Essential role of PDK1 in regulating endothelial cell migration

Dysregulation of Lymphatic Endothelial VEGFR3 Signaling in Disease

Vascular endothelial growth factor (VEGF) receptor 3 (VEGFR3), a receptor tyrosine kinase encoded by the FLT4 gene, plays a significant role in the morphogenesis and maintenance of lymphatic vessels. Under both normal and pathologic conditions, VEGF-C and VEGF-D bind VEGFR3 on the surface of lymphatic endothelial cells (LECs) and induce lymphatic proliferation, migration, and survival by activating intracellular PI3K-Akt and MAPK-ERK signaling pathways. Impaired lymphatic function and VEGFR3 signaling has been linked with a myriad of commonly encountered clinical conditions. This review provides a brief overview of intracellular VEGFR3 signaling in LECs and explores examples of dysregulated VEGFR3 signaling in various disease states, including (1) lymphedema, (2) tumor growth and metastasis, (3) obesity and metabolic syndrome, (4) organ transplant rejection, and (5) autoimmune disorders. A more complete understanding of the molecular mechanisms underlying the lymphatic pathology of each disease will allow for the development of novel strategies to treat these chronic and often debilitating illnesses.

Dual inhibitors of ASK1 and PDK1 kinases: Design, synthesis, molecular docking and mechanism studies of N-benzyl pyridine-2-one containing derivatives as anti-fibrotic agents

Utilizing fragment-based hybrid designing strategies, 24 N-benzyl pyridine-2-one containing derivatives were synthesized by successfully incorporating 6-(4H-1,2,4-triazol-3-yl) pyridin-2-amine of scaffold of ASK1 inhibitor (GS-444217). These newly synthesized compounds were screened in cell-free ASK1 and PDK1 kinase and cellular vitality assays. Among all compounds tested, both 21c and 21d displayed single digit potency of 9.13, 1.73 nM in inhibiting ASK1, and exhibited excellent enzyme inhibitory activity against PDK1 (the inhibition rates at 10 μM were 13.63% and 23.80%, respectively). Specifically, both compounds inhibited the TGF-β1 induced fibrotic response and blocked the up-regulated protein expression levels of ASK1-p38/JNK signaling pathways and possessed the potency in reducing PDK1/Akt phosphorylation. The results herein showed the potential lead characteristics of 21c or 21d as dual inhibitors ASK1/PDK1 kinases.

Hsa_circ_0000851 promotes PDK1/p-AKT-mediated cell proliferation and migration by regulating miR-1183 in triple-negative breast cancer

Breast cancer (BC) is the most common cause of cancer-related mortality in women worldwide. Circular RNAs (circRNAs), a type of non-coding RNA, have garnered interest because of their unique looped structure. In recent years, circRNAs have been shown to be involved in various diseases, including carcinogenesis, and to serve as biomarkers for early risk assessment and survival prediction of different tumour types. This study aimed to identify a novel circRNA, hsa_circ_0000851, generated from the sixth intron of the oncogene TCF4, reported to be involved in BC pathogenesis. Our study showed that hsa_circ_0000851 was mainly located in the cytoplasm of BC cells and upregulated in BC cell lines and tissue samples. Higher hsa_circ_0000851 expression levels resulted in increased proliferation of BC cells both in vitro and in vivo, while treatment of BC cells with hsa_circ_0000851 siRNA decreased their proliferation. We found that hsa_circ_0000851 bound directly to miR-1183, accelerating the expression of its target gene PDK1, which facilities BC cell proliferation and migration through PDK1/p-AKT.

Brusatol suppresses the tumor growth and metastasis of colorectal cancer via upregulating ARRDC4 expression through modulating PI3K/YAP1/TAZ Pathway

BACKGROUND

Colorectal cancer (CRC) is one of the most commonly diagnosed cancers with high metastasis and lethality. Arrestin domain-containing 4 (ARRDC4) is involved in inhibiting cancer glycolytic phenotypes. Brusatol (BR), extracted from Bruceae Fructus, exerts good anti-cancer effects against a number of cancers.

PURPOSE

In the present study, we aimed to explore the efficacy of BR on inhibiting CRC metastasis and elucidate the underlying mechanisms involving the upregulation of the ARRDC4 expression.

METHODS

Cell viability, colony formation, wound healing and transwell assay were used to detect the anti-proliferative and anti-metastatic effects of BR against CRC in vitro. Microarray analysis was performed to find out differential genes in CRC cells after treatment with BR. Analysis of the CRC patients tumor samples and GEPIA database were first conducted to identify the expression of ARRDC4 on CRC. Stable overexpression and knockdown of ARRDC4 CRC cells were established by lentiviral transfection. The role of ARRDC4 in mediating the anti-metastatic effects of BR on CRC was measured using qRT-PCR, western blotting, immunohistochemical and immunofluorescence analysis. Orthotopic xenograft and pulmonary metastasis mouse models of CRC were established to determine the anti-cancer and anti-metastatic effects of ARRDC4 and BR.

RESULTS

BR markedly suppressed the cell proliferation, migration, invasion and inhibited tumor growth and tumor metastasis. Microarray analysis demonstrated that BR treatment markedly increased the gene expression of ARRDC4 in CRC cells. ARRDC4 was significantly repressed in CRC in the clinical samples and GEPIA analysis. ARRDC4 overexpression plus BR produced better inhibitory effects on CRC metastasis than BR treatment alone, while ARRDC4 knockdown could partially eliminate the inhibitory effects of BR against CRC metastasis. BR exerted anti-metastatic effects against CRC via upregulating ARRDC4 and inhibiting epithelial-mesenchymal transition (EMT) processing through modulating PI3K/Hippo pathway.

CONCLUSION

This study reported for the first time that BR is a potent ARRDC4 agonist, and is worthy of further development into a new therapeutic strategy for CRC.

Exosomes derived from M2 macrophages induce angiogenesis to promote wound healing

There is an urgent clinical need for an appropriate method to shorten skin healing time. Among most factors related to wound healing, M2 macrophages will be recruited to the wound area and play a pivotal role in a time-limiting factor, angiogenesis. The exploration of exosomes derived from M2 in angiogenesis promotion is an attractive research field. In this project, we found that exosomes from M2 (M2-EXO) promoted the angiogenic ability of HUVECs in vitro. With a series of characteristic experiments, we demonstrated that M2-EXO inhibited PTEN expression in HUVECs by transferring miR-21, and further activated AKT/mTOR pathway. Then, using a full-thickness cutaneous wound mice model, we demonstrated that M2-EXO could be used as a promotor of angiogenesis and regeneration in vivo. Furthermore, M2-EXO-treated skin wounds exhibited regeneration of functional microstructures. These results demonstrate that M2-EXO can be used as a promising nanomedicine strategy for therapeutic exploration of skin healing with the potential to be translated into clinical practice.

MiR-34b-3p Impaired HUVECs Viability and Migration via Targeting PDK1 in an In Vitro Model of Gestational Diabetes Mellitus

Gestational diabetes mellitus (GDM) leads to poor pregnancy outcomes. The methods for GDM early diagnosis and treatment are still unknown. This study aimed to investigate the expression and diagnostic potential of miR-34b-3p in GDM patients and further analyzed the effects of miR-34b-3p on HUVECs viability and migration. The expression of miR-34b-3p was detected in HUVECs of GDM and normal pregnant women by qRT-PCR. Then the HUVECs were isolated from normal pregnant women. High glucose (HG) was used to treat the HUVECs to mimic the GDM in vitro. The cell viability and migration were determined by MTT, wound healing assay, and transwell assay. The interaction between miR-34b-3p and PDK1 was evaluated by luciferase activity assay. Our results showed that miR-34b-3p was up-regulated in HUVECs of GDM patients. Then the HUVECs were isolated from normal pregnant women and they were treated with HG to mimic the GDM in vitro. Interestingly, knockdown of miR-34b-3p restored the impairment of HG treatment-induced effects in HUVECs. More importantly, PDK1 was proved to be a potential target of miR-34b-3p. Finally, the rescue experiments confirmed that miR-34b-3p impaired cell viability and migration ability in HUVECs by targeting PDK1. These findings concluded that miR-34b-3p impaired HUVECs viability and migration in GDM by targeting PDK1, which might provide a novel perspective for the pathogenesis and underlying therapeutic target for GDM.

Molecular dynamic study on PTEN frameshift mutations in breast cancer provide c2 domain as a potential biomarker

PTEN is a tumour suppressor gene known for regulating apoptosis, cell growth, and many other pathways. It is one of the most frequently mutated genes comprising the phosphatase domain (PD) and C terminal domain (C2). Direct therapeutic methods are not applicable for targeting PTEN because once gets mutated, it needs restoration. For mutant detection and restoration using PTEN mRNA there is a need to explore various mutations taking place in PTEN, identify their particular domains, and study their interactions within the cellular system. Here, we have tried to highlight a few such regions in the mutated PTEN of breast cancer patients. In this study, we have selected the top-most-occurring PTEN mutation in breast cancer and compared them to determine the specific properties of each mutation and its effect on functionality. Molecular dynamic simulation for 50 ns was performed on five structures to compare the structural behaviour of mutated PTEN in the system. Our finding suggests that frameshift mutations are more damaging and affect the c2 domain. Frameshift mutant fs_ACTT is the highest occurring as well as the most damaging mutation in all the compared structures. Docking study shows that substitution mutations D92H and R130Q causes loss of binding ability towards PIP2 in normal PTEN, interfering the dephosphorylation process. Overall, the C2 domain is more frequently mutated, and the amino acid residues in the C2 domain show more fluctuations compared to the other regions. Our study can provide the basis for selecting frequently mutated C2 domain as a potential therapeutic marker.Communicated by Ramaswamy H. Sarma.

PS48 promotes in vitro maturation and developmental competence of porcine oocytes through activating PI3K/Akt signalling pathway

Oocyte maturation plays a vitally important role in porcine reproduction. Regrettably, the quality of oocytes matured in vitro is weaker than that of in vivo matured oocytes. We collected and cultivated porcine cumulus oocyte complexes (COCs) in vitro with phosphoinositide-dependent kinase 1 (PDK1) activator 5-(4-chloro-phenyl)-3-phenyl-pent-2-enoic acid (PS48), whose concentrations were 0, 2, 5, 10 and 20 µM to investigate whether the phosphatidylinositol-3-kinase/protein kinase B (PI3K/Akt) signalling pathway would impact the oocyte quality. The results showed that 10 µM PS48 increased the oocyte proportion of metaphase II (MII) stage and improved the expansion of cumulus cells (CCs). What's more, the activation of PI3K/Akt signalling pathway could regulate the expression of maturation-related genes and proteins. The results of quantitative real-time PCR showed that 10 µM PS48 increased the mRNA and protein levels of Akt and regulated maturation-related genes, including cyclin B1, MOS, BMP15, GDF9, CDC2, mTOR, BAX, BCL2 and caspase-3. The results of Western blot indicated that 10µM PS48 increased the protein abundance of Akt, phosphorylation of Akt Thr308 (p-Akt^Thr308 ) and cyclin B1, but decreased the protein abundance of pro-apoptotic BAX. These results suggested that adding 10 µM PS48 to mature culture medium could promote the maturation of porcine oocytes, potentially through activating the PI3K/Akt signalling pathway.

Naringin inhibits colorectal cancer cell growth by repressing the PI3K/AKT/mTOR signaling pathway

In recent years, the incidence of colorectal cancer (CRC) has increased and research into new treatment methods for CRC has become a hot topic. Naringin has an inhibitory effect on the PI3k/AKT/mTOR signaling pathway in various tumor cell types and the effect of naringin is closely related to the occurrence and proliferation of tumor cells. The aim of this present study was to investigate whether naringin could inhibit the proliferation of CRC cells by inhibiting the PI3K/AKT/mTOR signaling pathway. This could provide a more mechanism-based treatment for CRC. MTT assays were used to detect the proliferation of CRC cells treated with various concentrations of naringin. The degree of apoptosis and the expression of apoptosis-related proteins (Bcl-2 and Bax) in CRC cells stimulated by naringin was detected using flow cytometry and western blot assays, respectively. The expression levels of PI3K/AKT/mTOR-related proteins [PI3K, AKT, mTOR, phosphorylated (p)-PI3K, p-AKT and p-mTOR] after naringin stimulation in CRC cells were detected using western blot assays. Naringin inhibited the proliferation of CRC cells in a dose-dependent manner. Naringin promoted the apoptosis of CRC cells and inhibited the activation of the PI3K/AKT/mTOR signaling pathway in a dose-dependent manner. The results demonstrated that naringin may be a promising therapeutic agent for the treatment of CRC, which may inhibit the proliferation of CRC cells and induce apoptosis by inhibiting the PI3K/AKT/mTOR signaling pathway.

Xuesaitong Protects Podocytes from Apoptosis in Diabetic Rats through Modulating PTEN-PDK1-Akt-mTOR Pathway

Diabetic kidney disease (DKD) is a major cause of end-stage renal disease (ESRD), and therapeutic strategies for delaying its progression are limited. Loss of podocytes by apoptosis characterizes the early stages of DKD. To identify novel therapeutic options, we investigated the effects of Xuesaitong (XST), consisting of total saponins from Panax notoginseng, on podocyte apoptosis in streptozotocin- (STZ-) induced diabetic rats. XST (5 mg/kg·d) or Losartan (10 mg/kg·d) was given to diabetic rats for 12 weeks. Albuminuria, renal function markers, and renal histopathology morphological changes were examined. Podocyte apoptosis was determined by triple immunofluorescence labelling including a TUNEL assay, WT1, and DAPI. Renal expression of Nox4, miRNA-214, PTEN, PDK1, phosphorylated Akt, mTOR, and mTORC1 was detected. In diabetic rats, severe hyperglycaemia and albuminuria developed, and apoptotic podocytes were markedly increased in diabetic kidneys. However, XST attenuated albuminuria, mesangial expansion, podocyte apoptosis, and morphological changes of podocytes in diabetic rats. Decreased expression of PTEN, as well as increased expression of Nox4, miRNA-214, PDK1, phosphorylated Akt, mTOR, and mTORC1, was detected. These abnormalities were partially restored by XST treatment. Thus, XST ameliorated podocyte apoptosis partly through modulating the PTEN-PDK1-Akt-mTOR pathway. These novel findings might point the way to a natural therapeutic strategy for treating DKD.

Pivotal role of PDK1 in megakaryocyte cytoskeletal dynamics and polarization during platelet biogenesis

The investigators explore the role of PDK1 (phosphoinositide-dependent protein kinase 1) in the cytoskeletal regulation of platelet production and furnish new insights into megakaryocyte maturation and proplatelet formation.

Polyphyllin I induces autophagy and cell cycle arrest via inhibiting PDK1/Akt/mTOR signal and downregulating cyclin B1 in human gastric carcinoma HGC-27 cells

Paris polyphylla. is a traditional medicinal herb that has long been used to prevent cancer in many Asian countries. Polyphyllin I (PPI), an important bioactive constituent of Paris polyphylla, has been found to exhibit a wide variety of anticancer activities in many types of cancer cells. However, the effects of PPI on human gastric carcinoma cells and its mechanism of action remain unclear. In this study, we examined the effective anti-gastric carcinoma activity of PPI and its underlying mechanism of action in HGC-27 cells. In vitro, sub-micromolar concentrations of PPI inhibited HGC-27 cell proliferation with an IC₅₀ of 0.34 ± 0.06 μM after a 72-h treatment. In vivo, 3 mg/kg PPI significantly inhibited proliferation of HGC-27 tumor cells, with a 78.8% inhibition rate compared to paclitaxel, and demonstrated higher safety. Analysis of MDC and mGFP-LC3 fluorescence, Western blotting and flow cytometry indicated that PPI induced cell cycle arrest in HGC-27 cells by promoting the conversion of LC3-I to LC3-II and by downregulating cyclin B1. Furthermore, Western blotting showed that PPI inhibited the autophagy-regulating PDK1/Akt/mTOR signaling pathway in vitro and in vivo. In addition, immunohistochemistry and TUNEL staining revealed that PPI decreased Ki67 expression and increased the percentage of apoptotic cells in HGC-27 xenograft tumors. These data indicate that PPI is an PDK1/Akt/mTOR signaling inhibitor and of therapeutic relevance for gastric cancer treatment and that the rhizome of Paris polyphylla deserves further clinical investigation as an alternative therapy for gastric cancer.

A patent update on PDK1 inhibitors (2015-present)

INTRODUCTION

3-Phosphoinositide-dependent kinase 1 (PDK1), the 'master kinase of the AGC protein kinase family', plays a key role in cancer development and progression. Although it has been rather overlooked, in the last decades a growing number of molecules have been developed to effectively modulate the PDK1 enzyme.

AREAS COVERED

This review collects different PDK1 inhibitors patented from October 2014 to December 2018. The molecules have been classified on the basis of the chemical structure/type of inhibition, and for each general structure, examples have been discussed in extenso.

EXPERT OPINION

The role of PDK1 in cancer development and progression as well as in metastasis formation and in chemoresistance has been confirmed by many studies. Therefore, the pharmaceutical discovery in both public and private institutions is still ongoing despite the plentiful molecules already published. The majority of the new molecules synthetized interact with binding sites different from the ATP binding site (i.e. PIF pocket or DFG-out conformation). However, many researchers are still looking for innovative PDK1 modulation strategy such as combination of well-known inhibitory agents or multitarget ligands, aiming to block, together with PDK1, other different critical players in the wide panorama of proteins involved in tumor pathways.

HIF-1α Regulates Glucocorticoid-Induced Osteoporosis Through PDK1/AKT/mTOR Signaling Pathway

Long-term and high dose glucocorticoid treatment can cause decreased viability and function of osteoblasts, which leads to osteoporosis and osteonecrosis. In this study, we investigated the role and mechanism of action of HIF-1α in glucocorticoid-induced osteogenic inhibition in MC3T3-E1 cells. Our results showed that HIF-1α protein expression was reduced when MC3T3-E1 cells were exposed to dexamethasone (Dex) at varying concentrations ranging from 10^-9 to 10^-6 M. PDK1 expression was also decreased in MC3T3-E1 cells after dexamethasone treatment. MC3T3-E1 cells when treated with the glucocorticoid receptor antagonist RU486 along with dexamethasone showed enhanced HIF-1α expression. In addition, upregulated expression of HIF-1α was capable of promoting the osteogenic ability of MC3T3-E1 cells and PDK1 expression. However, the HIF-1α antagonist 2-methoxyestradiol (2-ME) had a reverse effect in MC3T3-E1 cells exposed to dexamethasone. Furthermore, the PDK1 antagonist dichloroacetate could repress the osteogenic ability of MC3T3-E1 cells, although HIF-1α was upregulated when transduced with adenovirus-HIF-1α construct. The PDK1 agonist PS48 was able to promote the osteogenic ability of MC3T3-E1 cells treated with dexamethasone. Importantly, the protein levels of p-AKT and p-mTOR were increased in MC3T3-E1 cells treated with dexamethasone after PS48 treatment. in vivo, the PDK1 agonist PS48 could maintain the bone mass of mice treated with dexamethasone. This study provides a new understanding of the mechanism of glucocorticoid-induced osteoporosis.

PI3K/mTOR inhibition promotes the regression of experimental vascular malformations driven by PIK3CA-activating mutations

Somatic activating mutations within the PIK3CA gene have been recently detected in sporadic lymphatic and venous malformations, and in vascular malformations (VM) associated to overgrowth syndromes, such as CLOVES and Klippel-Trenaunay syndrome. Although VM are often limited to specific tissue areas and can be well treated, in extended or recurrent lesions novel therapeutic approaches are needed. We generated a mouse model of VM by local expression of PIK3CA-activating mutation in endothelial cells. PIK3CA-driven lesions are characterized by large areas of hemorrhage, hyperplastic vessels, infiltrates of inflammatory cells, and elevated endothelial cell density. Such vascular lesions are ameliorated by administration of dual PI3K/mTOR inhibitor, BEZ235, and mTOR inhibitor, Everolimus. Unexpectedly, the expression of PIK3CA-activating mutations in human endothelial cells results in both increased proliferation rates and senescence. Moreover, active forms of PIK3CA strongly promote the angiogenic sprouting. Treatment with PI3K/mTOR inhibitors restores normal endothelial cell proliferation rate and reduces the amount of senescent cells, whereas treatment with Akt inhibitor is less effective. Our findings reveal that PIK3CA mutations have a key role in the pathogenesis of VM and PIK3CA-driven experimental lesions can be effectively treated by PI3K/mTOR inhibitors.

Zinc enhances the cellular energy supply to improve cell motility and restore impaired energetic metabolism in a toxic environment induced by OTA

Exogenous nutrient elements modulate the energetic metabolism responses that are prerequisites for cellular homeostasis and metabolic physiology. Although zinc is important in oxidative stress and cytoprotection processes, its role in the regulation of energetic metabolism remains largely unknown. In this study, we found that zinc stimulated aspect in cell motility and was essential in restoring the Ochratoxin A (OTA)-induced energetic metabolism damage in HEK293 cells. Moreover, using zinc supplementation and zinc deficiency models, we observed that zinc is conducive to mitochondrial pyruvate transport, oxidative phosphorylation, carbohydrate metabolism, lipid metabolism and ultimate energy metabolism in both normal and toxic-induced oxidative stress conditions in vitro, and it plays an important role in restoring impaired energetic metabolism. This zinc-mediated energetic metabolism regulation could also be helpful for DNA maintenance, cytoprotection and hereditary cancer traceability. Therefore, zinc can widely adjust energetic metabolism and is essential in restoring the impaired energetic metabolism of cellular physiology.

Curcumin modulates endothelial permeability and monocyte transendothelial migration by affecting endothelial cell dynamics

Curcumin is a phenolic compound that exhibits beneficial properties for cardiometabolic health. We previously showed that curcumin reduced the infiltration of immune cells into the vascular wall and prevented atherosclerosis development in mice. This study aimed to investigate the effect of curcumin on monocyte adhesion and transendothelial migration (TEM) and to decipher the underlying mechanisms of these actions. Human umbilical vein endothelial cells (HUVECs) were exposed to curcumin (0.5-1μM) for 3h prior to their activation by Tumor Necrosis Factor alpha (TNF-α). Endothelial permeability, monocyte adhesion and transendothelial migration assays were conducted under static condition and shear stress that mimics blood flow. We further investigated the impact of curcumin on signaling pathways and on the expression of genes using macroarrays. Pre-exposure of endothelial cells to curcumin reduced monocyte adhesion and their transendothelial migration in both static and shear stress conditions. Curcumin also prevented changes in both endothelial permeability and the area of HUVECs when induced by TNF-α. We showed that curcumin modulated the expression of 15 genes involved in the control of cytoskeleton and endothelial junction dynamic. Finally, we showed that curcumin inhibited NF-κB signaling likely through an antagonist interplay with several kinases as suggested by molecular docking analysis. Our findings demonstrate the ability of curcumin to reduce monocyte TEM through a multimodal regulation of the endothelial cell dynamics with a potential benefit on the vascular endothelial function barrier.

Triptolide Suppresses Glomerular Mesangial Cell Proliferation in Diabetic Nephropathy Is Associated with Inhibition of PDK1/Akt/mTOR Pathway

Mesangial cell proliferation has been identified as a mainly contributing factor to glomerulosclerosis, which is typical of diabetic nephropathy. However, the specific mechanisms and therapies remain unclear. PDK1 is a critical regulator of cell proliferation, but the specific role of PDK1 in diabetic nephropathy has not been fully illuminated. In the current study, we demonstrated that triptolide (TP) ameliorated albuminuria in the high fat diet/STZ-induced diabetic rats. TP also suppressed the increased proliferating cell markers Ki-67 and PCNA in the kidney tissues. Our results of MTT and cell cycle analysis further confirmed that TP significantly inhibited mesangial cell proliferation, and the inhibition of PDK1/Akt/mTOR pathway might be the underlying mechanisms. In addition, we also found that the PDK1 activator (PS48) could reverse the cell proliferation inhibition role of TP. These data suggest that TP may be useful in prevention of diabetic glomerulosclerosis and that PDK1/Akt/mTOR pathway might be the underlying mechanism.

Synaptic Activity and Muscle Contraction Increases PDK1 and PKCβI Phosphorylation in the Presynaptic Membrane of the Neuromuscular Junction

Conventional protein kinase C βI (cPKCβI) is a conventional protein kinase C (PKC) isoform directly involved in the regulation of neurotransmitter release in the neuromuscular junction (NMJ). It is located exclusively at the nerve terminal and both synaptic activity and muscle contraction modulate its protein levels and phosphorylation. cPKCβI molecular maturation includes a series of phosphorylation steps, the first of which is mediated by phosphoinositide-dependent kinase 1 (PDK1). Here, we sought to localize PDK1 in the NMJ and investigate the hypothesis that synaptic activity and muscle contraction regulate in parallel PDK1 and cPKCβI phosphorylation in the membrane fraction. To differentiate the presynaptic and postsynaptic activities, we abolished muscle contraction with μ-conotoxin GIIIB (μ-CgTx-GIIIB) in some experiments before stimulation of the phrenic nerve (1 Hz, 30 min). Then, we analyzed total and membrane/cytosol fractions of skeletal muscle by Western blotting. Results showed that PDK1 is located exclusively in the nerve terminal of the NMJ. After nerve stimulation with and without coincident muscle contraction, total PDK1 and phosphorylated PDK1 (pPDK1) protein levels remained unaltered. However, synaptic activity specifically enhanced phosphorylation of PDK1 in the membrane, an important subcellular location for PDK1 function. This increase in pPDK1 coincides with a significant increase in the phosphorylation of its substrate cPKCβI also in the membrane fraction. Moreover, muscle contraction maintains PDK1 and pPDK1 but increases cPKCβI protein levels and its phosphorylation. Thus, even though PDK1 activity is maintained, pcPKCβI levels increase in concordance with total cPKCβI. Together, these results indicate that neuromuscular activity could induce the membrane targeting of pPDK1 in the nerve terminal of the NMJ to promote the phosphorylation of the cPKCβI, which is involved in ACh release.

Akt3 is responsible for the survival and proliferation of embryonic stem cells

The phosphatidylinositol 3-kinase (PI3K)/protein kinase B (PKB/Akt) pathway plays an important role in regulating cell proliferation, metabolism, and survival. However, the distinct roles of Akt isoforms (Akt1, Akt2, and Akt3) in pluripotent stem cell maintenance are not fully defined. Using mouse embryonic stem cells (ESCs), we show that direct inhibition of Akt activity leads to ESC apoptosis. The Akt3, but not Akt1 or Akt2, activity specifically regulates this effect. Inhibiting Akt3 also leads to a cell cycle arrest at G1 phase. These regulatory roles of Akt3 are dependent on its kinase activity. Blocking the expression of Akt1 plus Akt2 in ESCs does not affect cell survival or proliferation, although blocking Akt1 aggravates the apoptotic effect induced by depletion of Akt3. We further show that blocking Akt3 in ESCs results in significant nuclear accumulation of p53, as well as the activation of its downstream targets, such as Mdm2, p21, and Fas. Inhibiting p53 and its downstream targets partially rescued the effects caused by Akt3-depletion. Our results revealed an Akt3 isoform-specific mechanism for ESC survival and proliferation involving the control of p53 activity.

Summary: We identified that Akt isoform 3, but not Akt1 or Akt2, specifically regulates embryonic stem cell survival and proliferation. Mechanistically, this is achieved partially through controlling the p53 pathway activity.

Serine/Threonine Kinase 3-Phosphoinositide-Dependent Protein Kinase-1 (PDK1) as a Key Regulator of Cell Migration and Cancer Dissemination

Dissecting the cellular signaling that governs the motility of eukaryotic cells is one of the fundamental tasks of modern cell biology, not only because of the large number of physiological processes in which cell migration is crucial, but even more so because of the pathological ones, in particular tumor invasion and metastasis. Cell migration requires the coordination of at least four major processes: polarization of intracellular signaling, regulation of the actin cytoskeleton and membrane extension, focal adhesion and integrin signaling and contractile forces generation and rear retraction. Among the molecular components involved in the regulation of locomotion, the phosphatidylinositol-3-kinase (PI3K) pathway has been shown to exert fundamental role. A pivotal node of such pathway is represented by the serine/threonine kinase 3-phosphoinositide-dependent protein kinase-1 (PDPK1 or PDK1). PDK1, and the majority of its substrates, belong to the AGC family of kinases (related to cAMP-dependent protein kinase 1, cyclic Guanosine monophosphate-dependent protein kinase and protein kinase C), and control a plethora of cellular processes, downstream either to PI3K or to other pathways, such as RAS GTPase-MAPK (mitogen-activated protein kinase). Interestingly, PDK1 has been demonstrated to be crucial for the regulation of each step of cell migration, by activating several proteins such as protein kinase B/Akt (PKB/Akt), myotonic dystrophy-related CDC42-binding kinases alpha (MRCKα), Rho associated coiled-coil containing protein kinase 1 (ROCK1), phospholipase C gamma 1 (PLCγ1) and β3 integrin. Moreover, PDK1 regulates cancer cell invasion as well, thus representing a possible target to prevent cancer metastasis in human patients. The aim of this review is to summarize the various mechanisms by which PDK1 controls the cell migration process, from cell polarization to actin cytoskeleton and focal adhesion regulation, and finally, to discuss the evidence supporting a role for PDK1 in cancer cell invasion and dissemination.

Quercetin Attenuates Cell Survival, Inflammation, and Angiogenesis via Modulation of AKT Signaling in Murine T-Cell Lymphoma

AKT signaling is important to maintaining normal physiology. Hyperactivation of AKT signaling is frequent in cancer, which maintains a high oxidative state in a tumor microenvironment that is needed for tumor adaptation. Therefore, antioxidants are proposed to exhibit anticancer properties by interfering with the tumor microenvironment. Quercetin is an ubiquitous bioactive antioxidant rich in vegetables and beverages. The present study aimed to analyze cancer preventive property of quercetin in ascite cells of Dalton's lymphoma-bearing mice. Protein level was determined by Western blotting. Nitric oxide (NO) level was estimated spectrophotometrically using Griess reagent. Results show downregulation in phosphorylation of AKT and PDK1 by quercetin, which was consistent with decreased phosphorylation of downstream survival factors such as BAD, GSK-3β, mTOR, and IkBα. Further, quercetin attenuated the levels of angiogenic factor VEGF-A and inflammatory enzymes COX-2 and iNOS as well as NO levels, whereas it increased the levels of phosphatase PTEN. Overall results suggest that quercetin modulates AKT signaling leading to attenuation of cell survival, inflammation, and angiogenesis in lymphoma-bearing mice.

Molecular mechanisms of OLIG2 transcription factor in brain cancer

Oligodendrocyte lineage transcription factor 2 (OLIG2) plays a pivotal role in glioma development. Here we conducted a comprehensive study of the critical gene regulatory networks involving OLIG2. These include the networks responsible for OLIG2 expression, its translocation to nucleus, cell cycle, epigenetic regulation, and Rho-pathway interactions. We described positive feedback loops including OLIG2: loops of epigenetic regulation and loops involving receptor tyrosine kinases. These loops may be responsible for the prolonged oncogenic activity of OLIG2. The proposed schemes for epigenetic regulation of the gene networks involving OLIG2 are confirmed by patient survival (Kaplan-Meier) curves based on the cancer genome atlas (TCGA) datasets. Finally, we elucidate the Coherent-Gene Modules (CGMs) networks-framework of OLIG2 involvement in cancer. We showed that genes interacting with OLIG2 formed eight CGMs having a set of intermodular connections. We showed also that among the genes involved in these modules the most connected hub is EGFR, then, on lower level, HSP90 and CALM1, followed by three lower levels including epigenetic genes KDM1A and NCOR1. The genes on the six upper levels of the hierarchy are involved in interconnections of all eight CGMs and organize functionally defined gene-signaling subnetworks having specific functions. For example, CGM1 is involved in epigenetic control. CGM2 is significantly related to cell proliferation and differentiation. CGM3 includes a number of interconnected helix-loop-helix transcription factors (bHLH) including OLIG2. Many of these TFs are partially controlled by OLIG2. The CGM4 is involved in PDGF-related: angiogenesis, tumor cell proliferation and differentiation. These analyses provide testable hypotheses and approaches to inhibit OLIG2 pathway and relevant feed-forward and feedback loops to be interrogated. This broad approach can be applied to other TFs.

A Small Molecule Inhibitor of PDK1/PLCγ1 Interaction Blocks Breast and Melanoma Cancer Cell Invasion

Strong evidence suggests that phospholipase Cγ1 (PLCγ1) is a suitable target to counteract tumourigenesis and metastasis dissemination. We recently identified a novel signalling pathway required for PLCγ1 activation which involves formation of a protein complex with 3-phosphoinositide-dependent protein kinase 1 (PDK1). In an effort to define novel strategies to inhibit PLCγ1-dependent signals we tested here whether a newly identified and highly specific PDK1 inhibitor, 2-O-benzyl-myo-inositol 1,3,4,5,6-pentakisphosphate (2-O-Bn-InsP₅), could affect PDK1/PLCγ1 interaction and impair PLCγ1-dependent cellular functions in cancer cells. Here, we demonstrate that 2-O-Bn-InsP₅ interacts specifically with the pleckstrin homology domain of PDK1 and impairs formation of a PDK1/PLCγ1 complex. 2-O-Bn-InsP₅ is able to inhibit the epidermal growth factor-induced PLCγ1 phosphorylation and activity, ultimately resulting in impaired cancer cell migration and invasion. Importantly, we report that 2-O-Bn-InsP₅ inhibits cancer cell dissemination in zebrafish xenotransplants. This work demonstrates that the PDK1/PLCγ1 complex is a potential therapeutic target to prevent metastasis and it identifies 2-O-Bn-InsP₅ as a leading compound for development of anti-metastatic drugs.

Locking PDK1 in DFG-out conformation through 2-oxo-indole containing molecules: Another tools to fight glioblastoma

The phosphoinositide-dependent kinase-1 (PDK1) is one of the main components of the PI3K/Akt pathway. Also named the "master kinase" of the AGC family, PDK1 plays a critical role in tumorigenesis, by enhancing cell proliferation and inhibiting apoptosis, as well as in cell invasion and metastasis formation. Although there have been done huge efforts in discovering specific compounds targeting PDK1, nowadays no PDK1 inhibitor has yet entered the clinic. With the aim to pick out novel and potent PDK1 inhibitors, herein we report the design and synthesis of a new class of molecules obtained by merging the 2-oxo-indole nucleus with the 2-oxo-pyridonyl fragment, two moieties with high affinity for the PDK1 hinge region and its DFG-out binding site, respectively. To this purpose, a small series of compounds were synthesised and a tandem application of docking and Molecular Dynamic (MD) was employed to get insight into their mode of binding. The OXID-pyridonyl hybrid 8, possessing the lower IC50 (IC50 = 112 nM), was also tested against recombinant kinases involved in the PI3K/PDK1/Akt pathway and was subjected to vitro studies to evaluate the cytotoxicity and the inhibition of tumour cell migration. All together the results let us to consider 8, as a lead compound of a new generation of PDK1 inhibitors and encourage us to further studies in this direction.

AMIGO2, a novel membrane anchor of PDK1, controls cell survival and angiogenesis via Akt activation

AMIGO2 is a novel scaffold protein that regulates PDK1 membrane localization and Akt activation in endothelial cells, and inhibition of the interaction between PDK1–AMIGO2 results in impaired neovascularization, pathological angiogenesis, and tumor angiogenesis.

The phosphoinositide 3-kinase–Akt signaling pathway is essential to many biological processes, including cell proliferation, survival, metabolism, and angiogenesis, under pathophysiological conditions. Although 3-phosphoinositide–dependent kinase 1 (PDK1) is a primary activator of Akt at the plasma membrane, the optimal activation mechanism remains unclear. We report that adhesion molecule with IgG-like domain 2 (AMIGO2) is a novel scaffold protein that regulates PDK1 membrane localization and Akt activation. Loss of AMIGO2 in endothelial cells (ECs) led to apoptosis and inhibition of angiogenesis with Akt inactivation. Amino acid residues 465–474 in AMIGO2 directly bind to the PDK1 pleckstrin homology domain. A synthetic peptide containing the AMIGO2 465–474 residues abrogated the AMIGO2–PDK1 interaction and Akt activation. Moreover, it effectively suppressed pathological angiogenesis in murine tumor and oxygen-induced retinopathy models. These results demonstrate that AMIGO2 is an important regulator of the PDK1–Akt pathway in ECs and suggest that interference of the PDK1–AMIGO2 interaction might be a novel pharmaceutical target for designing an Akt pathway inhibitor.

The critical role of Akt in cardiovascular function

Akt kinase, a member of AGC kinases, is important in many cellular functions including proliferation, migration, cell growth and metabolism. There are three known Akt isoforms which play critical and diverse roles in the cardiovascular system. Akt activity is regulated by its upstream regulatory pathways at transcriptional and post-translational levels. Beta-catenin/Tcf-4, GLI1 and Stat-3 are some of few known transcriptional regulators of AKT gene. Threonine 308 and serine 473 are the two critical phosphorylation sites of Akt1. Translocation of Akt to the cell membrane facilitates PDK1 phosphorylation of the threonine site. The serine site is phosphorylated by mTORC2. Ack1, Src, PTK6, TBK1, IKBKE and IKKε are some of the non-canonical pathways which affect the Akt activity. Protein-protein interactions of Akt to actin and Hsp90 increase the Akt activity while Akt binding to other proteins such as CTMP and TRB3 reduces the Akt activity. The action of Akt on its downstream targets determines its function in cardiovascular processes such as cell survival, growth, proliferation, angiogenesis, vasorelaxation, and cell metabolism. Akt promotes cell survival via caspase-9, YAP, Bcl-2, and Bcl-x activities. Inhibition of FoxO proteins by Akt also increases cell survival by transcriptional mechanisms. Akt stimulates cell growth and proliferation through mTORC1. Akt also increases VEGF secretion and mediates eNOS phosphorylation, vasorelaxation and angiogenesis. Akt can increase cellular metabolism through its downstream targets GSK3 and GLUT4. The alterations of Akt signaling play an important role in many cardiovascular pathological processes such as atherosclerosis, cardiac hypertrophy, and vascular remodeling. Several Akt inhibitors have been developed and tested as anti-tumor agents. They could be potential novel therapeutics for the cardiovascular diseases.

Phosphatidylinositol-3,4,5-triphosphate and cellular signaling: implications for obesity and diabetes

Phosphatidylinositol-3,4,5-triphosphate (PtdIns(3,4,5)P₃) is one of the most important phosphoinositides and is capable of activating a wide range of proteins through its interaction with their specific binding domains. Localization and activation of these effector proteins regulate a number of cellular functions, including cell survival, proliferation, cytoskeletal rearrangement, intracellular vesicle trafficking, and cell metabolism. Phosphoinositides have been investigated as an important agonist-dependent second messenger in the regulation of diverse physiological events depending upon the phosphorylation status of their inositol group. Dysregulation in formation as well as metabolism of phosphoinositides is associated with various pathophysiological disorders such as inflammation, allergy, cardiovascular diseases, cancer, and metabolic diseases. Recent studies have demonstrated that the impaired metabolism of PtdIns(3,4,5)P₃ is a prime mediator of insulin resistance associated with various metabolic diseases including obesity and diabetes. This review examines the current status of the role of PtdIns(3,4,5)P₃ signaling in the regulation of various cellular functions and the implications of dysregulated PtdIns(3,4,5)P₃ signaling in obesity, diabetes, and their associated complications.

PDK1 regulates focal adhesion disassembly through modulation of αvβ3 integrin endocytosis

Non-amoeboid cell migration is characterised by dynamic competition among multiple protrusions to establish new adhesion sites at the cell's leading edge. However, the mechanisms that regulate the decision to disassemble or to grow nascent adhesions are not fully understood.

Here we show that in endothelial cells (EC) 3-phosphoinositide-dependent protein (PDK1) promotes focal adhesions (FA) turnover by controlling endocytosis of integrin αvβ3 in a PI3K-dependent manner. We demonstrate that PDK1 binds and phosphorylates integrin αvβ3. Down-regulation of PDK1 increases FA size and slows down their disassembly. This process requires both PDK1 kinase activity and PI3K activation but does not involve Akt. Moreover, PDK1 silencing stabilizes FA in membrane protrusions decreasing EC migration on vitronectin.

These results indicate that modulation of integrin endocytosis by PDK1 hampers EC adhesion and migration on extracellular matrix, thus unveiling a novel role for this kinase.

Molecular and cellular effects of in vitro shockwave treatment on lymphatic endothelial cells

Extracorporeal shockwave treatment was shown to improve orthopaedic diseases and wound healing and to stimulate lymphangiogenesis in vivo. The aim of this study was to investigate in vitro shockwave treatment (IVSWT) effects on lymphatic endothelial cell (LEC) behavior and lymphangiogenesis. We analyzed migration, proliferation, vascular tube forming capability and marker expression changes of LECs after IVSWT compared with HUVECs. Finally, transcriptome- and miRNA analyses were conducted to gain deeper insight into the IVSWT-induced molecular mechanisms in LECs. The results indicate that IVSWT-mediated proliferation changes of LECs are highly energy flux density-dependent and LEC 2D as well as 3D migration was enhanced through IVSWT. IVSWT suppressed HUVEC 3D migration but enhanced vasculogenesis. Furthermore, we identified podoplaninhigh and podoplaninlow cell subpopulations, whose ratios changed upon IVSWT treatment. Transcriptome- and miRNA analyses on these populations showed differences in genes specific for signaling and vascular tissue. Our findings help to understand the cellular and molecular mechanisms underlying shockwave-induced lymphangiogenesis in vivo.

Nuclear Akt2 opposes limbal keratinocyte stem cell self-renewal by repressing a FOXO-mTORC1 signaling pathway

Signals downstream of Akt can either favor or oppose stem cell (SC) maintenance, but how this dual role can be achieved is still undefined. Using human limbal keratinocyte stem cells (LKSCs), a SC type used in transplantation therapies for corneal regeneration, we show that Akt signaling is prominent in SC populations both in vivo and in vitro, and that Akt1 promotes while Akt2 opposes SC self-renewal. Noteworthy, loss of Akt2 signaling enhances LKSC maintenance ex vivo, whereas Akt1 depletion anticipates SC exhaustion. Mechanistically, the antagonistic functions of Akt1 and Akt2 in SC control are mainly dictated by their differential subcellular distribution, being nuclear Akt2 selectively implicated in FOXO inhibition. Akt2 downregulation favors LKSC maintenance as a result of a gain of FOXO functions, which attenuates the mechanistic target of rapamycin complex one signaling via tuberous sclerosis one gene induction, and promotes growth factor signaling through Akt1. Consistently, Akt2 deficiency also enhances limbal SCs in vivo. Thus, our findings reveal distinct roles for nuclear versus cytosolic Akt signaling in normal epithelial SC control and suggest that the selective Akt2 inhibition may provide novel pharmacological strategies for human LKSC expansion in therapeutic settings and mechanistic research.

PDK1-mediated activation of MRCKα regulates directional cell migration and lamellipodia retraction

Directional cell migration is of paramount importance in both physiological and pathological processes, such as development, wound healing, immune response, and cancer invasion. Here, we report that 3-phosphoinositide-dependent kinase 1 (PDK1) regulates epithelial directional migration and invasion by binding and activating myotonic dystrophy kinase-related CDC42-binding kinase α (MRCKα). We show that the effect of PDK1 on cell migration does not involve its kinase activity but instead relies on its ability to bind membrane phosphatidylinositol (3,4,5)-trisphosphate. Upon epidermal growth factor (EGF) stimulation, PDK1 and MRCKα colocalize at the cell membrane in lamellipodia. We demonstrate that PDK1 positively modulates MRCKα activity and drives its localization within lamellipodia. Likewise, the retraction phase of lamellipodia is controlled by PDK1 through an MRCKα-dependent mechanism. In summary, we discovered a functional pathway involving PDK1-mediated activation of MRCKα, which links EGF signaling to myosin contraction and directional migration.

Role of phospholipase C in cell invasion and metastasis

Phospholipases are enzymes that use phospholipids as substrate and are classified in three major classes A, C and D based on the reaction they catalyse. Phosphatidylinositol-specific Phospholipase C enzymes utilize phosphatidylinositol 4,5-bisphosphate as substrate and cleave the bond between the glycerol and the phosphate to produce important second messenger such as inositol trisphosphate and diacylglycerol. The Phospholipase C members are the most well-known phospholipases for their role in lipid signalling and cell proliferation and comprise 13 isoforms classified in 6 distinct sub-families. In particular, signalling activated by Phospholipase C γ, mostly activated by receptor and non-receptor tyrosine kinases, is well characterized in different cell systems. Increasing evidence suggest that Phospholipase C γ plays a key role in cell migration and invasion. Because of its role in cell growth and invasion, aberrant Phospholipase C γ signalling can contribute to carcinogenesis. A major challenge facing investigators who seek to target Phospholipase C γ directly is the fact that it is considered an "undruggable" protein. Indeed, isoform specificity and toxicity represents a big hurdle in the development of Phospholipase C γ small molecule inhibitors. Therefore, a future development in the field could be the identification of interacting partners as therapeutic targets that could be more druggable than Phospholipase C γ.

The PH domain of phosphoinositide-dependent kinase-1 exhibits a novel, phospho-regulated monomer-dimer equilibrium with important implications for kinase domain activation: single-molecule and ensemble studies

Phosphoinositide-dependent kinase-1 (PDK1) is an essential master kinase recruited to the plasma membrane by the binding of its C-terminal PH domain to the signaling lipid phosphatidylinositol-3,4,5-trisphosphate (PIP3). Membrane binding leads to PDK1 phospho-activation, but despite the central role of PDK1 in signaling and cancer biology, this activation mechanism remains poorly understood. PDK1 has been shown to exist as a dimer in cells, and one crystal structure of its isolated PH domain exhibits a putative dimer interface. It has been proposed that phosphorylation of PH domain residue T513 (or the phospho-mimetic T513E mutation) may regulate a novel PH domain dimer-monomer equilibrium, thereby converting an inactive PDK1 dimer to an active monomer. However, the oligomeric states of the PH domain on the membrane have not yet been determined, nor whether a negative charge at position 513 is sufficient to regulate its oligomeric state. This study investigates the binding of purified wild-type (WT) and T513E PDK1 PH domains to lipid bilayers containing the PIP3 target lipid, using both single-molecule and ensemble measurements. Single-molecule analysis of the brightness of the fluorescent PH domain shows that the PIP3-bound WT PH domain on membranes is predominantly dimeric while the PIP3-bound T513E PH domain is monomeric, demonstrating that negative charge at the T513 position is sufficient to dissociate the PH domain dimer and is thus likely to play a central role in PDK1 monomerization and activation. Single-molecule analysis of two-dimensional (2D) diffusion of PH domain-PIP3 complexes reveals that the dimeric WT PH domain diffuses at the same rate as a single lipid molecule, indicating that only one of its two PIP3 binding sites is occupied and there is little penetration of the protein into the bilayer as observed for other PH domains. The 2D diffusion of T513E PH domain is slower, suggesting the negative charge disrupts local structure in a way that allows deeper insertion of the protein into the viscous bilayer, thereby increasing the diffusional friction. Ensemble measurements of PH domain affinity for PIP3 on plasma membrane-like bilayers reveal that the dimeric WT PH domain possesses a one order of magnitude higher target membrane affinity than the previously characterized monomeric PH domains, consistent with a dimerization-triggered, allosterically enhanced affinity for one PIP3 molecule (a much larger affinity enhancement would be expected for dimerization-triggered binding to two PIP3 molecules). The monomeric T513E PDK1 PH domain, like other monomeric PH domains, exhibits a PIP3 affinity and bound state lifetime that are each 1 order of magnitude lower than those of the dimeric WT PH domain, which is predicted to facilitate release of activated, monomeric PDK1 to the cytoplasm. Overall, the study yields the first molecular picture of PH domain regulation via electrostatic control of dimer-monomer conversion.

MiR-492 impairs the angiogenic potential of endothelial cells

Endothelial cells growing in high glucose-containing medium show reduced cell proliferation and in vitro angiogenesis. Evidence suggests that the molecular pathways leading to these cellular responses are controlled by microRNAs, endogenous post-transcriptional regulators of gene expression. To identify the microRNAs and their targeted genes involved in the glucose responses, we performed the miRNA signature of Human Umbelical Vein Endothelial Cells (HUVECs) exposed and unexposed to high glucose. Among differentially expressed microRNAs, we analysed miR-492 and showed that its overexpression was able to reduce proliferation, migration and tube formation of HUVEC. These effects were accompanied by the down-regulation of eNOS, a key regulator of the endothelial cell function. We showed that eNOS was indirectly down-regulated by miR-492 and we discovered that miR-492 was able to bind mRNAs involved in proliferation, migration, tube formation and regulation of eNOS activity and expression. Moreover, we found that miR-492 decreased VEGF expression in HUVEC and impaired in vivo angiogenesis in a tumour xenograft model, suggesting a role also in modulating the secretion of pro-angiogenic factors. Taken together, the data indicate that miR-492 exerts a potent anti-angiogenic activity in endothelial cells and therefore miR-492 seems a promising tool for anti-angiogenic therapy.

miR-214 coordinates melanoma progression by upregulating ALCAM through TFAP2 and miR-148b downmodulation

Malignant melanoma is one of the most aggressive human cancers, but the mechanisms governing its metastatic dissemination are not fully understood. Upregulation of miR-214 and ALCAM and the loss of TFAP2 expression have been implicated in this process, with TFAP2 a direct target of miR-214. Here, we link miR-214 and ALCAM as well as identify a core role for miR-214 in organizing melanoma metastasis. miR-214 upregulated ALCAM, acting transcriptionally through TFAP2 and also posttranscriptionally through miR-148b (itself controlled by TFAP2), both negative regulators of ALCAM. We also identified several miR-214-mediated prometastatic functions directly promoted by ALCAM. Silencing ALCAM in miR-214-overexpressing melanoma cells reduced cell migration and invasion without affecting growth or anoikis in vitro, and it also impaired extravasation and metastasis formation in vivo. Conversely, cell migration and extravasation was reduced in miR-214-overexpressing cells by upregulation of either miR-148b or TFAP2. These findings were consistent with patterns of expression of miR-214, ALCAM, and miR-148b in human melanoma specimens. Overall, our results define a pathway involving miR-214, miR-148b, TFAP2, and ALCAM that is critical for establishing distant metastases in melanoma.

3-phosphoinositide-dependent kinase 1 controls breast tumor growth in a kinase-dependent but Akt-independent manner

3-phosphoinositide-dependent protein kinase 1 (PDK1) is the pivotal element of the phosphatidylinositol 3 kinase (PI3K) signaling pathway because it phosphorylates Akt/PKB through interactions with phosphatidylinositol 3,4,5 phosphate. Recent data indicate that PDK1 is overexpressed in many breast carcinomas and that alterations of PDK1 are critical in the context of oncogenic PI3K activation. However, the role of PDK1 in tumor progression is still controversial. Here, we show that PDK1 is required for anchorage-independent and xenograft growth of breast cancer cells harboring either PI3KCA or KRAS mutations. In fact, PDK1 silencing leads to increased anoikis, reduced soft agar growth, and pronounced apoptosis inside tumors. Interestingly, these phenotypes are reverted by PDK1 wild-type but not kinase-dead mutant, suggesting a relevant role of PDK1 kinase activity, even if PDK1 is not relevant for Akt activation here. Indeed, the expression of constitutively active forms of Akt in PDK1 knockdown cells is unable to rescue the anchorage-independent growth. In addition, Akt down-regulation and pharmacological inhibition do not inhibit the effects of PDK1 overexpression. In summary, these results suggest that PDK1 may contribute to breast cancer, even in the absence of PI3K oncogenic mutations and through both Akt-dependent and Akt-independent mechanisms.

Fer kinase limits neutrophil chemotaxis toward end target chemoattractants

Neutrophil recruitment and directional movement toward chemotactic stimuli are important processes in innate immune responses. This study examines the role of Fer kinase in neutrophil recruitment and chemotaxis to various chemoattractants in vitro and in vivo. Mice targeted with a kinase-inactivating mutation (Fer(DR/DR)) or wild type (WT) were studied using time-lapse intravital microscopy to examine leukocyte recruitment and chemotaxis in vivo. In response to keratinocyte-derived cytokine, no difference in leukocyte chemotaxis was observed between WT and Fer(DR/DR) mice. However, in response to the chemotactic peptide WKYMVm, a selective agonist of the formyl peptide receptor, a 2-fold increase in leukocyte emigration was noted in Fer(DR/DR) mice (p < 0.05). To determine whether these defects were due to Fer signaling in the endothelium or other nonhematopoietic cells, bone marrow chimeras were generated. WKYMVm-induced leukocyte recruitment in chimeric mice (WT bone marrow to Fer(DR/DR) recipients or vice versa) was similar to WT mice, suggesting that Fer kinase signaling in both leukocytes and endothelial cells serves to limit chemotaxis. Purified Fer(DR/DR) neutrophils demonstrated enhanced chemotaxis toward end target chemoattractants (WKYMVm and C5a) compared with WT using an under-agarose gel chemotaxis assay. These defects were not observed in response to intermediate chemoattractants (keratinocyte-derived cytokine, MIP-2, or LTB(4)). Increased WKYMVm-induced chemotaxis of Fer(DR/DR) neutrophils correlated with sustained PI3K activity and reduced reliance on the p38 MAPK pathway compared with WT neutrophils. Together, these data identify Fer as a novel inhibitory kinase for neutrophil chemotaxis toward end target chemoattractants through modulation of PI3K activity.

Role of phosphatidylinositol 3,4,5-trisphosphate in cell signaling

Many lipids present in cellular membranes are phosphorylated as part of signaling cascades and participate in the recruitment, localization, and activation of downstream protein effectors. Phosphatidylinositol (3,4,5)-trisphosphate (PtdIns(3,4,5)P3) is one of the most important second messengers and is capable of interacting with a variety of proteins through specific PtdIns(3,4,5)P3 binding domains. Localization and activation of these effector proteins controls a myriad of cellular functions including cell survival, proliferation, cytoskeletal rearrangement, and gene expression. Aberrations in the production and metabolism of PtdIns(3,4,5)P3 have been implicated in many human diseases including cancer, diabetes, inflammation, and heart disease. This chapter provides an overview of the role of PtdIns(3,4,5)P3 in cellular regulation and the implications of PtdIns(3,4,5)P3 dysregulation in human diseases. Additionally, recent attempts at targeting PtdIns(3,4,5)P3 signaling via small molecule inhibitors are summarized.

The 16p13.3 (PDPK1) Genomic Gain in Prostate Cancer: A Potential Role in Disease Progression

BACKGROUND

Prostate cancer (PCa) is a leading cause of cancer death, and distinguishing aggressive from indolent tumors is a major challenge. Identification and characterization of genomic alterations associated with advanced disease can provide new markers of progression and better therapeutic approaches.

METHODS

We performed fluorescence in situ hybridization to detect the copy number gain of chromosome 16p13.3 in 75 PCa samples including 10 lymph node (LN) metastases and their matched primary tumors, 9 samples of castration-resistant prostate cancer (CRPC), and 46 additional primary PCa specimens with clinicopathologic parameters.

RESULTS

We detected the gain in 5 of 10 LN metastases and 3 of 5 matched primary tumors, 3 of 9 CRPC samples, and 9 of 46 (20%) primary tumors where the 16p13.3 alteration was associated with high Gleason score and elevated preoperative prostate-specific antigen levels. The level of 16p13.3 gain was higher in LN metastasis and CRPC specimens compared to primary PCa. Chromosome mapping revealed the gain spans PDPK1 encoding the 3-phosphoinositide-dependent protein kinase-1 (PDK1). Knockdown of PDK1 in three PCa cell lines reduced migration without affecting growth and re-expressing PDK1 rescued motility.

CONCLUSION

Our findings support a prognostic value of the 16p13.3 gain and a role of PDK1 in PCa progression through migration.

PI3K signaling in the regulation of branching morphogenesis

Branching morphogenesis drives the formation of epithelial organs including the mammary gland, lung, kidney, salivary gland and prostate. Branching at the cellular level also drives development of the nervous and vascular systems. A variety of signaling pathways are orchestrated together to establish the pattern of these branched organs. The phosphoinositide 3-kinase (PI3K) signaling network is of particular interest because of the diverse outcomes it generates, including proliferation, motility, growth, survival and cell death. Here, we focus on the role of the PI3K pathway in the development of branched tissues. Cultured cells, explants and transgenic mice have revealed that the PI3K pathway is critical for the regulation of cell proliferation, apoptosis and motility during branching of tissues.

Semaphorin 4A exerts a proangiogenic effect by enhancing vascular endothelial growth factor-A expression in macrophages

The axon guidance cues semaphorins (Semas) and their receptors plexins have been shown to regulate both physiological and pathological angiogenesis. Sema4A plays an important role in the immune system by inducing T cell activation, but to date, the role of Sema4A in regulating the function of macrophages during the angiogenic and inflammatory processes remains unclear. In this study, we show that macrophage activation by TLR ligands LPS and polyinosinic-polycytidylic acid induced a time-dependent increase of Sema4A and its receptors PlexinB2 and PlexinD1. Moreover, in a thioglycollate-induced peritonitis mouse model, Sema4A was detected in circulating Ly6C(high) inflammatory monocytes and peritoneal macrophages. Acting via PlexinD1, exogenous Sema4A strongly increased macrophage migration. Of note, Sema4A-activated PlexinD1 enhanced the expression of vascular endothelial growth factor-A, but not of inflammatory chemokines. Sema4A-stimulated macrophages were able to activate vascular endothelial growth factor receptor-2 and the PI3K/serine/threonine kinase Akt pathway in endothelial cells and to sustain their migration and in vivo angiogenesis. Remarkably, in an in vivo cardiac ischemia/reperfusion mouse model, Sema4A was highly expressed in macrophages recruited at the injured area. We conclude that Sema4A activates a specialized and restricted genetic program in macrophages able to sustain angiogenesis and participates in their recruitment and activation in inflammatory injuries.

Lentiviral gene transfer method to study integrin function in T lymphocytes

Integrins play critical roles in adhesion and migration of T cells during an immune response and inflammation. It is of great importance to understand the molecular pathways that regulate integrin function in T cells. Lentiviral vector-based gene transfer method has emerged in the past decade as an efficient means of transferring genes into both resting and activated hard-to-transfect cells, including T cells to knockdown gene expression. Therefore, this technology could be utilized effectively to study different aspects of integrin function or even to perform genome-wide RNAi screens to look globally for regulators of integrin function in T cells. In this chapter, we provide the simplest protocol to infect activated CD4(+) human T cells with high efficiency.

PI3K/AKT/mTOR Pathway in Angiogenesis

The phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) pathway is activated in the majority of human cancers. This pathway is known to play a key role in numerous cellular functions including proliferation, adhesion, migration, invasion, metabolism, and survival, but in the current review we focus on its role in angiogenesis. PI3K activation may occur via RAS mutation, loss of phosphatase and tensin homolog (PTEN), or by increased expression of growth factor receptors such as epidermal growth factor receptor. There is a connection between the PI3K pathway and angiogenesis. Hypoxia leads to HIF-1α stabilization and is a major stimulus for increased vascular endothelial growth factor (VEGF) production by tumor cells. However, activation of the PI3K/AKT pathway in tumor cells can also increase VEGF secretion, both by hypoxia-inducible factor 1 (HIF-1) dependent and independent mechanisms. The PI3K/AKT pathway also modulates the expression of other angiogenic factors such as nitric oxide and angiopoietins. Numerous inhibitors targeting the PI3K/AKT/mTOR pathway have been developed, and these agents have been shown to decrease VEGF secretion and angiogenesis. The effect of these inhibitors on tumor vasculature can be difficult to predict. The vasculature of tumors is aberrant, leading to sluggish bloodflow and elevated interstitial blood pressure, which can be perpetuated by the high levels of VEGF. Hence, decreasing VEGF expression can paradoxically lead to vascular normalization and improved bloodflow in some tumors. In addition to its importance in cancer, the PI3K pathway also plays an essential role in the formation of normal blood vessels during development. Embryos with kinase-dead p110α catalytic subunit of PI3K develop vascular defects. Stimulation of endothelial cells by VEGF leads to activation of the PI3K pathway within these cells, which is important for cell migration. Sustained endothelial activation of AKT1 has been shown to induce the formation of structurally abnormal blood vessels that recapitulate the aberrations of tumor vessels. Hence, the PI3K pathway plays an important role in regulating angiogenesis both in normal tissues and in cancers.