Distinct functional roles of Akt isoforms for proliferation, survival, migration and EGF-mediated signalling in lung cancer derived disseminated tumor cells

K-Ras(V12) differentially affects the three Akt isoforms in lung and pancreatic carcinoma cells and upregulates E-cadherin and NCAM via Akt3

K-Ras is the most frequently mutated Ras variant in pancreatic, colon and non-small cell lung adenocarcinoma. Activating mutations in K-Ras result in increased amounts of active Ras-GTP and subsequently a hyperactivation of effector proteins and downstream signaling pathways. Here, we demonstrate that oncogenic K-Ras(V12) regulates tumor cell migration by activating the phosphatidylinositol 3-kinases (PI3-K)/Akt pathway and induces the expression of E-cadherin and neural cell adhesion molecule (NCAM) by upregulation of Akt3. In vitro interaction and co-precipitation assays identified PI3-Kα as a bona fide effector of active K-Ras4B but not of H-Ras or N-Ras, resulting in enhanced Akt phosphorylation. Moreover, K-Ras(V12)-induced PI3-K/Akt activation enhanced migration in all analyzed cell lines. Interestingly, Western blot analyses with Akt isoform-specific antibodies as well as qPCR studies revealed, that the amount and the activity of Akt3 was markedly increased whereas the amount of Akt1 and Akt2 was downregulated in EGFP-K-Ras(V12)-expressing cell clones. To investigate the functional role of each Akt isoform and a possible crosstalk of the isoforms in more detail, each isoform was stably depleted in PANC-1 pancreatic and H23 lung carcinoma cells. Akt3, the least expressed Akt isoform in most cell lines, is especially upregulated and active in Akt2-depleted cells. Since expression of EGFP-K-Ras(V12) reduced E-cadherin-mediated cell-cell adhesion by induction of polysialylated NCAM, Akt3 was analyzed as regulator of E-cadherin and NCAM. Western blot analyses revealed pronounced reduction of E-cadherin and NCAM in the Akt3-kd cells, whereas Akt1 and Akt2 depletion upregulated E-cadherin, especially in H23 lung carcinoma cells. In summary, we identified oncogenic K-Ras4B as a key regulator of PI3-Kα-Akt signaling and Akt3 as a crucial regulator of K-Ras4B-induced modulation of E-cadherin and NCAM expression and localization.

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.

The Multifunctional Nature of the MicroRNA/AKT3 Regulatory Axis in Human Cancers

Serine/threonine kinase (AKT) signaling regulates diverse cellular processes and is one of the most important aberrant cell survival mechanisms associated with tumorigenesis, metastasis, and chemoresistance. Targeting AKT has become an effective therapeutic strategy for the treatment of many cancers. AKT3 (PKBγ), the least studied isoform of the AKT family, has emerged as a major contributor to malignancy. AKT3 is frequently overexpressed in human cancers, and many regulatory oncogenic or tumor suppressor small non-coding RNAs (ncRNAs), including microRNAs (miRNAs), have recently been identified to be involved in regulating AKT3 expression. Therefore, a better understanding of regulatory miRNA/AKT3 networks may reveal novel biomarkers for the diagnosis of patients with cancer and may provide invaluable information for developing more effective therapeutic strategies. The aim of this review was to summarize current research progress in the isoform-specific functions of AKT3 in human cancers and the roles of dysregulated miRNA/AKT3 in specific types of human cancers.

Tumor cell integrin β4 and tumor stroma E-/P-selectin cooperatively regulate tumor growth in vivo

BACKGROUND

The immunological composition of the tumor microenvironment has a decisive influence on the biological course of cancer and is therefore of profound clinical relevance. In this study, we analyzed the cooperative effects of integrin β4 (ITGB4) on tumor cells and E-/P-selectin on endothelial cells within the tumor stroma for regulating tumor growth by shaping the local and systemic immune environment.

METHODS

We used several preclinical mouse models for different solid human cancer types (xenograft and syngeneic) to explore the role of ITGB4 (shRNA-mediated knockdown in tumor cells) and E-/P-selectins (knockout in mice) for tumor growth; effects on apoptosis, proliferation and intratumoral signaling pathways were determined by histological and biochemical methods and 3D in vitro experiments; changes in the intratumoral and systemic immune cell composition were determined by flow cytometry and immunohistochemistry; chemokine levels and their attracting potential were measured by ELISA and 3D invasion assays.

RESULTS

We observed a very robust synergism between ITGB4 and E-/P-selectin for the regulation of tumor growth, accompanied by an increased recruitment of CD11b⁺ Gr-1^Hi cells with low granularity (i.e., myeloid-derived suppressor cells, MDSCs) specifically into ITGB4-depleted tumors. ITGB4-depleted tumors undergo apoptosis and actively attract MDSCs, well-known to promote tumor growth in several cancers, via increased secretion of different chemokines. MDSC trafficking into tumors crucially depends on E-/P-selectin expression. Analyses of clinical samples confirmed an inverse relationship between ITGB4 expression in tumors and number of tumor-infiltrating leukocytes.

CONCLUSIONS

These findings suggest a distinct vulnerability of ITGB4^Lo tumors for MDSC-directed immunotherapies.

miR-126 regulates the proliferation, migration, invasion, and apoptosis of non-small lung cancer cells via AKT2/HK2 axis

This study tended to clarify the role of miR-126 in non-small cell lung cancer (NSCLC) cell biological behaviors in vitro, containing cell proliferation, migration, invasion, and apoptosis. miRNA expression microarray related to NSCLC was accessed from gene expression omnibus (GEO) database and subjected to differential analysis using the "limma" package. Real-time quantitative PCR was conducted to assess the expression of miR-126 in NSCLC cell lines. wIn vitro experiments including 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide (MTT), wound healing assay, Transwell, and flow cytometry assay were used for evaluating the effect of miR-126 on cell proliferation, migration, invasion, and apoptosis. Additionally, target mRNA for miR-126 was predicted and further validated by bioinformatics analysis and dual-luciferase reporter assay, respectively. It suggested that miR-126 was significantly down-regulated in NSCLS based on the expression microarray, and similar expression trend was exhibited in cancer cell lines. In the meantime, overexpression of miR-126 was found to result in inhibition of cell proliferation, migration, and invasion while promotion of cell apoptosis, with reductions in protein expression of AKT2 and phosphorylated HK2 (p-HK2) as well. AKT2, identified to be a direct target of miR-126 in NSCLC as judged by dual-luciferase reporter assay. Additionally, overexpression of AKT2 was observed to have the ability of elevating p-HK2 protein expression and reversing the effect of miR-126 on NSCLC cell proliferation, migration, and invasion. Given the above findings, we can see that miR-126 exerts its role in NSCLC cell proliferation, migration, invasion, and apoptosis with the aid of AKT2/HK2 axis.

AKT Isoforms in the Immune Response in Cancer

AKT is a protein kinase that exists in three isoforms: AKT1, AKT2, and AKT3. Though similar in structure, these isoforms display different effects. AKT is activated downstream of PI3K, and together, this signaling pathway helps regulate cellular processes including cell growth, proliferation, metabolism, survival, and apoptosis. Disruption in these pathways has been associated with disorders including cardiovascular diseases, developmental disorders, inflammatory responses, autoimmune diseases, neurologic disorders, type 2 diabetes, and several cancers. In cancer, deregulation in the PI3K/AKT pathway can be manifested as tumorigenesis, pathological angiogenesis, and metastasis. Increased activity has been correlated with tumor progression and resistance to cancer treatments. Recent studies have suggested that inhibition of the PI3K/AKT pathway plays a significant role in the development, expansion, and proliferation of cells of the immune system. Additionally, AKT has been found to play an important role in differentiating regulatory T cells, activating B cells, and augmenting tumor immunosurveillance. This emphasizes AKT as a potential target for inhibition in cancer therapy. This chapter reviews AKT structure and regulation, its different isoforms, its role in immune cells, and its modulation in oncotherapy.

Perifosine, a Bioavailable Alkylphospholipid Akt Inhibitor, Exhibits Antitumor Activity in Murine Models of Cancer Brain Metastasis Through Favorable Tumor Exposure

Metastatic brain tumors are regarded as the most advanced stage of certain types of cancer; however, chemotherapy has played a limited role in the treatment of brain metastases. Here, we established murine models of brain metastasis using cell lines derived from human brain metastatic tumors, and aimed to explore the antitumor efficacy of perifosine, an orally active allosteric Akt inhibitor. We evaluated the effectiveness of perifosine by using it as a single agent in ectopic and orthotopic models created by injecting the DU 145 and NCI-H1915 cell lines into mice. Initially, the injected cells formed distant multifocal lesions in the brains of NCI-H1915 mice, making surgical resection impractical in clinical settings. We determined that perifosine could distribute into the brain and remain localized in that region for a long period. Perifosine significantly prolonged the survival of DU 145 and NCI-H1915 orthotopic brain tumor mice; additionally, complete tumor regression was observed in the NCI-H1915 model. Perifosine also elicited much stronger antitumor responses against subcutaneous NCI-H1915 growth; a similar trend of sensitivity to perifosine was also observed in the orthotopic models. Moreover, the degree of suppression of NCI-H1915 tumor growth was associated with long-term exposure to a high level of perifosine at the tumor site and the resultant blockage of the PI3K/Akt signaling pathway, a decrease in tumor cell proliferation, and increased apoptosis. The results presented here provide a promising approach for the future treatment of patients with metastatic brain cancers and emphasize the importance of enriching a patient population that has a higher probability of responding to perifosine.

Biological and clinical implications of metastasis-associated circular RNAs in oesophageal squamous cell carcinoma

Oesophageal squamous cell carcinoma (OSCC) is a prevalent malignancy with high morbidity and mortality as a result of early metastasis and poor prognosis. Metastasis is a multistep process, involving various signalling pathways. Circular RNAs (circRNAs) are a class of covalently closed noncoding RNAs, the aberrant expression of which is reported to be involved in several biological events, including cell transformation, proliferation, migration, invasion, apoptosis and metastasis. Several studies have reported interactions between circRNAs and metastasis-associated signalling pathways. The abundance, stability and highly specific expression of candidate circRNAs make them potential biomarkers and therapeutic targets in OSCC. In this review article, we comprehensively describe metastasis-related circRNAs and their interactions with epithelial-mesenchymal transition-associated molecules. We also describe the molecular mechanisms and clinical relevance of circRNAs in OSCC progression and metastasis.

Novel approaches to target the microenvironment of bone metastasis

Bone metastases are a frequent and severe complication of advanced-stage cancers. Breast and prostate cancers, the most common malignancies in women and men, respectively, have a particularly high propensity to metastasize to bone. Conceptually, circulating tumour cells (CTCs) in the bloodstream and disseminated tumour cells (DTCs) in the bone marrow provide a snapshot of the dissemination and colonization process en route to clinically apparent bone metastases. Many cell types that constitute the bone microenvironment, including osteoblasts, osteocytes, osteoclasts, adipocytes, endothelial cells, haematopoietic stem cells and immune cells, engage in a dialogue with tumour cells. Some of these cells modify tumour biology, while others are disrupted and out-competed by tumour cells, thus leading to distinct phases of tumour cell migration, dormancy and latency, and therapy resistance and progression to overt bone metastases. Several current bone-protective therapies act by interrupting these interactions, mainly by targeting tumour cell-osteoclast interactions. In this Review, we describe the functional roles of the bone microenvironment and its components in the initiation and propagation of skeletal metastases, outline the biology and clinical relevance of CTCs and DTCs, and discuss established and future therapeutic approaches that specifically target defined components of the bone microenvironment to prevent or treat skeletal metastases.

AKT3 and related molecules as potential biomarkers responsible for cryptorchidism and cryptorchidism-induced azoospermia

BACKGROUND

Cryptorchidism is a common congenital malformation strongly related to future oligospermia and male infertility. Normally functioning early-stage spermatogonia are vital to ensure fertility. The present study aimed to identify new differentially expressed genes (DEGs) associated with signaling pathways related to spermatogonial stem cell (SSC) maintenance during early spermatogenesis.

METHODS

GEO2R was used to screen for genes differentially regulated in cryptorchidism using mRNA expression profiling data in the GEO database. DAVID was used to perform GO and KEGG enrichment analysis of DEGs to analyze their functions. A protein-protein interaction (PPI) network of DEGs was constructed using the STRING database. The hub genes in the PPI networks were identified using Maximal Clique Centrality (MCC) in Cytohubba, and the top 50 genes were displayed as hub genes using Cytoscape software. Then, the miRNAs targeting hub genes were predicted using miRWalk and an mRNA-miRNA interaction network was constructed using Cytoscape. We took the intersection of these target miRNAs and the differentially expressed miRNAs identified from a non-coding RNA sequencing dataset, GSE149084. Furthermore, the intersected miRNAs and their predicted target genes were validated in the testicular tissue of rats with cryptorchidism.

RESULTS

A total of 474 DEGs were identified, most of which were annotated to the PI3K-AKT-mTOR signaling pathway. Hub genes related to the pathway were predicted to be targeted by 27 miRNAs. Further miRNA mining revealed that miRNA-7-5p and miRNA-519d-3p were both dysregulated in cryptorchidism patients. Further, we found that these two miRNAs were predicted with high confidence to share a common target gene, AKT3. In the testicular tissue of rats with cryptorchidism, miRNA-519d-3p was upregulated while miRNA-7-5p and AKT3 were downregulated. We also found that AKT3 plays an essential role in regulating SSC state through the PI3K-AKT-mTOR signaling pathway and that AKT3 is one of the key genes related to SSC self-renewal, proliferation, and differentiation.

CONCLUSIONS

The PI3K-AKT-mTOR signaling pathway functions in SSC maintenance, and alterations in this pathway may explain defects in spermatogenesis. AKT3-related miRNAs, including hsa-miR-7-5p and hsa-miR-519d-3p, might be responsible for cryptorchidism and cryptorchidism-induced azoospermia and serve as potential biomarkers.

Prostate Cancer Dormancy and Reactivation in Bone Marrow

Prostate cancer has a variable clinical course, ranging from curable local disease to lethal metastatic spread. Eradicating metastatic cells is a unique challenge that is rarely met with the available therapies. Thus, targeting prostate cancer cells in earlier disease states is a crucial window of opportunity. Interestingly, cancer cells migrate from their primary site during pre-cancerous and malignant phases to seed secondary organs. These cells, known as disseminated cancer cells (DCCs), may remain dormant for months or decades before activating to form metastases. Bone marrow, a dormancy-permissive site, is the major organ for housed DCCs and eventual metastases in prostate cancer. The dynamic interplay between DCCs and the primary tumor microenvironment (TME), as well as that between DCCs and the secondary organ niche, controls the conversion between states of dormancy and activation. Here, we discuss recent discoveries that have improved our understanding of dormancy signaling and the role of the TME in modulating the epigenetic reprogramming of DCCs. We offer potential strategies to target DCCs in prostate cancer.

Proximal variants in CCND2 associated with microcephaly, short stature, and developmental delay: A case series and review of inverse brain growth phenotypes

Cyclin D2 (CCND2) is a critical cell cycle regulator and key member of the cyclin D2-CDK4 (DC) complex. De novo variants of CCND2 clustering in the distal part of the protein have been identified as pathogenic causes of brain overgrowth (megalencephaly, MEG) and severe cortical malformations in children including the megalencephaly-polymicrogyria-polydactyly-hydrocephalus (MPPH) syndrome. Megalencephaly-associated CCND2 variants are localized to the terminal exon and result in accumulation of degradation-resistant protein. We identified five individuals from three unrelated families with novel variants in the proximal region of CCND2 associated with microcephaly, mildly simplified cortical gyral pattern, symmetric short stature, and mild developmental delay. Identified variants include de novo frameshift variants and a dominantly inherited stop-gain variant segregating with the phenotype. This is the first reported association between proximal CCND2 variants and microcephaly, to our knowledge. This series expands the phenotypic spectrum of CCND2-related disorders and suggests that distinct classes of CCND2 variants are associated with reciprocal effects on human brain growth (microcephaly and megalencephaly due to possible loss or gain of protein function, respectively), adding to the growing paradigm of inverse phenotypes due to dysregulation of key brain growth genes.

Evolution of Metastasis Study Models toward Metastasis-On-A-Chip: The Ultimate Model?

For decades, several attempts have been made to obtain a mimetic model for the study of metastasis, the reason of most of deaths caused by cancer, in order to solve the unknown phenomena surrounding this disease. To better understand this cellular dissemination process, more realistic models are needed that are capable of faithfully recreating the entire and essential tumor microenvironment (TME). Thus, new tools known as tumor-on-a-chip and metastasis-on-a-chip have been recently proposed. These tools incorporate microfluidic systems and small culture chambers where TME can be faithfully modeled thanks to 3D bioprinting. In this work, a literature review has been developed about the different phases of metastasis, the remaining unknowns and the use of new models to study this disease. The aim is to provide a global vision of the current panorama and the great potential that these systems have for in vitro translational research on the molecular basis of the pathology. In addition, these models will allow progress toward a personalized medicine, generating chips from patient samples that mimic the original tumor and the metastatic process to perform a precise pharmacological screening by establishing the most appropriate treatment protocol.

Cysteine-Rich Angiogenic Inducer 61: Pro-Survival Function and Role as a Biomarker for Disseminating Breast Cancer Cells

Simple Summary

Metastasis is the leading cause of death in breast cancer, and it can be predicted by the detection of circulating tumor cells in the blood and disseminated tumor cells in the bone marrow, which are usually detected by epithelial marker proteins. However, tumor cells with mesenchymal attributes down-regulate the expression of epithelial marker proteins, and are therefore difficult to detect. Here, we found that the protein-cysteine–rich angiogenetic inducer 61 (Cyr61) is strongly expressed in tumor cells with mesenchymal attributes. Cyr61 expression was undetectable in normal blood cells, suggesting that Cyr61 might represent a tumor-associated protein. Functional experiments showed that the loss of Cyr61 reduces the viability of breast tumor cells. Thus, Cyr61 might represent an interesting anti-metastatic target that needs to be explored in future studies.

Abstract

(1) Background: the early detection of cancer cells in the blood or bone marrow of breast cancer patients improves the understanding of metastasis. Disseminating tumor cells in the bone marrow with a pronounced manifestation of mesenchymal markers (mDTC) are difficult to detect by epithelial markers, but they are relevant in the initiation of metastasis. (2) Methods: the breast cancer mDTC cell line BC-M1 was analyzed by mass spectrometry, which revealed high levels of the protein-cysteine–rich angiogenic inducer 61 (Cyr61). The function of Cyr61 was investigated using shRNA and hypoxia. Peripheral blood samples from 35 breast cancer patients were investigated for CTCs defined as cytokeratin-positive/CD45-negative cells. (3) Results: the Cyr61 levels are elevated in mDTC lines from breast, lung, and prostate cancer patients. The loss of Cyr61 resulted in the diminished expression of hypoxia-inducible factor 1-alpha, and increased apoptosis. Cyr61 was present in 47 (43%) of the 109 detected circulating tumor cells (CTCs), while the blood and bone marrow cells from healthy controls were Cyr61-negative. (4) Conclusions: Cyr61 is expressed in mDTC lines, supports the viability of cancer cells, and classifies a new subset of cytokeratin-positive CTCs, which deserves further investigation.

Tick-Borne Flaviviruses Depress AKT Activity during Acute Infection by Modulating AKT1/2

Tick-borne flaviviruses (TBFVs) are reemerging public health threats. To develop therapeutics against these pathogens, increased understanding of their interactions with the mammalian host is required. The PI3K-AKT pathway has been implicated in TBFV persistence, but its role during acute virus infection remains poorly understood. Previously, we showed that Langat virus (LGTV)-infected HEK 293T cells undergo a lytic crisis with a few surviving cells that become persistently infected. We also observed that AKT2 mRNA is upregulated in cells persistently infected with TBFV. Here, we investigated the virus-induced effects on AKT expression over the course of acute LGTV infection and found that total phosphorylated AKT (pAKT), AKT1, and AKT2 decrease over time, but AKT3 increases dramatically. Furthermore, cells lacking AKT1 or AKT2 were more resistant to LGTV-induced cell death than wild-type cells because they expressed higher levels of pAKT and antiapoptotic proteins, such as XIAP and survivin. The differential modulation of AKT by LGTV may be a mechanism by which viral persistence is initiated, and our results demonstrate a complicated manipulation of host pathways by TBFVs.

High Sensitivity of Circulating Tumor Cells Derived from a Colorectal Cancer Patient for Dual Inhibition with AKT and mTOR Inhibitors

Circulating tumor cells (CTCs) are cells shed from the primary tumor into the bloodstream. While many studies on solid tumor cells exist, data on CTCs are scarce. The mortality of cancer is mostly associated with metastasis and recent research identified CTCs as initiators of metastasis. The PI3K/AKT/mTOR signaling pathway is an intracellular pathway that regulates essential functions including protein biosynthesis, cell growth, cell cycle control, survival and migration. Importantly, activating oncogenic mutations and amplifications in this pathway are frequently observed in a wide variety of cancer entities, underlining the significance of this signaling pathway. In this study, we analyzed the functional role of the PI3K/AKT/mTOR signaling pathway in the CTC-MCC-41 line, derived from a patient with metastatic colorectal cancer. One striking finding in our study was the strong sensitivity of this CTC line against AKT inhibition using MK2206 and mTOR inhibition using RAD001 within the nanomolar range. This suggests that therapies targeting AKT and mTOR could have been beneficial for the patient from which the CTC line was isolated. Additionally, a dual targeting approach of AKT/mTOR inside the PI3K/AKT/mTOR signaling pathway in the colorectal CTCs showed synergistic effects in vitro. Depending on the phenotypical behavior of CTC-MCC-41 in cell culture (adherent vs. suspension), we identified altered phosphorylation levels inside the PI3K/AKT/mTOR pathway. We observed a downregulation of the PI3K/AKT/mTOR signaling pathway, but not of the RAS/RAF/MAPK pathway, in CTCs growing in suspension in comparison to adherent CTCs. Our results highlight distinct functions of AKT isoforms in CTC-MCC-41 cells with respect to cell proliferation. Knockdown of AKT1 and AKT2 leads to significantly impaired proliferation of CTC-MCC-41 cells in vitro. Therefore, our data demonstrate that the PI3K/AKT/mTOR signaling pathway plays a key role in the proliferation of CTC-MCC-41.

Targeting disseminated estrogen-receptor-positive breast cancer cells in bone marrow

Estrogen receptor-positive (ER+) breast cancer can recur up to 20 years after initial diagnosis. Delayed recurrences arise from disseminated tumors cells (DTCs) in sites such as bone marrow that remain quiescent during endocrine therapy and subsequently proliferate to produce clinically detectable metastases. Identifying therapies that eliminate DTCs and/or effectively target cells transitioning to proliferation promises to reduce risk of recurrence. To tackle this problem, we utilized a 3D co-culture model incorporating ER+ breast cancer cells and bone marrow mesenchymal stem cells to represent DTCs in a bone marrow niche. 3D co-cultures maintained cancer cells in a quiescent, viable state as measured by both single-cell and population-scale imaging. Single-cell imaging methods for metabolism by fluorescence lifetime (FLIM) of NADH and signaling by kinases Akt and ERK revealed that breast cancer cells utilized oxidative phosphorylation and signaling by Akt to a greater extent both in 3D co-cultures and a mouse model of ER+ breast cancer cells in bone marrow. Using our 3D co-culture model, we discovered that combination therapies targeting oxidative phosphorylation via the thioredoxin reductase (TrxR) inhibitor, D9, and the Akt inhibitor, MK-2206, preferentially eliminated breast cancer cells without altering viability of bone marrow stromal cells. Treatment of mice with disseminated ER+ human breast cancer showed that D9 plus MK-2206 blocked formation of new metastases more effectively than tamoxifen. These data establish an integrated experimental system to investigate DTCs in bone marrow and identify combination therapy against metabolic and kinase targets as a promising approach to effectively target these cells and reduce risk of recurrence in breast cancer.

Ectopic Expression of Hematopoietic SHIP1 in Human Colorectal Cancer

Colorectal cancer (CRC) is a heterogeneous disease that results from the accumulation of mutations in colonic mucosa cells. A subclass of CRC is characterized by microsatellite instability, which is thought to occur mainly through inactivation of the DNA mismatch repair genes MLH1 and MSH2. The inositol 5-phosphatase SHIP1 is expressed predominantly in hematopoietic cells. In this study, the expression of SHIP1 in carcinomas and its putative correlation with clinicopathologic parameters, expression of DNA repair genes and microsatellite instability was investigated. By analyzing a multi-tumor tissue microarray, expression of SHIP1 was detected in 48 out of 72 cancer entities analyzed. The expression of SHIP1 protein of 145 kDa was confirmed by Western blot analysis in 7 out of 14 carcinoma cell lines. Analysis of a large colorectal cancer tissue microarray with 1009 specimens revealed SHIP1 expression in 62% of the samples analyzed. SHIP1 expression was inversely correlated with lymph node metastasis, vascular invasion and tumor grade, and it was positively associated with left-sided tumor localization. Interestingly, a strong relationship between the expression of SHIP1 and nuclear and membranous beta-catenin and the DNA repair genes MLH1 and MSH2 was observed.

A Network Pharmacology-Based Study on the Anti-Lung Cancer Effect of Dipsaci Radix

Objective

Dipsaci Radix (DR) has been used to treat fracture and osteoporosis. Recent reports have shown that myeloid cells from bone marrow can promote the proliferation of lung cancer. However, the action and mechanism of DR has not been well defined in lung cancer. The aim of the present study was to define molecular mechanisms of DR as a potential therapeutic approach to treat lung cancer.

Methods

Active compounds of DR with oral bioavailability ≥30% and drug-likeness index ≥0.18 were obtained from the traditional Chinese medicine systems pharmacology database and analysis platform. The potential target genes of the active compounds and bone were identified by PharmMapper and GeneCards, respectively. The compound-target network and protein-protein interaction network were built by Cytoscape software and Search Tool for the Retrieval of Interacting Genes webserver, respectively. GO analysis and pathway enrichment analysis were performed using R software.

Results

Our study demonstrated that DR had 6 active compounds, including gentisin, sitosterol, Sylvestroside III, 3,5-Di-O-caffeoylquinic acid, cauloside A, and japonine. There were 254 target genes related to these active compounds as well as to bone. SRC, AKT1, and GRB2 were the top 3 hub genes. Metabolisms and signaling pathways associated with these hub genes were significantly enriched.

Conclusions

This study indicated that DR could exhibit the anti-lung cancer effect by affecting multiple targets and multiple pathways. It reflects the traditional Chinese medicine characterized by multicomponents and multitargets. DR could be considered as a candidate for clinical anticancer therapy by regulating bone physiological functions.

Combined Targeting of AKT and mTOR Inhibits Proliferation of Human NF1-Associated Malignant Peripheral Nerve Sheath Tumour Cells In Vitro but not in a Xenograft Mouse Model In Vivo

Persistent signalling via the PI3K/AKT/mTOR pathway is a major driver of malignancy in NF1-associated malignant peripheral nerve sheath tumours (MPNST). Nevertheless, single targeting of this pathway is not sufficient to inhibit MPNST growth. In this report, we demonstrate that combined treatment with the allosteric pan-AKT inhibitor MK-2206 and the mTORC1/mTORC2 inhibitor AZD8055 has synergistic effects on the viability of MPNST cell lines in comparison to the treatment with each compound alone. However, when treating animals bearing experimental MPNST with the combined AKT/mTOR regime, no influence on tumour growth was observed. Further analysis of the MPNST xenograft tumours resistant to AKT/mTOR treatment revealed a reactivation of both AKT and mTOR in several tumour samples. Additional targeting of the RAS/RAF/MEK/MAPK pathway with the allosteric MEK1/2 inhibitor AZD6244 showed synergistic effects on the viability of MPNST cell lines in vitro in comparison to the dual AKT/mTOR inhibition. In summary, these data indicate that combined treatment with AKT and mTOR inhibitors is effective on MPNST cells in vitro but tumour resistance can occur rapidly in vivo by restoration of AKT/mTOR signalling. Our data further suggest that a triple treatment with inhibitors against AKT, mTORC1/2 and MEK1/2 may be a promising treatment option that should be further analysed in an experimental MPNST mouse model in vivo.

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.

Akt1 and Akt2 Isoforms Play Distinct Roles in Regulating the Development of Inflammation and Fibrosis Associated with Alcoholic Liver Disease

Akt kinase isoforms (Akt1, Akt2, and Akt3) have generally been thought to play overlapping roles in phosphoinositide 3-kinase (PI3K)-mediated-signaling. However, recent studies have suggested that they display isoform-specific roles in muscle and fat. To determine whether such isoform-specificity is observed with respect to alcoholic liver disease (ALD) progression, we examined the role of Akt1, Akt2, and Akt3 in hepatic inflammation, and pro-fibrogenic proliferation and migration using Kupffer cells, hepatic stellate cells (HSC), and hepatocytes in an ethanol and lipopolysaccharide (LPS)-induced two-hit model in vitro and in vivo. We determined that siRNA-directed silencing of Akt2, but not Akt1, significantly suppressed cell inflammatory markers in HSC and Kupffer cells. Although both Akt1 and Akt2 inhibited cell proliferation in HSC, only Akt2 inhibited cell migration. Both Akt1 and Akt2, but not Akt3, inhibited fibrogenesis in hepatocytes and HSC. In addition, our in vivo results show that administration of chronic ethanol, binge ethanol and LPS (EBL) in wild-type C57BL/6 mice activated all three Akt isoforms with concomitant increases in activated forms of phosphoinositide dependent kinase-1 (PDK1), mammalian target-of-rapamycin complex 2 (mTORC2), and PI3K, resulting in upregulation in expression of inflammatory, proliferative, and fibrogenic genes. Moreover, pharmacological blocking of Akt2, but not Akt1, inhibited EBL-induced inflammation while blocking of both Akt1 and Akt2 inhibited pro-fibrogenic marker expression and progression of fibrosis. Our findings indicate that Akt isoforms play unique roles in inflammation, cell proliferation, migration, and fibrogenesis during EBL-induced liver injury. Thus, close attention must be paid when targeting all Akt isoforms as a therapeutic intervention.

Isoform-Specific Role of Akt in Oral Squamous Cell Carcinoma

Protein kinase B (Akt) plays a very significant role in various cancers including oral cancer. However, it has three isoforms (Akt1, Akt2, and Akt3) and they perform distinct functions and even play contrasting roles in different cancers. Therefore, it becomes essential to evaluate the isoform-specific role of Akt in oral cancer. In the present study, an attempt has been made to elucidate the isoform-specific role of Akt in oral cancer. The immunohistochemical analysis of oral cancer tissues showed an overexpression of Akt1 and 2 isoforms but not Akt3. Moreover, the dataset of "The Cancer Genome Atlas" for head and neck cancer has suggested the genetic alterations of Akt1 and 2 tend to be associated with the utmost poor clinical outcome in oral cancer. Further, treatment of oral cancer cells with tobacco and its components such as benzo(a)pyrene and nicotine caused increased mRNA levels of Akt1 and 2 isoforms and also enhanced the aggressiveness of oral cancer cells in terms of proliferation, and clonogenic and migration potential. Finally, silencing of Akt1 and 2 isoforms caused decreased cell survival and induced cell cycle arrest at the G2/M phase. Akt1/2 silencing also reduced tobacco-induced aggressiveness by decreasing the clonogenic and migration potential of oral cancer cells. Moreover, silencing of Akt1 and 2 isoforms was found to decrease the expression of proteins regulating cancer cell survival and proliferation such as cyclooxygenase-2, B-cell lymphoma 2 (Bcl-2), cyclin D1, and survivin. Thus, the important role of Akt1 and 2 isoforms have been elucidated in oral cancer with in-depth mechanistic analysis.

New Insights into Protein Kinase B/Akt Signaling: Role of Localized Akt Activation and Compartment-Specific Target Proteins for the Cellular Radiation Response

Genetic alterations driving aberrant activation of the survival kinase Protein Kinase B (Akt) are observed with high frequency during malignant transformation and cancer progression. Oncogenic gene mutations coding for the upstream regulators or Akt, e.g., growth factor receptors, RAS and phosphatidylinositol-3-kinase (PI3K), or for one of the three Akt isoforms as well as loss of the tumor suppressor Phosphatase and Tensin Homolog on Chromosome Ten (PTEN) lead to constitutive activation of Akt. By activating Akt, these genetic alterations not only promote growth, proliferation and malignant behavior of cancer cells by phosphorylation of various downstream signaling molecules and signaling nodes but can also contribute to chemo- and radioresistance in many types of tumors. Here we review current knowledge on the mechanisms dictating Akt’s activation and target selection including the involvement of miRNAs and with focus on compartmentalization of the signaling network. Moreover, we discuss recent advances in the cross-talk with DNA damage response highlighting nuclear Akt target proteins with potential involvement in the regulation of DNA double strand break repair.

Akt isoform specific effects in ovarian cancer progression

Ovarian cancer remains a significant therapeutic problem and novel, effective therapies are needed. Akt is a serine-threonine kinase that is overexpressed in numerous cancers, including ovarian. Mammalian cells express three Akt isoforms which are encoded by distinct genes. Although there are several Akt inhibitors in clinical trials, most indiscriminately target all isoforms. Current in vitro data and animal knockout experiments suggest that the Akt isoforms may have divergent roles. In this paper, we determined the isoform-specific functions of Akt in ovarian cancer cell proliferation in vitro and in ovarian cancer progression in vivo. For in vitro experiments, murine and human ovarian cancer cells were treated with Akt inhibitors and cell viability was assessed. We used two different in vivo approaches to identify the roles of Akt isoforms in ovarian cancer progression and their influence on the primary tumor and tumor microenvironment. In one experiment, wild-type C57Bl6 mice were orthotopically injected with ID8 cells with stable knockdown of Akt isoforms. In a separate experiment, mice null for Akt 1-3 were orthotopically injected with WT ID8 cells (Figure 1). Our data show that inhibition of Akt1 significantly reduced ovarian cancer cell proliferation and inhibited tumor progression in vivo. Conversely, disruption of Akt2 increased tumor growth. Inhibition of Akt3 had an intermediate phenotype, but also increased growth of ovarian cancer cells. These data suggest that there is minimal redundancy between the Akt isoforms in ovarian cancer progression. These findings have important implications in the design of Akt inhibitors for the effective treatment of ovarian cancer.

PTEN mediates the cross talk between breast and glial cells in brain metastases leading to rapid disease progression

Despite improvement of therapeutic treatments for breast cancer, the development of brain metastases has become a major limitation to life expectancy for many patients. Brain metastases show very commonly alterations in EGFR and HER2 driven pathways, of which PTEN is an important regulator. Here, we analyzed PTEN expression in 111 tissue samples of breast cancer brain metastases (BCBM). Loss of PTEN was found in a substantial proportion of BCBM samples (48.6%) and was significantly associated with triple-negative breast cancer (67.5%, p = 0.001) and a shorter survival time after surgical resection of brain metastases (p = 0.048). Overexpression of PTEN in brain-seeking MDA-MB-231 BR cells in vitro reduced activation of the AKT pathway, notably by suppression of Akt1 kinase activity. Furthermore, the migration of MDA-MB-231 BR cells in vitro was promoted by co-culturing with both astrocytes and microglial cells. Interestingly, when PTEN was overexpressed the migration was significantly inhibited. Moreover, in an ex vivo organotypic brain slice model, PTEN overexpression reduced invasion of tumor cells. This was accompanied by reduced astrocyte activation that was mediated by autocrine and paracrine activation of GM-CSF/ CSF2RA and AKT/ PTEN pathways. In conclusion, loss of PTEN is frequently detected in triple-negative BCBM patients and associated with poor prognosis. The findings of our functional studies suggest that PTEN loss promotes a feedback loop between tumor cells and glial cells, which might contribute to disease progression.

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.

The PI3K/AKT signaling pathway in regulatory T-cell development, stability, and function

The PI3K/AKT signaling pathway is an essential node in mammalian cells that controls cell growth, migration, proliferation, and metabolism. During the last decade, a number of works have demonstrated an important role for the PI3K/AKT pathway in regulatory T cell development, function, and stability. This review summarizes our current knowledge of how the PI3K/AKT pathway regulates thymic and peripheral Treg generation and function, with an emphasis on translation of these observations to therapies targeting Tregs in several pathologies.

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.

Akt1 Controls the Timing and Amplitude of Vascular Circadian Gene Expression

The AKT signaling pathway is important for circadian rhythms in mammals and flies ( Drosophila). However, AKT signaling in mammals is more complicated since there are 3 isoforms of AKT, each performing slightly different functions. Here we study the most ubiquitous AKT isoform, Akt1, and its role at the organismal level in the central and vascular peripheral clocks. Akt1^-/- mice exhibit relatively normal behavioral rhythms with only minor differences in circadian gene expression in the liver and heart. However, circadian gene expression in the Akt1^-/- aorta, compared with control aorta, follows a distinct pattern. In the Akt1^-/- aorta, positive regulators of circadian transcription have lower amplitude rhythms and peak earlier in the day, and negative circadian regulators are expressed at higher amplitudes and peak later in the day. In endothelial cells, negative circadian regulators exhibit an increased amplitude of expression, while the positive circadian regulators are arrhythmic with a decreased amplitude of expression. This indicates that Akt1 conditions the normal circadian rhythm in the vasculature more so than in other peripheral tissues where other AKT isoforms or kinases might be important for daily rhythms.

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.

Role of Akt2 in regulation of metastasis suppressor 1 expression and colorectal cancer metastasis

Survival signaling is critical for the metastatic program of cancer cells. The current study investigated the role of Akt survival proteins in colorectal cancer (CRC) metastasis and explored potential mechanisms of Akt-mediated metastasis regulation. Using an orthotopic implantation model in mice, which uniquely recapitulates the entire multistep process of CRC metastasis, combined with an inducible system of short hairpin RNA-mediated Akt isoform knockdown in human CRC cells, our studies confirm a role of Akt2 in CRC cell dissemination to distant organs in vivo. Akt2 deficiency profoundly inhibited the development of liver lesions in mice, whereas Akt1 had no effect under the experimental conditions used in the study. Array analysis of human metastatic genes identified the scaffolding protein metastasis suppressor 1 (MTSS1) as a novel Akt2-regulated gene. Inducible loss of Akt2 in CRC cells robustly upregulated MTSS1 at the messenger RNA and protein level, and the accumulated protein was functionally active as shown by its ability to engage an MTSS1-Src-cortactin inhibitory axis. MTSS1 expression led to a marked reduction in levels of functional cortacin (pcortactin Y421), an actin nucleation-promoting factor that has a crucial role in cancer cell invasion and metastasis. MTSS1 was also shown to mediate suppressive effects of Akt2 deficiency on CRC cell viability, survival, migration and actin polymerization in vitro. The relevance of these findings to human CRC is supported by analysis of The Cancer Genome Atlas (TCGA) and NCBI GEO data sets, which demonstrated inverse changes in expression of Akt2 and MTSS1 during CRC progression. Taken together, the data identify MTSS1 as a new Akt2-regulated gene, and point to suppression of MTSS1 as a key step in the metastasis-promoting effects of Akt2 in CRC cells.

Hypoxia-inducible factor-1α mediates the toll-like receptor 4 signaling pathway leading to anti-tumor effects in human hepatocellular carcinoma cells under hypoxic conditions

Hypoxia-inducible factor-1α (HIF-1α) and toll-like receptor 4 (TLR4) are involved in numerous mechanisms of cancer biology, including cell proliferation and survival; however the interaction of the two factors under hypoxic conditions remains unclear. The present study investigated the in vitro mechanism that results in the suppression of tumor cell growth and cellular functions when HIF-1α is silenced. In the present study, the human hepatocellular carcinoma HepG2 cell line was transfected with short hairpin RNA (shRNA) against HIF-1α and cultured under hypoxic conditions (1% O₂ for 24 h). The expression of HIF-1α and various growth factors, including epidermal growth factor (EGF), hepatocyte growth factor (HGF), vascular endothelial growth factor (VEGF) and fibroblast growth factor 2 (FGF2), were examined using quantitative polymerase chain reaction and immunoblotting. Tumor growth was measured using a Cell Counting Kit-8 assay and tumor activity was measured using tumor cell invasion and migration assays. Lipopolysaccharide and TAK-242 were used to activate and inhibit TLR4, respectively, to observe the role of TLR4 in the HIF-1α silenced tumor cells. The expression of TLR4 signaling pathway associates, including myeloid differentiation primary response gene 88 (MyD88), apoptosis signal-regulating kinase 1 (ASK1), p38 mitogen-activated protein kinases and HIF-1α, were analyzed by western blot assay. Under hypoxic conditions, silencing of HIF-1α expression suppressed tumor cell growth and regulated the expression of tumor growth-associated genes, including EGF, HGF, VEGF and FG2. Suppression of tumor cell invasion and migration was also observed in the HIF-1α silenced HepG2 cell line. In addition, TLR4 was identified to be involved in HIF-1α and MyD88 accumulation, and activation of ASK1 and p38 were demonstrated to be critical for TLR4-mediated HIF-1α pathway. In conclusion, silencing of HIF-1α expression may induce anti-tumor effects under hypoxic conditions in HepG2 cells via the TLR4 mediated pathway, suggesting that the HIF-1α/TLR4 signaling cohort may act as a novel therapeutic target for the treatment of hepatocellular cancer.

Dual Targeting of Akt and mTORC1 Impairs Repair of DNA Double-Strand Breaks and Increases Radiation Sensitivity of Human Tumor Cells

Inhibition of mammalian target of rapamycin-complex 1 (mTORC1) induces activation of Akt. Because Akt activity mediates the repair of ionizing radiation-induced DNA double-strand breaks (DNA-DSBs) and consequently the radioresistance of solid tumors, we investigated whether dual targeting of mTORC1 and Akt impairs DNA-DSB repair and induces radiosensitization. Combining mTORC1 inhibitor rapamycin with ionizing radiation in human non-small cell lung cancer (NSCLC) cells (H661, H460, SK-MES-1, HTB-182, A549) and in the breast cancer cell line MDA-MB-231 resulted in radiosensitization of H661 and H460 cells (responders), whereas only a very slight effect was observed in A549 cells, and no effect was observed in SK-MES-1, HTB-182 or MDA-MB-231 cells (non-responders). In responder cells, rapamycin treatment did not activate Akt1 phosphorylation, whereas in non-responders, rapamycin mediated PI3K-dependent Akt activity. Molecular targeting of Akt by Akt inhibitor MK2206 or knockdown of Akt1 led to a rapamycin-induced radiosensitization of non-responder cells. Compared to the single targeting of Akt, the dual targeting of mTORC1 and Akt1 markedly enhanced the frequency of residual DNA-DSBs by inhibiting the non-homologous end joining repair pathway and increased radiation sensitivity. Together, lack of radiosensitization induced by rapamycin was associated with rapamycin-mediated Akt1 activation. Thus, dual targeting of mTORC1 and Akt1 inhibits repair of DNA-DSB leading to radiosensitization of solid tumor cells.

Akt3 knockdown induces mitochondrial dysfunction in human cancer cells

Akt/PKB plays a pivotal role in cell proliferation and survival. However, the isotype-specific roles of Akt in mitochondrial function have not been fully addressed. In this study, we explored the role of Akt in mitochondrial function after stable knockdown of the Akt isoforms in EJ human bladder cancer cells. We found that the mitochondrial mass was significantly increased in the Akt1- and Akt3-knockdown cells, and this increase was accompanied by an increase in TFAM and NRF1. Akt2 knockdown did not cause a similar effect. Interestingly, Akt3 knockdown also led to severe structural defects in the mitochondria, an increase in doxorubicin-induced senescence, and impairment of cell proliferation in galactose medium. Consistent with these observations, the mitochondrial oxygen consumption rate was significantly reduced in the Akt3-knockdown cells. An Akt3 deficiency-induced decrease in mitochondrial respiration was also observed in A549 lung cancer cells. Collectively, these results suggest that the Akt isoforms play distinct roles in mitochondrial function and that Akt3 is critical for proper mitochondrial respiration in human cancer cells.

PI3K-Akt signaling pathway upregulates hepatitis C virus RNA translation through the activation of SREBPs

Hepatitis C virus (HCV) activates PI3K-Akt signaling to enhance entry and replication. Here, we found that this pathway also increased HCV translation. Knocking down the three Akt isoforms significantly decreased, whereas ectopic expression increased HCV translation. HCV translation upregulation by Akt required their kinase activities because Akt kinase-dead mutants downregulated HCV translation; and was dependent on PI3K activity since it was sensitive to PI3K inhibitor wortmannin. The viral 3'UTR was not involved in translation upregulation by Akt. HCV NS5A increased Akt phosphorylation/activity and HCV translation in the absence of the viral 3'UTR. Sterol regulatory element-binding proteins (SREBPs) were the downstream effectors of the PI3K-Akt pathway in regulating HCV translation because Akt1 and Akt2 activated both SREBP-1 and SREBP-2, whereas Akt3 upregulated SREBP-1. Knocking down SREBPs significantly decreased, while ectopic expression of SREBPs increased HCV translation. Taken together, we showed that the PI3K-Akt signaling pathway positively regulates HCV translation through SREBPs.

Functional studies on circulating and disseminated tumor cells in carcinoma patients

Despite numerous clinical studies indicating the clinical relevance of circulating tumor cells (CTCs) in blood and disseminated tumor cells (DTCs) in the bone marrow of cancer patients, the functional properties of these cells are largely unknown. The focus of this review is to emphasize how functional studies on viable CTCs and DTCs can enlarge the spectrum of applications of "liquid biopsies". The low number of CTCs in the peripheral blood and DTCs in the bone marrow and the fact that carcinoma cells are difficult to culture are major challenges. Significant advances in the in vitro and in vivo expansion of CTCs and DTCs from cancer patients have been achieved, which enable us now to study the functional properties of these cells. Here, we discuss published data about functional studies on CTCs and DTCs using in vitro cultivation and in vivo xenograft models. Functional analyses on CTCs and DTCs offer the possibility to identify the metastasis-initiating cells. Moreover, CTC-derived cell lines and xenografts might point to new therapeutic targets and can be used for drug development.

Inhibition of breast cancer invasion by TIS21/BTG2/Pc3-Akt1-Sp1-Nox4 pathway targeting actin nucleators, mDia genes

The mammalian homolog of Drosophila diaphanous (mDia), actin nucleator, has been known to participate in the process of invasion and metastasis of cancer cells via regulating a number of actin-related biological processes. We have previously reported that tumor suppressor TIS21(/BTG2/Pc3) (TIS21) inhibits invadopodia formation by downregulating reactive oxygen species (ROS) in MDA-MB-231 cells. We herein report that TIS21(/BTG2/Pc3) downregulates diaphanous-related formin (DRF) expression via reducing NADPH oxidase 4 (Nox4)-derived ROS generation by Akt1 activation and subsequently impairs invasion activity of the highly invasive breast cancer cells. Knockdown of Akt1 by RNA interference recovered the TIS21(/BTG2/Pc3)-inhibited F-actin remodeling and ROS generation by recovering Nox4 expression. Furthermore, Sp1-mediated Nox4 transcription was downregulated by TIS21(/BTG2/Pc3)-Akt1 signals, leading to the inhibition of cancer cell invasion via F-actin remodeling by mDia genes. To our best knowledge, this is the first study to show that TIS21(/BTG2/Pc3)-Akt1 inhibited Sp1-Nox4-ROS cascade, subsequently reducing invasion activity via inhibition of mDia family genes.

Downregulation of AKT3 Increases Migration and Metastasis in Triple Negative Breast Cancer Cells by Upregulating S100A4

BACKGROUND

Treatment of breast cancer patients with distant metastases represents one of the biggest challenges in today's gynecological oncology. Therefore, a better understanding of mechanisms promoting the development of metastases is of paramount importance. The serine/threonine kinase AKT was shown to drive cancer progression and metastasis. However, there is emerging data that single AKT isoforms (i.e. AKT1, AKT2 and AKT3) have different or even opposing functions in the regulation of cancer cell migration in vitro, giving rise to the hypothesis that inhibition of distinct AKT isoforms might have undesirable effects on cancer dissemination in vivo.

METHODS

The triple negative breast cancer cell line MDA-MB-231 was used to investigate the functional roles of AKT in migration and metastasis. AKT single and double knockdown cells were generated using isoform specific shRNAs. Migration was analyzed using live cell imaging, chemotaxis and transwell assays. The metastatic potential of AKT isoform knockdown cells was evaluated in a subcutaneous xenograft mouse model in vivo.

RESULTS

Depletion of AKT3, but not AKT1 or AKT2, resulted in increased migration in vitro. This effect was even more prominent in AKT2,3 double knockdown cells. Furthermore, combined downregulation of AKT2 and AKT3, as well as AKT1 and AKT3 significantly increased metastasis formation in vivo. Screening for promigratory proteins revealed that downregulation of AKT3 increases the expression of S100A4 protein. In accordance, depletion of S100A4 by siRNA approach reverses the increased migration induced by knockdown of AKT3.

CONCLUSIONS

We demonstrated that knockdown of AKT3 can increase the metastatic potential of triple negative breast cancer cells. Therefore, our results provide a rationale for the development of AKT isoform specific inhibitors.

Disseminated Tumor Cells Persist in the Bone Marrow of Breast Cancer Patients through Sustained Activation of the Unfolded Protein Response

Disseminated tumor cells (DTC), which share mesenchymal and epithelial properties, are considered to be metastasis-initiating cells in breast cancer. However, the mechanisms supporting DTC survival are poorly understood. DTC extravasation into the bone marrow may be encouraged by low oxygen concentrations that trigger metabolic and molecular alterations contributing to DTC survival. Here, we investigated how the unfolded protein response (UPR), an important cytoprotective program induced by hypoxia, affects the behavior of stressed cancer cells. DTC cell lines established from the bone marrow of patients with breast cancer (BC-M1), lung cancer, (LC-M1), and prostate cancer (PC-E1) were subjected to hypoxic and hypoglycemic conditions. BC-M1 and LC-M1 exhibiting mesenchymal and epithelial properties adapted readily to hypoxia and glucose starvation. Upregulation of UPR proteins, such as the glucose-regulated protein Grp78, induced the formation of filamentous networks, resulting in proliferative advantages and sustained survival under total glucose deprivation. High Grp78 expression correlated with mesenchymal attributes of breast and lung cancer cells and with poor differentiation in clinical samples of primary breast and lung carcinomas. In DTCs isolated from bone marrow specimens from breast cancer patients, Grp78-positive stress granules were observed, consistent with the likelihood these cells were exposed to acute cell stress. Overall, our findings provide the first evidence that the UPR is activated in DTC in the bone marrow from cancer patients, warranting further study of this cell stress pathway as a predictive biomarker for recurrent metastatic disease.

Discontinuing MEK inhibitors in tumor cells with an acquired resistance increases migration and invasion

BACKGROUND

Development of small molecular inhibitors against BRAF and MEK has been a breakthrough in the treatment of malignant melanoma. However, the long-term effect is foiled in virtually all patients by the emergence of resistant tumor cell populations. Therefore, mechanisms resulting in the acquired resistance against BRAF and MEK inhibitors have gained much attention and several strategies have been proposed to overcome tumor resistance, including interval treatment or withdrawal of these compounds after disease progression.

METHODS

Using a panel of cell lines with an acquired resistance against MEK inhibitors, we have evaluated the sensitivity of these cells against compounds targeting AKT/mTOR signaling, as well as novel ERK1/2 inhibitors. Furthermore, the effects of withdrawal of MEK inhibitor on migration in resistant cell lines were analyzed.

RESULTS

We demonstrate that withdrawal of BRAF or MEK inhibitors in tumor cells with an acquired resistance results in reactivation of ERK1/2 signaling and upregulation of EMT-inducing transcription factors, leading to a highly migratory and invasive phenotype of cancer cells. Furthermore, we show that migration in these cells is independent from AKT/mTOR signaling. However, combined targeting of AKT/mTOR using MK-2206 and AZD8055 efficiently inhibits proliferation in all resistant tumor cell lines analyzed.

CONCLUSIONS

We propose that combined targeting of MEK/AKT/mTOR or treatment with a novel ERK1/2 inhibitor downstream of BRAF/MEK suppresses proliferation as well as migration and invasion in resistant tumor cells. We provide a rationale against the discontinuation of BRAF or MEK inhibitors in patients with an acquired resistance, and provide a rationale for combined targeting of AKT/mTOR and MEK/ERK1/2, or direct targeting of ERK1/2 as an effective treatment strategy.

Vertical Targeting of AKT and mTOR as Well as Dual Targeting of AKT and MEK Signaling Is Synergistic in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the sixth most common cancer, and the third most common cause of cancer related death worldwide. The multi-kinase inhibitor Sorafenib represents the only systemic treatment option until today, and results from clinical trials with allosteric mTOR inhibitors were sobering. Since the PI3K/AKT/mTOR and RAF/MEK/ERK signaling pathways are frequently upregulated in HCC, we have analyzed the effects of AKT inhibitor MK-2206, MEK inhibitor AZD6244 (ARRY 142886) and mTOR kinase inhibitor AZD8055, given as single drugs or in combination, on proliferation and apoptosis of three HCC cell lines in vitro. We show that all three inhibitor combinations synergistically inhibit proliferation of the three HCC cell lines, with the strongest synergistic effect observed after vertical inhibition of AKT and mTORC1/2. We demonstrate that AKT kinase activity is restored 24h after blockade of mTORC1/2 by increased phosphorylation of T308, providing a rationale for combined targeting of AKT and mTOR inhibition in HCC. Our data suggest that a combination of inhibitors targeting those respective pathways may be a viable approach for future application in patients with hepatocellular carcinoma.

A Novel Inhibitor of AKT1-PDPK1 Interaction Efficiently Suppresses the Activity of AKT Pathway and Restricts Tumor Growth In Vivo

The serine/threonine kinase AKT/PKB has a critical role in the regulation of cell proliferation. Because AKT signaling is deregulated in numerous human malignancies, it has become an attractive anticancer drug target. A number of small molecule AKT kinase inhibitors have been developed; however, severe side effects have prevented their use in clinical trials. To find inhibitors of AKT1 signaling with principally novel mechanism of action, we carried out a live cell-based screen for small molecule inhibitors of physical interaction between AKT1 and its primary activator PDPK1. The screen revealed one molecule-NSC156529, which downregulated AKT1 signaling, efficiently decreased the proliferation of human cancer cells in vitro, and substantially inhibited the growth of prostate tumor xenografts in vivo. Interestingly, the treated tumor xenografts exhibited higher expression level of normal prostate differentiation markers but did not show augmented cell death, suggesting that the identified compound primarily enhances the differentiation of malignant cells toward normal prostate epithelium and thus poses as an attractive lead compound for developing novel antitumor agents with less cytotoxic side effects.

Akt2 knock-down reveals its contribution to human lung cancer cell proliferation, growth, motility, invasion and endothelial cell tube formation

The Akt/PKB serine/threonine protein kinase consists of three isoforms: Akt-1, -2 and -3. Their overexpression has been detected in human cancers, but their roles in cancer progression are unclear. We investigated the impact of specific silencing of Akt1 and Akt2 on human lung cancer cell proliferation, colony growth, motility, and invasion in vitro as well as tumor growth in vivo using human Non-Small Cell Lung Cancer cells LNM35, and on the vascular tube formation using HUVEC cells. Although silencing of Akt1 decreased cellular invasion at least in part via COX-2 inhibition, it had almost no effect on cell motility, proliferation, colony formation, and angiogenesis. Transient as well as stable silencing of Akt2 resulted in a strong inhibition of Rb phosphorylation associated with a decrease in cellular proliferation and colony formation, leading to the inhibition of tumor growth in the xenograft model. Silencing of Akt2 also reduced cellular motility and invasion in vitro, presumably via COX-2 inhibition. Moreover, silencing of Akt2 in the HUVEC cells resulted in the inhibition of their spontaneous angiogenic phenotype. Altogether, these results indicate that Akt2 plays an important role in lung cancer progression and can be a promising target for lung cancer therapy.

Combining AKT inhibition with chloroquine and gefitinib prevents compensatory autophagy and induces cell death in EGFR mutated NSCLC cells

Although non-small cell lung cancer (NSCLC) patients with EGFR mutation positive (EGFR M+) tumors initially respond well to EGFR tyrosine kinase inhibitor (TKI) monotherapy, the responses are usually incomplete. In this study we show that AKT inhibition, most importantly AKT2 inhibition, synergises with EGFR TKI inhibition to increase cell killing in EGFR M+ NSCLC cells. However, our data also suggest that the synergistic pro-apoptotic effects may be stunted due to a prosurvival autophagy response induced by AKT inhibition. Consequently, inhibiting autophagy with chloroquine significantly enhanced tumor cell death induced by gefitinib and AKT inhibitors in EGFR M+ cells in vitro, and produced greater tumor shrinkage in EGFR M+ xenografts in vivo. Together, our findings suggest that adding chloroquine to EGFR and AKT inhibition has the potential to improve tumor responses in EGFR M+ NSCLC, and that selective targeting of AKT2 may provide a new treatment option in NSCLC.

Suppression of early hematogenous dissemination of human breast cancer cells to bone marrow by retinoic Acid-induced 2

Regulatory pathways that drive early hematogenous dissemination of tumor cells are insufficiently defined. Here, we used the presence of disseminated tumor cells (DTC) in the bone marrow to define patients with early disseminated breast cancer and identified low retinoic acid-induced 2 (RAI2) expression to be significantly associated with DTC status. Low RAI2 expression was also shown to be an independent poor prognostic factor in 10 different cancer datasets. Depletion of RAI2 protein in luminal breast cancer cell lines resulted in dedifferentiation marked by downregulation of ERα, FOXA1, and GATA3, together with increased invasiveness and activation of AKT signaling. Functional analysis of the previously uncharacterized RAI2 protein revealed molecular interaction with CtBP transcriptional regulators and an overlapping function in controlling the expression of a number of key target genes involved in breast cancer. These results suggest that RAI2 is a new metastasis-associated protein that sustains differentiation of luminal breast epithelial cells.

SIGNIFICANCE

We identified downregulation of RAI2 as a novel metastasis-associated genetic alteration especially associated with early occurring bone metastasis in ERα-positive breast tumors. We specified the role of the RAI2 protein to function as a transcriptional regulator that controls the expression of several key regulators of breast epithelial integrity and cancer.