Akt1 and akt2 play distinct roles in the initiation and metastatic phases of mammary tumor progression

Research progress on the PI3K/AKT signaling pathway in gynecological cancer (Review)

The phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway is involved in the regulation of multiple cellular physiological processes by activating downstream corresponding effector molecules, which serve an important role in the cell cycle, growth and proliferation. This is a common phenomenon; overactivation of the pathway is present in human malignancies and has been implicated in cancer progression, hence one of the important approaches to the treatment of tumors is rational drug design using molecular targets in the PI3K/AKT signaling pathway. In brief, the present review analyzed the effects of the PI3K/AKT signaling pathway on certain gynecological cancer types.

Enhancer Domains in Gastrointestinal Stromal Tumor Regulate KIT Expression and Are Targetable by BET Bromodomain Inhibition

Gastrointestinal stromal tumor (GIST) is a mesenchymal neoplasm characterized by activating mutations in the related receptor tyrosine kinases KIT and PDGFRA. GIST relies on expression of these unamplified receptor tyrosine kinase (RTK) genes through a large enhancer domain, resulting in high expression levels of the oncogene required for tumor growth. Although kinase inhibition is an effective therapy for many patients with GIST, disease progression from kinase-resistant mutations is common and no other effective classes of systemic therapy exist. In this study, we identify regulatory regions of the KIT enhancer essential for KIT gene expression and GIST cell viability. Given the dependence of GIST upon enhancer-driven expression of RTKs, we hypothesized that the enhancer domains could be therapeutically targeted by a BET bromodomain inhibitor (BBI). Treatment of GIST cells with BBIs led to cell-cycle arrest, apoptosis, and cell death, with unique sensitivity in GIST cells arising from attenuation of the KIT enhancer domain and reduced KIT gene expression. BBI treatment in KIT-dependent GIST cells produced genome-wide changes in the H3K27ac enhancer landscape and gene expression program, which was also seen with direct KIT inhibition using a tyrosine kinase inhibitor (TKI). Combination treatment with BBI and TKI led to superior cytotoxic effects in vitro and in vivo, with BBI preventing tumor growth in TKI-resistant xenografts. Resistance to select BBI in GIST was attributable to drug efflux pumps. These results define a therapeutic vulnerability and clinical strategy for targeting oncogenic kinase dependency in GIST. SIGNIFICANCE: Expression and activity of mutant KIT is essential for driving the majority of GIST neoplasms, which can be therapeutically targeted using BET bromodomain inhibitors.

AKT isoform-specific expression and activation across cancer lineages

Background

Aberrant AKT activation is prevalent across human cancer lineages, providing an important therapeutic target. AKT comprises three isoforms that mediate critical non-redundant, even opposing functions in cancer pathophysiology. Therefore, targeting specific AKT isoforms in particular cancers may be more effective than pan-AKT inhibition while avoiding disadvantages of pan-AKT inhibition. Currently, AKT isoform-specific expression and activation in cancer are not clearly characterized.

Methods

We systematically characterized AKT isoform-specific expression and activation in 211 cancer cell lines derived from different lineages and genetic backgrounds using a reverse-phase protein array platform.

Results

We found that phosphorylation, but not expression, of AKT1 and AKT2 was coordinated in most but not all cells. Different cancer lineages displayed differential AKT1 and AKT2 expression and phosphorylation. A PIK3CA hotspot mutation H1047R but not E545K was associated with selective activation of AKT2 but not AKT1.

Conclusions

Our study identified and validated AKT isoform-specific expression and phosphorylation in certain cell lines and demonstrated that genetic changes can affect AKT isoform-specific activation. These results provide a more precise understanding of AKT isoform-specific signaling and, in addition, facilitate AKT isoform targeting for personalized cancer therapies.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4654-5) contains supplementary material, which is available to authorized users.

Vav1 downmodulates Akt in different breast cancer subtypes: a new promising chance to improve breast cancer outcome

Targeting different members of the Akt pathways is a promising therapeutic chance in solid tumors including breast cancer. The variable expression levels of Akt isoforms with opposite effects on tumor growth and metastasis, however, make it difficult to select the inhibitors to be used for specific breast tumor subtypes. Using in vitro and in vivo models, we demonstrated here that Vav1, ectopically expressed in invasive breast tumors derived cells, downmodulates Akt acting at expression and/or activation levels depending on tumor subtype. The decreased p‐Akt1 (Ser473) levels are a common effect of Vav1 upmodulation, suggesting that, in breast tumor‐derived cells and independently of their phenotype, Vav1 interferes with signaling pathways ended to specifically recruit Akt1. Only in ER‐negative cell lines, the silencing of Vav1 induced the expression but not the activation of Akt2. A retrospective analysis of early invasive breast tumors allowed to establish the prognostic significance of the p‐Akt/Vav1 relationship. In particular, low Vav1 levels negatively influence the follow‐up of patients with low p‐Akt in their primary tumors and subjected to adjuvant chemotherapy. As the use of specific or pan Akt inhibitors may not be sufficient or may even be detrimental, increasing the levels of Vav1 could be a new approach to improve breast cancer outcomes. This might be particularly relevant for tumors with a triple‐negative phenotype, for which target‐based therapies are not currently available.

Role of Akt Isoforms Controlling Cancer Stem Cell Survival, Phenotype and Self-Renewal

The cancer stem cell (CSC) hypothesis suggests that tumours are maintained by a subpopulation of cells with stem cell properties. Although the existence of CSCs was initially described in human leukaemia, less evidence exists for CSCs in solid tumours. Recently, a CD133+ cell subpopulation was isolated from human brain tumours exhibiting stem cell properties in vitro as well as the capacity to initiate tumours in vivo. In the present work, we try to summarize the data showing that some elements of the Phosphoinositide 3-kinase Class I (PI3K)/ Thymoma viral oncogene protein kinase (Akt) pathway, such the activity of PI3K Class I or Akt2, are necessary to maintain the CSC-like phenotype as well as survival of CSCs (also denoted as tumour-initiating cells (TICs)). Our data and other laboratory data permit a working hypothesis in which each Akt isoform plays an important and specific role in CSC/TIC growth, self-renewal, maintaining survival, and epithelial-mesenchymal transition (EMT) phenotype, not only in breast cancer, but also in glioma. We suggest that a more complete understanding is needed of the possible roles of isoforms in human tumours (iso-signalling determination). Thus, a comprehensive analysis of how hierarchical signalling is assembled during oncogenesis, how cancer landmarks are interconnected to favour CSC and tumour growth, and how some protein isoforms play a specific role in CSCs to ensure that survival and proliferation must be done in order to propose/generate new therapeutic approaches (alone or in combination with existing ones) to use against cancer.

AKT1 restricts the invasive capacity of head and neck carcinoma cells harboring a constitutively active PI3 kinase activity

Background

In mammals, the AKT/PKB protein kinase family comprises three members (AKT1–3). PI3-Kinase (PI3K), a key oncogene involved in a wide variety of cancers, drives AKT activity. Constitutive activation of the PI3K/AKT pathway has been associated with tumorigenic properties including uncontrolled cell proliferation and survival, angiogenesis, promotion of cellular motility, invasiveness and metastasis. However, AKT1 activity has also been recently shown to repress the invasive properties of breast cancer cells in specific contexts.

Methods

This study used both pharmacological and shRNA approaches to inhibit AKT function, microscopy to characterize the cellular morphology, 3D spheroid models to assess migratory and invasive cellular capacities and a phenotypic screening approach based on electrical properties of the cells.

Results

Here we demonstrate that the alternative action of AKT1 on invasive properties of breast cancers can be extended to head and neck carcinomas, which exhibit constitutive activation of the PI3K/AKT pathway. Indeed, inhibition of AKT1 function by shRNA or a specific pharmacological inhibitor resulted in cellular spreading and an invasive phenotype. A phenotypic screening approach based on cellular electrical properties corroborated microscopic observations and provides a foundation for future high-throughput screening studies. This technique further showed that the inhibition of AKT1 signaling is phenocopied by blocking the mTORC1 pathway with rapamycin.

Conclusion

Our study suggests that the repressive action of PI3K/AKT1 on cellular invasive properties may be a mechanism common to several cancers. Current and future studies involving AKT inhibitors must therefore consider this property to prevent metastases and consequently to improve survival.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4169-0) contains supplementary material, which is available to authorized users.

PHLPP1 mediates melanoma metastasis suppression through repressing AKT2 activation

PI3K/AKT pathway activation is thought to be a driving force in metastatic melanomas. Members of the pleckstrin homology (PH) domain leucine-rich repeat protein Ser/Thr specific phosphatase family (PHLPP1 and PHLPP2) can regulate AKT activation. By dephosphorylating specific serine residues in the hydrophobic motif, PHLPP1 and PHLPP2 restrain AKT signalings, thereby regulating cell proliferation and survival. We here show that PHLPP1 expression was significantly downregulated or lost and correlated with metastatic potential in melanoma. Forcing expression of either PHLPP1 or PHLPP2 in melanoma cells inhibited cell proliferation, migration, and colony formation in soft agar; but PHLPP1 had the most profound inhibitory effect on metastasis. Moreover, expression of PH mutant forms of PHLPP1 continued to inhibit metastasis, whereas a phosphatase-dead C-terminal mutant did not. The introduction of activated PHLPP1-specific targets AKT2 or AKT3 also promoted melanoma metastasis, while the non-PHLPP1 target AKT1 did not. AKT2 and AKT3 could even rescue the PHLPP1-mediated inhibition of metastasis. An AKT inhibitor blocked the activity of AKT2 and inhibited AKT2-mediated tumor growth and metastasis in a preclinical mouse model. Our data demonstrate that PHLPP1 functions as a metastasis suppressor through its phosphatase activity, and suggest that PHLPP1 represents a novel diagnostic and therapeutic marker for metastatic melanoma.

AKT3 drives adenoid cystic carcinoma development in salivary glands

Salivary gland cancer is an aggressive and painful cancer, but a rare tumor type accounting for only ~0.5% of cancer cases. Tumors of the salivary gland exhibit heterogeneous histologic and genetic features and they are subdivided into different subtypes, with adenoid cystic carcinomas (ACC) being one of the most abundant. Treatment of ACC patients is afflicted by high recurrence rates, the high potential of the tumors to metastasize, as well as the poor response of ACC to chemotherapy. A prerequisite for the development of targeted therapies is insightful genetic information for driver core cancer pathways. Here, we developed a transgenic mouse model toward establishment of a preclinical model. There is currently no available mouse model for adenoid cystic carcinomas as a rare disease entity to serve as a test system to block salivary gland tumors with targeted therapy. Based on tumor genomic data of ACC patients, a key role for the activation of the PI3K-AKT-mTOR pathway was suggested in tumors of secretory glands. Therefore, we investigated the role of Akt3 expression in tumorigenesis and report that Akt3 overexpression results in ACC of salivary glands with 100% penetrance, while abrogation of transgenic Akt3 expression could revert the phenotype. In summary, our findings validate a novel mouse model to study ACC and highlight the druggable potential of AKT3 in the treatment of salivary gland patients.

Akt Protein Kinase, miR-200/miR-182 Expression and Epithelial-Mesenchymal Transition Proteins in Hibernating Ground Squirrels

Hibernating 13-lined ground squirrels (Ictidomys tridecemlineatus; TLGS) rank among the most brain hypoperfusion-tolerant mammals known. Herein we provide some evidence of cycling between an epithelial phenotype and a hybrid epithelial/mesenchymal (E/M) phenotype (partial EMT) within the brains of TLGS during each bout of hibernation torpor. During hibernation torpor, expression of the epithelial marker E-cadherin (E-CDH) was reduced, while expression of the well-known mesenchymal markers vimentin and Sox2 were increased. P-cadherin (P-CDH), which has recently been proposed as a marker of intermediate/partial EMT, also increased during torpor, suggesting that a partial EMT may be taking place during hibernation torpor. Members of the miR-200 family and miR-182 cluster and Akt isoforms (Akt1, Akt2), well-known EMT regulators, were also differentially regulated in the TLGS brain during hibernation bouts. Using SHSY5Y cells, we also demonstrate that the Akt1/Akt2 ratio determined the expression levels of miR-200/miR-182 miRNA family members, and that these miRNAs controlled the expression of EMT-related proteins. Accordingly, we propose that such cell state transitions (EMT/MET) may be one of the mechanisms underlying the extraordinary ischemic tolerance of the TLGS brain during hibernation bouts; hibernator brain cells appear to enter reversible states that confer the stress survival characteristics of cancer cells without the risk of neoplastic transformation.

Protein kinase B: emerging mechanisms of isoform-specific regulation of cellular signaling in cancer

The serine/threonine protein kinase B (PKB), also known as Akt, is one of the multifaceted kinases in the human kinome, existing in three isoforms. PKB plays a vital role in phosphoinositide 3-kinase (PI3K)-mediated oncogenesis in various malignancies and is one of the attractive targets for cancer drug discovery. Recent studies have shown that the functional significance of an individual isoform of PKB is not redundant in cancer. It has been found that PKB isoforms play distinct roles in the regulation of cellular invasion and migration during tumorigenesis. PKB activation plays a central role during epithelial-mesenchymal transition, a cellular program required for the cancer cell invasion and migration. However, the differential behavior of each PKB isoform has been shown in the regulation of epithelial-mesenchymal transition. Recent studies have suggested that PKBα (Akt1) plays a conflicting role in tumorigenesis by acting either as a pro-oncogenic factor by suppressing the apoptotic machinery or by restricting tumor invasion. PKBβ (Akt2) promotes cell migration and invasion and similarly PKBγ (Akt3) has been reported to promote tumor migration. As PKB is known for its pro-oncogenic properties, it needs to be unraveled how three isoforms of PKB compensate during tumor progression. In this review, we attempted to sum up how different isoforms of PKB play a role in cancer progression, metastasis, and drug resistance.

Inhibition of AKT1 signaling promotes invasion and metastasis of non-small cell lung cancer cells with K-RAS or EGFR mutations

Accumulating evidence supports a role of the PI3K-AKT pathway in the regulation of cell motility, invasion and metastasis. AKT activation is known to promote metastasis, however under certain circumstances, it also shows an inhibitory activity on metastatic processes, and the cause of such conflicting results is largely unclear. Here we found that AKT1 is an important regulator of metastasis and down-regulation of its activity is associated with increased metastatic potential of A549 cells. Inhibition of AKT1 enhanced migration and invasion in KRAS- or EGFR-mutant non-small cell lung cancer (NSCLC) cells. The allosteric AKT inhibitor MK-2206 promoted metastasis of KRAS-mutated A549 cells in vivo. We next identified that the phosphorylation of Myristoylated alanine-rich C-kinase substrate (MARCKS) and LAMC2 protein level were increased with AKT1 inhibition, and MARCKS or LAMC2 knockdown abrogated migration and invasion induced by AKT1 inhibition. This study unravels an anti-metastatic role of AKT1 in the NSCLC cells with KRAS or EGFR mutations, and establishes an AKT1-MARCKS-LAMC2 feedback loop in this regulation.

Differential control of ageing and lifespan by isoforms and splice variants across the mTOR network

Ageing can be defined as the gradual deterioration of physiological functions, increasing the incidence of age-related disorders and the probability of death. Therefore, the term ageing not only reflects the lifespan of an organism but also refers to progressive functional impairment and disease. The nutrient-sensing kinase mTOR (mammalian target of rapamycin) is a major determinant of ageing. mTOR promotes cell growth and controls central metabolic pathways including protein biosynthesis, autophagy and glucose and lipid homoeostasis. The concept that mTOR has a crucial role in ageing is supported by numerous reports on the lifespan-prolonging effects of the mTOR inhibitor rapamycin in invertebrate and vertebrate model organisms. Dietary restriction increases lifespan and delays ageing phenotypes as well and mTOR has been assigned a major role in this process. This may suggest a causal relationship between the lifespan of an organism and its metabolic phenotype. More than 25 years after mTOR's discovery, a wealth of metabolic and ageing-related effects have been reported. In this review, we cover the current view on the contribution of the different elements of the mTOR signalling network to lifespan and age-related metabolic impairment. We specifically focus on distinct roles of isoforms and splice variants across the mTOR network. The comprehensive analysis of mouse knockout studies targeting these variants does not support a tight correlation between lifespan prolongation and improved metabolic phenotypes and questions the strict causal relationship between them.

AKT/PKB Signaling: Navigating the Network

The Ser and Thr kinase AKT, also known as protein kinase B (PKB), was discovered 25 years ago and has been the focus of tens of thousands of studies in diverse fields of biology and medicine. There have been many advances in our knowledge of the upstream regulatory inputs into AKT, key multifunctional downstream signaling nodes (GSK3, FoxO, mTORC1), which greatly expand the functional repertoire of AKT, and the complex circuitry of this dynamically branching and looping signaling network that is ubiquitous to nearly every cell in our body. Mouse and human genetic studies have also revealed physiological roles for the AKT network in nearly every organ system. Our comprehension of AKT regulation and functions is particularly important given the consequences of AKT dysfunction in diverse pathological settings, including developmental and overgrowth syndromes, cancer, cardiovascular disease, insulin resistance and type 2 diabetes, inflammatory and autoimmune disorders, and neurological disorders. There has also been much progress in developing AKT-selective small molecule inhibitors. Improved understanding of the molecular wiring of the AKT signaling network continues to make an impact that cuts across most disciplines of the biomedical sciences.

Linoleic acid induces migration and invasion through FFAR4- and PI3K-/Akt-dependent pathway in MDA-MB-231 breast cancer cells

An increased risk of developing breast cancer has been associated with high levels of dietary fat intake. Linoleic acid (LA) is an essential fatty acid and the major ω-6 polyunsaturated fatty acid in occidental diets, which is able to induce inappropriate inflammatory responses that contribute to several chronic diseases including cancer. In breast cancer cells, LA induces migration. However, the signal transduction pathways that mediate migration and whether LA induces invasion in MDA-MB-231 breast cancer cells have not been studied in detail. We demonstrate here that LA induces Akt2 activation, invasion, an increase in NFκB-DNA binding activity, miR34a upregulation and miR9 downregulation in MDA-MB-231 cells. Moreover, Akt2 activation requires EGFR and PI3K activity, whereas migration and invasion are dependent on FFAR4, EGFR and PI3K/Akt activity. Our findings demonstrate, for the first time, that LA induces migration and invasion through an EGFR-/PI3K-/Akt-dependent pathway in MDA-MB-231 breast cancer cells.

Maximising the potential of AKT inhibitors as anti-cancer treatments

PI3K/AKT signalling is commonly disrupted in human cancers, with AKT being a central component of the pathway, influencing multiple processes that are directly involved in tumourigenesis. Targeting AKT is therefore a highly attractive anti-cancer strategy with multiple AKT inhibitors now in various stages of clinical development. In this review, we summarise the role and regulation of AKT signalling in normal cellular physiology. We highlight the mechanisms by which AKT signalling can be hyperactivated in cancers and discuss the past, present and future clinical strategies for AKT inhibition in oncology.

Comparison of the PI3KCA pathway in circulating tumor cells and corresponding tumor tissue of patients with metastatic breast cancer

The aim of the present study was to compare the phosphatidylinositol 3-kinase (PI3KCA)-AKT serine/threonine kinase (AKT) pathway in circulating tumor cells (CTCs) and corresponding cancerous tissues. Stemness-like circulating tumor cells (slCTCs) and CTCs in epithelial-mesenchymal transition (EMT) have been implicated as the active source of metastatic spread in breast cancer (BC). In this regard, the PI3KCA-AKT signaling pathway was demonstrated to be implicated in and to be frequently mutated in BC. The present study compared this pathway in slCTCs/CTCs in EMT and the corresponding tumor tissues of 90 metastatic BC patients (pts). slCTCs and CTCs in EMT were isolated using the AdnaTest EMT-1/StemCell for the detection of aldehyde dehydrogenase 1 family member A1 (ALDH1) (singleplex PCR) and PI3KCA, AKT2 and twist family bHLH transcription factor 1 (multiplex PCR). Tumor tissue was investigated for PI3KCA hotspot mutations using Sanger sequencing of genomic DNA from micro-dissected formalin-fixed paraffin-embedded tissue, and for the expression of ALDH1 and phosphorylated AKT (pAKT), and phosphatase and tensin homolog (PTEN) loss, by immunohistochemistry. slCTCs were identified in 23% of pts (21/90 pts) and CTCs in EMT in 56% (50/90 pts) of pts. pAKT and ALDH1 positivity in tumor tissue was identified in 47 and 9% of cases, respectively, and a PTEN loss was observed in 18% of pts. A significant association was detected between pAKT expression in cancerous tissue and AKT2 expression in CTCs (P=0.037). PI3KCA mutations were detected in 32% of pts, most frequently on exons 21 (55%) and 10 (45%). Pts with PI3KCA mutations in tumor tissue had a significantly longer overall survival than pts with wild-type PI3KCA expression (P=0.007). Similar results were obtained for pts with aberrant PI3KCA signaling in CTCs and/or aberrant signaling in cancerous tissue (P=0.009). Therapy-resistant CTCs, potentially derived from the primary tumor or metastatic tissue, may be eliminated with specific PI3K pathway inhibitors, alone or in combination, to improve the prognosis of metastatic BC pts.

AKT1 and AKT2 isoforms play distinct roles during breast cancer progression through the regulation of specific downstream proteins

The purpose of this study was to elucidate the mechanisms associated with the specific effects of AKT1 and AKT2 isoforms in breast cancer progression. We modulated the abundance of specific AKT isoforms in IBH-6 and T47D human breast cancer cell lines and showed that AKT1 promoted cell proliferation, through S6 and cyclin D1 upregulation, but it inhibited cell migration and invasion through β1-integrin and focal adhesion kinase (FAK) downregulation. In contrast, AKT2 promoted cell migration and invasion through F-actin and vimentin induction. Thus, while overexpression of AKT1 promoted local tumor growth, downregulation of AKT1 or overexpression of AKT2 promoted peritumoral invasion and lung metastasis. Furthermore, we evaluated The Cancer Genome Atlas (TCGA) dataset for invasive breast carcinomas and found that increased AKT2 but not AKT1 mRNA levels correlated with a worse clinical outcome. We conclude that AKT isoforms play specific roles in different steps of breast cancer progression, with AKT1 involved in the local tumor growth and AKT2 involved in the distant tumor dissemination, having AKT2 a poorer prognostic value and consequently being a worthwhile target for therapy.

Regulation of PI3K effector signalling in cancer by the phosphoinositide phosphatases

Class I phosphoinositide 3-kinase (PI3K) generates phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P₃) at the plasma membrane in response to growth factors, activating a signalling cascade that regulates many cellular functions including cell growth, proliferation, survival, migration and metabolism. The PI3K pathway is commonly dysregulated in human cancer, and drives tumorigenesis by promoting aberrant cell growth and transformation. PtdIns(3,4,5)P₃ facilitates the activation of many pleckstrin homology (PH) domain-containing proteins including the serine/threonine kinase AKT. There are three AKT isoforms that are frequently hyperactivated in cancer through mutation, amplification or dysregulation of upstream regulatory proteins. AKT isoforms have converging and opposing functions in tumorigenesis. PtdIns(3,4,5)P₃ signalling is degraded and terminated by phosphoinositide phosphatases such as phosphatase and tensin homologue (PTEN), proline-rich inositol polyphosphate 5-phosphatase (PIPP) (INPP5J) and inositol polyphosphate 4-phosphatase type II (INPP4B). PtdIns(3,4,5)P₃ is rapidly hydrolysed by PIPP to generate phosphatidylinositol 3,4-bisphosphate (PtdIns(3,4)P₂), which is further hydrolysed by INPP4B to form phosphatidylinositol 3-phosphate (PtdIns3P). PtdIns(3,4)P₂ and PtdIns3P are also important signalling molecules; PtdIns(3,4)P₂ together with PtdIns(3,4,5)P₃ are required for maximal AKT activation and PtdIns3P activates PI3K-dependent serum and glucocorticoid-regulated kinase (SGK3) signalling. Loss of Pten, Pipp or Inpp4b expression or function promotes tumour growth in murine cancer models through enhanced AKT isoform-specific signalling. INPP4B inhibits PtdIns(3,4)P₂-mediated AKT activation in breast and prostate cancer; however, INPP4B expression is increased in acute myeloid leukaemia (AML), melanoma and colon cancer where it paradoxically promotes cell proliferation, transformation and/or drug resistance. This review will discuss how PTEN, PIPP and INPP4B distinctly regulate PtdIns(3,4,5)P₃ signalling downstream of PI3K and how dysregulation of these phosphatases affects cancer outcomes.

BAY 1125976, a selective allosteric AKT1/2 inhibitor, exhibits high efficacy on AKT signaling-dependent tumor growth in mouse models

The PI3K-AKT-mTOR signaling cascade is activated in the majority of human cancers, and its activation also plays a key role in resistance to chemo and targeted therapeutics. In particular, in both breast and prostate cancer, increased AKT pathway activity is associated with cancer progression, treatment resistance and poor disease outcome. Here, we evaluated the activity of a novel allosteric AKT1/2 inhibitor, BAY 1125976, in biochemical, cellular mechanistic, functional and in vivo efficacy studies in a variety of tumor models. In in vitro kinase activity assays, BAY 1125976 potently and selectively inhibited the activity of full-length AKT1 and AKT2 by binding into an allosteric binding pocket formed by kinase and PH domain. In accordance with this proposed allosteric binding mode, BAY 1125976 bound to inactive AKT1 and inhibited T308 phosphorylation by PDK1, while the activity of truncated AKT proteins lacking the pleckstrin homology domain was not inhibited. In vitro, BAY 1125976 inhibited cell proliferation in a broad panel of human cancer cell lines. Particularly high activity was observed in breast and prostate cancer cell lines expressing estrogen or androgen receptors. Furthermore, BAY 1125976 exhibited strong in vivo efficacy in both cell line and patient-derived xenograft models such as the KPL4 breast cancer model (PIK3CA^H1074R mutant), the MCF7 and HBCx-2 breast cancer models and the AKT^E17K mutant driven prostate cancer (LAPC-4) and anal cancer (AXF 984) models. These findings indicate that BAY 1125976 is a potent and highly selective allosteric AKT1/2 inhibitor that targets tumors displaying PI3K/AKT/mTOR pathway activation, providing opportunities for the clinical development of new, effective treatments.

The UPR inducer DPP23 inhibits the metastatic potential of MDA-MB-231 human breast cancer cells by targeting the Akt-IKK-NF-κB-MMP-9 axis

(E)-3-(3,5-dimethoxyphenyl)-1-(2-methoxyphenyl)prop-2-en-1-one (DPP23) is a synthetic polyphenol derivative that selectively induces apoptosis in cancer cells through the unfolded protein response pathway. In the present study, we evaluated the effect of DPP23 on tumour invasion and metastasis. Here, we show that DPP23 inhibited tumour necrosis factor alpha (TNFα)-induced motility, F-actin formation, and the invasive capability of MDA-MB-231 cells. DPP23 inhibited NF-κB-dependent MMP-9 expression at the transcriptional level. Akt is involved in the activation of IKK, an upstream regulator of NF-κB. DPP23 inhibited IKK and Akt, and knockdown of Akt2 significantly inhibited TNFα-induced IKK phosphorylation. We found that DPP23 bound to the catalytic domain of Akt2, as revealed by an in silico molecular docking analysis. These results suggest that DPP23 prevents TNFα-induced invasion of highly metastatic MDA-MB-231 breast cancer cells by inhibiting Akt–IKK–NF-κB axis-mediated MMP-9 gene expression. In addition, DPP23 attenuated experimental liver metastasis in a syngenic intrasplenic transplantation model using 4T1 mouse mammary carcinoma cells. Collectively, these results suggest that DPP23 could be used as a potential platform for the prevention of invasion and metastasis of early-stage breast cancer or as an adjuvant for chemo/radiotherapy.

Upregulation of AKT3 Confers Resistance to the AKT Inhibitor MK2206 in Breast Cancer

Acquired resistance to molecular targeted therapy represents a major challenge for the effective treatment of cancer. Hyperactivation of the PI3K/AKT pathway is frequently observed in virtually all human malignancies, and numerous PI3K and AKT inhibitors are currently under clinical evaluation. However, mechanisms of acquired resistance to AKT inhibitors have yet to be described. Here, we use a breast cancer preclinical model to identify resistance mechanisms to a small molecule allosteric AKT inhibitor, MK2206. Using a step-wise and chronic high-dose exposure, breast cancer cell lines harboring oncogenic PI3K resistant to MK2206 were established. Using this model, we reveal that AKT3 expression is markedly upregulated in AKT inhibitor-resistant cells. Induction of AKT3 is regulated epigenetically by the bromodomain and extra terminal domain proteins. Importantly, knockdown of AKT3, but not AKT1 or AKT2, in resistant cells restores sensitivity to MK2206. AKT inhibitor-resistant cells also display an epithelial to mesenchymal transition phenotype as assessed by alterations in the levels of E-Cadherin, N-Cadherin, and vimentin, as well as enhanced invasiveness of tumor spheroids. Notably, the invasive morphology of resistant spheroids is diminished upon AKT3 depletion. We also show that resistance to MK2206 is reversible because upon drug removal resistant cells regain sensitivity to AKT inhibition, accompanied by reexpression of epithelial markers and reduction of AKT3 expression, implying that epigenetic reprogramming contributes to acquisition of resistance. These findings provide a rationale for developing therapeutics targeting AKT3 to circumvent acquired resistance in breast cancer. Mol Cancer Ther; 15(8); 1964-74. ©2016 AACR.

Interaction of human biliverdin reductase with Akt/protein kinase B and phosphatidylinositol-dependent kinase 1 regulates glycogen synthase kinase 3 activity: a novel mechanism of Akt activation

Biliverdin reductase A (BVR) and Akt isozymes have overlapping pleiotropic functions in the insulin/PI3K/MAPK pathway. Human BVR (hBVR) also reduces the hemeoxygenase activity product biliverdin to bilirubin and is directly activated by insulin receptor kinase (IRK). Akt isoenzymes (Akt1-3) are downstream of IRK and are activated by phosphatidylinositol-dependent kinase 1 (PDK1) phosphorylating T(308) before S(473) autophosphorylation. Akt (RxRxxSF) and PDK1 (RFxFPxFS) binding motifs are present in hBVR. Phosphorylation of glycogen synthase kinase 3 (GSK3) isoforms α/β by Akts inhibits their activity; nonphosphorylated GSK3β inhibits activation of various genes. We examined the role of hBVR in PDK1/Akt1/GSK3 signaling and Akt1 in hBVR phosphorylation. hBVR activates phosphorylation of Akt1 at S(473) independent of hBVR's kinase competency. hBVR and Akt1 coimmunoprecipitated, and in-cell Förster resonance energy transfer (FRET) and glutathione S-transferase pulldown analyses identified Akt1 pleckstrin homology domain as the interactive domain. hBVR activates phosphorylation of Akt1 at S(473) independent of hBVR's kinase competency. Site-directed mutagenesis, mass spectrometry, and kinetic analyses identified S(230) in hBVR (225)RNRYLSF sequence as the Akt1 target. Underlined amino acids are the essential residues of the signaling motifs. In cells, hBVR-activated Akt1 increased both GSK3α/β and forkhead box of the O class transcription class 3 (FoxO3) phosphorylation and inhibited total GSK3 activity; depletion of hBVR released inhibition and stimulated glucose uptake. Immunoprecipitation analysis showed that PDK1 and hBVR interact through hBVR's PDK1 binding (161)RFGFPAFS motif and formation of the PDK1/hBVR/Akt1 complex. sihBVR blocked complex formation. Findings identify hBVR as a previously unknown coactivator of Akt1 and as a key mediator of Akt1/GSK3 pathway, as well as define a key role for hBVR in Akt1 activation by PDK1.-Miralem, T., Lerner-Marmarosh, N., Gibbs, P. E. M., Jenkins, J. L., Heimiller, C., Maines, M. D. Interaction of human biliverdin reductase with Akt/protein kinase B and phosphatidylinositol-dependent kinase 1 regulates glycogen synthase kinase 3 activity: a novel mechanism of Akt activation.

The ErbB2ΔEx16 splice variant is a major oncogenic driver in breast cancer that promotes a pro-metastatic tumor microenvironment

Amplification and over expression of erbB2/neu proto-oncogene is observed in 20–30% human breast cancer and is inversely correlated with the survival of the patient. Despite this, somatic activating mutations within erbB2 in human breast cancers are rare. However, we have previously reported that a splice isoform of erbB2, containing an in-frame deletion of exon 16 (herein referred to as ErbB2ΔEx16), results in oncogenic activation of erbB2 due to constitutive dimerization of the ErbB2 receptor. Here, we demonstrate that the ErbB2ΔEx16 is a major oncogenic driver in breast cancer that constitutively signals from the cell surface. We further show that inducible expression of the ErbB2Ex16 variant in mammary gland of transgenic mice results in the rapid development of metastatic multifocal mammary tumors. Genetic and biochemical characterization of the ErbB2ΔEx16 derived mammary tumors exhibit several unique features that distinguish it from the conventional ErbB2 models expressing the erbB2 proto-oncogene in mammary epithelium. Unlike the wild-type ErbB2 derived tumors that express luminal keratins, ErbB2ΔEx16 derived tumors exhibit high degree of intra-tumoral heterogeneity co-expressing both basal and luminal keratins. Consistent with these distinct pathological features, the ErbB2ΔEx16 tumors exhibited distinct signaling and gene expression profiles that correlated with activation of number of key transcription factors implicated in breast cancer metastasis and cancer stem cell renewal.

Dlc1 interaction with non-muscle myosin heavy chain II-A (Myh9) and Rac1 activation

The Deleted in liver cancer 1 (Dlc1) gene codes for a Rho GTPase-activating protein that also acts as a tumour suppressor gene. Several studies have consistently found that overexpression leads to excessive cell elongation, cytoskeleton changes and subsequent cell death. However, none of these studies have been able to satisfactorily explain the Dlc1-induced cell morphological phenotypes and the function of the different Dlc1 isoforms. Therefore, we have studied the interacting proteins associated with the three major Dlc1 transcriptional isoforms using a mass spectrometric approach in Dlc1 overexpressing cells. We have found and validated novel interacting partners in constitutive Dlc1-expressing cells. Our study has shown that Dlc1 interacts with non-muscle myosin heavy chain II-A (Myh9), plectin and spectrin proteins in different multiprotein complexes. Overexpression of Dlc1 led to increased phosphorylation of Myh9 protein and activation of Rac1 GTPase. These data support a role for Dlc1 in induced cell elongation morphology and provide some molecular targets for further analysis of this phenotype.

Low doses of PEG-coated gold nanoparticles sensitize solid tumors to cold plasma by blocking the PI3K/AKT-driven signaling axis to suppress cellular transformation by inhibiting growth and EMT

Metastasis, the primary cause of tumor cell transformation, is often activated during cancer invasion and progression and is associated with poor therapeutic outcomes. The effects of combined treatments that included PEG-coated gold nanoparticles (GNP) and cold plasma on epithelial-mesenchymal transition (EMT) and the maintenance of cancer stem cells (CSC) have not been described so far. Here, we report that co-treatment with GNP and cold plasma inhibited proliferation in cancer cells by abolishing the activation of the PI3K/AKT signaling axis. In addition, co-treatment reversed EMT in solid tumor cells by reducing the secretion of a number of proteins, resulting in the upregulation of epithelial markers such as E-cadherin along with down-regulation of N-Cadherin, Slug and Zeb-1. The inhibition of the PI3K/AKT pathway and the reversal of EMT by co-treatment prevented tumor cells growth in solid tumors. Furthermore, we show that GNP and plasma also suppresses tumor growth by decreasing mesenchymal markers in tumor xenograft mice models. Importantly, co-treatment resulted in a substantial decrease in sphere formation and the self-renewal capacity of glioma-like stem cells. Together, these results indicate a direct link between a decrease of EMT and an increase in cell death in solid tumors following co-treatment with cold plasma and GNP.

Regulation of PtdIns(3,4,5)P3/Akt signalling by inositol polyphosphate 5-phosphatases

The phosphoinositide 3-kinase (PI3K) generated lipid signals, PtdIns(3,4,5)P3 and PtdIns(3,4)P2, are both required for the maximal activation of the serine/threonine kinase proto-oncogene Akt. The inositol polyphosphate 5-phosphatases (5-phosphatases) hydrolyse the 5-position phosphate from the inositol head group of PtdIns(3,4,5)P3 to yield PtdIns(3,4)P2. Extensive work has revealed several 5-phosphatases inhibit PI3K-driven Akt signalling, by decreasing PtdIns(3,4,5)P3 despite increasing cellular levels of PtdIns(3,4)P2. The roles that 5-phosphatases play in suppressing cell proliferation and transformation are slow to emerge; however, the 5-phosphatase PIPP [proline-rich inositol polyphosphate 5-phosphatase; inositol polyphosphate 5-phosphatase (INPP5J)] has recently been identified as a putative tumour suppressor in melanoma and breast cancer and SHIP1 [SH2 (Src homology 2)-containing inositol phosphatase 1] inhibits haematopoietic cell proliferation. INPP5E regulates cilia stability and INPP5E mutations have been implicated ciliopathy syndromes. This review will examine 5-phosphatase regulation of PI3K/Akt signalling, focussing on the role PtdIns(3,4,5)P3 5-phosphatases play in developmental diseases and cancer.

ANP32B deficiency impairs proliferation and suppresses tumor progression by regulating AKT phosphorylation

The acidic leucine-rich nuclear phosphoprotein 32B (ANP32B) is reported to impact normal development, with Anp32b-knockout mice exhibiting smaller size and premature aging. However, its cellular and molecular mechanisms, especially its potential roles in tumorigenesis, remain largely unclear. Here, we utilize 'knockout' models, RNAi silencing and clinical cohorts to more closely investigate the role of this enigmatic factor in cell proliferation and cancer phenotypes. We report that, compared with Anp32b wild-type (Anp32b^+/+) littermates, a broad panel of tissues in Anp32b-deficient (Anp32b^−/−) mice are demonstrated hypoplasia. Anp32b^−/− mouse embryo fibroblast cell has a slower proliferation, even after oncogenic immortalization. ANP32B knockdown also significantly inhibits in vitro and in vivo growth of cancer cells by inducing G₁ arrest. In line with this, ANP32B protein has higher expression in malignant tissues than adjacent normal tissues from a cohort of breast cancer patients, and its expression level positively correlates with their histopathological grades. Moreover, ANP32B deficiency downregulates AKT phosphorylation, which involves its regulating effect on cell growth. Collectively, our findings suggest that ANP32B is an oncogene and a potential therapeutic target for breast cancer treatment.

AKT signaling in ERBB2-amplified breast cancer

The PI3K/AKT pathway is the focus of several targeted therapeutic agents for a variety of malignancies. In ERBB2-amplified breast cancer, the hyperactivation of this signaling cascade is associated with resistance to ERBB2-targeted therapy. This can occur through gain-of-function alterations or compensatory mechanisms that enter into play upon pharmacological pressure. The strong rationale in combining anti-ERBB2 agents with PI3K/AKT inhibitors, together with the identification of genomic alterations conferring sensitivity to targeted inhibition, are guiding the design of clinical studies aimed at preventing the emergence of drug resistance and achieving more durable response. In the present review, we describe the involvement of this pathway in breast cancer pathogenesis, with an emphasis on AKT kinases, and provide insight into currently available targeted agents for the treatment of ERBB2-amplified breast cancer. Finally, we provide preliminary data on a novel AKT3 mutation detected in the context of resistance to anti-ERBB2 therapy as an example of genomics-based approaches towards uncovering novel actionable targets in this setting.

Phosphorylated AKT1 is associated with poor prognosis in esophageal squamous cell carcinoma

BACKGROUND

The epidermal growth factor receptor (EGFR) signaling pathway is important in regulating biological behaviors in many malignancies. We explored whether expression and activation of EGFR and several components on its downstream pathways have prognostic significance in patients with esophageal squamous cell carcinoma (ESCC).

METHODS

Expression of EGFR, phosphorylated (p)-EGFR, AKT1, p-AKT1, AKT2, p-AKT2, ERK1, ERK2, p-ERK1/2, STAT3, and p-STAT3 was assessed by immunohistochemical analysis of tissue microarrays for 275 ESCC patients who had undergone complete three-field lymphadenectomy. Spearman rank correlation tests were used to determine the relationships among protein expression, and Cox regression analyses were performed to determine the prognostic factors on overall survival (OS).

RESULTS

p-EGFR expression was correlated statistically with all of the other phosphorylated markers. Gender, N stage, and p-AKT1 expression were found to be independent prognostic factors for OS. Increased expression of p-AKT1 was associated with decreased patient survival. EGFR and p-EGFR expression was not significantly associated with patient survival.

CONCLUSION

Activation of AKT1 was associated with poor prognosis in ESCC.

The Inositol Polyphosphate 5-Phosphatase PIPP Regulates AKT1-Dependent Breast Cancer Growth and Metastasis

Metastasis is the major cause of breast cancer mortality. Phosphoinositide 3-kinase (PI3K) generated PtdIns(3,4,5)P3 activates AKT, which promotes breast cancer cell proliferation and regulates migration. To date, none of the inositol polyphosphate 5-phosphatases that inhibit PI3K/AKT signaling have been reported as tumor suppressors in breast cancer. Here, we show depletion of the inositol polyphosphate 5-phosphatase PIPP (INPP5J) increases breast cancer cell transformation, but reduces cell migration and invasion. Pipp ablation accelerates oncogene-driven breast cancer tumor growth in vivo, but paradoxically reduces metastasis by regulating AKT1-dependent tumor cell migration. PIPP mRNA expression is reduced in human ER-negative breast cancers associated with reduced long-term outcome. Collectively, our findings identify PIPP as a suppressor of oncogenic PI3K/AKT signaling in breast cancer.

The PI3K/AKT Pathway and Renal Cell Carcinoma

The phosphatidylinositol 3 kinase (PI3K)/AKT pathway is genetically targeted in more pathway components and in more tumor types than any other growth factor signaling pathway, and thus is frequently activated as a cancer driver. More importantly, the PI3K/AKT pathway is composed of multiple bifurcating and converging kinase cascades, providing many potential targets for cancer therapy. Renal cell carcinoma (RCC) is a high-risk and high-mortality cancer that is notoriously resistant to traditional chemotherapies or radiotherapies. The PI3K/AKT pathway is modestly mutated but highly activated in RCC, representing a promising drug target. Indeed, PI3K pathway inhibitors of the rapalog family are approved for use in RCC. Recent large-scale integrated analyses of a large number of patients have provided a molecular basis for RCC, reiterating the critical role of the PI3K/AKT pathway in this cancer. In this review, we summarize the genetic alterations of the PI3K/AKT pathway in RCC as indicated in the latest large-scale genome sequencing data, as well as treatments for RCC that target the aberrant activated PI3K/AKT pathway.

Implications of Akt2/Twist crosstalk on breast cancer metastatic outcome

Akt2 is a pivotal player in a complex web of signaling pathways controlling cell growth, proliferation, and survival. The deregulation or aberrations of Akt2 have been associated with tumor progression, metastatic spread, and, lastly, chemoresistance. The impairment of its activity has gained more attention because Akt2 is intertwined with a range of signaling paths, including the Phosphatidylinositol 3 kinase/Akt/Mammalian target of rapamycin (PI3K/mTOR) signaling axis, which are involved in macromolecules synthesis and metabolism. Here, we focus on Akt2 because of its involvement in the acquisition of stem cell-like properties, responsible for invasiveness and chemoresistance, also promoted by Twist. We also suggest therapeutic strategies targeting Akt2 to overcome the drawbacks of current cancer therapies.

Signalling specificity in the Akt pathway in breast cancer

Aberrant activation of fundamental cellular processes, such as proliferation, migration and survival, underlies the development of numerous human pathophysiologies, including cancer. One of the most frequently hyperactivated pathways in cancer is the phosphoinositide 3-kinase (PI3K)/Akt signalling cascade. Three isoforms of the serine/threonine protein kinase Akt (Akt1, Akt2 and Akt3) function to regulate cell survival, growth, proliferation and metabolism. Strikingly, non-redundant and even opposing functions of Akt isoforms in the regulation of phenotypes associated with malignancy in humans have been described. However, the mechanisms by which Akt isoform-specificity is conferred are largely unknown. In the present review, we highlight recent findings that have contributed to our understanding of the complexity of Akt isoform-specific signalling and discussed potential mechanisms by which this isoform-specificity is conferred. An understanding of the mechanisms of Akt isoform-specificity has important implications for the development of isoform-specific Akt inhibitors and will be critical to finding novel targets to treat disease.

Functional specificity of Akt isoforms in cancer progression

Akt/PKB kinases are central mediators of cell homeostasis. There are three highly homologous Akt isoforms, Akt1/PKBα, Akt2/PKBβ and Akt3/PKBγ. Hyperactivation of Akt signaling is a key node in the progression of a variety of human cancer, by modulating tumor growth, chemoresistance and cancer cell migration, invasion and metastasis. It is now clear that, to understand the mechanisms on how Akt affects specific cancer cells, it is necessary to consider the relative importance of each of the three Akt isoforms in the altered cells. Akt1 is involved in tumor growth, cancer cell invasion and chemoresistance and is the predominant altered isoform found in various carcinomas. Akt2 is related to cancer cell invasion, metastasis and survival more than tumor induction. Most of the Akt2 alterations are observed in breast, ovarian, pancreatic and colorectal carcinomas. As Akt3 expression is limited to some tissues, its implication in tumor growth and resistance to drugs mostly occurs in melanomas, gliomas and some breast carcinomas. To explain how Akt isoforms can play different or even opposed roles, three mechanisms have been proposed: tissue-specificity expression/activation of Akt isoforms, distinct effect on same substrate as well as specific localization through the cyto-skeleton network. It is becoming clear that to develop an effective anticancer Akt inhibitor drug, it is necessary to target the specific Akt isoform which promotes the progression of the specific tumor.

High nuclear level of Vav1 is a positive prognostic factor in early invasive breast tumors: a role in modulating genes related to the efficiency of metastatic process

Vav1 is one of the signalling proteins normally restricted to hematopoietic cells that results ectopically expressed in solid tumors, including breast cancer. By immunohistochemical analysis on TMAs containing invasive breast tumor from patients without lymph node involvement, we have found that Vav1 is expressed in almost all investigated cancers and shows a peculiar localization inside the nucleus of tumor cells. High amounts of nuclear Vav1 are positively correlated with low incidence of relapse, regardless phenotype and molecular subtype of breast neoplasia. In particular, Kaplan-Meier plots showed an elevated risk of distant metastasis in patients with low Vav1 expression compared with patients with high Vav1 expression in their tumors. Experiments performed with breast tumor-derived cells indicated that Vav1 negatively modulates their invasiveness in vitro and their metastatic efficiency in vivo, possibly by affecting the expression of genes involved in invasion and/or metastasis of breast tumors. Since the high heterogeneity of breast tumors makes difficult to predict the evolution of early breast neoplasias, the evaluation of nuclear Vav1 levels may help in the characterization and management of early breast cancer patients. In particular, Vav1 may serve as a prognostic biomarker and a target for new therapies aimed to prevent breast cancer progression.

In Vivo Role of INPP4B in Tumor and Metastasis Suppression through Regulation of PI3K-AKT Signaling at Endosomes

The phosphatases PTEN and INPP4B have been proposed to act as tumor suppressors by antagonizing PI3K-AKT signaling and are frequently dysregulated in human cancer. Although PTEN has been extensively studied, little is known about the underlying mechanisms by which INPP4B exerts its tumor-suppressive function and its role in tumorigenesis in vivo. Here, we show that a partial or complete loss of Inpp4b morphs benign thyroid adenoma lesions in Pten heterozygous mice into lethal and metastatic follicular-like thyroid cancer (FTC). Importantly, analyses of human thyroid cancer cell lines and specimens reveal INPP4B downregulation in FTC. Mechanistically, we find that INPP4B, but not PTEN, is enriched in the early endosomes of thyroid cancer cells, where it selectively inhibits AKT2 activation and in turn tumor proliferation and anchorage-independent growth. We therefore identify INPP4B as a novel tumor suppressor in FTC oncogenesis and metastasis through localized regulation of the PI3K-AKT pathway at the endosomes.

SIGNIFICANCE

Although both PTEN and INPP4B can inhibit PI3K-AKT signaling through their lipid phosphatase activities, here we demonstrate lack of an epistatic relationship between the two tumor suppressors. Instead, the qualitative regulation of PI3K-AKT2 signaling by INPP4B provides a mechanism for their cooperation in suppressing thyroid tumorigenesis and metastasis.

TSC1 activates TGF-β-Smad2/3 signaling in growth arrest and epithelial-to-mesenchymal transition

The tuberous sclerosis proteins TSC1 and TSC2 are key integrators of growth factor signaling. They suppress cell growth and proliferation by acting in a heteromeric complex to inhibit the mammalian target of rapamycin complex 1 (mTORC1). In this study, we identify TSC1 as a component of the transforming growth factor β (TGF-β)-Smad2/3 pathway. Here, TSC1 functions independently of TSC2. TSC1 interacts with the TGF-β receptor complex and Smad2/3 and is required for their association with one another. TSC1 regulates TGF-β-induced Smad2/3 phosphorylation and target gene expression and controls TGF-β-induced growth arrest and epithelial-to-mesenchymal transition (EMT). Hyperactive Akt specifically activates TSC1-dependent cytostatic Smad signaling to induce growth arrest. Thus, TSC1 couples Akt activity to TGF-β-Smad2/3 signaling. This has implications for cancer treatments targeting phosphoinositide 3-kinases and Akt because they may impair tumor-suppressive cytostatic TGF-β signaling by inhibiting Akt- and TSC1-dependent Smad activation.

Beclin 1 regulates growth factor receptor signaling in breast cancer

Beclin 1 is a haploinsufficient tumor suppressor that is decreased in many human tumors. The function of beclin 1 in cancer has been attributed primarily to its role in the degradative process of macroautophagy. However, beclin 1 is a core component of the vacuolar protein sorting 34 (Vps34)/class III phosphatidylinositoI-3 kinase (PI3KC3) and Vps15/p150 complex that regulates multiple membrane-trafficking events. In the current study, we describe an alternative mechanism of action for beclin 1 in breast cancer involving its control of growth factor receptor signaling. We identify a specific stage of early endosome maturation that is regulated by beclin 1, the transition of APPL1-containing phosphatidyIinositol 3-phosphate-negative (PI3P(-)) endosomes to PI3P(+) endosomes. Beclin 1 regulates PI3P production in response to growth factor stimulation to control the residency time of growth factor receptors in the PI3P(-)/APPL(+)-signaling-competent compartment. As a result, suppression of BECN1 sustains growth factor-stimulated AKT and ERK activation resulting in increased breast carcinoma cell invasion. In human breast tumors, beclin 1 expression is inversely correlated with AKT and ERK phosphorylation. Our data identify a novel role for beclin 1 in regulating growth factor signaling and reveal a mechanism by which loss of beclin 1 expression would enhance breast cancer progression.

KDM5B is overexpressed in gastric cancer and is required for gastric cancer cell proliferation and metastasis

Epigenetic alterations such as aberrant expression of histone-modifying enzymes have been implicated in tumorigenesis. KDM5B (also known as JARID1B) is a newly identified histone demethylase that regulates chromatin structure or gene expression by removing methyl residues from trimethylated lysine 4 on histone H3. Recent observations have shown oncogenic activity of KDM5B. However, the role of KDM5B in gastric cancer carcinogenesis remains unclear. In this study, we aimed to investigate the role of KDM5B in gastric cancer. Immunohistochemical analysis, western blotting, and qRT-PCR were used to measure the levels of KDM5B in gastric cancer cell lines, 45 pairs of gastric cancer tissues and the adjacent nonneoplastic tissues. KDM5B and shKDM5B were transfected into gastric cancer cells to investigate its role on regulating cell proliferation which was measured by MTT and colony formation assay. Cell's migration and invasion were measured by Transwell and Matrigel analysis in vitro. PCNA expression was measured by immunofluorescence staining and immunohistochemical analysis. The in vivo tumorigenesis and metastasis assays were performed in SCID mice. In clinical gastric cancer samples, we found that KDM5B expression was significantly up-regulated in cancer lesions compared with paired normal gastric tissues. By silencing or overexpressing KDM5B in gastric cancer cells, we found that KDM5B could promote cell growth and metastasis in vitro. An in vivo assay showed that KDM5B not only dramatically promoted gastric cancer cell xenograft formation and growth but also promoted gastric cancer cell metastasis in a liver metastasis model. Moreover, we demonstrated that KDM5B promoted gastric cancer metastasis via regulation of the Akt pathway. Our study provided evidence that KDM5B functions as a novel tumor oncogene in gastric cancer and may be a potential therapeutic target for gastric cancer management.

Reprogramming during epithelial to mesenchymal transition under the control of TGFβ

Epithelial-mesenchymal transition (EMT) refers to plastic changes in epithelial tissue architecture. Breast cancer stromal cells provide secreted molecules, such as transforming growth factor β (TGFβ), that promote EMT on tumor cells to facilitate breast cancer cell invasion, stemness and metastasis. TGFβ signaling is considered to be abnormal in the context of cancer development; however, TGFβ acting on breast cancer EMT resembles physiological signaling during embryonic development, when EMT generates or patterns new tissues. Interestingly, while EMT promotes metastatic fate, successful metastatic colonization seems to require the inverse process of mesenchymal-epithelial transition (MET). EMT and MET are interconnected in a time-dependent and tissue context-dependent manner and are coordinated by TGFβ, other extracellular proteins, intracellular signaling cascades, non-coding RNAs and chromatin-based molecular alterations. Research on breast cancer EMT/MET aims at delivering biomolecules that can be used diagnostically in cancer pathology and possibly provide ideas for how to improve breast cancer therapy.

mTOR signaling in tumorigenesis

mTOR (the mechanistic target of rapamycin) is an atypical serine/threonine kinase involved in regulating major cellular functions including growth and proliferation. Deregulation of the mTOR signaling pathway is one of the most commonly observed pathological alterations in human cancers. To this end, oncogenic activation of the mTOR signaling pathway contributes to cancer cell growth, proliferation and survival, highlighting the potential for targeting the oncogenic mTOR pathway members as an effective anti-cancer strategy. In order to do so, a thorough understanding of the physiological roles of key mTOR signaling pathway components and upstream regulators would guide future targeted therapies. Thus, in this review, we summarize available genetic mouse models for mTORC1 and mTORC2 components, as well as characterized mTOR upstream regulators and downstream targets, and assign a potential oncogenic or tumor suppressive role for each evaluated molecule. Together, our work will not only facilitate the current understanding of mTOR biology and possible future research directions, but more importantly, provide a molecular basis for targeted therapies aiming at key oncogenic members along the mTOR signaling pathway.

Astrocyte elevated gene-1 interacts with Akt isoform 2 to control glioma growth, survival, and pathogenesis

The oncogene astrocyte elevated gene-1 (AEG-1; MTDH) is highly expressed in glioblastoma multiforme (GBM) and many other types of cancer, where it activates multiple signaling pathways that drive proliferation, invasion, angiogenesis, chemoresistance, radioresistance, and metastasis. AEG-1 activates the Akt signaling pathway and Akt and c-Myc are positive regulators of AEG-1 transcription, generating a positive feedback loop between AEG-1 and Akt in regulating tumorigenesis. Here, we describe in GBM cells a direct interaction between an internal domain of AEG-1 and the PH domain of Akt2, a major driver in GBM. Expression and interaction of AEG-1 and Akt2 are elevated in GBM and contribute to tumor cell survival, proliferation, and invasion. Clinically, in silico gene expression and immunohistochemical analyses of patient specimens showed that AEG-1 and Akt2 expression correlated with GBM progression and reduced patient survival. AEG-1-Akt2 interaction prolonged stabilization of Akt2 phosphorylation at S474, regulating downstream signaling cascades that enable cell proliferation and survival. Disrupting AEG-1-Akt2 interaction by competitive binding of the Akt2-PH domain led to reduced cell viability and invasion. When combined with AEG-1 silencing, conditional expression of Akt2-PH markedly increased survival in an orthotopic mouse model of human GBM. Our study uncovers a novel molecular mechanism by which AEG-1 augments glioma progression and offers a rationale to block AEG-1-Akt2 signaling function as a novel GBM treatment.

let-7b/g silencing activates AKT signaling to promote gastric carcinogenesis

Background

Aberrant AKT activation contributes to gastric cancer cell survival and chemotherapy resistance, however its regulation is poorly understood. microRNAs have been established to be important regulators in gastric carcinogenesis. Here, we showed the functional role and putative target of let-7b and let-7g (let-7b/g) in gastric carcinogenesis.

Methods

The expression of let-7b/g in gastric cancer cell lines and primary tumors were evaluated by miRNA qRT-PCR. The putative target gene of let-7b/g was explored by TargetScan followed by further validation. Functional analyses including MTT proliferation, monolayer colony formation, cell invasion assays and in vivo study were performed in both ectopic expression and knockdown approaches.

Results

let-7b/g was found down-regulated in gastric cancer and its downregulation was associated with poor survival and correlated with lymph node metastasis. let-7b/g inhibited AKT2 expression by directly binding to its 3’UTR, reduced p-AKT (S473) activation and suppressed expression of the downstream effector pS6. AKT2 mRNA expression showed negative correlation with the expression of let-7b/g in primary tumors. Short interfering RNA (siRNA) mediated knockdown of AKT2 phenocopied the tumor-suppressive effects of let-7b/g. Moreover, AKT2 re-expression partly abrogated the growth-inhibitory effect of let-7b/g.

Conclusion

In conclusion, our findings reveal decreased let-7b/g contributes to aberrant AKT activation in gastric tumorigenesis and provide a potential therapeutic strategy for gastric cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-014-0281-3) contains supplementary material, which is available to authorized users.

Macrophage deficiency of Akt2 reduces atherosclerosis in Ldlr null mice

Macrophages play crucial roles in the formation of atherosclerotic lesions. Akt, a serine/threonine protein kinase B, is vital for cell proliferation, migration, and survival. Macrophages express three Akt isoforms, Akt1, Akt2, and Akt3, but the roles of Akt1 and Akt2 in atherosclerosis in vivo remain unclear. To dissect the impact of macrophage Akt1 and Akt2 on early atherosclerosis, we generated mice with hematopoietic deficiency of Akt1 or Akt2. After 8 weeks on Western diet, Ldlr^−/− mice reconstituted with Akt1^−/− fetal liver cells (Akt1^−/−→Ldlr^−/−) had similar atherosclerotic lesion areas compared with control mice transplanted with WT cells (WT→Ldlr^−/−). In contrast, Akt2^−/−→Ldlr^−/− mice had dramatically reduced atherosclerotic lesions compared with WT→Ldlr^−/− mice of both genders. Similarly, in the setting of advanced atherosclerotic lesions, Akt2^−/−→Ldlr^−/− mice had smaller aortic lesions compared with WT→Ldlr^−/− and Akt1^−/−→Ldlr^−/− mice. Importantly, Akt2^−/−→Ldlr^−/− mice had reduced numbers of proinflammatory blood monocytes expressing Ly-6C^hi and chemokine C-C motif receptor 2. Peritoneal macrophages isolated from Akt2^−/− mice were skewed toward an M2 phenotype and showed decreased expression of proinflammatory genes and reduced cell migration. Our data demonstrate that loss of Akt2 suppresses the ability of macrophages to undergo M1 polarization reducing both early and advanced atherosclerosis.

The E2F transcription factors regulate tumor development and metastasis in a mouse model of metastatic breast cancer

While the E2F transcription factors (E2Fs) have a clearly defined role in cell cycle control, recent work has uncovered new functions. Using genomic signature methods, we predicted a role for the activator E2F transcription factors in the mouse mammary tumor virus (MMTV)-polyomavirus middle T oncoprotein (PyMT) mouse model of metastatic breast cancer. To genetically test the hypothesis that the E2Fs function to regulate tumor development and metastasis, we interbred MMTV-PyMT mice with E2F1, E2F2, or E2F3 knockout mice. With the ablation of individual E2Fs, we noted alterations of tumor latency, histology, and vasculature. Interestingly, we noted striking reductions in metastatic capacity and in the number of circulating tumor cells in both the E2F1 and E2F2 knockout backgrounds. Investigating E2F target genes that mediate metastasis, we found that E2F loss led to decreased levels of vascular endothelial growth factor (Vegfa), Bmp4, Cyr61, Nupr1, Plod 2, P4ha1, Adamts1, Lgals3, and Angpt2. These gene expression changes indicate that the E2Fs control the expression of genes critical to angiogenesis, the remodeling of the extracellular matrix, tumor cell survival, and tumor cell interactions with vascular endothelial cells that facilitate metastasis to the lungs. Taken together, these results reveal that the E2F transcription factors play key roles in mediating tumor development and metastasis in addition to their well-characterized roles in cell cycle control.