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

Application of Gene Editing in Triple-Negative Breast Cancer Research

With the rapid development of gene editing technology, its application in breast cancer has gradually become the focus of research. This article reviews the application of gene editing technology in the treatment of breast cancer, and discusses its challenges and future development directions. The key application areas of gene editing technology in the treatment of breast cancer will be outlined, including the discovery of new therapeutic targets and the development of drugs related to the pathway. Gene editing technology has played an important role in the discovery of new therapeutic targets. Through the use of gene editing technology, breast cancer-related genes are systematically edited to regulate key regulatory factors on related pathways or key tumor suppressor genes such as FOXC1 and BRCA, and the results are analyzed in cell or animal experiments, and the target is obtained from the experimental results, which provides important clues for the development of new drugs. This approach provides an innovative way to find more effective treatment strategies and inhibit tumor growth. In addition, gene editing technology has also promoted the personalization of breast cancer treatment. By analyzing a patient's genomic information, researchers can pinpoint key genetic mutations in a patient's tumor and design personalized treatments. This personalized treatment approach is expected to improve the therapeutic effect and reduce adverse reactions. Finally, the application of gene editing technology also provides support for the development of breast cancer immunotherapy. By editing immune cells to make them more potent against tumors, researchers are trying to develop more effective immunotherapies to bring new treatment options to breast cancer patients.

AKT kinases as therapeutic targets

AKT, or protein kinase B, is a central node of the PI3K signaling pathway that is pivotal for a range of normal cellular physiologies that also underlie several pathological conditions, including inflammatory and autoimmune diseases, overgrowth syndromes, and neoplastic transformation. These pathologies, notably cancer, arise if either the activity of AKT or its positive or negative upstream or downstream regulators or effectors goes unchecked, superimposed on by its intersection with a slew of other pathways. Targeting the PI3K/AKT pathway is, therefore, a prudent countermeasure. AKT inhibitors have been tested in many clinical trials, primarily in combination with other drugs. While some have recently garnered attention for their favorable profile, concern over resistance and off-target effects have continued to hinder their widespread adoption in the clinic, mandating a discussion on alternative modes of targeting. In this review, we discuss isoform-centric targeting that may be more effective and less toxic than traditional pan-AKT inhibitors and its significance for disease prevention and treatment, including immunotherapy. We also touch on the emerging mutant- or allele-selective covalent allosteric AKT inhibitors (CAAIs), as well as indirect, novel AKT-targeting approaches, and end with a briefing on the ongoing quest for more reliable biomarkers predicting sensitivity and response to AKT inhibitors, and their current state of affairs.

Down-Regulation of AKT Proteins Slows the Growth of Mutant-KRAS Pancreatic Tumors

Serine/threonine kinase AKT isoforms play a well-established role in cell metabolism and growth. Most pancreatic adenocarcinomas (PDACs) harbor activation mutations of KRAS, which activates the PI3K/AKT signaling pathway. However, AKT inhibitors are not effective in the treatment of pancreatic cancer. To better understand the role of AKT signaling in mutant-KRAS pancreatic tumors, this study utilized proteolysis-targeting chimeras (PROTACs) and CRISPR-Cas9-genome editing to investigate AKT proteins. The PROTAC down-regulation of AKT proteins markedly slowed the growth of three pancreatic tumor cell lines harboring mutant KRAS. In contrast, the inhibition of AKT kinase activity alone had very little effect on the growth of these cell lines. The concurrent genetic deletion of all AKT isoforms (AKT1, AKT2, and AKT3) in the KPC (KrasG12D; Trp53R172H; Pdx1-Cre) pancreatic cancer cell line also dramatically slowed its growth in vitro and when orthotopically implanted in syngeneic mice. Surprisingly, insulin-like growth factor-1 (IGF-1), but not epidermal growth factor (EGF), restored KPC cell growth in serum-deprived conditions, and the IGF-1 growth stimulation effect was AKT-dependent. The RNA-seq analysis of AKT1/2/3-deficient KPC cells suggested that reduced cholesterol synthesis may be responsible for the decreased response to IGF-1 stimulation. These results indicate that the presence of all three AKT isoforms supports pancreatic tumor cell growth, and the pharmacological degradation of AKT proteins may be more effective than AKT catalytic inhibitors for treating pancreatic cancer.

Down-regulation of AKT proteins slows the growth of mutant-KRAS pancreatic tumors

Serine/threonine kinase AKT isoforms play a well-established role in cell metabolism and growth. Most pancreatic adenocarcinoma (PDAC) harbors activation mutations of KRAS, which activates the PI3K/AKT signaling pathway. However, AKT inhibitors are not effective in the treatment of pancreatic cancer. To better understand the role of AKT signaling in mutant-KRAS pancreatic tumors, this study utilizes proteolysis-targeting chimeras (PROTACs) and CRISPR-Cas9-genome editing to investigate AKT proteins. PROTAC down-regulation of AKT proteins markedly slowed the growth of three pancreatic tumor cell lines harboring mutant KRAS. In contrast, inhibition of AKT kinase activity alone had very little effect on the growth of these cell lines. Concurrent genetic deletion of all AKT isoforms (AKT1, AKT2, and AKT3) in the KPC (KrasG12D; Trp53R172H; Pdx1-Cre) pancreatic cancer cell line also dramatically slowed its growth in vitro and when orthotopically implanted in syngeneic mice. Surprisingly, insulin-like growth factor-1 (IGF-1), but not epidermal growth factor (EGF), restored KPC cell growth in serum-deprived conditions and the IGF-1 growth stimulation effect was AKT dependent. RNA-seq analysis of AKT1/2/3-deficient KPC cells suggested that reduced cholesterol synthesis may be responsible for the decreased response to IGF-1 stimulation. These results indicate that the presence of all three AKT isoforms supports pancreatic tumor cell growth and pharmacological degradation of AKT proteins may be more effective than AKT catalytic inhibitors for treating pancreatic cancer.

The PI3K/AKT/mTOR signaling pathway in breast cancer: Review of clinical trials and latest advances

Breast cancer (BC) is the most commonly diagnosed cancer and the leading cause of cancer mortality in women. As the phosphatidylinositol 3-kinase (PI3K) signaling pathway is involved in a wide range of physiological functions of cells including growth, proliferation, motility, and angiogenesis, any alteration in this axis could induce oncogenic features; therefore, numerous preclinical and clinical studies assessed agents able to inhibit the components of this pathway in BC patients. To the best of our knowledge, this is the first study that analyzed all the registered clinical trials investigating safety and efficacy of the PI3K/AKT/mTOR axis inhibitors in BC. Of note, we found that the trends of PI3K inhibitors in recent years were superior as compared with the inhibitors of either AKT or mTOR. However, most of the trials entering phase III and IV used mTOR inhibitors (majorly Everolimus) followed by PI3K inhibitors (majorly Alpelisib) leading to the FDA approval of these drugs in the BC context. Despite favorable efficacies, our analysis shows that the majority of trials are utilizing PI3K pathway inhibitors in combination with hormone therapy and chemotherapy; implying monotherapy cannot yield huge clinical benefits, at least partly, due to the activation of compensatory mechanisms. To emphasize the beneficial effects of these inhibitors in combined-modal strategies, we also reviewed recent studies which investigated the conjugation of nanocarriers with PI3K inhibitors to reduce harmful toxicities, increase the local concentration, and improve their efficacies in the context of BC therapy.

Substrate preference of protein kinase B isoforms can vary depending on the cell line

Many proteins in higher eukaryotes, especially those with crucial functions, have multiple isoforms with redundant roles providing protection against potential functional deficiencies in one isoform. However, these isoforms can also have some unique roles. Protein kinase B, also known as Akt, is one such protein that has three isoforms encoded on different genes. Due to high sequence similarity and the general lack of specific reagents, most studies on Akt generalize their findings and do not distinguish between the isoforms. Using an established chemical genetic strategy and a set of known Akt substrates, this work explores substrate specificity of Akt isoforms under steady state conditions in two commonly used cell lines. This strategy can be applied to study any Akt isoform-specific substrates of interest in any cell line of choice as long as the cell line can be transfected.

Targeted Inhibition of Hsp90 in Combination with Metformin Modulates Programmed Cell Death Pathways in A549 Lung Cancer Cells

The pathophysiology of lung cancer is dependent on the dysregulation in the apoptotic and autophagic pathways. The intricate link between apoptosis and autophagy through shared signaling pathways complicates our understanding of how lung cancer pathophysiology is regulated. As drug resistance is the primary reason behind treatment failure, it is crucial to understand how cancer cells may respond to different therapies and integrate crosstalk between apoptosis and autophagy in response to them, leading to cell death or survival. Thus, in this study, we have tried to evaluate the crosstalk between autophagy and apoptosis in A549 lung cancer cell line that could be modulated by employing a combination therapy of metformin (6 mM), an anti-diabetic drug, with gedunin (12 µM), an Hsp90 inhibitor, to provide insights into the development of new cancer therapeutics. Our results demonstrated that metformin and gedunin were cytotoxic to A549 lung cancer cells. Combination of metformin and gedunin generated ROS and promoted MMP loss and DNA damage. The combination further increased the expression of AMPKα1 and promoted the nuclear localization of AMPKα1/α2. The expression of Hsp90 was downregulated, further decreasing the expression of its clients, EGFR, PIK3CA, AKT1, and AKT3. Inhibition of the EGFR/PI3K/AKT pathway upregulated TP53 and inhibited autophagy. The combination was promoting nuclear localization of p53; however, some cytoplasmic signals were also detected. Further increase in the expression of caspase 9 and caspase 3 was observed. Thus, we concluded that the combination of metformin and gedunin upregulates apoptosis by inhibiting the EGFR/PI3K/AKT pathway and autophagy in A549 lung cancer cells.

Inhibitors of phosphoinositide 3-kinase (PI3K) and phosphoinositide 3-kinase-related protein kinase family (PIKK)

Phosphoinositide 3-kinases (PI3K) and phosphoinositide 3-kinase-related protein kinases (PIKK) are two structurally related families of kinases that play vital roles in cell growth and DNA damage repair. Dysfunction of PIKK members and aberrant stimulation of the PI3K/AKT/mTOR signalling pathway are linked to a plethora of diseases including cancer. In recent decades, numerous inhibitors related to the PI3K/AKT/mTOR signalling have made great strides in cancer treatment, like copanlisib and sirolimus. Notably, most of the PIKK inhibitors (such as VX-970 and M3814) related to DNA damage response have also shown good efficacy in clinical trials. However, these drugs still require a suitable combination therapy to overcome drug resistance or improve antitumor activity. Based on the aforementioned facts, we summarised the efficacy of PIKK, PI3K, and AKT inhibitors in the therapy of human malignancies and the resistance mechanisms of targeted therapy, in order to provide deeper insights into cancer treatment.

Impact of AKT1 on cell invasion and radiosensitivity in a triple negative breast cancer cell line developing brain metastasis

Introduction

The PI3K/AKT pathway is activated in 43-70% of breast cancer (BC)-patients and promotes the metastatic potential of BC cells by increasing cell proliferation, invasion and radioresistance. Therefore, AKT1-inhibition in combination with radiotherapy might be an effective treatment option for triple-negative breast cancer (TNBC)-patients with brain metastases.

Methods

The impact of AKT1-knockout (AKT1_KO) and AKT-inhibition using Ipatasertib on MDA-MB-231 BR cells was assessed using in vitro cell proliferation and migration assays. AKT1-knockout in MDA-MB-231BR cells was performed using CRISPR/Cas9. The effect of AKT1-knockout on radiosensitivity of MDA-MB-231BR cell lines was determined via colony formation assays after cell irradiation. To detect genomic variants in AKT1_KO MDA-MB-231BR cells, whole-genome sequencing (WGS) was performed.

Results

Pharmacological inhibition of AKT with the pan-AKT inhibitor Ipatasertib led to a significant reduction of cell viability but did not impact cell migration. Moreover, only MDA-MB-231BR cells were sensitized following Ipatasertib-treatment. Furthermore, specific AKT1-knockout in MDA-MB-231BR showed reduced cell viability in comparison to control cells, with significant effect in one of two analyzed clones. Unexpectedly, AKT1 knockout led to increased cell migration and clonogenic potential in both AKT1_KO clones. RNAseq-analysis revealed the deregulation of CTSO, CYBB, GPR68, CEBPA, ID1, ID4, METTL15, PBX1 and PTGFRN leading to the increased cell migration, higher clonogenic survival and decreased radiosensitivity as a consequence of the AKT1 knockout in MDA-MB-231BR.

Discussion

Collectively, our results demonstrate that Ipatasertib leads to radiosensitization and reduced cell proliferation of MDA-MB-231BR. AKT1-inhibition showed altered gene expression profile leading to modified cell migration, clonogenic survival and radioresistance in MDA-MB-231BR. We conclude, that AKT1-inhibition in combination with radiotherapy contribute to novel treatment strategies for breast cancer brain metastases.

Essential Protein PHB2 and Its Regulatory Mechanisms in Cancer

Prohibitins (PHBs) are a highly conserved class of proteins and have an essential role in transcription, epigenetic regulation, nuclear signaling, mitochondrial structural integrity, cell division, and cellular membrane metabolism. Prohibitins form a heterodimeric complex, consisting of two proteins, prohibitin 1 (PHB1) and prohibitin 2 (PHB2). They have been discovered to have crucial roles in regulating cancer and other metabolic diseases, functioning both together and independently. As there have been many previously published reviews on PHB1, this review focuses on the lesser studied prohibitin, PHB2. The role of PHB2 in cancer is controversial. In most human cancers, overexpressed PHB2 enhances tumor progression, while in some cancers, it suppresses tumor progression. In this review, we focus on (1) the history, family, and structure of prohibitins, (2) the essential location-dependent functions of PHB2, (3) dysfunction in cancer, and (4) the promising modulators to target PHB2. At the end, we discuss future directions and the clinical significance of this common essential gene in cancer.

Nucleocytoplasmic transport of active HER2 causes fractional escape from the DCIS-like state

Activation of HER2/ErbB2 coincides with escape from ductal carcinoma in situ (DCIS) premalignancy and disrupts 3D organization of cultured breast-epithelial spheroids. The 3D phenotype is infrequent, however, and mechanisms for its incomplete penetrance have been elusive. Using inducible HER2/ErbB2-EGFR/ErbB1 heterodimers, we match phenotype penetrance to the frequency of co-occurring transcriptomic changes and uncover a reconfiguration in the karyopherin network regulating ErbB nucleocytoplasmic transport. Induction of the exportin CSE1L inhibits nuclear accumulation of ErbBs, whereas nuclear ErbBs silence the importin KPNA1 by inducing miR-205. When these negative feedbacks are incorporated into a validated systems model of nucleocytoplasmic transport, steady-state localization of ErbB cargo becomes ultrasensitive to initial CSE1L abundance. Erbb2-driven carcinomas with Cse1l deficiency outgrow less irregularly from mammary ducts, and NLS-attenuating mutants or variants of HER2 favor escape in 3D culture. We conclude here that adaptive nucleocytoplasmic relocalization of HER2 creates a systems-level molecular switch at the premalignant-to-malignant transition.

Interfering with the Ubiquitin-Mediated Regulation of Akt as a Strategy for Cancer Treatment

The serine/threonine kinase Akt modulates the functions of numerous substrates, many of them being involved in cell proliferation and growth, metabolism, angiogenesis, resistance to hypoxia and migration. Akt is frequently deregulated in many types of human cancers, its overexpression or abnormal activation being associated with the increased proliferation and survival of cancer cells. A promising avenue for turning off the functionality of Akt is to either interfere with the K63-linked ubiquitination that is necessary for Akt membrane recruitment and activation or increase the K48-linked polyubiquitination that aims to target Akt to the proteasome for its degradation. Recent evidence indicates that targeting the ubiquitin proteasome system is effective for certain cancer treatments. In this review, the functions and roles of Akt in human cancer will be discussed, with a main focus on molecules and compounds that target various elements of the ubiquitination processes that regulate the activation and inactivation of Akt. Moreover, their possible and attractive implications for cancer therapy will be discussed.

Extracellular vesicles from MDA-MB-231 breast cancer cells stimulated with insulin-like growth factor 1 mediate an epithelial-mesenchymal transition process in MCF10A mammary epithelial cells

Insulin-like growth factor-1 (IGF-1) plays an important role in function and development of the mammary gland. However, high levels of IGF-1 has been associated with an increased risk of breast cancer development. Epithelial-mesenchymal transition (EMT) is a process where epithelial cells lose their epithelial characteristics and acquire a mesenchymal phenotype, which is considered one of the most important mechanisms in cancer initiation and promotion of metastasis. Extracellular vesicles (EVs) are released into the extracellular space by different cell types, which mediate intercellular communication and play an important role in different physiological and pathological processes, such as cancer. In this study, we demonstrate that EVs from MDA-MB-231 breast cancer cells stimulated with IGF-1 (IGF-1 EVs) decrease the levels of E-cadherin, increase the expression of vimentin and N-cadherin and stimulate the secretion of metalloproteinase-9 in mammary non-tumorigenic epithelial cells MCF10A. IGF-1 EVs also induce the expression of Snail1, Twist1 and Sip1, which are transcription factors involved in EMT. Moreover, IGF-1 EVs induce activation of ERK1/2, Akt1 and Akt2, migration and invasion. In summary, we demonstrate, for the first time, that IGF-1 EVs induce an EMT process in mammary non-tumorigenic epithelial cells MCF10A.

Akt: a key transducer in cancer

Growth factor signaling plays a pivotal role in diverse biological functions, such as cell growth, apoptosis, senescence, and migration and its deregulation has been linked to various human diseases. Akt kinase is a central player transmitting extracellular clues to various cellular compartments, in turn executing these biological processes. Since the discovery of Akt three decades ago, the tremendous progress towards identifying its upstream regulators and downstream effectors and its roles in cancer has been made, offering novel paradigms and therapeutic strategies for targeting human diseases and cancers with deregulated Akt activation. Unraveling the molecular mechanisms for Akt signaling networks paves the way for developing selective inhibitors targeting Akt and its signaling regulation for the management of human diseases including cancer.

AKT Regulation of ORAI1-Mediated Calcium Influx in Breast Cancer Cells

Simple Summary

A remodeling in calcium homeostasis and the protein kinase AKT signaling pathway often promotes tumorigenic traits in cancer cells. Changes in calcium signaling can be mediated through altered expression or activity of calcium channels and pumps, which constitute a class of targetable therapeutic targets. Currently, the interplay between the two signaling pathways in breast cancer cells is unclear. A better understanding of the association between calcium and AKT signaling, and the molecular players involved may identify novel therapeutic strategies for breast cancers with abnormal AKT signaling. Using fluorescence calcium imaging and gene silencing/knockout techniques, we showed that increased AKT activation results in increased calcium entry, and that this is mediated through ORAI1 calcium channels. Future studies exploring therapeutic strategies to target PTEN-deficient or hyperactivated AKT cancers should consider this novel correlation between AKT activation and ORAI1-mediated calcium influx.

Abstract

Although breast cancer cells often exhibit both abnormal AKT signaling and calcium signaling, the association between these two pathways is unclear. Using a combination of pharmacological tools, siRNA and CRISPR/Cas9 gene silencing techniques, we investigated the association between PTEN, AKT phosphorylation and calcium signaling in a basal breast cancer cell line. We found that siRNA-mediated PTEN silencing promotes AKT phosphorylation and calcium influx in MDA-MB-231 cells. This increase in AKT phosphorylation and calcium influx was phenocopied by the pharmacological AKT activator, SC79. The increased calcium influx associated with SC79 is inhibited by silencing AKT2, but not AKT1. This increase in calcium influx is suppressed when the store-operated calcium channel, ORAI1 is silenced. The results from this study open a novel avenue for therapeutic targeting of cancer cells with increased AKT activation. Given the association between ORAI1 and breast cancer, ORAI1 is a possible therapeutic target in cancers with abnormal AKT signaling.

Study on the effect of Pogostemon cablin Benth on skin aging based on network pharmacology

BACKGROUND

At present, there is still little research on the anti-aging effect of Pogostemon cablin Benth (PCB) on human skin. In this paper, the mechanism of anti-aging effect of PCB on human skin was studied by using network pharmacology and molecular docking methods.

OBJECTIVE

To analyze the pharmacological mechanism of PCB in the treatment of skin aging, so as to provide reference for new drug development and clinical application.

METHODS

Active ingredients and related targets of PCB and skin aging-related disease targets are obtained through public databases, and the "drug-disease-target" and protein-protein interaction (PPI) network diagrams were constructed with the help of software to screen the core targets; Then GO analysis and KEGG pathway analysis were performed on the target; Finally, the molecular docking between the components and the targets were verified.

RESULTS

After screening, 112 intersection targets of active compounds of skin aging and PCB were obtained. Through GO and KEGG enrichment analysis, it is found that these biological processes mainly focus on epithelial cell proliferation, aging, growth factors, longevity regulation pathway, cancer pathway, AGE-RAGE signal pathway, PI3K Akt signal pathway and IL-17 signal pathway. The molecular docking results showed that quercetin, apigenin, irisnepalensis isoflavone, 3,23-dihydroxy-12-oleorene-28-oleic acid, 5-hydroxy-7,4'- dimethoxyflavone and other major compounds were connected with TP53, JUN, HSP90AAL, AKT1 and MAPK1 through hydrogen bonds, and there was high binding energy between them.

CONCLUSION

Through multi-target prediction and molecular docking verification, it shows that PCB provides a strong effect in the treatment of skin aging, which provides a reference for its further research.

AKT1 Transcriptomic Landscape in Breast Cancer Cells

Overexpression and hyperactivation of the serine/threonine protein kinase B (AKT) pathway is one of the most common cellular events in breast cancer progression. However, the nature of AKT1-specific genome-wide transcriptomic alterations in breast cancer cells and breast cancer remains unknown to this point. Here, we delineate the impact of selective AKT1 knock down using gene-specific siRNAs or inhibiting the AKT activity with a pan-AKT inhibitor VIII on the nature of transcriptomic changes in breast cancer cells using the genome-wide RNA-sequencing analysis. We found that changes in the cellular levels of AKT1 lead to changes in the levels of a set of differentially expressed genes and, in turn, imply resulting AKT1 cellular functions. In addition to an expected positive relationship between the status of AKT1 and co-expressed cellular genes, our study unexpectedly discovered an inherent role of AKT1 in inhibiting the expression of a subset of genes in both unstimulated and growth factor stimulated breast cancer cells. We found that depletion of AKT1 leads to upregulation of a subset of genes—many of which are also found to be downregulated in breast tumors with elevated high AKT1 as well as upregulated in breast tumors with no detectable AKT expression. Representative experimental validation studies in two breast cancer cell lines showed a reasonable concurrence between the expression data from the RNA-sequencing and qRT-PCR or data from ex vivo inhibition of AKT1 activity in cancer patient-derived cells. In brief, findings presented here provide a resource for further understanding of AKT1-dependent modulation of gene expression in breast cancer cells and broaden the scope and significance of AKT1 targets and their functions.

Platelet-Derived miR-126-3p Directly Targets AKT2 and Exerts Anti-Tumor Effects in Breast Cancer Cells: Further Insights in Platelet-Cancer Interplay

Among the surrounding cells influencing tumor biology, platelets are recognized as novel players as they release microvesicles (MVs) that, once delivered to cancer cells, modulate signaling pathways related to cell growth and dissemination. We have previously shown that physiological delivery of platelet MVs enriched in miR-126 exerted anti-tumor effects in different breast cancer (BC) cell lines. Here, we seek further insight by identifying AKT2 kinase as a novel miR-126-3p direct target, as assessed by bioinformatic analysis and validated by luciferase assay. Both ectopic expression and platelet MV-mediated delivery of miR-126-3p downregulated AKT2 expression, thus suppressing proliferating and invading properties, in either triple negative (BT549 cells) or less aggressive Luminal A (MCF-7 cells) BC subtypes. Accordingly, as shown by bioinformatic analysis, both high miR-126 and low AKT2 levels were associated with favorable long-term prognosis in BC patients. Our results, together with the literature data, indicate that miR-126-3p exerts suppressor activity by specifically targeting components of the PIK3/AKT signaling cascade. Therefore, management of platelet-derived MV production and selective delivery of miR-126-3p to tumor cells may represent a useful tool in multimodal therapeutic approaches in BC patients.

Loss of ASAP1 in the MMTV-PyMT model of luminal breast cancer activates AKT, accelerates tumorigenesis, and promotes metastasis

ASAP1 is a multi-domain adaptor protein that regulates cytoskeletal dynamics, receptor recycling and intracellular vesicle trafficking. Its expression is associated with poor prognosis in a variety of cancers, and can promote cell migration, invasion and metastasis. Although amplification and expression of ASAP1 has been associated with poor survival in breast cancer, we found that in the autochthonous MMTV-PyMT model of luminal breast cancer, ablation of ASAP1 resulted in an earlier onset of tumor initiation and increased metastasis. This was due to tumor cell-intrinsic effects of ASAP1 deletion, as ASAP1 deficiency in tumor, but not in stromal cells was sufficient to replicate the enhanced tumorigenicity and metastasis observed in the ASAP1-null MMTV-PyMT mice. Loss of ASAP1 in MMTV-PyMT mice had no effect on proliferation, apoptosis, angiogenesis or immune cell infiltration, but enhanced mammary gland hyperplasia and tumor cell invasion, indicating that ASAP1 can accelerate tumor initiation and promote dissemination. Mechanistically, these effects were associated with a potent activation of AKT. Importantly, lower ASAP1 levels correlated with poor prognosis and enhanced AKT activation in human ER+/luminal breast tumors, validating our findings in the MMTV-PyMT mouse model for this subtype of breast cancer. Taken together, our findings reveal that ASAP1 can have distinct functions in different tumor types and demonstrate a tumor suppressive activity for ASAP1 in luminal breast cancer.

Targeting PI3K/Akt signal transduction for cancer therapy

The phosphatidylinositol 3-kinase (PI3K)/Akt pathway plays a crucial role in various cellular processes and is aberrantly activated in cancers, contributing to the occurrence and progression of tumors. Examining the upstream and downstream nodes of this pathway could allow full elucidation of its function. Based on accumulating evidence, strategies targeting major components of the pathway might provide new insights for cancer drug discovery. Researchers have explored the use of some inhibitors targeting this pathway to block survival pathways. However, because oncogenic PI3K pathway activation occurs through various mechanisms, the clinical efficacies of these inhibitors are limited. Moreover, pathway activation is accompanied by the development of therapeutic resistance. Therefore, strategies involving pathway inhibitors and other cancer treatments in combination might solve the therapeutic dilemma. In this review, we discuss the roles of the PI3K/Akt pathway in various cancer phenotypes, review the current statuses of different PI3K/Akt inhibitors, and introduce combination therapies consisting of signaling inhibitors and conventional cancer therapies. The information presented herein suggests that cascading inhibitors of the PI3K/Akt signaling pathway, either alone or in combination with other therapies, are the most effective treatment strategy for cancer.

Role of mammalian target of rapamycin complex 2 in primary and secondary liver cancer

The mammalian target of rapamycin (mTOR) acts in two structurally and functionally distinct protein complexes, mTOR complex 1 (mTORC1) and mTOR complex 2 (mTORC2). Upon deregulation, activated mTOR signaling is associated with multiple processes involved in tumor growth and metastasis. Compared with mTORC1, much less is known about mTORC2 in cancer, mainly because of the unavailability of a selective inhibitor. However, existing data suggest that mTORC2 with its two distinct subunits Rictor and mSin1 might play a more important role than assumed so far. It is one of the key effectors of the PI3K/AKT/mTOR pathway and stimulates cell growth, cell survival, metabolism, and cytoskeletal organization. It is not only implicated in tumor progression, metastasis, and the tumor microenvironment but also in resistance to therapy. Rictor, the central subunit of mTORC2, was found to be upregulated in different kinds of cancers and is associated with advanced tumor stages and a bad prognosis. Moreover, AKT, the main downstream regulator of mTORC2/Rictor, is one of the most highly activated proteins in cancer. Primary and secondary liver cancer are major problems for current cancer therapy due to the lack of specific medical treatment, emphasizing the need for further therapeutic options. This review, therefore, summarizes the role of mTORC2/Rictor in cancer, with special focus on primary liver cancer but also on liver metastases.

The Role of Akt in Acquired Cetuximab Resistant Head and Neck Squamous Cell Carcinoma: An In Vitro Study on a Novel Combination Strategy

The epidermal growth factor receptor (EGFR) is a therapeutic target in head and neck squamous cell carcinoma (HNSCC). Resistance to EGFR-targeted therapies, such as cetuximab, poses a challenging problem. This study aims to characterize acquired cetuximab resistance mechanisms in HNSCC cell lines by protein phosphorylation profiling. Through this, promising combination treatments can be identified to possibly overcome acquired cetuximab resistance in HNSCC. Protein phosphorylation profiling showed increased phosphorylation of Akt1/2/3 after cetuximab treatment in acquired cetuximab resistant cells compared to cetuximab sensitive cells, which was confirmed by western blotting. Based on this protein phosphorylation profile, a novel combination treatment with cetuximab and the Akt1/2/3 inhibitor MK2206 was designed. Synergy between cetuximab and MK2206 was observed in two cetuximab sensitive HNSCC cell lines and one acquired cetuximab resistant variant in simultaneous treatment schedules. In conclusion, this study demonstrates that increased Akt1/2/3 phosphorylation seems to be characteristic for acquired cetuximab resistance in HNSCC cell lines. Our results also show an additive to synergistic interaction between cetuximab and MK2206 in simultaneous treatment schedules. These data support the hypothesis that the combination of cetuximab with PI3K/Akt pathway inhibition might be a promising novel therapeutic strategy to overcome acquired cetuximab resistance in HNSCC patients.

Targeting Akt in cancer for precision therapy

Biomarkers-guided precision therapeutics has revolutionized the clinical development and administration of molecular-targeted anticancer agents. Tailored precision cancer therapy exhibits better response rate compared to unselective treatment. Protein kinases have critical roles in cell signaling, metabolism, proliferation, survival and migration. Aberrant activation of protein kinases is critical for tumor growth and progression. Hence, protein kinases are key targets for molecular targeted cancer therapy. The serine/threonine kinase Akt is frequently activated in various types of cancer. Activation of Akt promotes tumor progression and drug resistance. Since the first Akt inhibitor was reported in 2000, many Akt inhibitors have been developed and evaluated in either early or late stage of clinical trials, which take advantage of liquid biopsy and genomic or molecular profiling to realize personalized cancer therapy. Two inhibitors, capivasertib and ipatasertib, are being tested in phase III clinical trials for cancer therapy. Here, we highlight recent progress of Akt signaling pathway, review the up-to-date data from clinical studies of Akt inhibitors and discuss the potential biomarkers that may help personalized treatment of cancer with Akt inhibitors. In addition, we also discuss how Akt may confer the vulnerability of cancer cells to some kinds of anticancer agents.

Akt Isoforms: A Family Affair in Breast Cancer

Simple Summary

Breast cancer is the second leading cause of cancer-related death in women in the United States. The Akt signaling pathway is deregulated in approximately 70% of patients with breast cancer. While targeting Akt is an effective therapeutic strategy for the treatment of breast cancer, there are several members in the Akt family that play distinct roles in breast cancer. However, the function of Akt isoforms depends on many factors. This review analyzes current progress on the isoform-specific functions of Akt isoforms in breast cancer.

Abstract

Akt, also known as protein kinase B (PKB), belongs to the AGC family of protein kinases. It acts downstream of the phosphatidylinositol 3-kinase (PI3K) and regulates diverse cellular processes, including cell proliferation, cell survival, metabolism, tumor growth and metastasis. The PI3K/Akt signaling pathway is frequently deregulated in breast cancer and plays an important role in the development and progression of breast cancer. There are three closely related members in the Akt family, namely Akt1(PKBα), Akt2(PKBβ) and Akt3(PKBγ). Although Akt isoforms share similar structures, they exhibit redundant, distinct as well as opposite functions. While the Akt signaling pathway is an important target for cancer therapy, an understanding of the isoform-specific function of Akt is critical to effectively target this pathway. However, our perception regarding how Akt isoforms contribute to the genesis and progression of breast cancer changes as we gain new knowledge. The purpose of this review article is to analyze current literatures on distinct functions of Akt isoforms in breast cancer.

Long Intergenic Non-Coding RNAs in HNSCC: From "Junk DNA" to Important Prognostic Factor

Head and neck squamous cell carcinoma is one of the most common and fatal cancers worldwide. Even a multimodal approach consisting of standard chemo- and radiotherapy along with surgical resection is only effective in approximately 50% of the cases. The rest of the patients develop a relapse of the disease and acquire resistance to treatment. Especially this group of individuals needs novel, personalized, targeted therapy. The first step to discovering such solutions is to investigate the tumor microenvironment, thus understanding the role and mechanism of the function of coding and non-coding sequences of the human genome. In recent years, RNA molecules gained great interest when the complex character of their impact on our biology allowed them to come out of the shadows of the "junk DNA" label. Furthermore, long non-coding RNAs (lncRNA), specifically the intergenic subgroup (lincRNA), are one of the most aberrantly expressed in several malignancies, which makes them particularly promising future diagnostic biomarkers and therapeutic targets. This review contains characteristics of known and validated lincRNAs in HNSCC, such as XIST, MALAT, HOTAIR, HOTTIP, lincRNA-p21, LINC02487, LINC02195, LINC00668, LINC00519, LINC00511, LINC00460, LINC00312, and LINC00052, with a description of their prognostic abilities. Even though much work remains to be done, lincRNAs are important factors in cancer biology that will become valuable biomarkers of tumor stage, outcome prognosis, and contribution to personalized medicine.

Emerging Roles for AKT Isoform Preference in Cancer Progression Pathways

The phosphoinositol-3 kinase (PI3K)-AKT pathway is one of the most mutated in human cancers, predominantly associated with the loss of the signaling antagonist, PTEN, and to lesser extents, with gain-of-function mutations in PIK3CA (encoding PI3K-p110α) and AKT1. In addition, most oncogenic driver pathways activate PI3K/AKT signaling. Nonetheless, drugs targeting PI3K or AKT have fared poorly against solid tumors in clinical trials as monotherapies, yet some have shown efficacy when combined with inhibitors of other oncogenic drivers, such as receptor tyrosine kinases or nuclear hormone receptors. There is growing evidence that AKT isoforms, AKT1, AKT2, and AKT3, have different, often distinct roles in either promoting or suppressing specific parameters of oncogenic progression, yet few if any isoform-preferred substrates have been characterized. This review will describe recent data showing that the differential activation of AKT isoforms is mediated by complex interplays between PTEN, PI3K isoforms and upstream tyrosine kinases, and that the efficacy of PI3K/AKT inhibitors will likely depend on the successful targeting of specific AKT isoforms and their preferred pathways.

Role of AMPK and Akt in triple negative breast cancer lung colonization

Triple negative breast cancer (TNBC) is an aggressive disease with a 5-y relative survival rate of 11% after distant metastasis. To survive the metastatic cascade, tumor cells remodel their signaling pathways by regulating energy production and upregulating survival pathways. AMP-activated protein kinase (AMPK) and Akt regulate energy homeostasis and survival, however, the individual or synergistic role of AMPK and Akt isoforms during lung colonization by TNBC cells is unknown. The purpose of this study was to establish whether targeting Akt, AMPKα or both Akt and AMPKα isoforms in circulating cancer cells can suppress TNBC lung colonization. Transient silencing of Akt1 or Akt2 dramatically decreased metastatic colonization of lungs by inducing apoptosis or inhibiting invasion, respectively. Importantly, transient pharmacologic inhibition of Akt activity with MK-2206 or AZD5363 inhibitors did not prevent colonization of lung tissue by TNBC cells. Knockdown of AMPKα1, AMPKα2, or AMPKα1/2 also had no effect on metastatic colonization of lungs. Taken together, these findings demonstrate that transient decrease in AMPK isoforms expression alone or in combination with Akt1 in circulating tumor cells does not synergistically reduce TNBC metastatic lung colonization. Our results also provide evidence that Akt1 and Akt2 expression serve as a bottleneck that can challenge colonization of lungs by TNBC cells.

Targeting ganglioneuromas with mTOR inhibitors

We recently identified activated protein kinase B (PKB/AKT) as a tumorigenic driver in childhood ganglioneuroma. Inhibition of the mechanistic target of rapamycin (mTOR), a serine/threonine kinase downstream of AKT, effectively reduced the tumor burden in zebrafish with ganglioneuroma. We propose a clinical trial of mTOR inhibitors as a means to shrink large ganglioneuromas prior to surgical resection.

Integrative analysis of histopathological images and chromatin accessibility data for estrogen receptor-positive breast cancer

BACKGROUND

Existing studies have demonstrated that the integrative analysis of histopathological images and genomic data can be used to better understand the onset and progression of many diseases, as well as identify new diagnostic and prognostic biomarkers. However, since the development of pathological phenotypes are influenced by a variety of complex biological processes, complete understanding of the underlying gene regulatory mechanisms for the cell and tissue morphology is still a challenge. In this study, we explored the relationship between the chromatin accessibility changes and the epithelial tissue proportion in histopathological images of estrogen receptor (ER) positive breast cancer.

METHODS

An established whole slide image processing pipeline based on deep learning was used to perform global segmentation of epithelial and stromal tissues. We then used canonical correlation analysis to detect the epithelial tissue proportion-associated regulatory regions. By integrating ATAC-seq data with matched RNA-seq data, we found the potential target genes that associated with these regulatory regions. Then we used these genes to perform the following pathway and survival analysis.

RESULTS

Using canonical correlation analysis, we detected 436 potential regulatory regions that exhibited significant correlation between quantitative chromatin accessibility changes and the epithelial tissue proportion in tumors from 54 patients (FDR < 0.05). We then found that these 436 regulatory regions were associated with 74 potential target genes. After functional enrichment analysis, we observed that these potential target genes were enriched in cancer-associated pathways. We further demonstrated that using the gene expression signals and the epithelial tissue proportion extracted from this integration framework could stratify patient prognoses more accurately, outperforming predictions based on only omics or image features.

CONCLUSION

This integrative analysis is a useful strategy for identifying potential regulatory regions in the human genome that are associated with tumor tissue quantification. This study will enable efficient prioritization of genomic regulatory regions identified by ATAC-seq data for further studies to validate their causal regulatory function. Ultimately, identifying epithelial tissue proportion-associated regulatory regions will further our understanding of the underlying molecular mechanisms of disease and inform the development of potential therapeutic targets.

An AKT2-specific nanobody that targets the hydrophobic motif induces cell cycle arrest, autophagy and loss of focal adhesions in MDA-MB-231 cells

The AKT kinase family is a high-profile target for cancer therapy. Despite their high degree of homology the three AKT isoforms (AKT1, AKT2 and AKT3) are non-redundant and can even have opposing functions. Small-molecule AKT inhibitors affect all three isoforms which severely limits their usefulness as research tool or therapeutic. Using AKT2-specific nanobodies we examined the function of endogenous AKT2 in breast cancer cells. Two AKT2 nanobodies (Nb8 and Nb9) modulate AKT2 and reduce MDA-MB-231 cell viability/proliferation. Nb8 binds the AKT2 hydrophobic motif and reduces IGF-1-induced phosphorylation of this site. This nanobody also affects the phosphorylation and/or expression levels of a wide range of proteins downstream of AKT, resulting in a G0/G1 cell cycle arrest, the induction of autophagy, a reduction in focal adhesion count and loss of stress fibers. While cell cycle progression is likely to be regulated by more than one isoform, our results indicate that both the effects on autophagy and the cytoskeleton are specific to AKT2. By using an isoform-specific nanobody we were able to map a part of the AKT2 pathway. Our results confirm AKT2 and the hydrophobic motif as targets for cancer therapy. Nb8 can be used as a research tool to study AKT2 signalling events and aid in the design of an AKT2-specific inhibitor.

PTEN and Other PtdIns(3,4,5)P3 Lipid Phosphatases in Breast Cancer

The phosphoinositide 3-kinase (PI3K)/AKT signalling pathway is hyperactivated in ~70% of breast cancers. Class I PI3K generates PtdIns(3,4,5)P₃ at the plasma membrane in response to growth factor stimulation, leading to AKT activation to drive cell proliferation, survival and migration. PTEN negatively regulates PI3K/AKT signalling by dephosphorylating PtdIns(3,4,5)P₃ to form PtdIns(4,5)P₂. PtdIns(3,4,5)P₃ can also be hydrolysed by the inositol polyphosphate 5-phosphatases (5-phosphatases) to produce PtdIns(3,4)P₂. Interestingly, while PTEN is a bona fide tumour suppressor and is frequently mutated/lost in breast cancer, 5-phosphatases such as PIPP, SHIP2 and SYNJ2, have demonstrated more diverse roles in regulating mammary tumourigenesis. Reduced PIPP expression is associated with triple negative breast cancers and reduced relapse-free and overall survival. Although PIPP depletion enhances AKT phosphorylation and supports tumour growth, this also inhibits cell migration and metastasis in vivo, in a breast cancer oncogene-driven murine model. Paradoxically, SHIP2 and SYNJ2 are increased in primary breast tumours, which correlates with invasive disease and reduced survival. SHIP2 or SYNJ2 overexpression promotes breast tumourigenesis via AKT-dependent and independent mechanisms. This review will discuss how PTEN, PIPP, SHIP2 and SYNJ2 distinctly regulate multiple functional targets, and the mechanisms by which dysregulation of these distinct phosphoinositide phosphatases differentially affect breast cancer progression.

Isoform- and Paralog-Switching in IR-Signaling: When Diabetes Opens the Gates to Cancer

Insulin receptor (IR) and IR-related signaling defects have been shown to trigger insulin-resistance in insulin-dependent cells and ultimately to give rise to type 2 diabetes in mammalian organisms. IR expression is ubiquitous in mammalian tissues, and its over-expression is also a common finding in cancerous cells. This latter finding has been shown to associate with both a relative and absolute increase in IR isoform-A (IR-A) expression, missing 12 aa in its EC subunit corresponding to exon 11. Since IR-A is a high-affinity transducer of Insulin-like Growth Factor-II (IGF-II) signals, a growth factor is often secreted by cancer cells; such event offers a direct molecular link between IR-A/IR-B increased ratio in insulin resistance states (obesity and type 2 diabetes) and the malignant advantage provided by IGF-II to solid tumors. Nonetheless, recent findings on the biological role of isoforms for cellular signaling components suggest that the preferential expression of IR isoform-A may be part of a wider contextual isoform-expression switch in downstream regulatory factors, potentially enhancing IR-dependent oncogenic effects. The present review focuses on the role of isoform- and paralog-dependent variability in the IR and downstream cellular components playing a potential role in the modulation of the IR-A signaling related to the changes induced by insulin-resistance-linked conditions as well as to their relationship with the benign versus malignant transition in underlying solid tumors.

AKT isoforms have discrete expression in triple negative breast cancers and roles in cisplatin sensitivity

AKT, a serine threonine kinase, exists in three different isoforms and is known for regulating several biological processes including tumorigenesis. In this study, we investigated the expression and net effect of the individual isoforms in triple negative breast cancers and response to cisplatin treatment using cellular, mice models and clinical samples. Interestingly, analysis of the expressions of AKT isoforms in clinical samples showed relatively higher expression of AKT1 in primary tissues; whereas lung and liver metastatic samples showed elevated expression of AKT2. Similarly, triple-negative breast cancer cell lines, BT-549 and MDA-MB-231, with high proliferative and invasive properties, displayed higher expression levels of AKT1/2. By modulating AKT isoform expression in MCF-10A and BT-549 cell lines, we found that presence of AKT2 was associated with invasiveness, stemness and sensitivity to drug treatment. It was observed that the silencing of AKT2 suppressed the cancer stem cell populations (CD44^high CD24^low, ALDH1), mammosphere formation, invasive and migratory potential in MCF-10A and BT-549 cells. It was further demonstrated that loss of function of AKT1 isoform is associated with reduced sensitivity towards cisplatin treatment in triple-negative breast cancers cellular and syngeneic mice models. The decrease in cisplatin treatment response in shAKT1 cells was allied with the upregulation in the expression of transporter protein ABCG2, whereas silencing of ABCG2 restored cisplatin sensitivity in these cells through AKT/SNAIL/ABCG2 axis. In conclusion, our study demonstrated the varied expression of AKT isoforms in triple-negative breast cancers and also confirmed differential role of isoforms in stemness, invasiveness and response towards the cisplatin treatment.

Akt isoform-specific effects on thyroid cancer development and progression in a murine thyroid cancer model

The Akt family is comprised of three unique homologous proteins with isoform-specific effects, but isoform-specific in vivo data are limited in follicular thyroid cancer (FTC), a PI3 kinase-driven tumor. Prior studies demonstrated that PI3K/Akt signaling is important in thyroid hormone receptor βPV/PV knock-in (PV) mice that develop metastatic thyroid cancer that most closely resembles FTC. To determine the roles of Akt isoforms in this model we crossed Akt1-/-, Akt2-/-, and Akt3-/- mice with PV mice. Over 12 months, thyroid size was reduced for the Akt null crosses (p < 0.001). Thyroid cancer development and local invasion were delayed in only the PVPV-Akt1 knock out (KO) mice in association with increased apoptosis with no change in proliferation. Primary-cultured PVPV-Akt1KO thyrocytes uniquely displayed a reduced cell motility. In contrast, loss of any Akt isoform reduced lung metastasis while vascular invasion was reduced with Akt1 or 3 loss. Microarray of thyroid RNA displayed incomplete overlap between the Akt KO models. The most upregulated gene was the dendritic cell (DC) marker CD209a only in PVPV-Akt1KO thyroids. Immunohistochemistry demonstrated an increase in CD209a-expressing cells in the PVPV-Akt1KO thyroids. In summary, Akt isoforms exhibit common and differential functions that regulate local and metastatic progression in this model of thyroid cancer.

RAGE Up-Regulation Differently Affects Cell Proliferation and Migration in Pancreatic Cancer Cells

The receptor for advanced glycation end products (RAGE) contributes to many cellular aspects of pancreatic cancer including cell proliferation, migration, and survival. Studies have shown that RAGE activation by its ligands promotes pancreatic tumor growth by stimulating both cell proliferation and migration. In this study, we investigated the effect of RAGE up-regulation on the proliferation and migration of the human pancreatic cancer Panc-1 cell-line. We show that moderate overexpression of RAGE in Panc-1 cells results in increased cell proliferation, but decreased cell migration. The observed cellular changes were confirmed to be RAGE-specific and reversible by using RAGE-specific siRNAs and the small molecule RAGE inhibitor FPS-ZM1. At the molecular level, we show that RAGE up-regulation was associated with decreased activity of FAK, Akt, Erk1/2, and NF-κB signaling pathways and greatly reduced levels of α2 and β1 integrin expression, which is in agreement with the observed decreases in cell migration. We also demonstrate that RAGE up-regulation changes the expression of key molecular markers of epithelial-to-mesenchymal transition (EMT). Our results suggest that in the absence of stimulation by external ligands, RAGE up-regulation can differently modulate cell proliferation and migration in pancreatic cancer cells and regulates partly EMT.

Specific Akt Family Members Impair Stress-Mediated Transactivation of Viral Promoters and Enhance Neuronal Differentiation: Important Functions for Maintaining Latency

Neurotropic Alphaherpesvirinae subfamily members such as bovine herpesvirus 1 (BoHV-1) and herpes simplex virus 1 (HSV-1) establish and maintain lifelong latent infections in neurons. Following infection of ocular, oral, or nasal cavities, sensory neurons within trigeminal ganglia (TG) are an important site for latency. Certain external stressors can trigger reactivation from latency, in part because activation of the glucocorticoid receptor (GR) stimulates productive infection and promoters that drive expression of key viral transcriptional regulators. The Akt serine/threonine protein kinase family is linked to maintaining latency. For example, Akt3 is detected in more TG neurons during BoHV-1 latency than in reactivation and uninfected calves. Furthermore, Akt signaling correlates with maintaining HSV-1 latency in certain neuronal models of latency. Finally, an active Akt protein kinase is crucial for the ability of the HSV-1 latency-associated transcript (LAT) to inhibit apoptosis in neuronal cell lines. Consequently, we hypothesized that viral and/or cellular factors impair stress-induced transcription and reduce the incidence of reactivation triggered by low levels of stress. New studies demonstrate that Akt1 and Akt2, but not Akt3, significantly reduced GR-mediated transactivation of the BoHV-1 immediate early transcription unit 1 (IEtu1) promoter, the HSV-1 infected cell protein 0 (ICP0) promoter, and the mouse mammary tumor virus long terminal repeat (MMTV-LTR). Akt3, but not Akt1 or Akt2, significantly enhanced neurite formation in mouse neuroblastoma cells, which correlates with repairing damaged neurons. These studies suggest that unique biological properties of the three Akt family members promote the maintenance of latency in differentiated neurons.IMPORTANCE External stressful stimuli are known to increase the incidence of reactivation of Alphaherpesvirinae subfamily members. Activation of the glucocorticoid receptor (GR) by the synthetic corticosteroid dexamethasone (DEX) stimulates bovine herpesvirus 1 (BoHV-1) and herpes simplex virus 1 (HSV-1) reactivation. Furthermore, GR and dexamethasone stimulate productive infection and promoters that drive expression of viral transcriptional regulators. These observations lead us to predict that stress-induced transcription is impaired by factors abundantly expressed during latency. Interestingly, activation of the Akt family of serine/threonine protein kinases is linked to maintenance of latency. New studies reveal that Akt1 and Ak2, but not Akt3, impaired GR- and dexamethasone-mediated transactivation of the BoHV-1 immediate early transcription unit 1 and HSV-1 ICP0 promoters. Strikingly, Akt3, but not Akt1 or Akt2, stimulated neurite formation in mouse neuroblastoma cells, a requirement for neurogenesis. These studies provide insight into how Akt family members may promote the maintenance of lifelong latency.

Development and characterization of protein kinase B/AKT isoform-specific nanobodies

The serine/threonine protein kinase AKT is frequently over-activated in cancer and is associated with poor prognosis. As a central node in the PI3K/AKT/mTOR pathway, which regulates various processes considered to be hallmarks of cancer, this kinase has become a prime target for cancer therapy. However, AKT has proven to be a highly complex target as it comes in three isoforms (AKT1, AKT2 and AKT3) which are highly homologous, yet non-redundant. The isoform-specific functions of the AKT kinases can be dependent on context (i.e. different types of cancer) and even opposed to one another. To date, there is no isoform-specific inhibitor available and no alternative to genetic approaches to study the function of a single AKT isoform. We have developed and characterized nanobodies that specifically interact with the AKT1 or AKT2 isoforms. These new tools should enable future studies of AKT1 and AKT2 isoform-specific functions. Furthermore, for both isoforms we obtained a nanobody that interferes with the AKT-PIP3-interaction, an essential step in the activation of the kinase. The nanobodies characterized in this study are a new stepping stone towards unravelling AKT isoform-specific signalling.

Vav1 Down-Modulates Akt2 Expression in Cells from Pancreatic Ductal Adenocarcinoma: Nuclear Vav1 as a Potential Regulator of Akt Related Malignancy in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is the most aggressive tumor malignancy worldwide, mainly due to uncontrolled metastasis. Among the numerous molecules deregulated in PDAC, different members of the Akt pathways are of great importance because they are involved in tumor cell proliferation, migration, and invasion. We have recently demonstrated that Vav1, ectopically expressed in solid tumors, is capable of down-modulating expression and/or activation of specific Akt isoforms in breast cancer cells. By using pancreatic cell lines expressing different basal levels of Vav1, we demonstrated here that Vav1 down-regulates the expression of Akt2, known to correlate with tumor metastases and resistance to therapy. In particular, while the silencing of Vav1 is sufficient to induce Akt2, its up-modulation reduces Akt2 levels only when Vav1 accumulates inside the nucleus of PDAC cells. Moreover, in PDAC tissues, we revealed that high nuclear levels of Vav1 correlate with low Akt2 expression. Although we cannot demonstrate the mechanisms involved, our results provide new insights into the role of Vav1 in PDAC and, as targeting specific members of the Akt family is a promising therapeutic chance in solid tumors, they suggest that Vav1, by down-modulating Akt2, has potential as a molecular target in PDAC.

Cell-Autonomous versus Systemic Akt Isoform Deletions Uncovered New Roles for Akt1 and Akt2 in Breast Cancer

Studies in three mouse models of breast cancer identified profound discrepancies between cell-autonomous and systemic Akt1- or Akt2-inducible deletion on breast cancer tumorigenesis and metastasis. Although systemic Akt1 deletion inhibits metastasis, cell-autonomous Akt1 deletion does not. Single-cell mRNA sequencing revealed that systemic Akt1 deletion maintains the pro-metastatic cluster within primary tumors but ablates pro-metastatic neutrophils. Systemic Akt1 deletion inhibits metastasis by impairing survival and mobilization of tumor-associated neutrophils. Importantly, either systemic or neutrophil-specific Akt1 deletion is sufficient to inhibit metastasis of Akt-proficient tumors. Thus, Akt1-specific inhibition could be therapeutic for breast cancer metastasis regardless of primary tumor origin. Systemic Akt2 deletion does not inhibit and exacerbates mammary tumorigenesis and metastasis, but cell-autonomous Akt2 deletion prevents breast cancer tumorigenesis by ErbB2. Elevated circulating insulin level induced by Akt2 systemic deletion hyperactivates tumor Akt, exacerbating ErbB2-mediated tumorigenesis, curbed by pharmacological reduction of the elevated insulin.

In vivo modeling of the EGFR family in breast cancer progression and therapeutic approaches

Modeling breast cancer through the generation of genetically engineered mouse models (GEMMs) has become the gold standard in the study of human breast cancer. Notably, the in vivo modeling of the epidermal growth factor receptor (EGFR) family has been key to the development of therapeutics and has helped better understand the signaling pathways involved in cancer initiation, progression and metastasis. The HER2/ErbB2 receptor is a member of the EGFR family and 20% of breast cancers are found to belong in the HER2-positive histological subtype. Historical and more recent advances in the field have shaped our understanding of HER2-positive breast cancer signaling and therapeutic approaches.

Loss of the Ste20-like kinase induces a basal/stem-like phenotype in HER2-positive breast cancers

HER2 is overexpressed in 20-30% of all breast cancers and is associated with an invasive disease and poor clinical outcome. The Ste20-like kinase (SLK) is activated downstream of HER2/Neu and is required for efficient epithelial-to-mesenchymal transition, cell cycle progression, and migration in the mammary epithelium. Here we show that loss of SLK in a murine model of HER2/Neu-positive breast cancers significantly accelerates tumor onset and decreases overall survival. Transcriptional profiling of SLK knockout HER2/Neu-derived tumor cells revealed a strong induction in the triple-negative breast cancer marker, Sox10, accompanied by an increase in mammary stem/progenitor activity. Similarly, we demonstrate that SLK and Sox10 expression are inversely correlated in patient samples, with the loss of SLK and acquisition of Sox10 marking the triple-negative subtype. Furthermore, pharmacological inhibition of AKT reduces SLK-null tumor growth in vivo and is rescued by ectopic Sox10 expression, suggesting that Sox10 is a critical regulator of tumor growth downstream of SLK/AKT. These findings highlight a role for SLK in negatively regulating HER2-induced mammary tumorigenesis and provide mechanistic insight into the regulation of Sox10 expression in breast cancer.

Targeting Functional Activity of AKT Has Efficacy against Aggressive Neuroblastoma

MYCN-amplified neuroblastoma is one of the deadliest forms of childhood cancer and remains a significant clinical challenge. Direct pharmacological inhibition of MYCN is not currently achievable. One strategy could be to target the AKT/GSK3β pathway, which directly regulates the stability of the MYCN protein. Numerous potent and isoform-specific small-molecule AKT inhibitors have been developed. However, the selection of the right drug combinations in the relevant indication will have a significant impact on AKT inhibitor clinical success. To maximally exploit the potential of AKT inhibitors, a better understanding of AKT isoform functions in cancer is crucial. Here using RNAi to downregulate specific AKT isoforms, we demonstrated that loss of total AKT activity rather than isoform-specific expression was necessary to decrease MYCN expression and cause a significant decrease in neuroblastoma cell proliferation. Consistent with these observations, isoform-specific pharmacological inhibition of AKT was substantially less effective than pan-AKT inhibition in combination with cytotoxic drugs in MYCN-amplified neuroblastoma. The allosteric pan-AKT inhibitor perifosine had promising in vitro and in vivo activity in combination with conventional cytotoxic drugs in MYCN-amplified neuroblastoma cells. Our results demonstrated that perifosine drug combination was able to induce apoptosis and downregulate ABC transporter expression. Collectively, this study shows that selecting pan-AKT inhibitors rather than isoform-specific drugs to synergize with first-line chemotherapy treatment should be considered for clinical trials for aggressive neuroblastoma and, potentially, other MYCN -driven cancers.

Phosphoproteomic analysis reveals Akt isoform-specific regulation of cytoskeleton proteins in human temporal lobe epilepsy with hippocampal sclerosis

Akt is one of the most important downstream effectors of phosphatidylinositol 3-kinase/mTOR pathway. Hyperactivation and expression of this pathway are seen in a variety of neurological disorders including human temporal lobe epilepsy with hippocampal sclerosis (TLE-HS). Nevertheless, the expression and activation profiles of the Akt isoforms, Akt1, Akt2, and Akt3 and their functional roles in human TLE-HS have not been studied. We examined the protein expression and activation (phosphorylation) patterns of Akt and its isoforms in human hippocampal tissue from TLE and non-TLE patients. A phosphoproteomic approach followed by interactome analysis of each Akt isoform was used to understand protein-protein interactions and their role in TLE-HS pathology. Our results demonstrated activation of the Akt/mTOR pathway as well as activation of Akt downstream substrates like GSK3β, mTOR, and S6 in TLE-HS samples. Akt1 isoform levels were significantly increased in the TLE-HS samples as compared to the non-TLE samples. Most importantly, different isoforms were activated in different TLE-HS samples, Akt2 was activated in three samples, Akt2 and Akt1 were simultaneously activated in one sample and Akt3 was activated in two samples. Our phosphoproteomic screen across six TLE-HS samples identified 183 proteins phosphorylated by Akt isoforms, 29 of these proteins belong to cytoskeletal modification. Also, we were able to identify proteins of several other classes involved in glycolysis, neuronal development, protein folding and excitatory amino acid transport functions as Akt substrates. Taken together, our data offer clues to understand the role of Akt and its isoforms in underlying the pathology of TLE-HS and further, modulation of Akt/mTOR pathway using Akt isoforms specific inhibitors may offer a new therapeutic window for treatment of human TLE-HS.

Distinct functions of AKT isoforms in breast cancer: a comprehensive review

BACKGROUND

AKT, also known as protein kinase B, is a key element of the PI3K/AKT signaling pathway. Moreover, AKT regulates the hallmarks of cancer, e.g. tumor growth, survival and invasiveness of tumor cells. After AKT was discovered in the early 1990s, further studies revealed that there are three different AKT isoforms, namely AKT1, AKT2 and AKT3. Despite their high similarity of 80%, the distinct AKT isoforms exert non-redundant, partly even opposing effects under physiological and pathological conditions. Breast cancer as the most common cancer entity in women, frequently shows alterations of the PI3K/AKT signaling.

MAIN CONTENT

A plethora of studies addressed the impact of AKT isoforms on tumor growth, metastasis and angiogenesis of breast cancer as well as on therapy response and overall survival in patients. Therefore, this review aimed to give a comprehensive overview about the isoform-specific effects of AKT in breast cancer and to summarize known downstream and upstream mechanisms. Taking account of conflicting findings among the studies, the majority of the studies reported a tumor initiating role of AKT1, whereas AKT2 is mainly responsible for tumor progression and metastasis. In detail, AKT1 increases cell proliferation through cell cycle proteins like p21, p27 and cyclin D1 and impairs apoptosis e.g. via p53. On the downside AKT1 decreases migration of breast cancer cells, for instance by regulating TSC2, palladin and EMT-proteins. However, AKT2 promotes migration and invasion most notably through regulation of β-integrins, EMT-proteins and F-actin. Whilst AKT3 is associated with a negative ER-status, findings about the role of AKT3 in regulation of the key properties of breast cancer are sparse. Accordingly, AKT1 is mutated and AKT2 is amplified in some cases of breast cancer and AKT isoforms are associated with overall survival and therapy response in an isoform-specific manner.

CONCLUSIONS

Although there are several discussed hypotheses how isoform specificity is achieved, the mechanisms behind the isoform-specific effects remain mostly unrevealed. As a consequence, further effort is necessary to achieve deeper insights into an isoform-specific AKT signaling in breast cancer and the mechanism behind it.

Long non-coding RNA LINC00460 promotes head and neck squamous cell carcinoma cell progression by sponging miR-612 to up-regulate AKT2

LncRNAs (long noncoding RNAs) have been shown to be potentially critical regulators in head and neck squamous cell carcinoma (HNSCC). LncRNA LINC00460 (long intergenic non-protein coding RNA 460), an "oncogene", regulates progression of various tumors. However, the tumorigenic mechanism of LINC00460 on HNSCC is yet to be investigated. In the current study, we discovered that LINC00460 was relatively up-regulated in both HNSCC cancer tissues and cell lines, and predicted a poor prognosis in HNSCC patients. Gain- and loss-of functional studies established that over-expression of LINC00460 promoted cell proliferation, invasion and migration of HNSCC cells in vitro, while the promotion abilities were suppressed via knockdown of LINC00460. Our results identified miR-612 as a novel target of LINC00460, whose expression suggested a negative correlation with LINC00460 in HNSCC tissues and cell lines. LINC00460 increased the expression of serine/threonine kinase AKT2 via sponging miR-612. Rescue experiments indicated that LINC00460 could promote HNSCC progression partially through inhibition of miR-612. Subcutaneous xenotransplanted tumor model confirmed that interference of LINC00460 suppressed in vivo tumorigenic ability of HNSCC via down-regulation of AKT2. In conclusion, our findings clarified the biologic significance of LINC00460/miR-612/AKT2 axis in HNSCC progression and provided novel evidence that LINC00460 may be a new potential therapeutic target for HNSCC.

The unconventional role of Akt1 in the advanced cancers and in diabetes-promoted carcinogenesis

Decades of research have elucidated the critical role of Akt isoforms in cancer as pro-tumorigenic and metastatic regulators through their specific effects on the cancer cells, tumor endothelial cells and the stromal cells. The pro-cancerous role of Akt isoforms through enhanced cell proliferation and suppression of apoptosis in cancer cells and the cells in the tumor microenvironment is considered a dogma. Intriguingly, studies also indicate that the Akt pathway is essential to protect the endothelial-barrier and prevent aberrant vascular permeability, which is also integral to tumor perfusion and metastasis. To complicate this further, a flurry of recent reports strongly indicates the metastasis suppressive role of Akt, Akt1 in particular in various cancer types. These reports emanated from different laboratories have elegantly demonstrated the paradoxical effect of Akt1 on cancer cell epithelial-to-mesenchymal transition, invasion, tumor endothelial-barrier disruption, and cancer metastasis. Here, we emphasize on the specific role of Akt1 in mediating tumor cell-vasculature reciprocity during the advanced stages of cancers and discuss how Akt1 differentially regulates cancer metastasis through mechanisms distinct from its pro-tumorigenic effects. Since Akt is integral for insulin signaling, endothelial function, and metabolic regulation, we also attempt to shed some light on the specific effects of diabetes in modulating Akt pathway in the promotion of tumor growth and metastasis.

Oncogenic Roles of the PI3K/AKT/mTOR Axis

The PI3K/AKT/mTOR pathway is frequently activated in various human cancers and has been considered a promising therapeutic target. Many of the positive regulators of the PI3K/AKT/mTOR axis, including the catalytic (p110α) and regulatory (p85α), of class IA PI3K, AKT, RHEB, mTOR, and eIF4E, possess oncogenic potentials, as demonstrated by transformation assays in vitro and by genetically engineered mouse models in vivo. Genetic evidences also indicate their roles in malignancies induced by activation of the upstream oncoproteins including receptor tyrosine kinases and RAS and those induced by the loss of the negative regulators of the PI3K/AKT/mTOR pathway such as PTEN, TSC1/2, LKB1, and PIPP. Possible mechanisms by which the PI3K/AKT/mTOR axis contributes to oncogenic transformation include stimulation of proliferation, survival, metabolic reprogramming, and invasion/metastasis, as well as suppression of autophagy and senescence. These phenotypic changes are mediated by eIF4E-induced translation of a subset of mRNAs and by other downstream effectors of mTORC1 including S6K, HIF-1α, PGC-1α, SREBP, and ULK1 complex.

Nodal pathway activation due to Akt1 suppression is a molecular switch for prostate cancer cell epithelial-to-mesenchymal transition and metastasis

Several studies have unraveled the negative role of Akt1 in advanced cancers, including metastatic prostate cancer (mPCa). Hence, understanding the consequences of targeting Akt1 in the mPCa and identifying its downstream novel targets is essential. We studied how Akt1 deletion in PC3 and DU145 cells activates the Nodal pathway and promotes PCa epithelial-to-mesenchymal transition (EMT) and metastasis. Here we show that Akt1 loss increases Nodal expression in PCa cells accompanied by activation of FoxO1/3a, and EMT markers Snail and N-cadherin as well as loss of epithelial marker E-cadherin. Treatment with FoxO inhibitor AS1842856 abrogated the Nodal expression in Akt1 deleted PCa cells. Akt1 deficient PCa cells exhibited enhanced cell migration and invasion in vitro and lung metastasis in vivo, which were attenuated by treatment with Nodal pathway inhibitor SB505124. Interestingly, Nodal mRNA analysis from two genomic studies in cBioportal showed a positive correlation between Nodal expression and Gleason score indicating the positive role of Nodal in human mPCa. Collectively, our data demonstrate Akt1-FoxO3a-Nodal pathway as an important mediator of PCa metastasis and present Nodal as a potential target to treat mPCa patients.

Akt Signaling in Macrophage Polarization, Survival, and Atherosclerosis

The PI3K/Akt pathway plays a crucial role in the survival, proliferation, and migration of macrophages, which may impact the development of atherosclerosis. Changes in Akt isoforms or modulation of the Akt activity levels in macrophages significantly affect their polarization phenotype and consequently atherosclerosis in mice. Moreover, the activity levels of Akt signaling determine the viability of monocytes/macrophages and their resistance to pro-apoptotic stimuli in atherosclerotic lesions. Therefore, elimination of pro-apoptotic factors as well as factors that antagonize or suppress Akt signaling in macrophages increases cell viability, protecting them from apoptosis, and this markedly accelerates atherosclerosis in mice. In contrast, inhibition of Akt signaling by the ablation of Rictor in myeloid cells, which disrupts mTORC2 assembly, significantly decreases the viability and proliferation of blood monocytes and macrophages with the suppression of atherosclerosis. In addition, monocytes and macrophages exhibit a threshold effect for Akt protein levels in their ability to survive. Ablation of two Akt isoforms, preserving only a single Akt isoform in myeloid cells, markedly compromises monocyte and macrophage viability, inducing monocytopenia and diminishing early atherosclerosis. These recent advances in our understanding of Akt signaling in macrophages in atherosclerosis may have significant relevance in the burgeoning field of cardio-oncology, where PI3K/Akt inhibitors being tested in cancer patients can have significant cardiovascular and metabolic ramifications.