, which constitutes a major component of the "intrapituitary feedback loop" regulating GH secretion and synthesis via autocrine/paracrine interactions between gonadotrophs and somatotrophs in the carp pituitary. To further investigate the signaling mechanisms mediating LH action at the transcriptional level, promoter studies were performed in GH3 cells co-transfected with the expression vector for carp LH receptor and luciferase-expressing reporter constructs with grass carp GH promoter. In this cell model, treatment with human chorionic gonadotropin (hCG) was effective in increasing GH promoter activity and the responsive sequence was mapped to position -616 and -572 of the grass carp GH promoter. GH promoter activation induced by hCG occurred with concurrent rise in cAMP production, CREB phosphorylation, and could be inhibited by inactivation of adenylate cyclase (AC), PKA, MEK1/2, P(38) MAPK, PI3K and mTOR. AC activation, presumably via cAMP production, could mimic hCG-induced CREB phosphorylation and GH promoter activity, and these stimulatory effects were also sensitive to the blockade of PKA-, MAPK- and PI3K- dependent cascades. These results, as a whole, suggest that LH receptor activation in the carp pituitary may trigger GH gene transcription through CREB phosphorylation as a result of the functional crosstalk of the cAMP/PKA pathway with MAPK-and PI3K-dependent cascades.

PKD1 mediates negative feedback of PI3K/Akt activation in response to G protein-coupled receptors

We examined whether protein kinase D1 (PKD1) mediates negative feeback of PI3K/Akt signaling in intestinal epithelial cells stimulated with G protein-coupled receptor (GPCR) agonists. Exposure of intestinal epithelial IEC-18 cells to increasing concentrations of the PKD family inhibitor kb NB 142­70, at concentrations that inhibited PKD1 activation, strikingly potentiated Akt phosphorylation at Thr³⁰⁸ and Ser⁴⁷³ in response to the mitogenic GPCR agonist angiotensin II (ANG II). Enhancement of Akt activation by kb NB 142-70 was also evident in cells with other GPCR agonists, including vasopressin and lysophosphatidic acid. Cell treatment rovincial Hospital Affiliated to Shandong University, Jinan, China with the structurally unrelated PKD family inhibitor CRT0066101 increased Akt phosphorylation as potently as kb NB 142–70. Knockdown of PKD1 with two different siRNAs strikingly enhanced Akt phosphorylation in response to ANG II stimulation in IEC-18 cells. To determine whether treatment with kb NB 142–70 enhances accumulation of phosphatidylinositol (3,4,5)-trisphosphate (PIP₃) in the plasma membrane, we monitored the redistribution of Akt-pleckstrin homology domain-green fluorescent protein (Akt-PH-GFP) in single IEC-18 cells. Exposure to kb NB 142–70 strikingly increased membrane accumulation of Akt-PH-GFP in response to ANG II. The translocation of the PIP₃ sensor to the plasma membrane and the phosphorylation of Akt was completed prevented by prior exposure to the class I p110α specific inhibitor A66. ANG II markedly increased the phosphorylation of p85α detected by a PKD motif-specific antibody and enhanced the association of p85α with PTEN. Transgenic mice overexpressing PKD1 showed a reduced phosphorylation of Akt at Ser⁴⁷³ in intestinal epithelial cells compared to wild type littermates. Collectively these results indicate that PKD1 activation mediates feedback inhibition of PI3K/Akt signaling in intestinal epithelial cells in vitro and in vivo.

Phosphodiesterase III inhibition increases cAMP levels and augments the infarct size limiting effect of a DPP-4 inhibitor in mice with type-2 diabetes mellitus

PURPOSE

We assessed whether phosphodiesterase-III inhibition with cilostazol (Cil) augments the infarct size (IS)-limiting effects of MK0626 (MK), a dipeptidyl-peptidase-4 (DPP4) inhibitor, by increasing intracellular cAMP in mice with type-2 diabetes.

METHODS

Db/Db mice received 3-day MK (0, 1, 2 or 3 mg/kg/d) with or without Cil (15 mg/kg/d) by oral gavage and were subjected to 30 min coronary artery occlusion and 24 h reperfusion.

RESULTS

Cil and MK at 2 and 3 mg/kg/d significantly reduced IS. Cil and MK had additive effects at all three MK doses. IS was the smallest in the MK-3+Cil. MK in a dose dependent manner and Cil increased cAMP levels (p < 0.001). cAMP levels were higher in the combination groups at all MK doses. MK-2 and Cil increased PKA activity when given alone; however, PKA activity was significantly higher in the MK-2+Cil group than in the other groups. Both MK-2 and Cil increased myocardial levels of Ser(133) P-CREB, Ser(523) P-5-lipoxygenase, Ser(473)P-Akt and Ser(633) P-eNOS. These levels were significantly higher in the MK-2+Cil group. Myocardial PTEN (Phosphatase and tensin homolog on chromosome ten) levels were significantly higher in the Db/Db mice compared to nondiabetic mice. MK-2 and Cil normalized PTEN levels. PTEN levels tended to be lower in the combination group than in the MK and Cil alone groups.

CONCLUSION

MK and Cil have additive IS-limiting effects in diabetic mice. The additive effects are associated with an increase in myocardial cAMP levels and PKA activity with downstream phosphorylation of Akt, eNOS, 5-lipoxygenase and CREB and downregulation of PTEN expression.

Mechanism of sperm capacitation and the acrosome reaction: role of protein kinases

Mammalian sperm must undergo a series of biochemical and physiological modifications, collectively called capacitation, in the female reproductive tract prior to the acrosome reaction (AR). The mechanisms of these modifications are not well characterized though protein kinases were shown to be involved in the regulation of intracellular Ca(2+) during both capacitation and the AR. In the present review, we summarize some of the signaling events that are involved in capacitation. During the capacitation process, phosphatidyl-inositol-3-kinase (PI3K) is phosphorylated/activated via a protein kinase A (PKA)-dependent cascade, and downregulated by protein kinase C α (PKCα). PKCα is active at the beginning of capacitation, resulting in PI3K inactivation. During capacitation, PKCα as well as PP1γ2 is degraded by a PKA-dependent mechanism, allowing the activation of PI3K. The activation of PKA during capacitation depends mainly on cyclic adenosine monophosphate (cAMP) produced by the bicarbonate-dependent soluble adenylyl cyclase. This activation of PKA leads to an increase in actin polymerization, an essential process for the development of hyperactivated motility, which is necessary for successful fertilization. Actin polymerization is mediated by PIP(2) in two ways: first, PIP(2) acts as a cofactor for phospholipase D (PLD) activation, and second, as a molecule that binds and inhibits actin-severing proteins such as gelsolin. Tyrosine phosphorylation of gelsolin during capacitation by Src family kinase (SFK) is also important for its inactivation. Prior to the AR, gelsolin is released from PIP(2) and undergoes dephosphorylation/activation, resulting in fast F-actin depolymerization, leading to the AR.

Phosphodiesterase-3 inhibition augments the myocardial infarct size-limiting effects of exenatide in mice with type 2 diabetes

Glucagon-like peptide (GLP)-1 receptor activation increases intracellular cAMP with downstream activation of PKA. Cilostazol (CIL), a phosphodiesterase-3 inhibitor, prevents cAMP degradation. We assessed whether CIL amplifies the exenatide (EX)-induced increase in myocardial cAMP levels and PKA activity and augments the infarct size (IS)-limiting effects of EX in db/db mice. Mice fed a Western diet received oral CIL (10 mg/kg) or vehicle by oral gavage 24 h before surgery. One hour before surgery, mice received EX (1 μg/kg sc) or vehicle. Additional mice received H-89, a PKA inhibitor, alone or with CIL + EX. Mice underwent 30 min of coronary artery occlusion and 24 h of reperfusion. Both EX and CIL increased myocardial cAMP levels and PKA activity. Levels were significantly higher in the EX + CIL group. Both EX and CIL reduced IS. IS was the smallest in the CIL + EX group. H-89 completely blocked the IS-limiting effects of EX + CIL. EX + CIL decreased phosphatase and tensin homolog on chromosome 10 upregulation and increased Akt and ERK1/2 phosphorylation after ischemia-reperfusion. These effects were blocked by H-89. In conclusion, EX and CIL have additive effects on IS limitation in diabetic mice. The additive effects are related to cAMP-induced PKA activation, as H-89 blocked the protective effect of CIL + EX.

Regulation of alveolar macrophage p40phox: hierarchy of activating kinases and their inhibition by PGE2

PGE(2), produced in the lung during infection with microbes such as Klebsiella pneumoniae, inhibits alveolar macrophage (AM) antimicrobial functions by preventing H(2)O(2) production by NADPH oxidase (NADPHox). Activation of the NADPHox complex is poorly understood in AMs, although in neutrophils it is known to be mediated by kinases including PI3K/Akt, protein kinase C (PKC) δ, p21-activated protein kinase (PAK), casein kinase 2 (CK2), and MAPKs. The p40phox cytosolic subunit of NADPHox has been recently recognized to function as a carrier protein for other subunits and a positive regulator of oxidase activation, a role previously considered unique to another subunit, p47phox. The regulation of p40phox remains poorly understood, and the effect of PGE(2) on its activation is completely undefined. We addressed these issues in rat AMs activated with IgG-opsonized K. pneumoniae. The kinetics of kinase activation and the consequences of kinase inhibition and silencing revealed a critical role for a PKCδ-PAK-class I PI3K/Akt1 cascade in the regulation of p40phox activation upon bacterial challenge in AMs; PKCα, ERK, and CK2 were not involved. PGE(2) inhibited the activation of p40phox, and its effects were mediated by protein kinase A type II, were independent of interactions with anchoring proteins, and were directed at the distal class I PI3K/Akt1 activation step. Defining the kinases that control AM p40phox activation and that are the targets for inhibition by PGE(2) provides new insights into immunoregulation in the infected lung.

Multiple roles for the p85α isoform in the regulation and function of PI3K signalling and receptor trafficking

The p85α protein is best known as the regulatory subunit of class 1A PI3Ks (phosphoinositide 3-kinases) through its interaction, stabilization and repression of p110-PI3K catalytic subunits. PI3Ks play multiple roles in the regulation of cell survival, signalling, proliferation, migration and vesicle trafficking. The present review will focus on p85α, with special emphasis on its important roles in the regulation of PTEN (phosphatase and tensin homologue deleted on chromosome 10) and Rab5 functions. The phosphatidylinositol-3-phosphatase PTEN directly counteracts PI3K signalling through dephosphorylation of PI3K lipid products. Thus the balance of p85α–p110 and p85α–PTEN complexes determines the signalling output of the PI3K/PTEN pathway, and under conditions of reduced p85α levels, the p85α–PTEN complex is selectively reduced, promoting PI3K signalling. Rab5 GTPases are important during the endocytosis, intracellular trafficking and degradation of activated receptor complexes. The p85α protein helps switch off Rab5, and if defective in this p85α function, results in sustained activated receptor tyrosine kinase signalling and cell transformation through disrupted receptor trafficking. The central role for p85α in the regulation of PTEN and Rab5 has widened the scope of p85α functions to include integration of PI3K activation (p110-mediated), deactivation (PTEN-mediated) and receptor trafficking/signalling (Rab5-mediated) functions, all with key roles in maintaining cellular homoeostasis.

Inhibition of insulin signaling in endothelial cells by protein kinase C-induced phosphorylation of p85 subunit of phosphatidylinositol 3-kinase (PI3K)

The regulation of endothelial function by insulin is consistently abnormal in insulin-resistant states and diabetes. Protein kinase C (PKC) activation has been reported to inhibit insulin signaling selectively in endothelial cells via the insulin receptor substrate/PI3K/Akt pathway to reduce the activation of endothelial nitric-oxide synthase (eNOS). In this study, it was observed that PKC activation differentially inhibited insulin receptor substrate 1/2 (IRS1/2) signaling of insulin's activation of PI3K/eNOS by decreasing only tyrosine phosphorylation of IRS2. In addition, PKC activation, by general activator and specifically by angiotensin II, increased the phosphorylation of p85/PI3K, which decreases its association with IRS1 and activation. Thr-86 of p85/PI3K was identified to be phosphorylated by PKC activation and confirmed to affect IRS1-mediated activation of Akt/eNOS by insulin and VEGF using a deletion mutant of the Thr-86 region of p85/PI3K. Thus, PKC and angiotensin-induced phosphorylation of Thr-86 of p85/PI3K may partially inhibit the activation of PI3K/eNOS by multiple cytokines and contribute to endothelial dysfunction in metabolic disorders.

Structural basis for activation and inhibition of class I phosphoinositide 3-kinases

Phosphoinositide 3-kinases (PI3Ks) are implicated in a broad spectrum of cellular activities, such as growth, proliferation, differentiation, migration, and metabolism. Activation of class I PI3Ks by mutation or overexpression correlates with the development and maintenance of various human cancers. These PI3Ks are heterodimers, and the activity of the catalytic subunits is tightly controlled by the associated regulatory subunits. Although the same p85 regulatory subunits associate with all class IA PI3Ks, the functional outcome depends on the isotype of the catalytic subunit. New PI3K partners that affect the signaling by the PI3K heterodimers have been uncovered, including phosphate and tensin homolog (PTEN), cyclic adenosine monophosphate-dependent protein kinase (PKA), and nonstructural protein 1. Interactions with PI3K regulators modulate the intrinsic membrane affinity and either the rate of phosphoryl transfer or product release. Crystal structures for the class I and class III PI3Ks in complexes with associated regulators and inhibitors have contributed to developing isoform-specific inhibitors and have shed light on the numerous regulatory mechanisms controlling PI3K activation and inhibition.

Overexpression of 14-3-3ζ in cancer cells activates PI3K via binding the p85 regulatory subunit

The ubiquitously expressed 14-3-3 proteins regulate many pathways involved in transformation. Previously, we found that 14-3-3ζ overexpression increased Akt phosphorylation in human mammary epithelial cells. Here, we investigated the clinical relevance and molecular mechanism of 14-3-3ζ overexpression-mediated Akt phosphorylation and the potential impact on breast cancer progression. We found that 14-3-3ζ overexpression was significantly (P = 0.005) associated with increased Akt phosphorylation in human breast tumors. Additionally, 14-3-3ζ overexpression combined with strong Akt phosphorylation was significantly (P=0.01) associated with increased cancer recurrence in patients. In contrast, knockdown of 14-3-3ζ expression by siRNA in cancer cell lines and tumor xenografts reduced Akt phosphorylation. Furthermore, 14-3-3ζ enhanced Akt phosphorylation through activation of PI3K. Mechanistically, 14-3-3ζ bound to the p85 regulatory subunit of PI3K and increased PI3K translocation to the cell membrane. A single 14-3-3 binding motif encompassing serine 83 on p85 is largely responsible for 14-3-3ζ-mediated p85 binding and PI3K/Akt activation. Mutation of serine 83 to alanine on p85 inhibited 14-3-3ζ binding to the p85 subunit of PI3K, reduced PI3K membrane localization and activation, impeded anchorage independent growth and enhanced stress induced apoptosis. These findings revealed a novel mechanism by which 14-3-3ζ overexpression activates PI3K, a key node in the mitogenic signaling network known to promote malignancies in many cell types.

Protein kinase A-alpha directly phosphorylates FoxO1 in vascular endothelial cells to regulate expression of vascular cellular adhesion molecule-1 mRNA

FoxO1, a forkhead box O class transcription factor, is abundant in insulin-responsive tissues. Akt, downstream from phosphatidylinositol 3-kinase in insulin signaling, phosphorylates FoxO1 at Thr(24), Ser(256), and Ser(319), negatively regulating its function. We previously reported that dehydroepiandrosterone-stimulated phosphorylation of FoxO1 in endothelial cells requires cAMP-dependent protein kinase α (PKA-α). Therefore, we hypothesized that FoxO1 is a novel direct substrate for PKA-α. Using an immune complex kinase assay with [γ-(32)P]ATP, purified PKA-α directly phosphorylated wild-type FoxO1 but not FoxO1-AAA (mutant with alanine substitutions at known Akt phosphorylation sites). Phosphorylation of wild-type FoxO1 (but not FoxO1-AAA) was detectable using phospho-specific antibodies. Similar results were obtained using purified GST-FoxO1 protein as the substrate. Thus, FoxO1 is a direct substrate for PKA-α in vitro. In bovine aortic endothelial cells, interaction between endogenous PKA-α and endogenous FoxO1 was detected by co-immunoprecipitation. In human aortic endothelial cells (HAEC), pretreatment with H89 (PKA inhibitor) or siRNA knockdown of PKA-α decreased forskolin- or prostaglandin E(2)-stimulated phosphorylation of FoxO1. In HAEC transfected with a FoxO-promoter luciferase reporter, co-expression of the catalytic domain of PKA-α, catalytically inactive mutant PKA-α, or siRNA against PKA-α caused corresponding increases or decreases in transactivation of the FoxO promoter. Expression of vascular cellular adhesion molecule-1 mRNA, up-regulated by FoxO1 in endothelial cells, was enhanced by siRNA knockdown of PKA-α or treatment of HAEC with the PKA inhibitor H89. Adhesion of monocytes to endothelial cells was enhanced by H89 treatment or overexpression of FoxO1-AAA, similar to effects of TNF-α treatment. We conclude that FoxO1 is a novel physiological substrate for PKA-α in vascular endothelial cells.

Norepinephrine induces VEGF expression and angiogenesis by a hypoxia-inducible factor-1α protein-dependent mechanism

A growing number of studies have demonstrated that physiological factors can influence the progression of several cancers via cellular immune function, angiogenesis and metastasis. Recently, stress-induced catecholamines have been shown to increase the expression of various cancer progressive factors, including vascular endothelial growth factor (VEGF), matrix metalloproteinases and interleukins. However, a detailed mechanism remains to be identified. In this study, we investigated the role of adrenergic receptors and hypoxia-inducible factor (HIF)-1α protein in catecholamine-induced VEGF expression and angiogenesis. Treatment of the cells with norepinephrine (NE) or isoproterenol induced VEGF expression and HIF-1α protein amount in a dose-dependent manner. Induction of VEGF expression by NE was abrogated when the cells were transfected with HIF-1α-specific siRNA. Similarly, adenylate cyclase activator forskolin and cyclic AMP-dependent protein kinase A inhibitor H-89 enhanced and decreased HIF-1α protein amount, respectively. More importantly, conditioned medium of NE-stimulated cancer cells induced angiogenesis in a HIF-1α protein-dependent manner. In addition, pretreatment of cells with propranolol, a β-adrenergic receptor (AR) blocker, completely abolished induction of VEGF expression and HIF-1α protein amount by NE in all of the tested cancer cells. However, treatment with the α1-AR blocker prazosin inhibited NE-induced HIF-1α protein amount and angiogenesis in SK-Hep1 and PC-3 but not MDA-MB-231 cells. Collectively, our results suggest that ARs and HIF-1α protein have critical roles in NE-induced VEGF expression in cancer cells, leading to stimulation of angiogenesis. These findings will help to understand the mechanism of cancer progression by stress-induced catecholamines and design therapeutic strategies for cancer angiogenesis.

Leptin potentiates antiproliferative action of cAMP elevation via protein kinase A down-regulation in breast cancer cells

Previously, we have shown that leptin potentiates the antiproliferative action of cAMP elevating agents in breast cancer cells and that the protein kinase A (PKA) inhibitor KT-5720 prevented the antiproliferative effects induced by the leptin plus cAMP elevation. The present experiments were designed to gain a better understanding about the PKA role in the antitumor interaction between leptin and cAMP elevating agents and on the underlying signaling pathways. Here we show that exposure of MDA-MB-231 breast cancer cells to leptin resulted in a strong phosphorylation of both ERK1/2 and STAT3. Interestingly, intracellular cAMP elevation upon forskolin pretreatment completely abrogated both ERK1/2 and STAT3 phosphorylation in response to leptin and was accompanied by a consistent CREB phosphorylation. Notably, leptin plus forskolin cotreatments resulted in a strong decrease of both PKA regulatory RIα and catalytic subunits protein levels. Importantly, pretreatment with the PKA inhibitor KT-5720 blocked the forskolin-induced CREB phosphorylation and prevented both the inhibition by forskolin of leptin-induced ERK1/2 and STAT3 phosphorylation and the PKA subunits down-regulation induced by the combination of leptin and forskolin. Altogether, our results indicate that leptin-dependent signaling pathways are influenced by cAMP elevation and identify PKA as relevantly involved in the pharmacological antitumor interaction between leptin and cAMP elevating drugs in MDA-MB-231 cells. We propose a molecular model by which PKA confers its effects. Potential therapeutic applications by our data will be discussed.

Protein kinase A and protein kinase C(alpha)/PPP1CC2 play opposing roles in the regulation of phosphatidylinositol 3-kinase activation in bovine sperm

In order to acquire fertilization competence, spermatozoa have to undergo biochemical changes in the female reproductive tract, known as capacitation. Signaling pathways that take place during the capacitation process are much investigated issue. However, the role and regulation of phosphatidylinositol 3-kinase (PI3K) in this process are still not clear. Previously, we reported that short-time activation of protein kinase A (PRKA, PKA) leads to PI3K activation and protein kinase C(alpha)(PRKCA, PKC(alpha)) inhibition. In the present study, we found that during the capacitation PI3K phosphorylation/activation increases. PI3K activation was PRKA dependent, and down-regulated by PRKCA. PRKCA is found to be highly active at the beginning of the capacitation, conditions in which PI3K is not active. Moreover, inhibition of PRKCA causes significant activation of PI3K. Similar activation of PI3K is seen when the phosphatase PPP1 is blocked suggesting that PPP1 regulates PI3K activity. We found that during the capacitation PRKCA and PPP1CC2 (PP1gamma2) form a complex, and the two enzymes were degraded during the capacitation, suggesting that this degradation enables the activation of PI3K. This degradation is mediated by PRKA, indicating that in addition to the direct activation of PI3K by PRKA, this kinase can enhance PI3K phosphorylation indirectly by enhancing the degradation and inactivation of PRKCA and PPP1CC2.

cAMP/CREB-mediated transcriptional regulation of ectonucleoside triphosphate diphosphohydrolase 1 (CD39) expression

CD39 is a transmembrane enzyme that inhibits platelet reactivity and inflammation by phosphohydrolyzing ATP and ADP to AMP. Cyclic AMP (cAMP), an essential second messenger, is particularly important in regulating genes controlling vascular homeostasis. These experiments test the hypothesis that cAMP might positively regulate the expression of CD39 and thereby modulate important vascular homeostatic properties. Cd39 mRNA was induced by 13.8- fold in RAW cells treated with a membrane-permeant cAMP analogue (8-bromo-cyclic AMP; 8-Br-cAMP), stimulation of adenylate cyclase, or prostanoids known to drive cAMP response. Fluorescence-activated cell sorting, immunofluorescence, and TLC assays demonstrated that both CD39 protein expression and enzymatic activity were increased in cells treated with 8-Br-cAMP but not in cells transfected with short hairpin RNA against CD39. This analogue drove a significant increase in transcriptional activity at the Cd39 promoter although not when the promoter's cAMP-response element sites were mutated. Pretreatment with cAMP-dependent protein kinase (PKA), phosphoinositide 3-kinase (PI3K), or ERK inhibitors nearly obliterated the cAMP-driven increase in Cd39 mRNA, protein expression, and promoter activity. 8-Br-cAMP greatly increased the phosphorylation of CREB1 (Ser(133)) and ATF2 (Thr(71)) in a PKA-, PI3K-, and ERK-dependent fashion. Chromatin immunoprecipitation assays demonstrated that binding of phosphorylated CREB1 and ATF2 to cAMP-response element-like sites was significantly increased with 8-Br-cAMP treatment and that binding was reduced with PKA, PI3K, and ERK inhibition, whereas transfection of Creb1 and Atf2 overexpression constructs enhanced cAMP-driven Cd39 mRNA expression. Transfection of RAW cells with mutated Creb1 (S133A) reduced cAMP-driven Cd39 mRNA expression. Furthermore, the cAMP-mediated induction of Cd39 mRNA, protein, and phosphohydrolytic activity was replicated in primary peritoneal macrophages. These data identify cAMP as a crucial regulator of macrophage CD39 expression and demonstrate that cAMP acts through the PKA/CREB, PKA/PI3K/ATF2, and PKA/ERK/ATF2 pathways to control a key vascular homeostatic mediator.

Role and regulation of PI3K in sperm capacitation and the acrosome reaction

Mammalian spermatozoa undergo several signaling and biochemical transformations in the female genital tract, collectively called capacitation. The capacitated spermatozoon binds to the egg zona pellucida, where it undergoes the acrosome reaction (AR), a process enabling it to penetrate and fertilize the egg. Actin polymerization occurs in sperm capacitation and depolymerization prior to the AR. In this review we describe the possible role and regulation of PI3K in sperm capacitation and the acrosome reaction. We claim that PI3K is activated by protein kinase A and suppressed by protein kinase C. Only partial activation of PI3K is seen during the capacitation time, however towards the end of incubation, full activation is observed. Actin polymerization during capacitation is independent on PI3K activity, suggesting that the enzyme is not involved in sperm capacitation. However, the full activation of PI3K towards the end of the capacitation suggests that it might mediate the AR, as indeed was found.

Protein kinase A activation confers resistance to trastuzumab in human breast cancer cell lines

PURPOSE

Trastuzumab is a monoclonal antibody targeted to the Her2 receptor and approved for treatment of Her2-positive breast cancer. Among patients who initially respond to trastuzumab therapy, resistance typically arises within 1 year. BT/Her(R) cells are trastuzumab-resistant variants of Her2-positive BT474 breast cancer cells. The salient feature of BT/Her(R) cells is failure to downregulate phosphoinositide 3-kinase/Akt signaling on trastuzumab binding. The current work addresses the mechanism of sustained signaling in BT/Her(R) cells, focusing on the protein kinase A (PKA) pathway.

EXPERIMENTAL DESIGN

We performed microarray analysis on BT/Her(R) and BT474 cell lines to identify genes that were upregulated or downregulated in trastuzumab-resistant cells. Specific genes in the PKA pathway were quantified using reverse transcription-PCR and Western hybridization. Small interfering RNA transfection was used to determine the effects of gene knockdown on cellular response to trastuzumab. Electrophoretic mobility shift assays were used to measure cyclic AMP-responsive element binding activity under defined conditions. Immunohistochemistry was used to analyze protein expression in clinical samples.

RESULTS

BT/Her(R) cells had elevated PKA signaling activity and several genes in the PKA regulatory network had altered expression in these cells. Downregulation of one such gene, the PKA-RIIalpha regulatory subunit, conferred partial trastuzumab resistance in Her2-positive BT474 and SK-Br-3 cell lines. Forskolin activation of PKA also produced significant protection against trastuzumab-mediated Akt dephosphorylation. In patient samples, PKA signaling appeared to be enhanced in residual disease remaining after trastuzumab-containing neoadjuvant therapy.

CONCLUSIONS

Activation of PKA signaling may be one mechanism contributing to trastuzumab resistance in Her2-positive breast cancer. We propose a molecular model by which PKA confers its effects.

Differential regulation of vascular smooth muscle and endothelial cell proliferation in vitro and in vivo by cAMP/PKA-activated p85alphaPI3K

cAMP inhibits proliferation in most cell types, triggering different and sometimes opposing molecular pathways. p85alpha (phosphatidylinositol 3-kinase regulatory subunit) is phosphorylated by cAMP/PKA in certain cell lineages, but its effects on vascular smooth muscle cells (VSMCs) and endothelial cells (ECs) are unknown. In the present study, we evaluated 1) the role of p85alpha in the integration of cAMP/PKA-dependent signaling on the regulation of VSMC and EC growth in vitro; and 2) the effects of PKA-modified p85alpha on neointimal hyperplasia and endothelial healing after balloon injury in vivo. Plasmid constructs carrying wild-type and PKA-modified p85alpha were employed in VSMCs and ECs in vitro and after balloon injury in rat carotid arteries in vivo. cAMP/PKA reduced VSMC proliferation through p85alpha phosphorylation. Transfected PKA-activated p85alpha binds p21ras, reducing ERK1/2 activation and VSMC proliferation in vitro. In contrast, EC proliferation inhibition by cAMP is independent from PKA modification of p85alpha and ERK1/2 inhibition; indeed, PKA-activated p85alpha did not inhibit per se ERK1/2 activation and proliferation in ECs in vitro. Interestingly, cAMP reduced both VSMC and EC apoptotic death through p85alpha phosphorylation. Accordingly, PKA-activated p85alpha triggered Akt activation, reducing both VSMC and EC apoptosis in vitro. Finally, compared with controls, vascular gene transfer of PKA-activated p85alpha significantly reduced neointimal formation after balloon injury in rats, without inhibiting endothelial regeneration of the injured arterial segment. In conclusions, PKA-activated p85alpha integrates cAMP/PKA signaling differently in VSMCs and ECs. By reducing neointimal hyperplasia without inhibiting endothelial regeneration, it exerts a protective effect against restenosis after balloon injury.

Glucagon induces the gene expression of aquaporin-8 but not that of aquaporin-9 water channels in the rat hepatocyte

Glucagon stimulates the vesicle trafficking of aquaporin-8 (AQP8) water channels to the rat hepatocyte canalicular membranes, a process thought to be relevant to glucagon-induced bile secretion. In this study, we investigated whether glucagon is able to modulate the gene expression of hepatocyte AQP8. Glucagon was administered to rats at 0.2 mg/100 g body wt ip in 2, 3, or 6 equally spaced doses for 8, 16, and 36 h, respectively. Immunoblotting analysis showed that hepatic 34-kDa AQP8 was significantly increased by 79 and 107% at 16 and 36 h, respectively. Hepatic AQP9 protein expression remained unaltered. AQP8 mRNA expression, assessed by real-time PCR, was not modified over time, suggesting a posttranscriptional mechanism of AQP8 protein increase. Glucagon effects on AQP8 were directly studied in primary cultured rat hepatocytes. Immunoblotting and confocal immunofluorescence microscopy confirmed the specific glucagon-induced AQP8 upregulation. The RNA polymerase II inhibitor actinomycin D was unable to prevent glucagon effect, providing additional support to the nontranscriptional upregulation of AQP8. Cycloheximide also showed no effect, suggesting that glucagon-induced AQP8 expression does not depend on protein synthesis but rather on protein degradation. Inhibitory experiments suggest that a reduced calpain-mediated AQP8 proteolysis could be involved. The action of glucagon on hepatocyte AQP8 was mimicked by dibutyryl cAMP and suppressed by PKA or phosphatidylinositol-3-kinase (PI3K) inhibitors. In conclusion, our data suggest that glucagon induces the gene expression of rat hepatocyte AQP8 by reducing its degradation, a process that involves cAMP-PKA and PI3K signal pathways.

Aquaporins: Their role in cholestatic liver disease

This review focuses on current knowledge on hepatocyte aquaporins (AQPs) and their significance in bile formation and cholestasis. Canalicular bile secretion results from a combined interaction of several solute transporters and AQP water channels that facilitate water flow in response to the osmotic gradients created. During choleresis, hepatocytes rapidly increase their canalicular membrane water permeability by modulating the abundance of AQP8. The question was raised as to whether the opposite process, i.e. a decreased canalicular AQP8 expression would contribute to the development of cholestasis. Studies in several experimental models of cholestasis, such as extrahepatic obstructive cholestasis, estrogen-induced cholestasis, and sepsis-induced cholestasis demonstrated that the protein expression of hepatocyte AQP8 was impaired. In addition, biophysical studies in canalicular plasma membranes revealed decreased water permeability associated with AQP8 protein downregulation. The combined alteration in hepatocyte solute transporters and AQP8 would hamper the efficient coupling of osmotic gradients and canalicular water flow. Thus cholestasis may result from a mutual occurrence of impaired solute transport and decreased water permeability.

Dynamic localization of hepatocellular transporters in health and disease

Vesicle-based trafficking of hepatocellular transporters involves delivery of the newly-synthesized carriers from the rough endoplasmic reticulum to either the plasma membrane domain or to an endosomal, submembrane compartment, followed by exocytic targeting to the plasma membrane. Once delivered to the plasma membrane, the transporters usually undergo recycling between the plasma membrane and the endosomal compartment, which usually serves as a reservoir of pre-existing transporters available on demand. The balance between exocytic targeting and endocytic internalization from/to this recycling compartment is therefore a chief determinant of the overall capability of the liver epithelium to secrete bile and to detoxify endo and xenobiotics. Hence, it is a highly regulated process. Impaired regulation of this balance may lead to abnormal localization of these transporters, which results in bile secretory failure due to endocytic internalization of key transporters involved in bile formation. This occurs in several experimental models of hepatocellular cholestasis, and in most human cholestatic liver diseases. This review describes the molecular bases involved in the biology of the dynamic localization of hepatocellular transporters and its regulation, with a focus on the involvement of signaling pathways in this process. Their alterations in different experimental models of cholestasis and in human cholestatic liver disease are reviewed. In addition, the causes explaining the pathological condition (e.g. disorganization of actin or actin-transporter linkers) and the mediators involved (e.g. activation of cholestatic signaling transduction pathways) are also discussed. Finally, several experimental therapeutic approaches based upon the administration of compounds known to stimulate exocytic insertion of canalicular transporters (e.g. cAMP, tauroursodeoxycholate) are described.