Exploring the gain of function contribution of AKT to mammary tumorigenesis in mouse models

The AKT1E17K Allele Promotes Breast Cancer in Mice

Simple Summary

The main finding reported in this manuscript is that the gain-of-function mutation AKT1E17K is a bona fide oncogene for mammary epithelium, being able to efficiently initiate breast cancer in mice. On the basis of high-molecular-weight cytokeratins expressed by AKT1E17K-derived tumors supported by additional integrative gene expression analysis these tumors resulted similar to human basal-like cancer, phenotypically and molecularly. These results indicate that the AKTE17K strain may represent an appropriate model of human basal-like breast cancer for the identification of novel therapies specific for this type of tumor.

Abstract

The gain-of-function mutation in the pleckstrin homology domain of AKT1 (AKT1E17K) occurs in lung and breast cancer. Through the use of human cellular models and of a AKT1E17K transgenic Cre-inducible murine strain (R26-AKT1E17K mice), we have demonstrated that AKT1E17K is a bona fide oncogene for lung epithelial cells. However, the role of AKT1E17K in breast cancer remains to be determined. Here, we report the generation and the characterization of a MMTV-CRE; R26-AKT1E17K mouse strain that expresses the mutant AKT1E17K allele in the mammary epithelium. We observed that AKT1E17K stimulates the development of mammary tumors classified as ductal adenocarcinoma of medium–high grade and presented a variety of proliferative alterations classified as adenosis with low-to-high grade dysplasia in the mammary epithelium. A subsequent immunohistochemical characterization suggested they were PR⁻/HER2⁻/ER⁺, basal-like and CK8⁻/CK10⁻/CK5⁺/CK14⁺. We also observed that, in parallel with an increased proliferation rate, tumors expressing mutant AKT1E17K presented an activation of the GSK3/cyclin D1 pathway in the mammary epithelium and cluster significantly with the human basal-like tumors. In conclusion, we demonstrate AKT1E17K is a bona fide oncogene that can initiate tumors at high efficiency in murine mammary epithelium in vivo.

Parecoxib inhibits esophageal squamous cell carcinoma progression via the PDK1-AKT pathway

BACKGROUND

Parecoxib plays an important role in inhibition of human cancer. However, the effect of parecoxib on esophageal squamous cell carcinoma (ESCC) is still not well known. The purpose of this study was to investigate the effect of parecoxib on ESCC and its underlying mechanism.

METHODS

RNA-sequence analysis was performed to identify functional alterations and mechanisms. Cell cycle, proliferation, invasion, and migration were assessed using flow cytometry, CCK-8 assay, colony formation, transwell, and wound healing assays. Extracellular matrix (ECM) degradation was detected by substrate gel zymography and 3D cell culture assay. Western blotting was used to detect parecoxib-dependent mechanisms involving cell cycle, proliferation, invasion, and migration. Tumor formation in vivo was detected by mouse assay.

RESULTS

Functional experiments indicated that parecoxib induced ESCC cell cycle arrest in G2 phase, and inhibited cell proliferation, invasion, and migration in vitro. Western blotting revealed that parecoxib downregulated the phosphorylation levels of AKT and PDK1, as well as the expression of the mutant p53, cyclin B1, and CDK1, while upregulating p21waf1. Parecoxib inhibited matrix metalloproteinase-2 (MMP2) secretion and invadopodia formation, which were related to ECM degradation. Furthermore, we found that parecoxib suppressed ESCC growth in heterotopic tumor models.

CONCLUSION

Parecoxib inhibits ESCC progression, including cell cycle, proliferation, invasion, and migration, via the PDK1-AKT signaling pathway.

DNA-PK promotes activation of the survival kinase AKT in response to DNA damage through an mTORC2-ECT2 pathway

[Figure: see text].

Common Genomic Aberrations in Mouse and Human Breast Cancers with Concurrent P53 Deficiency and Activated PTEN-PI3K-AKT Pathway

Simultaneous P53 loss and activation of the PTEN-restricted PI3K-AKT pathway frequently occur in aggressive breast cancers. P53 loss causes genome instability, while PTEN loss and/or activating mutations of PIK3CA and AKT promote cancer cell proliferation that also increases incidences of genomic aberrations. However, the genomic alterations associated with P53 loss and activated PTEN-PI3K-AKT signaling in breast cancer have not been defined. Spatiotemporally controlled breast cancer models with inactivation of both P53 and Pten in adult mice have not been established for studying genomic alterations. Herein, we deleted both floxed Pten and Tp53 genes in the mammary gland epithelial cells in adult mice using a RCAS virus-mediated Cre-expressing system. These mice developed small tumors in 21 weeks, and poorly differentiated larger tumors in 26 weeks. In these tumors, we identified 360 genes mutated by nonsynonymous point mutations and small insertions and deletions (NSPMs/InDels), 435 genes altered by copy number amplifications (CNAs), and 450 genes inactivated by copy number deletions (CNDs). Importantly, 22.2%, 75.9% and 27.3% of these genes were also altered in human breast tumors with P53 and PTEN losses or P53 loss and activated PI3K-AKT signaling by NSPMs/InDels, CNAs and CNDs, respectively. Therefore, inactivation of P53 and Pten in adult mice causes rapid-growing breast tumors, and these tumors recapitulate a significant number of genetic aberrations in human breast tumors with inactivated P53 and activated PTEN-PI3K-AKT signaling. Further characterization of these commonly altered genes in breast cancer should help to identify novel cancer-driving genes and molecular targets for developing therapeutics.

PRMT5-mediated arginine methylation activates AKT kinase to govern tumorigenesis

AKT is involved in a number of key cellular processes including cell proliferation, apoptosis and metabolism. Hyperactivation of AKT is associated with many pathological conditions, particularly cancers. Emerging evidence indicates that arginine methylation is involved in modulating AKT signaling pathway. However, whether and how arginine methylation directly regulates AKT kinase activity remain unknown. Here we report that protein arginine methyltransferase 5 (PRMT5), but not other PRMTs, promotes AKT activation by catalyzing symmetric dimethylation of AKT1 at arginine 391 (R391). Mechanistically, AKT1-R391 methylation cooperates with phosphatidylinositol 3,4,5 trisphosphate (PIP3) to relieve the pleckstrin homology (PH)-in conformation, leading to AKT1 membrane translocation and subsequent activation by phosphoinositide-dependent kinase-1 (PDK1) and the mechanistic target of rapamycin complex 2 (mTORC2). As a result, deficiency in AKT1-R391 methylation significantly suppresses AKT1 kinase activity and tumorigenesis. Lastly, we show that PRMT5 inhibitor synergizes with AKT inhibitor or chemotherapeutic drugs to enhance cell death. Altogether, our study suggests that R391 methylation is an important step for AKT activation and its oncogenic function.

Molecular stratification within triple-negative breast cancer subtypes

Triple-negative breast cancer (TNBC) has been subdivided into six distinct subgroups: basal-like 1 (BL1), basal-like 2 (BL2), mesenchymal (M), mesenchymal stem-like (MSL), immunomodulatory (IM), and luminal androgen receptor (LAR). We recently identified a subgroup of TNBC with loss of the tumor suppressor PTEN and five specific microRNAs that exhibits exceedingly poor clinical outcome and contains TP53 mutation, RB1 loss and high MYC and WNT signalling. Here, show that these PTEN-low/miRNA-low lesions cluster with BL1 TNBC. These tumors exhibited high RhoA signalling and were significantly stratified on the basis of PTEN-low/RhoA-signalling-high with hazard ratios (HRs) of 8.2 (P = 0.0009) and 4.87 (P = 0.033) in training and test cohorts, respectively. For BL2 TNBC, we identified AKT1 copy gain/high mRNA expression as surrogate for poor prognosis (HR = 3.9; P = 0.02 and HR = 6.1; P = 0.0032). In IM, programmed cell death 1 (PD1) was elevated and predictive of poor prognosis (HR = 5.3; P = 0.01 and HR = 3.5; P < 0.004). Additional alterations, albeit without prognostic power, characterized each subtype including high E2F2 and TGFβ signalling and CXCL8 expression in BL2, high IFNα and IFNγ signalling and CTLA4 expression in IM, and high EGFR signalling in MSL, and may be targeted for therapy. This study identified PTEN-low/RhoA-signalling-high, and high AKT1 and PD1 expression as potent prognostications for BL1, BL2 and IM subtypes with survival differences of over 14, 2.75 and 10.5 years, respectively. This intrinsic heterogeneity could be exploited to prioritize patients for precision medicine.

AKT in cancer: new molecular insights and advances in drug development

The phosphatidylinositol-3 kinase (PI3K)-AKT pathway is one of the most commonly dysregulated pathways in all of cancer, with somatic mutations, copy number alterations, aberrant epigenetic regulation and increased expression in a number of cancers. The carefully maintained homeostatic balance of cell division and growth on one hand, and programmed cell death on the other, is universally disturbed in tumorigenesis, and downstream effectors of the PI3K-AKT pathway play an important role in this disturbance. With a wide array of downstream effectors involved in cell survival and proliferation, the well-characterized direct interactions of AKT make it a highly attractive yet elusive target for cancer therapy. Here, we review the salient features of this pathway, evidence of its role in promoting tumorigenesis and recent progress in the development of therapeutic agents that target AKT.

Disruptive chemicals, senescence and immortality

Carcinogenesis is thought to be a multistep process, with clonal evolution playing a central role in the process. Clonal evolution involves the repeated 'selection and succession' of rare variant cells that acquire a growth advantage over the remaining cell population through the acquisition of 'driver mutations' enabling a selective advantage in a particular micro-environment. Clonal selection is the driving force behind tumorigenesis and possesses three basic requirements: (i) effective competitive proliferation of the variant clone when compared with its neighboring cells, (ii) acquisition of an indefinite capacity for self-renewal, and (iii) establishment of sufficiently high levels of genetic and epigenetic variability to permit the emergence of rare variants. However, several questions regarding the process of clonal evolution remain. Which cellular processes initiate carcinogenesis in the first place? To what extent are environmental carcinogens responsible for the initiation of clonal evolution? What are the roles of genotoxic and non-genotoxic carcinogens in carcinogenesis? What are the underlying mechanisms responsible for chemical carcinogen-induced cellular immortality? Here, we explore the possible mechanisms of cellular immortalization, the contribution of immortalization to tumorigenesis and the mechanisms by which chemical carcinogens may contribute to these processes.

Therapeutic targeting of replicative immortality

One of the hallmarks of malignant cell populations is the ability to undergo continuous proliferation. This property allows clonal lineages to acquire sequential aberrations that can fuel increasingly autonomous growth, invasiveness, and therapeutic resistance. Innate cellular mechanisms have evolved to regulate replicative potential as a hedge against malignant progression. When activated in the absence of normal terminal differentiation cues, these mechanisms can result in a state of persistent cytostasis. This state, termed “senescence,” can be triggered by intrinsic cellular processes such as telomere dysfunction and oncogene expression, and by exogenous factors such as DNA damaging agents or oxidative environments. Despite differences in upstream signaling, senescence often involves convergent interdependent activation of tumor suppressors p53 and p16/pRB, but can be induced, albeit with reduced sensitivity, when these suppressors are compromised. Doses of conventional genotoxic drugs required to achieve cancer cell senescence are often much lower than doses required to achieve outright cell death. Additional therapies, such as those targeting cyclin dependent kinases or components of the PI3K signaling pathway, may induce senescence specifically in cancer cells by circumventing defects in tumor suppressor pathways or exploiting cancer cells’ heightened requirements for telomerase. Such treatments sufficient to induce cancer cell senescence could provide increased patient survival with fewer and less severe side effects than conventional cytotoxic regimens. This positive aspect is countered by important caveats regarding senescence reversibility, genomic instability, and paracrine effects that may increase heterogeneity and adaptive resistance of surviving cancer cells. Nevertheless, agents that effectively disrupt replicative immortality will likely be valuable components of new combinatorial approaches to cancer therapy.

The PTEN/PI3K/AKT Pathway in vivo, Cancer Mouse Models

When PI3K (phosphatidylinositol-3 kinase) is activated by receptor tyrosine kinases, it phosphorylates PIP2 to generate PIP3 and activates the signaling pathway. Phosphatase and tensin homolog deleted on chromosome 10 dephosphorylates PIP3 to PIP2, and thus, negatively regulates the pathway. AKT (v-akt murine thymoma viral oncogene homolog; protein kinase B) is activated downstream of PIP3 and mediates physiological processes. Furthermore, substantial crosstalk exists with other signaling networks at all levels of the PI3K pathway. Because of its diverse array, gene mutations, and amplifications and also as a consequence of its central role in several signal transduction pathways, the PI3K-dependent axis is frequently activated in many tumors and is an attractive therapeutic target. The preclinical testing and analysis of these novel therapies requires appropriate and well-tailored systems. Mouse models in which this pathway has been genetically modified have been essential in understanding the role that this pathway plays in the tumorigenesis process. Here, we review cancer mouse models in which the PI3K/AKT pathway has been genetically modified.

PI3K/Akt-mediated regulation of p53 in cancer

Mutations activating the PI3K (phosphoinositide 3-kinase)/Akt signalling pathway and inactivating the TP53 tumour-suppressor gene are common mechanisms that cancer cells require to proliferate and escape pre-programmed cell death. In a well-described mechanism, Akt mediates negative control of p53 levels through enhancing MDM2 (murine double minute 2)-mediated targeting of p53 for degradation. Accumulating evidence is beginning to suggest that, in certain circumstances, PTEN (phosphatase and tensin homologue deleted on chromosome 10)/PI3K/Akt also promotes p53 translation and protein stability, suggesting that additional mechanisms may be involved in the Akt-mediated regulation of p53 in tumours. In the present article, we discuss these aspects in the light of clinical PI3K/Akt inhibitors, where information regarding the effect on p53 activity will be a crucial factor that will undoubtedly influence therapeutic efficacy.

Pten regulates development and lactation in the mammary glands of dairy cows

Pten is a tumor suppressor gene regulating many cellular processes, including growth, adhesion, and apoptosis. In the aim of investigating the role of Pten during mammary gland development and lactation of dairy cows, we analyzed Pten expression levels in the mammary glands of dairy cows by using western blotting, immunohistochemistry, and quantitative polymerase chain reaction (qPCR) assays. Dairy cow mammary epithelial cells (DCMECs) were used to study the function of Pten in vitro. We determined concentrations of β-casein, triglyceride, and lactose in the culture medium following Pten overexpression and siRNA inhibition. To determine whether Pten affected DCMEC viability and proliferation, cells were analyzed by CASY-TT and flow cytometry. Genes involved in lactation-related signaling pathways were detected. Pten expression was also assessed by adding prolactin and glucose to cell cultures. When Pten was overexpressed, proliferation of DCMECs and concentrations for β-casein, triglyceride, and lactose were significantly decreased. Overexpression of Pten down-regulated expression of MAPK, CYCLIN D1, AKT, MTOR, S6K1, STAT5, SREBP1, PPARγ, PRLR, and GLUT1, but up-regulated 4EBP1 in DCMECs. The Pten siRNA inhibition experiments revealed results that opposed those from the gene overexpression experiments. Introduction of prolactin (PRL) increased secretion of β-casein, triglyceride, and lactose, but decreased Pten expression levels. Introduction of glucose also increased β-casein and triglyceride concentrations, but did not significantly alter Pten expression levels. The Pten mRNA and protein expression levels were decreased 0.3- and 0.4-fold in mammary glands of lactating cows producing high quality milk (milk protein >3.0%, milk fat >3.5%), compared with those cows producing low quality milk (milk protein <3.0%, milk fat <3.5%). In conclusion, Pten functions as an inhibitor during mammary gland development and lactation in dairy cows. It can down-regulate DCMECs secretion of β-casein, triglyceride, and lactose, and plays a critical role in lactation related signaling pathways.

Activation of Akt1 accelerates carcinogen-induced tumorigenesis in mammary gland of virgin and post-lactating transgenic mice

Background

Data from in vivo and in vitro studies suggest that activation of Akt regulates cell survival signaling and plays a key role in tumorigenesis. Hence, transgenic mice were created to explore the oncogenic role of Akt1 in the development of mammary tumors.

Methods

The transgenic mice were generated by expressing myristoylated-Akt1 (myr-Akt1) under the control of the MMTV-LTR promoter. The carcinogen 7, 12 dimethyl-1,2-benzanthracene (DMBA) was used to induce tumor formation.

Results

The MMTV driven myr-Akt1 transgene expression was detected primarily in the mammary glands, uterus, and ovaries. The expression level increased significantly in lactating mice, suggesting that the response was hormone dependent. The total Akt expression level in the mammary gland was also higher in the lactating mice. Interestingly, the expression of MMTVmyr-Akt1 in the ovaries of the transgenic mice caused significant increase in circulating estrogen levels, even at the post-lactation stage. Expression of myr-Akt1 in mammary glands alone did not increase the frequency of tumor formation. However, there was an increased susceptibility of forming mammary tumors induced by DMBA in the transgenic mice, especially in mice post-lactation. Within 34 weeks, DMBA induced mammary tumors in 42.9% of transgenic mice post-lactation, but not in wild-type mice post-lactation. The myr-Akt1 mammary tumors induced by DMBA had increased phosphorylated-Akt1 and showed strong expression of estrogen receptor (ERα) and epidermal growth factor receptor (EGFR). In addition, Cyclin D1 was more frequently up-regulated in mammary tumors from transgenic mice compared to tumors from wild-type mice. Overexpression of Cyclin D1, however, was not completely dependent on activated Akt1. Interestingly, mammary tumors that had metastasized to secondary sites had increased expression of Twist and Slug, but low expression of Cyclin D1.

Conclusions

In summary, the MMTVmyr-Akt1 transgenic mouse model could be useful to study mechanisms of ER-positive breast tumor development.

The novel miR-9500 regulates the proliferation and migration of human lung cancer cells by targeting Akt1

MicroRNAs have crucial roles in lung cancer cell development. They regulate cell growth, proliferation and migration by mediating the expression of tumor suppressor genes and oncogenes. We identified and characterized the novel miR-9500 in human lung cancer cells. The miR-9500 forms a stem-loop structure and is conserved in other mammals. The expression levels of miR-9500 were reduced in lung cancer cells and lung cancer tissues compared with normal tissues, as verified by TaqMan miRNA assays. It was confirmed that the putative target gene, Akt1, was directly suppressed by miR-9500, as demonstrated by a luciferase reporter assay. The miR-9500 significantly repressed the protein expression levels of Akt1, as demonstrated via western blot, but did not affect the corresponding mRNA levels. Akt1 has an important role in lung carcinogenesis, and depletion of Akt1 has been shown to have antiproliferative and anti-migratory effects in previous studies. In the current study, the overexpression of miR-9500 inhibited cell proliferation and the expression of cell cycle-related proteins. Likewise, the overexpression of miR-9500 impeded cell migration in human lung cancer cells. In an in vivo assay, miR-9500 significantly suppressed Fluc expression compared with NC and ASO-miR-9500, suggesting that cell proliferation was inhibited in nude mice. Likewise, miR-9500 repressed tumorigenesis and metastasis by targeting Akt1. These data indicate that miR-9500 might be applicable for lung cancer therapy.

Markers of cellular senescence

Cellular senescence is a tumor suppression mechanism that evolved to limit duplication in somatic cells. Senescence is imposed by natural replicative boundaries or stress-induced signals, such as oncogenic transformation. Neoplastic cells can be forced to undergo senescence through genetic manipulations and epigenetic factors, including anticancer drugs, radiation, and differentiating agents. Senescent cells show distinct phenotypic and molecular characteristics, both in vitro or in vivo. These biomarkers might either cause or result from senescence induction, but could also be the byproducts of physiological changes in these non-replicating cells.

Rapid identification of ETP-46992, orally bioavailable PI3K inhibitor, selective versus mTOR

Phosphoinositide-3-kinases (PI3K) are a family of lipid kinases mediating numerous cell processes such as proliferation, migration and differentiation. PI3K is an important target for cancer therapeutics due to the deregulation of this signaling pathway in a wide variety of human cancers. Herein, we describe the rapid identification of ETP-46992, within 2-aminocarbonyl imidazo [1,2-a] pyrazine series, with suitable pharmacokinetic (PK) properties that allows the establishment of mechanism of action and efficacy in vivo studies. ETP-46992 showed tumor growth inhibition in a GEMM mouse tumor model driven by a K-Ras(G12V) oncogenic mutation and in tumor xenograft models with PI3K pathway deregulated (BT474).

Identification of ETP-46321, a potent and orally bioavailable PI3K α, δ inhibitor

Phosphoinositide-3-kinase (PI3K) is an important target for cancer therapeutics due to the deregulation of this signaling pathway in a wide variety of human cancers. Herein, we describe the optimization of imidazo [1,2-a] pyrazines, which allow us to identify compound 14 (ETP-46321), with potent biochemical and cellular activity and good pharmacokinetic properties (PK) after oral dosing. ETP-46321 PK/PD studies showed time dependent downregulation of AKT(Ser473) phosphorylation, which correlates with compound levels in tumor tissue and demonstrating to be efficacious in a GEMM mouse tumor model driven by a K-Ras(G12V) oncogenic mutation. Treatment with ETP-46321 resulted in significant tumor growth inhibition.

Roles of AKT1 and AKT2 in non-small cell lung cancer cell survival, growth, and migration

Although AKT ⁄ protein kinase B is constitutively active in nonsmall cell lung cancer (NSCLC) cells and is an attractive target for enhancing the cytotoxicity of therapeutic agents, the distinct roles of the AKT isoforms in NSCLC are largely unknown. In the present study, we investigated the roles of AKT1 and AKT2 in NSCLC cells using RNAi. The siRNA targeting of AKT1 or AKT2 effectively decreased protein levels of AKT1 and AKT2, respectively, in A549 and H460 cells. Cisplatin treatment of these cells increased apoptotic cell death compared with control. The siRNA-induced knockdown of AKT1 in H460 cells significantly decreased basal MEK⁄ ERK1 ⁄ 2 activity, resulting in nuclear factor-κB activation, whereas knockdown of AKT2 resulted in anti-apoptotic Bcl-2 family protein MCL-1 (MCL-1) cleavage, the collapse of mitochondrial membrane potential, cytochrome c release, and activation of the caspase cascade. Consequently, both siRNA treatments enhanced the chemosensitivity of H460 cells to cisplatin. However, neither AKT1 nor AKT2 siRNA treatment had any effect of p27 expression, and although both treatments tended to induced G₂ ⁄M phase arrest, the effect was not statistically significant. Treatment with AKT1 siRNA markedly decreased colony formation growth and migration, but AKT2 siRNA had no significant effects on these parameters. These data suggest that AKT1 and AKT2 both contribute to cell survival, albeit via different mechanisms, and that the effects on cell growth and migration are predominantly regulated by AKT1. These findings may aid in refining targeted strategies for the inhibition of AKT isoforms towards the sensitization of NSCLC cells to therapeutic agents.

Glucose metabolism measured by [¹⁸F]fluorodeoxyglucose positron emission tomography is independent of PTEN/AKT status in human colon carcinoma cells

The phosphoinositide 3-kinase (PI3K) signaling pathway is one of the most altered in cancer, leading to a range of cellular responses including enhanced proliferation, survival, and metabolism, and is thus an attractive target for anticancer drug development. Stimulation of the PI3K pathway can be initiated by alterations at different levels of the signaling cascade including growth factor receptor activation, as well as mutations in PIK3CA, PTEN, and AKT genes frequently found in a broad range of cancers. Given its role in glucose metabolism, we investigated the utility of [(18)F]fluorodeoxyglucose positron emission tomography ([(18)F]FDG PET) as a pharmacodynamic biomarker of PI3K pathway-induced glucose metabolism. PTEN deletion in human colon carcinoma cells led to constitutive AKT activation but did not confer a phenotype of increased cell proliferation or glucose metabolism advantage in vivo relative to isogenic tumors derived from cells with a wild-type allele. This was not due to the activation context, that is, phosphatase activity, per se because PIK3CA activation in xenografts derived from the same lineage failed to increase glucose metabolism. Acute inhibition of PI3K activity by LY294002, and hence decreased activated AKT expression, led to a significant reduction in tumor [(18)F]FDG uptake that could be explained at least in part by decreased membrane glucose transporter 1 expression. The pharmacodynamic effect was again independent of PTEN status. In conclusion, [(18)F]FDG PET is a promising pharmacodynamic biomarker of PI3K pathway inhibition; however, its utility to detect glucose metabolism is not directly linked to the magnitude of activated AKT protein expression.

Different conformations of phosphatase and tensin homolog, deleted on chromosome 10 (PTEN) protein within the nucleus and cytoplasm of neurons

PTEN is a critical gene involved in the regulation of many cellular processes. The product of this gene has dual phosphatase activity and is able to dephosphorylate the 5′ end of the phosphatidylinositol (3,4,5)-trisphosphate. Within the cellular nucleus, this protein has been associated with regulation of the expression of many genes, although the mechanism of this regulation remains unclear. In this paper, two specific oligonucleotide aptamers were developed and selected, using the SELEX procedure, according to their ability to detect the PTEN protein in different subcellular compartments of neurons. While one aptamer was able to detect PTEN in the nucleus, the other recognized PTEN in the cytoplasm. The recognition pattern of PTEN by both aptamers was confirmed using antibodies in western blots of the proteins purified from mouse cerebellar homogenates and subcellular fractions. Additionally, we demonstrated that the two aptamers recognized different epitopes of the target peptide. The results presented here could not be fully explained by the canonical phosphatase structure of PTEN, suggesting the existence of different conformations of phosphatase in the nucleus and the cytoplasm.

p53 and its mutants in tumor cell migration and invasion

In about half of all human cancers, the tumor suppressor p53 protein is either lost or mutated, frequently resulting in the expression of a transcriptionally inactive mutant p53 protein. Loss of p53 function is well known to influence cell cycle checkpoint controls and apoptosis. But it is now clear that p53 regulates other key stages of metastatic progression, such as cell migration and invasion. Moreover, recent data suggests that expression of mutant p53 is not the equivalent of p53 loss, and that mutant p53s can acquire new functions to drive cell migration, invasion, and metastasis, in part by interfering with p63 function.

Deciphering the role of PI3K/Akt/mTOR pathway in breast cancer biology and pathogenesis

The phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway mediates multiple cellular functions critical to tumor initiation, progression, and outcomes, including growth and proliferation, metabolism, motility, migration, invasion, angiogenesis, survival, and autophagy. Tight regulation of this pathway is paramount to ensure that multiple cellular inputs are integrated for appropriate cellular outcomes. Frequent deregulation and aberrations of this pathway have been implicated in breast cancer development and progression. This review focuses on the biology of this pathway and its role in breast cancer pathogenesis. The role of therapies directed at targeting mTOR in the PI3K/Akt/mTOR pathway, which are currently being evaluated in clinical trials, will also be reviewed.

The ethics of using transgenic non-human primates to study what makes us human

A flood of comparative genomic data is resulting in the identification of human lineage-specific (HLS) sequences. As apes are our closest evolutionary relatives, transgenic introduction of HLS sequences into these species has the greatest potential to produce 'humanized' phenotypes and also to illuminate the functions of these sequences. We argue that such transgenic apes would also be more likely than other species to experience harm from such research, which renders such studies ethically unacceptable in apes and justifies regulatory barriers between these species and other non-human primates for HLS transgenic research.