Analysis of PIK3CA Mutations and Activation Pathways in Triple Negative Breast Cancer

Background

Triple Negative Breast Cancer (TNBC) accounts for 12–24% of all breast carcinomas, and shows worse prognosis compared to other breast cancer subtypes. Molecular studies demonstrated that TNBCs are a heterogeneous group of tumors with different clinical and pathologic features, prognosis, genetic-molecular alterations and treatment responsivity. The PI3K/AKT is a major pathway involved in the regulation of cell survival and proliferation, and is the most frequently altered pathway in breast cancer, apparently with different biologic impact on specific cancer subtypes. The most common genetic abnormality is represented by PIK3CA gene activating mutations, with an overall frequency of 20–40%. The aims of our study were to investigate PIK3CA gene mutations on a large series of TNBC, to perform a wider analysis on genetic alterations involving PI3K/AKT and BRAF/RAS/MAPK pathways and to correlate the results with clinical-pathologic data.

Materials and Methods

PIK3CA mutation analysis was performed by using cobas® PIK3CA Mutation Test. EGFR, AKT1, BRAF, and KRAS genes were analyzed by sequencing. Immunohistochemistry was carried out to identify PTEN loss and to investigate for PI3K/AKT pathways components.

Results

PIK3CA mutations were detected in 23.7% of TNBC, whereas no mutations were identified in EGFR, AKT1, BRAF, and KRAS genes. Moreover, we observed PTEN loss in 11.3% of tumors. Deregulation of PI3K/AKT pathways was revealed by consistent activation of pAKT and p-p44/42 MAPK in all PIK3CA mutated TNBC.

Conclusions

Our data shows that PIK3CA mutations and PI3K/AKT pathway activation are common events in TNBC. A deeper investigation on specific TNBC genomic abnormalities might be helpful in order to select patients who would benefit from current targeted therapy strategies.     

Inhibitory role of bone marrow mesenchymal stem cells-derived exosome in non-small-cell lung cancer: microRNA-30b-5p,EZH2 and PI3K/AKT pathway

Exosomal microRNA (miRNA) exerts potential roles in non-small-cell lung cancer (NSCLC). The current study elucidated the role of miR-30b-5p shuttled by bone marrow mesenchymal stem cells (BMSCs)-derived exosomes in treating NSCLC. Bioinformatics analysis was performed with NSCLC-related miRNA microarray GSE169587 and mRNA data GSE74706 obtained for collection of the differentially expressed miRNAs and mRNAs. The relationship between miR-30b-5p and EZH2 was predicted and confirmed. Exosomes were isolated from BMSCs and identified. BMSCs-derived exosomes overexpressing miR-30b-5p were used to establish subcutaneous tumorigenesis models to study the effects of miR-30b-5p, EZH2 and PI3K/AKT signalling pathway on tumour growth. A total of 86 BMSC-exo-miRNAs were differentially expressed in NSCLC. Bioinfomatics analysis found that BMSC-exo-miR-30b-5p could regulate NSCLC progression by targeting EZH2, which was verified by in vitro cell experiments. Besides, the target genes of miR-30b-5p were enriched in PI3K/AKT signalling pathway. Animal experiments validated that BMSC-exo-miR-30b-5p promoted NSCLC cell apoptosis and prevented tumorigenesis in nude mice via EZH2/PI3K/AKT axis. Collectively, the inhibitory role of BMSC-derived exosomes-loaded miR-30b-5p in NSCLC was achieved through blocking the EZH2/PI3K/AKT axis.     

A novel SOS1 mutation in Costello/CFC syndrome affects signaling in both RAS and PI3K pathways

Abstract

Context: Pathological upregulation of the RAS/MAPK pathway causes Costello, Noonan and cardio–facio–cutaneous (CFC) syndrome; however, little is known about PI3K/AKT signal transduction in these syndromes. Previously, we found a novel mutation of the SOS1 gene (T158A) in a patient with Costello/CFC overlapping phenotype. Objective: The aim of this study was to investigate how this mutation affects RAS/MAPK as well as PI3K/AKT pathway signal transduction.

Materials and methods: Wild-type and mutant (T158A) Son of Sevenless 1 (SOS1) were transfected into 293T cells. The levels of phospho- and total ERK1/2, AKT, p70S6K and pS6 were examined under epidermal growth factor (EGF) stimulation. Results: After EGF stimulation, the ratio of phospho-ERK1/2 to total ERK1/2 was highest at 5?min in mutant (T158A) SOS1 cells, and at 15?min in wild-type SOS1 cells. Phospho-AKT was less abundant at 60?min in mutant than in wild-type SOS1 cells. Phosphorylation at various sites in p70S6K differed between wild-type and mutant cells. Eighteen hours after activation by EGF, the ratio of phospho-ERK1/2 to total ERK1/2 remained significantly higher in mutant than in wild-type SOS1 cells, but that of phospho-AKT to total AKT was unchanged. Discussion: T158A is located in the histone-like domain, which may have a role in auto-inhibition of RAS exchanger activity of SOS1. T158A may disrupt auto-inhibition and enhance RAS signaling. T158A also affects PI3K/AKT signaling, probably via negative feedback via phospho-p70S6K. Conclusion: The SOS1 T158A mutation altered the phosphorylation of gene products involved in both RAS/MAPK and PI3K/AKT pathways.     

Oncogenes in Myeloproliferative Disorders

Myeloproliferative disorders (MPDs) constitute a group of hematopoietic malignancies that feature enhanced proliferation and survival of one or more myeloid lineage cells. William Dameshek is credited for introducing the term “MPDs” in 1951 when he used it to group chronic myeloid leukemia (CML), polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (PMF) under one clinicopathologic category. Since then, other myeloid neoplasms have been added to the MPD member list: chronic neutrophilic (CNL), eosinophilic (CEL), and myelomonocytic (CMML) leukemias; juvenile myelomonocytic leukemia (JMML); hypereosinophilic syndrome (HES); systemic mastocytosis (SM); and others. Collectively, MPDs are stem cell-derived clonal proliferative diseases whose shared and diverse phenotypic characteristics can be attributed to dysregulated signal transduction—a consequence of acquired somatic mutations. The most recognized among the latter is BCR-ABL, the disease-causing mutation in CML. Other mutations of putative pathogenetic relevance in MPDs include: JAK2V617F in PV, ET, and PMF; JAK2 exon 12 mutations in PV; MPLW515L/K in PMF and ET; KITD816V in SM; FIP1L1-PDGFRA in CEL-SM; rearrangements of PDGFRB in CEL-CMML and FGFR1 in stem cell leukemia-lymphoma syndrome; and RAS/PTPN11/NF1 mutations in JMML. This increasing repertoire of mutant molecules has streamlined translational research and molecularly targeted drug development in MPDs.     

Computational Modeling of PI3K/AKT and MAPK Signaling Pathways in Melanoma Cancer

Background

Malignant melanoma is an aggressive tumor of the skin and seems to be resistant to current therapeutic approaches. Melanocytic transformation is thought to occur by sequential accumulation of genetic and molecular alterations able to activate the Ras/Raf/MEK/ERK (MAPK) and/or the PI3K/AKT (AKT) signalling pathways. Specifically, mutations of B-RAF activate MAPK pathway resulting in cell cycle progression and apoptosis prevention. According to these findings, MAPK and AKT pathways may represent promising therapeutic targets for an otherwise devastating disease.

Result

Here we show a computational model able to simulate the main biochemical and metabolic interactions in the PI3K/AKT and MAPK pathways potentially involved in melanoma development. Overall, this computational approach may accelerate the drug discovery process and encourages the identification of novel pathway activators with consequent development of novel antioncogenic compounds to overcome tumor cell resistance to conventional therapeutic agents. The source code of the various versions of the model are available as S1 Archive.     

Absence of AKT1 Mutations in Glioblastoma

Background

Oncogenic activation of the PI3K signalling pathway plays a pivotal role in the development of glioblastoma multiforme (GBM). A central node in PI3K downstream signalling is controlled by the serine-threonine kinase AKT1. A somatic mutation affecting residue E17 of the AKT1 gene has recently been identified in breast and colon cancer. The E17K change results in constitutive AKT1 activation, induces leukaemia in mice, and accordingly, may be therapeutically exploited to target the PI3K pathway. Assessing whether AKT1 is activated by somatic mutations in GBM is relevant to establish its role in this aggressive disease.

Methodology/Principal Findings

We performed a systematic mutational analysis of the complete coding sequence of the AKT1 gene in a panel of 109 tumor GBM samples and nine high grade astrocytoma cell lines. However, no somatic mutations were detected in the coding region of AKT1.

Conclusions/Significance

Our data indicate that in GBM oncogenic deregulation of the PI3K pathway does not involve somatic mutations in the coding region of AKT1.     

PTEN Negatively Regulates MAPK Signaling during Caenorhabditis elegans Vulval Development

Vulval development in Caenorhabditis elegans serves as an excellent model to examine the crosstalk between different conserved signaling pathways that are deregulated in human cancer. The concerted action of the RAS/MAPK, NOTCH, and WNT pathways determines an invariant pattern of cell fates in three vulval precursor cells. We have discovered a novel form of crosstalk between components of the Insulin and the RAS/MAPK pathways. The insulin receptor DAF-2 stimulates, while DAF-18 PTEN inhibits, RAS/MAPK signaling in the vulval precursor cells. Surprisingly, the inhibitory activity of DAF-18 PTEN on the RAS/MAPK pathway is partially independent of its PIP(3) lipid phosphatase activity and does not involve further downstream components of the insulin pathway, such as AKT and DAF-16 FOXO. Genetic and biochemical analyses indicate that DAF-18 negatively regulates vulval induction by inhibiting MAPK activation. Thus, mutations in the PTEN tumor suppressor gene may result in the simultaneous hyper-activation of two oncogenic signaling pathways.     

The role of the PI3K/AKT signalling pathway in the corneal epithelium: recent updates

Phosphatidylinositol 3 kinase (PI3K)/AKT (also called protein kinase B, PKB) signalling regulates various cellular processes, such as apoptosis, cell proliferation, the cell cycle, protein synthesis, glucose metabolism, and telomere activity. Corneal epithelial cells (CECs) are the outermost cells of the cornea; they maintain good optical performance and act as a physical and immune barrier. Various growth factors, including epidermal growth factor receptor (EGFR) ligands, insulin-like growth factor 1 (IGF1), neurokinin 1 (NK-1), and insulin activate the PI3K/AKT signalling pathway by binding their receptors and promote antiapoptotic, anti-inflammatory, proliferative, and migratory functions and wound healing in the corneal epithelium (CE). Reactive oxygen species (ROS) regulate apoptosis and inflammation in CECs in a concentration-dependent manner. Extreme environments induce excess ROS accumulation, inhibit PI3K/AKT, and cause apoptosis and inflammation in CECs. However, at low or moderate levels, ROS activate PI3K/AKT signalling, inhibiting apoptosis and stimulating proliferation of healthy CECs. Diabetes-associated hyperglycaemia directly inhibit PI3K/AKT signalling by increasing ROS and endoplasmic reticulum (ER) stress levels or suppressing the expression of growth factors receptors and cause diabetic keratopathy (DK) in CECs. Similarly, hyperosmolarity and ROS accumulation suppress PI3K/AKT signalling in dry eye disease (DED). However, significant overactivation of the PI3K/AKT signalling pathway, which mediates inflammation in CECs, is observed in both infectious and noninfectious keratitis. Overall, upon activation by growth factors and NK-1, PI3K/AKT signalling promotes the proliferation, migration, and anti-apoptosis of CECs, and these processes can be regulated by ROS in a concentration-dependent manner. Moreover, PI3K/AKT signalling pathway is inhibited in CECs from individuals with DK and DED, but is overactivated by keratitis.Subject terms: Growth factor signalling, Apoptosis, Extracellular matrix     

Combinatorial activation of FAK and AKT by transforming growth factor-beta1 confers an anoikis-resistant phenotype to myofibroblasts

Transforming growth factor-beta (TGF-beta) is a prototypical tumour-suppressor cytokine with cytostatic and pro-apoptotic effects on most target cells; however, mechanisms of its pro-survival/anti-apoptotic signalling in certain cell types and contexts remain unclear. In human lung fibroblasts, TGF-beta1 is known to induce myofibroblast differentiation in association with the delayed activation of focal adhesion kinase (FAK) and protein kinase B (PKB/AKT). Here, we demonstrate that FAK and AKT are independently regulated by early activation of SMAD3 and p38 MAPK, respectively. Pharmacologic or genetic approaches that disrupt SMAD3 signalling block TGF-beta1-induced activation of FAK, but not AKT; in contrast, disruption of early p38 MAPK signalling abrogates AKT activation, but does not alter FAK activation. TGF-beta1 is able to activate AKT in cells expressing mutant FAK or in cells treated with an RGD-containing peptide that interferes with integrin signalling, inhibits FAK activation and induces anoikis (apoptosis induced by loss of adhesion signalling). TGF-beta1 protects myofibroblasts from anoikis, in part, by activation of the PI3K-AKT pathway. Thus, TGF-beta1 co-ordinately and independently activates the FAK and AKT protein kinase pathways to confer an anoikis-resistant phenotype to myofibroblasts. Activation of these pro-survival/anti-anoikis pathways in myofibroblasts likely contributes to essential roles of TGF-beta1 in tissue fibrosis and tumour-promotion.     

大蒜阿霍烯抗胃癌的作用及分子机制*

目的: 探讨大蒜阿霍烯对胃癌细胞MGC-803的作用及相关分子机制。方法: 终浓度分别为0、1、5、25和125 μmol/L大蒜阿霍烯作用于细胞MGC-803 24 h、48 h和72 h,各设3复孔,MTS法检测细胞增殖活性,JC-1和Hoechst染色法观察线粒体膜电位和核型改变,LDH释放法检测细胞毒性,流式法分析细胞的凋亡和周期改变,RT-qPCR和Western blot检测P53、Caspase-3、RAS、ERK、BCL-2、AKT、mTOR、PI3K基因的表达,同时,取4周龄雄性BALB/C鼠随机分成5组,20只/组,腹股沟皮下接种胃癌细胞MGC-803,2 d后各组分别经皮下注射浓度为0 μmol/L、1 μmol/L、5 μmol/L、25 μmol/L、125 μmol/L的大蒜阿霍烯,0.1 ml/次,隔天注射一次,并于首次注射肿瘤细胞的第20日每组杀10只,取瘤组织,称重。记录剩余小鼠的存活期,观察大蒜阿霍烯对荷瘤小鼠胃癌生长及生存期的影响。结果: 大蒜阿霍烯可明显抑制MGC-803细胞增殖活性,诱导细胞凋亡(P＜0.01),显著上调P53、Caspase-3、BAX基因的转录和表达水平,抑制基因RAS、ERK1、BCL-2、AKT、mTOR和PI3K的表达(P＜0.01),显著抑制小鼠胃癌移植瘤生长,并延长荷瘤小鼠存活期(P＜0.01)。结论: 大蒜阿霍烯对胃癌有治疗作用,可通过调节PI3K-AKT-mTOR、RAS-RAF-MEK-ERK信号通路而抑制胃癌细胞增殖,诱导细胞凋亡。     

Synergistic targeted inhibition of MEK and dual PI3K/mTOR diminishes viability and inhibits tumor growth of canine melanoma underscoring its utility as a preclinical model for human mucosal melanoma

Human mucosal melanoma (MM), an uncommon, aggressive and diverse subtype, shares characteristics with spontaneous MM in dogs. Although BRAF and N‐RAS mutations are uncommon in MM in both species, the majority of human and canine MM evaluated exhibited RAS/ERK and/or PI3K/mTOR signaling pathway activation. Canine MM cell lines, with varying ERK and AKT/mTOR activation levels reflective of naturally occurring differences in dogs, were sensitive to the MEK inhibitor GSK1120212 and dual PI3K/mTOR inhibitor NVP‐BEZ235. The two‐drug combination synergistically decreased cell survival in association with caspase 3/7 activation, as well as altered expression of cell cycle regulatory proteins and Bcl‐2 family proteins. In combination, the two drugs targeted their respective signaling pathways, potentiating reduction of pathway mediators p‐ERK, p‐AKT, p‐S6, and 4E‐BP1 in vitro, and in association with significantly inhibited solid tumor growth in MM xenografts in mice. These findings provide evidence of synergistic therapeutic efficacy when simultaneously targeting multiple mediators in melanoma with Ras/ERK and PI3K/mTOR pathway activation.     

Characteristics of the PI3K/AKT and MAPK/ERK pathways involved in the maintenance of self-renewal in lung cancer stem-like cells

Lung cancer is the leading cause of cancer-related mortality worldwide due to its early asymptomatic and late metastasis. While cancer stem cells (CSCs) may play a vital role in oncogenesis and development of lung cancer, mechanisms underlying CSCs self‐renewal remain less clear. In the present study, we constructed a clinically relevant CSCs enrichment recognition model and evaluated the potential functions of phosphatidylinositol 3-kinase (PI3K)/AKT pathway (PI3K/AKT) and mitogen-activated protein kinases/extracellular signal-regulated kinase (MAPK/ERK) pathways in lung cancer via bioinformatic analysis, providing the basis for in depth mechanistic inquisition. Experimentally, we confirmed that PI3K/AKT pathway predominantly promotes proliferation through anti-apoptosis in lung adenocarcinoma cells, while MAPK/ERK pathway has an overwhelming superiority in regulating the proliferation in lung CSCs. Further, utilizing stemness score model, LLC-Symmetric Division (LLC-SD) cells and mouse orthotopic lung transplantation model, we elucidated an intricate cross-talk between the oncogenic pathway and the stem cell reprograming pathway that impact stem cell characteristics as well as cancer biology features of lung CSCs both in vitro and in vivo. In summary, our findings uncovered a new insight that PI3K/AKT and MAPK/ERK pathways as oncogenic signaling pathway and/or stem cell signaling pathway act distinctively and synergistically to regulate lung CSCs self-renewal.     

The C. elegans G-protein-coupled receptor SRA-13 inhibits RAS/MAPK signalling during olfaction and vulval development

In C. elegans, the RAS/MAPK pathway is used in different tissues to regulate various cell fate decisions. Several positive and negative regulators tightly control the activity of the RAS/MAPK pathway at different steps. We demonstrate a link between a G-protein-coupled receptor signalling pathway and the RAS/MAPK cascade. SRA-13, a member of the SRA family of chemosensory receptors, negatively regulates RAS/MAPK signalling during vulval induction and the olfaction of volatile attractants. Epistasis analysis indicates that SRA-13 inhibits the RAS/MAPK pathway at the level or upstream of MAPK. In both tissues, the vulval precursor cells and the chemosensory neurones, SRA-13 acts through the GPA-5 Galpha protein subunit, suggesting a common mechanism of crosstalk. Moreover, we find that vulval induction is repressed by food withdrawal during larval development and that SRA-13 activity is required for the suppression of vulval induction in response to food starvation. Thus, SRA-13 may serve to adapt the activity of the RAS/MAPK pathway to environmental conditions.     

PD-L1对细菌脓毒症免疫抑制的影响及其机制*

目的:探讨在脂多糖(LPS)所致细菌脓毒症免疫抑制中树突状细胞(DCs)程序性细胞死亡配体-1(PD-L1)的表达情况及其相关信号通路。方法:细菌脂多糖刺激骨髓来源树突状细胞诱导淋巴细胞免疫抑制模型,实验分为5组:对照组(Con)、脂多糖组(LPS)、2-(4-吗啉基)-8-苯基-4H-1-苯并吡喃-4-酮+脂多糖组(LY294002+LPS)、吡咯烷二硫代甲酸铵盐+脂多糖组(PDTC+LPS)和脂多糖+封闭PD-L1组(LPS+αPD-L1)。小鼠骨髓来源单核细胞用含粒细胞巨噬细胞集落刺激因子(rmGM-CSF 10 ng/ml)和白介素4(rmIL-4 1 ng/ml)的10%胎牛血清1640培养基于CO₂培养箱37℃静置培养4 d后,LPS(10 ng/ml)处理DCs静置12 h获得PD-L1高表达的DCs作为免疫抑制刺激细胞。通路抑制剂LY294002(10 μmol/L)、PDTC (20 μmol/L)作用1 h阻断PI3K和NF-κB信号。采用流式细胞分析、激光共聚焦显微成像检测LPS诱导树突状细胞PD-L1表达及磷脂酰肌醇3激酶/丝氨酸苏氨酸激酶B (PI3K/AKT) 信号通路活化情况;BrdU细胞增殖实验和γ-干扰素酶联免疫斑点实验检测LPS诱导树突状细胞PD-L1表达上调对抗原特异性T细胞增殖反应及细胞毒性T细胞杀伤作用的影响。结果:与对照组比较,LPS组DCs表面PD-L1阳性细胞百分比升高(P＜0.01),PD-L1荧光信号强度增强,且主要分布于细胞表面和细胞质,DCs介导的T细胞增殖水平降低(P＜0.01),γ-干扰素斑点形成细胞数下降(P＜0.01)。与LPS组比较,LY294002+LPS组、PDTC+LPS组和LPS+αPD-L1组PD-L1荧光信号强度降低,T细胞增殖水平升高(P＜0.01),γ-干扰素斑点形成细胞数上升(P＜0.01),改善树突状细胞介导的T细胞免疫抑制现象。 结论:PD-L1是介导脂多糖所致细菌脓毒症免疫抑制的关键分子,PI3K信号、NF-κB信号也参与此免疫抑制过程。     

MicroRNAs as important players in regulating cancer through PTEN/PI3K/AKT signalling pathways

Cancer being the leading cause of mortality has become a great threat worldwide. Current cancer therapeutics lack specificity and have side effects due to a lack of understanding of the molecular mechanisms and signalling pathways involved in carcinogenesis. In recent years, researchers have been focusing on several signalling pathways to pave the way for novel therapeutics. The PTEN/PI3K/AKT pathway is one of the important pathways involved in cell proliferation and apoptosis, leading to tumour growth. In addition, the PTEN/PI3K/AKT axis has several downstream pathways that could lead to tumour malignancy, metastasis and chemoresistance. On the other hand, microRNAs (miRNAs) are important regulators of various genes leading to disease pathogenesis. Hence studies of the role of miRNAs in regulating the PTEN/PI3K/AKT axis could lead to the development of novel therapeutics for cancer. Thus, in this review, we have focused on various miRNAs involved in the carcinogenesis of various cancer via the PTEN/PI3K/AKT axis.     

Features of the reversible sensitivity-resistance transition in PI3K/PTEN/AKT signalling network after HER2 inhibition

Systems biology approaches that combine experimental data and theoretical modelling to understand cellular signalling network dynamics offer a useful platform to investigate the mechanisms of resistance to drug interventions and to identify combination drug treatments. Extending our work on modelling the PI3K/PTEN/AKT signalling network (SN), we analyse the sensitivity of the SN output signal, phospho-AKT, to inhibition of HER2 receptor. We model typical aberrations in this SN identified in cancer development and drug resistance: loss of PTEN activity, PI3K and AKT mutations, HER2 overexpression, and overproduction of GSK3β and CK2 kinases controlling PTEN phosphorylation. We show that HER2 inhibition by the monoclonal antibody pertuzumab increases SN sensitivity, both to external signals and to changes in kinetic parameters of the proteins and their expression levels induced by mutations in the SN. This increase in sensitivity arises from the transition of SN functioning from saturation to non-saturation mode in response to HER2 inhibition. PTEN loss or PIK3CA mutation causes resistance to anti-HER2 inhibitor and leads to the restoration of saturation mode in SN functioning with a consequent decrease in SN sensitivity. We suggest that a drug-induced increase in SN sensitivity to internal perturbations, and specifically mutations, causes SN fragility. In particular, the SN is vulnerable to mutations that compensate for drug action and this may result in a sensitivity-to-resistance transition. The combination of HER2 and PI3K inhibition does not sensitise the SN to internal perturbations (mutations) in the PI3K/PTEN/AKT pathway: this combination treatment provides both synergetic inhibition and may prevent the SN from acquired mutations causing drug resistance. Through combination inhibition treatments, we studied the impact of upstream and downstream interventions to suppress resistance to the HER2 inhibitor in the SN with PTEN loss. Comparison of experimental results of PI3K inhibition in the PTEN upstream pathway with PDK1 inhibition in the PTEN downstream pathway shows that upstream inhibition abrogates resistance to pertuzumab more effectively than downstream inhibition. This difference in inhibition effect arises from the compensatory mechanism of an activation loop induced in the downstream pathway by PTEN loss. We highlight that drug target identification for combination anti-cancer therapy needs to account for the mutation effects on the upstream and downstream pathways.     

Activation of the PIK3CA/AKT pathway suppresses senescence induced by an activated RAS oncogene to promote tumorigenesis

Mutations in both RAS and the PTEN/PIK3CA/AKT signaling module are found in the same human tumors. PIK3CA and AKT are downstream effectors of RAS, and the selective advantage conferred by mutation of two genes in the same pathway is unclear. Based on a comparative molecular analysis, we show that activated PIK3CA/AKT is a weaker inducer of senescence than is activated RAS. Moreover, concurrent activation of RAS and PIK3CA/AKT impairs RAS-induced senescence. In?vivo, bypass of RAS-induced senescence by activated PIK3CA/AKT correlates with accelerated tumorigenesis. Thus, not all oncogenes are equally potent inducers of senescence, and, paradoxically, a weak inducer of senescence (PIK3CA/AKT) can be dominant over a strong inducer of senescence (RAS). For tumor growth, one selective advantage of concurrent mutation of RAS and PTEN/PIK3CA/AKT is suppression of RAS-induced senescence. Evidence is presented that this new understanding can be exploited in rational development and targeted application of prosenescence cancer therapies.     

Activation of the PI3K/AKT pathway in Merkel cell carcinoma

Merkel cell carcinoma (MCC) is a highly aggressive skin cancer with an increasing incidence. The understanding of the molecular carcinogenesis of MCC is limited. Here, we scrutinized the PI3K/AKT pathway, one of the major pathways activated in human cancer, in MCC. Immunohistochemical analysis of 41 tumor tissues and 9 MCC cell lines revealed high levels of AKT phosphorylation at threonine 308 in 88% of samples. Notably, the AKT phosphorylation was not correlated with the presence or absence of the Merkel cell polyoma virus (MCV). Accordingly, knock-down of the large and small T antigen by shRNA in MCV positive MCC cells did not affect phosphorylation of AKT. We also analyzed 46 MCC samples for activating PIK3CA and AKT1 mutations. Oncogenic PIK3CA mutations were found in 2/46 (4%) MCCs whereas mutations in exon 4 of AKT1 were absent. MCC cell lines demonstrated a high sensitivity towards the PI3K inhibitor LY-294002. This finding together with our observation that the PI3K/AKT pathway is activated in the majority of human MCCs identifies PI3K/AKT as a potential new therapeutic target for MCC patients.     

RNF7 promotes glioma growth via the PI3K/AKT signalling axis

RNF7 has been reported to play critical roles in various cancers. However, the underlying mechanisms of RNF7 in glioma development remain largely unknown. Herein, the expression level of RNF7 was examined in tissues by quantitative real-time PCR, Western blotting and immunohistochemistry. The effect of RNF7 on glioma progression was measured by performing CCK-8 and apoptosis assays, cell cycle-related experiments and animal experiments. The effect of RNF7 on PI3K/AKT signalling pathway was tested by Western blotting. First, we found that RNF7 was upregulated in tumour tissue compared with normal brain tissue, especially in high-grade glioma, and the high expression of RNF7 was significantly related to tumour size, Karnofsky Performance Scale score and a poor prognosis. Second, RNF7 overexpression facilitated tumour cell cycle progression and cell proliferation and suppressed apoptosis. Conversely, RNF7 knockdown suppressed tumour cell cycle progression and cell proliferation and facilitated apoptosis. Furthermore, follow-up mechanistic studies indicated that RNF7 could facilitate glioma cell proliferation and cell cycle progression and inhibit apoptosis by activating the PI3K/AKT signalling pathway. This study shows that RNF7 can clearly promote glioma cell proliferation by facilitating cell cycle progression and inhibiting apoptosis by activating the PI3K/AKT signalling pathway. Targeting the RNF7/PI3K/AKT axis may provide a new perspective on the prevention or treatment of glioma.