High cancer susceptibility and embryonic lethality associated with mutation of the PTEN tumor suppressor gene in mice

Genetics of the hamartomatous polyposis syndromes: a molecular review

BACKGROUND AND AIMS

Hamartomatous polyposis syndromes are a heterogeneous group of disorders that are inherited in an autosomal dominant fashion. These syndromes only represent a small number of the inherited gastrointestinal cancer predisposition syndromes. However, many of these syndromes carry a substantial risk for developing colorectal cancer, as well as extra-colonic malignancy.

MATERIALS AND METHODS

We searched for articles on inherited hamartomatous polyposis syndromes, including familial juvenile polyposis syndrome, Peutz-Jeghers syndrome, PTEN hamartoma tumor syndrome, multiple endocrine neoplasia syndrome 2B, hereditary mixed polyposis syndrome, Cronkhite-Canada syndrome, basal cell nevus syndrome, and neurofibromatosis 1, in PubMed, Embase, and Elsevier ScienceDirect. In this review, we briefly discuss the diagnosis and clinical features of these disorders and the molecular alterations responsible for these syndromes.

RESULTS AND CONCLUSION

Given the clinical similarities of these hamartomatous syndromes and the autosomal dominant pattern of inheritance, it is sometimes difficult to differentiate hamartomatous polyps, especially with atypical presentation. The molecular analysis and diagnosis make it possible to identify the subtype of these syndromes. In addition, these tests raise an intriguing possibility that surveillance and early medical intervention will allow for the identification of at-risk patients and the reduction of morbidity and mortality.

Molecular mechanisms underlying the activation of mammalian primordial follicles

In humans and other mammalian species, the pool of resting primordial follicles serves as the source of developing follicles and fertilizable ova for the entire length of female reproductive life. One question that has intrigued biologists is: what are the mechanisms controlling the activation of dormant primordial follicles. Studies from previous decades have laid a solid, but yet incomplete, foundation. In recent years, molecular mechanisms underlying follicular activation have become more evident, mainly through the use of genetically modified mouse models. As hypothesized in the 1990s, the pool of primordial follicles is now known to be maintained in a dormant state by various forms of inhibitory machinery, which are provided by several inhibitory signals and molecules. Several recently reported mutant mouse models have shown that a synergistic and coordinated suppression of follicular activation provided by multiple inhibitory molecules is necessary to preserve the dormant follicular pool. Loss of function of any of the inhibitory molecules for follicular activation, including PTEN (phosphatase and tensin homolog deleted on chromosome 10), Foxo3a, p27, and Foxl2, leads to premature and irreversible activation of the primordial follicle pool. Such global activation of the primordial follicle pool leads to the exhaustion of the resting follicle reserve, resulting in premature ovarian failure in mice. In this review, we summarize both historical and recent results on mammalian primordial follicular activation and focus on the up-to-date knowledge of molecular networks controlling this important physiological event. We believe that information obtained from mutant mouse models may also reflect the molecular machinery responsible for follicular activation in humans. These advances may provide a better understanding of human ovarian physiology and pathophysiology for future clinical applications.

Cell type specificity of PI3K signaling in Pdk1- and Pten-deficient brains

Loss of PTEN causes unregulated activation of downstream components of phosphatidylinositol 3-kinase (PI3K) signaling, including PDK1, and disrupts normal nervous system development and homeostasis. We tested the contribution of Pdk1 to the abnormalities induced by Pten deletion in the brain. Conditional deletion of Pdk1 caused microcephaly. Combined deletion of Pdk1 and Pten rescued hypertrophy, but not migration defects of Pten-deficient neurons. Pdk1 inactivation induced strikingly different effects on the regulation of phosphorylated Akt in glia versus neurons. Our results show Pdk1-dependent and Pdk1-independent abnormalities in Pten-deficient brains, and demonstrate cell type specific differences in feedback regulation of the ubiquitous PI3K pathway.

Mammalian phosphoinositide kinases and phosphatases

Phosphoinositides are lipids that are present in the cytoplasmic leaflet of a cell's plasma and internal membranes and play pivotal roles in the regulation of a wide variety of cellular processes. Phosphoinositides are molecularly diverse due to variable phosphorylation of the hydroxyl groups of their inositol rings. The rapid and reversible configuration of the seven known phosphoinositide species is controlled by a battery of phosphoinositide kinases and phosphoinositide phosphatases, which are thus critical for phosphoinositide isomer-specific localization and functions. Significantly, a given phosphoinositide generated by different isozymes of these phosphoinositide kinases and phosphatases can have different biological effects. In mammals, close to 50 genes encode the phosphoinositide kinases and phosphoinositide phosphatases that regulate phosphoinositide metabolism and thus allow cells to respond rapidly and effectively to ever-changing environmental cues. Understanding the distinct and overlapping functions of these phosphoinositide-metabolizing enzymes is important for our knowledge of both normal human physiology and the growing list of human diseases whose etiologies involve these proteins. This review summarizes the structural and biological properties of all the known mammalian phosphoinositide kinases and phosphoinositide phosphatases, as well as their associations with human disorders.

Simultaneous loss of the DLC1 and PTEN tumor suppressors enhances breast cancer cell migration

The phosphatase and tensin homolog (PTEN) gene is a tumor suppressor frequently deleted or mutated in sporadic tumors of the breast, prostate, endometrium and brain. The protein acts as a dual specificity phosphatase for lipids and proteins. PTEN loss confers a growth advantage to cells, protects from apoptosis and favors cell migration. The deleted in liver cancer 1 (DLC1) gene has emerged as a novel tumor suppressor downregulated in a variety of tumor types including those of the breast. DLC1 contains a Rho GTPase activating domain that is involved in the inhibition of cell proliferation, migration and invasion. To investigate how simultaneous loss of PTEN and DLC1 contributes to cell transformation, we downregulated both proteins by RNA interference in the non-invasive MCF7 breast carcinoma cell line. Joint depletion of PTEN and DLC1 resulted in enhanced cell migration in wounding and chemotactic transwell assays. Interestingly, both proteins were found to colocalize at the plasma membrane and interacted physically in biochemical pulldowns and coimmunoprecipitations. We therefore postulate that the concerted local inactivation of signaling pathways downstream of PTEN and DLC1, respectively, is required for the tight control of cell migration.

Rapamycin suppresses seizures and neuronal hypertrophy in a mouse model of cortical dysplasia

Malformations of the cerebral cortex known as cortical dysplasia account for the majority of cases of intractable childhood epilepsy. With the exception of the tuberous sclerosis complex, the molecular basis of most types of cortical dysplasia is completely unknown. Currently, there are no good animal models available that recapitulate key features of the disease, such as structural cortical abnormalities and seizures, hindering progress in understanding and treating cortical dysplasia. At the neuroanatomical level, cortical abnormalities may include dyslamination and the presence of abnormal cell types, such as enlarged and misoriented neurons and neuroglial cells. Recent studies in resected human brain tissue suggested that a misregulation of the PI3K (phosphoinositide 3-kinase)-Akt-mTOR (mammalian target of rapamycin) signaling pathway might be responsible for the excessive growth of dysplastic cells in this disease. Here, we characterize neuronal subset (NS)-Pten mutant mice as an animal model of cortical dysplasia. In these mice, the Pten gene, which encodes a suppressor of the PI3K pathway, was selectively disrupted in a subset of neurons by using Cre-loxP technology. Our data indicate that these mutant mice, like cortical dysplasia patients, exhibit enlarged cortical neurons with increased mTOR activity, and abnormal electroencephalographic activity with spontaneous seizures. We also demonstrate that a short-term treatment with the mTOR inhibitor rapamycin strongly suppresses the severity and the duration of the seizure activity. These findings support the possibility that this drug may be developed as a novel antiepileptic treatment for patients with cortical dysplasia and similar disorders.

Accumulating progenitor cells in the luminal epithelial cell layer are candidate tumor initiating cells in a Pten knockout mouse prostate cancer model

The PSA-Cre;Pten-loxP/loxP mouse prostate cancer model displays clearly defined stages of hyperplasia and cancer. Here, the initial stages of hyperplasia development are studied. Immunohistochemical staining showed that accumulated pAkt⁺ hyperplastic cells overexpress luminal epithelial cell marker CK8, and progenitor cell markers CK19 and Sca-1, but not basal epithelial cell markers. By expression profiling we identified novel hyperplastic cell markers, including Tacstd2 and Clu. Further we showed that at young age prostates of targeted Pten knockout mice contained in the luminal epithelial cell layer single pAkt⁺ cells, which overexpressed CK8, Sca-1, Tacstd2 and Clu; basal epithelial cells were always pAkt⁻. Importantly, in the luminal epithelial cell layer of normal prostates we detected rare Clu⁺Tacstd2⁺Sca-1⁺ progenitor cells. These novel cells are candidate tumor initiating cells in Pten knockout mice. Remarkably, all luminal epithelial cells in the proximal region of normal prostates were Clu⁺Tacstd2⁺Sca-1⁺. However, in PSA-Cre;Pten-loxP/loxP mice, the proximal prostate does not contain hyperplastic foci. Small hyperplastic foci in prostates of PSA-Cre;Pten-loxP/+ mice found at old age, showed complete Pten inactivation and a progenitor marker profile. Finally, we present a novel model of prostate development and renewal, including lineage-specific luminal epithelial progenitor cells. It is proposed that Pten deficiency induces a shift in the balance of differentiation to proliferation in these cells.

Prostate stem cell antigen: a prospective therapeutic and diagnostic target

The development of novel clinical tools to combat cancer is an intense field of research and recent efforts have been directed at the identification of proteins that may provide diagnostic, prognostic and/or therapeutic applications due to their restricted expression. To date, a number of protein candidates have emerged as potential clinical tools in the treatment of prostate cancer. Discovered over ten year ago, prostate stem cell antigen (PSCA) is a cell surface antigen that belongs to the Ly-6/Thy-1 family of glycosylphosphatidylinositol-anchored proteins. PSCA is highly overexpressed in human prostate cancer, with limited expression in normal tissues, making it an ideal target for both diagnosis and therapy. Several studies have now clearly correlated the expression of PSCA with relevant clinical benchmarks, such as Gleason score and metastasis, while others have demonstrated the efficacy of PSCA targeting in treatment through various modalities. The purpose of this review is to present the current body of knowledge about PSCA and its potential role in the treatment of human prostate cancer.

PTEN deficiency in a luminal ErbB-2 mouse model results in dramatic acceleration of mammary tumorigenesis and metastasis

Overexpression and/or amplification of the ErbB-2 oncogene as well as inactivation of the PTEN tumor suppressor are two important genetic events in human breast carcinogenesis. To address the biological impact of conditional inactivation of PTEN on ErbB-2-induced mammary tumorigenesis, we generated a novel transgenic mouse model that utilizes the murine mammary tumor virus (MMTV) promoter to directly couple expression of activated ErbB-2 and Cre recombinase to the same mammary epithelial cell (MMTV-NIC). Disruption of PTEN in the mammary epithelium of the MMTV-NIC model system dramatically accelerated the formation of multifocal and highly metastatic mammary tumors, which exhibited homogenous pathology. PTEN-deficient/NIC-induced tumorigenesis was associated with an increase in angiogenesis. Moreover, inactivation of PTEN in the MMTV-NIC mouse model resulted in hyperactivation of the phosphatidylinositol 3'-kinase/Akt signaling pathway. However, like the parental strain, tumors obtained from PTEN-deficient/NIC mice displayed histopathological and molecular features of the luminal subtype of primary human breast cancer. Taken together, our findings provide important implications in understanding the molecular determinants of mammary tumorigenesis driven by PTEN deficiency and ErbB-2 activation and could provide a valuable tool for testing the efficacy of therapeutic strategies that target these critical signaling pathways.

Mutations in phosphoinositide metabolizing enzymes and human disease

Phosphoinositides are implicated in the regulation of a wide variety of cellular functions. Their importance in cellular and organismal physiology is underscored by the growing number of human diseases linked to perturbation of kinases and phosphatases that catalyze interconversion from one phosphoinositide to another. Many such enzymes are attractive targets for therapeutic interventions. Here, we review diseases linked to inheritable or somatic mutations of these enzymes.

mTOR complex 2 is required for the development of prostate cancer induced by Pten loss in mice

mTOR complex 2 (mTORC2) contains the mammalian target of rapamycin (mTOR) kinase and the Rictor regulatory protein and phosphorylates Akt. Whether this function of mTORC2 is critical for cancer progression is unknown. Here, we show that transformed human prostate epithelial cells lacking PTEN require mTORC2 to form tumors when injected into nude mice. Furthermore, we find that Rictor is a haploinsufficient gene and that deleting one copy protects Pten heterozygous mice from prostate cancer. Finally, we show that the development of prostate cancer caused by Pten deletion specifically in prostate epithelium requires mTORC2, but that for normal prostate epithelial cells, mTORC2 activity is nonessential. The selective requirement for mTORC2 in tumor development suggests that mTORC2 inhibitors may be of substantial clinical utility.

PTEN deficiency accelerates tumour progression in a mouse model of thyroid cancer

Inactivation and silencing of PTEN have been observed in multiple cancers, including follicular thyroid carcinoma. PTEN (phosphatase and tensin homologue deleted from chromosome 10) functions as a tumour suppressor by opposing the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) signalling pathway. Despite correlative data, how deregulated PTEN signalling leads to thyroid carcinogenesis is not known. Mice harbouring a dominant-negative mutant thyroid hormone receptor beta (TRbeta(PV/PV) mice) spontaneously develop follicular thyroid carcinoma and distant metastases similar to human cancer. To elucidate the role of PTEN in thyroid carcinogenesis, we generated TRbeta(PV/PV) mice haploinsufficient for Pten (TRbeta(PV/PV)Pten(+/-) mouse). PTEN deficiency accelerated the progression of thyroid tumour and increased the occurrence of metastasis spread to the lung in TRbeta(PV/PV)Pten(+/-) mice, thereby significantly reducing their survival as compared with TRbeta(PV/PV)Pten(+/+) mice. AKT activation was further increased by two-fold in TRbeta(PV/PV)Pten(+/-) mice thyroids, leading to increased activity of the downstream mammalian target of rapamycin (mTOR)-p70S6K signalling and decreased activity of the forkhead family member FOXO3a. Consistently, cyclin D1 expression was increased. Apoptosis was decreased as indicated by increased expression of nuclear factor-kappaB (NF-kappaB) and decreased caspase-3 activity in the thyroids of TRbeta(PV/PV)Pten(+/-) mice. Our results indicate that PTEN deficiency resulted in increased cell proliferation and survival in the thyroids of TRbeta(PV/PV)Pten(+/-) mice. Altogether, our study provides direct evidence to indicate that in vivo, PTEN is a critical regulator in the follicular thyroid cancer progression and invasiveness.

Epithelial phosphatase and tensin homolog regulates intestinal architecture and secretory cell commitment and acts as a modifier gene in neoplasia

Phosphatase and tensin homolog (PTEN), a negative regulator of the phosphatidylinositol 3-kinase/Akt pathway, is one of the most frequently mutated/deleted tumor suppressor genes in human cancers. The aim of this study was to gain insight into the role played by PTEN in intestinal homeostasis and epithelial cell function. Using the Cre/loxP system, we have generated a mouse with a conditional intestinal epithelial Pten deficiency. Pten mutant mice and controls were sacrificed for histology, immunofluorescence, Western blot, and quantitative polymerase chain reaction analysis. Our results show that loss of epithelial Pten leads to an intestinalomegaly associated with an increase in epithelial cell proliferation. Histological analysis demonstrated significant perturbation of the crypt-villus architecture, a marked increase in goblet cells and a decrease in enteroendocrine cells, suggesting a role for Pten in the commitment of the multipotential-secretory precursor cell. Loss of epithelial Pten does not result in induction of nuclear beta-catenin protein levels, nor is it sufficient to promote tumorigenesis initiation. However, it severely enhances intestinal tumor load in Apc(Min/+) mice, in which c-Myc is already deregulated. These results reveal an unknown function for Pten signaling in the commitment of multipotential-secretory progenitor cells and suggest that epithelial Pten functions as a modifier gene in intestinal neoplasia.

A phosphorylation-dependent intramolecular interaction regulates the membrane association and activity of the tumor suppressor PTEN

The PI 3-phosphatase PTEN (phosphatase and tensin homologue deleted on chromosome 10), one of the most important tumor suppressors, must associate with the plasma membrane to maintain appropriate steady-state levels of phosphatidylinositol 3,4,5-triphosphate. Yet the mechanism of membrane binding has received little attention and the key determinants that regulate localization, a phosphatidylinositol 4,5-bisphosphate (PIP(2)) binding motif and a cluster of phosphorylated C-terminal residues, were not included in the crystal structure. We report that membrane binding requires PIP(2) and show that phosphorylation regulates an intramolecular interaction. A truncated version of the enzyme, PTEN(1-351), bound strongly to the membrane, an effect that was reversed by co-expression of the remainder of the molecule, PTEN(352-403). The separate fragments associated in vitro, an interaction dependent on phosphorylation of the C-terminal cluster, a portion of the PIP(2) binding motif, integrity of the phosphatase domain, and the CBR3 loop. Our investigation provides direct evidence for a model in which PTEN switches between open and closed states and phosphorylation favors the closed conformation, thereby regulating localization and function. Small molecules targeting these interactions could potentially serve as therapeutic agents in antagonizing Ras or PI3K-driven tumors. The study also stresses the importance of determining the structure of the native enzyme.

Genetic modelling of the PTEN/AKT pathway in cancer research

The focus on targeted therapies has been fuelled by extensive research on molecular pathways and their role in tumorigenesis. Novel models of human cancer have been created to evaluate the role of specific genes in the different stages of cancer. Currently, mouse modelling of human cancer is possible through the expression of oncogenes, specific genetic mutations or the inactivation of tumour suppressor genes, and these models have begun to provide us with an understanding of the molecular pathways involved in tumour initiation and progression at the physiological level. Additionally, these mouse models serve as an excellent system to evaluate the efficacy of currently developed molecular targeted therapies and identify new potential targets for future therapies. The PTEN/AKT pathway is implicated in signal transduction through tyrosine kinase receptors and heterotrimeric G protein-linked receptors. Deregulation of the PTEN/AKT pathway is a common event in human cancer. Despite the abundant literature, the physiological role of each element of the pathway has begun to be uncovered thanks to genetically engineered mice. This review will summarise some of the key animal models which have helped us to understand this signalling network and its contribution to tumorigenesis.

The role of PI3K signalling in the B cell response to antigen

The PI3K signalling pathway is crucial to normal B cell development and response to antigen. The p1108 catalytic subunit plays an important and non-redundant role within this pathway although other catalytic isoforms may also contribute. Although CD40, TLR and cytokines all activate PI3K the BCR seems especially dependent upon PI3K signalling. The downstream effects of PI3K may be mediated to a large extent by activation of PKB. In B cell development PI3K promotes development of MZ and Bl cells. In the response to antigen PI3K is crucial to BCR-mediated proliferation. PI3K activity has been shown to be inhibitory to CSR. The effects on immunoglobulin production and ASC differentiation are harder to disentangle from the developmental effects on cell populations and at present remain uncertain.

Irs2 inactivation suppresses tumor progression in Pten+/- mice

Mutations in the phosphatase and tensin homologue (PTEN)/phosphatidylinositol-3 kinase-alpha (PI3K) signaling pathway are frequently found in human cancer. In addition, Pten(+/-) mice develop tumors in multiple organs because of the activation of the PI3K signaling cascade. Because activation of PI3K signaling leads to feedback inhibition of insulin receptor substrate-2 (IRS2) expression, an upstream activator of PI3K, we therefore anticipated that IRS2 expression would be low in tumors that lack PTEN. Surprisingly, however, an elevation of IRS2 was often detected in tumor samples in which PTEN levels were compromised. To determine the potential contribution of Irs2 to tumor progression, Pten(+/-) mice were crossed with Irs2(+/-) mice. Deletion of Irs2 did not affect the initiation of neoplasia found in Pten(+/-) mice but suppressed cancer cell growth, proliferation, and invasion through the basement membrane. Deletion of Irs2 also attenuated the expression of Myc in prostatic intraepithelial neoplasia in Pten(+/-) mice. In addition, the expression levels of IRS2 and MYC were highly correlated in human prostate cancer, and IRS2 could stimulate MYC expression in cultured cells. Our findings provide evidence that the PI3K-activating adaptor Irs2 contributes to tumor progression in Pten(+/-) mice by stimulating both Myc and DNA synthesis.

PI3K/PTEN signaling in angiogenesis and tumorigenesis

Phosphatidylinositol 3-kinase (PI3K) and phosphatase and tensin homolog deleted on chromosome 10 (PTEN) signaling pathway play an important role in multiple cellular functions such as cell metabolism, proliferation, cell-cycle progression, and survival. PI3K is activated by growth factors and angiogenesis inducers such as vascular endothelial growth factor (VEGF) and angiopoietins. The amplification and mutations of PI3K and the loss of the tumor suppressor PTEN are common in various kinds of human solid tumors. The genetic alterations of upstream and downstream of PI3K signaling molecules such as receptor tyrosine kinases and AKT, respectively, are also frequently altered in human cancer. PI3K signaling regulates tumor growth and angiogenesis by activating AKT and other targets, and by inducing HIF-1 and VEGF expression. Angiogenesis is required for tumor growth and metastasis. In this review, we highlight the recent studies on the roles and mechanisms of PI3K and PTEN in regulating tumorigenesis and angiogenesis, and the roles of the downstream targets of PI3K for transmitting the signals. We also discuss the crosstalk of these signaling molecules and cellular events during tumor growth, metastasis, and tumor angiogenesis. Finally, we summarize the potential applications of PI3K, AKT, and mTOR inhibitors and their outcome in clinical trials for cancer treatment.

PTEN and the PI3-kinase pathway in cancer

PI3-kinase and PTEN are major positive and negative regulators, respectively, of the PI3-kinase pathway, which regulates growth, survival, and proliferation. These key signaling components are two of the most frequently mutated proteins in human cancers, resulting in unregulated activation of PI3K signaling and providing irrefutable genetic evidence of the central role of this pathway in tumorigenesis. PTEN regulates PI3K signaling by dephosphorylating the lipid signaling intermediate PIP(3), but PTEN may have additional phosphatase-independent activities, as well as other functions in the nucleus. In this review, we highlight current work showing cancer-relevant complexities in the regulation of PTEN and PI3K activity, potential novel functions for PTEN, and feedback regulation within the pathway. The significance and complexity of PI3K signaling make it an important but challenging therapeutic target for cancer.

The mechanism of action of the tumour suppressor gene PTEN

Intracellular levels of phosphorylation are regulated by the coordinated action of protein kinases and phosphatases. Disregulation of this balance can lead to cellular transformation. Here we review knowledge of the mechanisms of one protein phosphatase, the tumour suppressor PTEN/MMAC/TEP 1 apropos its role in tumorigenesis and signal transduction. PTEN plays an important role in the phosphatidyl-inositol-3-kinase (PI3-K) pathway by catalyzing degradation of phosphatidylinositol-(3,4,5)-triphosphate generated by PI3-K. This inhibits downstream targets mainly protein kinase B (PKB/Akt), cell survival and proliferation. PTEN contributes to cell cycle regulation by blockade of cells entering the S phase of the cell cycle, and by upregulation of p27(Kip1) which is recruited into the cyclin E/cdk2 complex. PTEN also modulates cell migration and motility by regulation of the extracellular signal-related kinase - mitogen activated protein kinase (ERK-MAPK) pathway and by dephosphorylation of focal adhesion kinase (FAK). We also emphasize the increasingly important role that PTEN has from an evolutionary point of view. A number of PTEN functions have been elucidated but more information is needed for utilization in clinical application and potential cancer therapy.

Genetically modified mouse models in cancer studies

Genetically modified animals represent a resource of immense potential for cancer research. Classically, genetic modifications in mice were obtained through selected breeding experiments or treatments with powerful carcinogens capable of inducing random mutagenesis. A new era began in the early 1980s when genetic modifications by inserting foreign DNA genes into the cells of an animal allowed for the development of transgenic mice. Since that moment, genetic modifications have been able to be made in a predetermined way. Gene targeting emerged later as a method of in vivo mutagenesis whereby the sequence of a predetermined gene is selectively modified within an intact cell. In this review we focus on how genetically modified mice can be created to study tumour development, and how these models have contributed to an understanding of the genetic alterations involved in human cancer. We also discuss the strengths and weaknesses of the different mouse models for identifying cancer genes, and understanding the consequences of their alterations in order to obtain the maximum benefit for cancer patients.

Phosphatase and tensin homolog (PTEN) regulates hepatic lipogenesis, microsomal triglyceride transfer protein, and the secretion of apolipoprotein B-containing lipoproteins

Hepatic apolipoprotein B (apoB) lipoprotein production is metabolically regulated via the phosphoinositide 3-kinase cascade; however, the role of the key negative regulator of this pathway, the tumor suppressor phosphatase with tensin homology (PTEN), is unknown. Here, we demonstrate that hepatic protein levels of apoB100 and microsomal triglyceride transfer protein (MTP) are significantly down-regulated (73% and 36%, respectively) in the liver of PTEN liver-specific knockout (KO) mice, and this is accompanied by increased triglyceride (TG) accumulation and lipogenic gene expression, and reduced hepatic apoB secretion in freshly isolated hepatocytes. MTP protein mass and lipid transfer activity were also significantly reduced in liver of PTEN KO mice. Overexpression of the dominant negative mutant PTEN C/S124 (adenovirus expressing PTEN C/S mutant [AdPTENC/S]) possessing constitutive phospoinositide 3-kinase activity in HepG2 cells led to significant reductions in both secreted apoB100 and cellular MTP mass (76% and 34%, respectively), and increased messenger RNA (mRNA) levels of sterol regulatory element binding protein 1c (SREBP-1c), fatty acid synthase (FAS), and acetyl-CoA carboxylase (ACC). Reduced apoB100 secretion induced by AdPTENC/S was associated with increased degradation of newly-synthesized cellular apoB100, in a lactacystin-sensitive manner, suggesting enhanced proteasomal degradation. AdPTENC/S also reduced apoB-lipoprotein production in McA-RH7777 and primary hamster hepatocytes. Our findings suggest a link between PTEN expression and hepatic production of apoB-containing lipoproteins. We postulate that perturbations in PTEN not only may influence hepatic insulin signaling and hepatic lipogenesis, but also may alter hepatic apoB-lipoprotein production and the MTP stability. On loss of PTEN activity, increased lipid substrate availability in the face of reduced hepatic lipoprotein production capacity can rapidly lead to hepatosteatosis and fatty liver.

Epithelial Pten is dispensable for intestinal homeostasis but suppresses adenoma development and progression after Apc mutation

PTEN acts as a tumor suppressor in a range of tissue types and has been implicated in the regulation of intestinal stem cells. To study Pten function in the intestine, we used various conditional transgenic strategies to specifically delete Pten from the mouse intestinal epithelium. We show that Pten loss specifically within the adult or embryonic epithelial cell population does not affect the normal architecture or homeostasis of the epithelium. However, loss of Pten in the context of Apc deficiency accelerates tumorigenesis through increased activation of Akt, leading to rapid development of adenocarcinoma. We conclude that Pten is redundant in otherwise normal intestinal epithelium and epithelial stem cells but, in the context of activated Wnt signaling, suppresses progression to adenocarcinoma through modulation of activated Akt levels.

Loss of PTEN expression is associated with colorectal cancer liver metastasis and poor patient survival

BACKGROUND

The tumour suppressor phosphatase and tensin homolog (PTEN) is an important negative regulator of cell-survival signaling. To evaluate the correlation between PTEN expression and clinicopathological characteristics of colorectal cancer patients with and without liver metastases, we investigated PTEN expression in primary colorectal cancer and colorectal cancer liver metastases.

METHODS

Sixty-nine pairs of primary colorectal cancer and corresponding liver metastasis specimens were analyzed immunohistochemically, and the correlation between immunohistochemical findings and clinicopathological factors was investigated. Seventy primary colorectal cancer specimens from patients without liver metastases were used as controls.

RESULTS

PTEN was strongly expressed in 44 (62.9%) colorectal cancer specimens from patients without liver metastases. In contrast, PTEN was weakly expressed in 52 (75.4%) primary colorectal cancer specimens from patients with liver metastases, and was absent in liver metastases. Weak PTEN expression in colorectal cancer tissues was significantly associated with advanced TNM stage (p < 0.01) and lymph node metastasis (p < 0.05). PTEN expression was significantly stronger in primary colorectal cancer specimens from patients without liver metastases. Furthermore, among colorectal cancer patients with liver metastases, the 5-year survival rate was significantly higher in patients with positive PTEN expression compared to those with negative PTEN expression (p = 0.012).

CONCLUSION

Our results suggest that loss of PTEN expression is involved with colorectal cancer aggressive capacity and that diagnostic evaluation of PTEN expression may provide valuable prognostic information to aid treatment strategies for colorectal cancer patients.

Akt as a therapeutic target in cancer

BACKGROUND

The phosphatidylinositol 3-kinase (PI3K)/phosphatase and tensin homolog (PTEN)/v-akt murine thymoma viral oncogene homolog (Akt)/mammalian target of rapamycin (mTOR) pathway is central in the transmission of growth regulatory signals originating from cell surface receptors.

OBJECTIVE

This review discusses how mutations occur that result in elevated expression the PI3K/PTEN/Akt/mTOR pathway and lead to malignant transformation, and how effective targeting of this pathway may result in suppression of abnormal growth of cancer cells.

METHODS

We searched the literature for articles which dealt with altered expression of this pathway in various cancers including: hematopoietic, melanoma, non-small cell lung, pancreatic, endometrial and ovarian, breast, prostate and hepatocellular.

RESULTS/CONCLUSIONS

The PI3K/PTEN/Akt/mTOR pathway is frequently aberrantly regulated in various cancers and targeting this pathway with small molecule inhibitors and may result in novel, more effective anticancer therapies.

The role of the PI3K-AKT kinase pathway in T-cell development beyond the beta checkpoint

The PI3K-AKT pathway can mediate diverse biological responses and is crucial for optimal immune responses and lymphocyte development. Deletion of PI3K subunits or AKT leads to blockage of T-cell development at the TCR-beta checkpoint. Studies with over-expression of constitutively activated AKT have implicated this pathway in anti-apoptosis of developing thymocytes and in development of regulatory T cells. However, the role of endogenous PI3K-AKT in T-cell development beyond the TCR-beta checkpoint remains unclear. Here, we inhibited the endogenous PI3K-AKT pathway in thymocytes after double negative stages by expressing the negative regulator, PTEN. These mice exhibit normal early T-cell development, but the transition from intermediate single positive to double positive (DP) thymocytes is inhibited, leading to a significantly decreased number of DP, single positive thymocytes and peripheral T cells. Proliferation of peripheral T cells is reduced but apoptosis of DP cells and subsequent T-cell maturation, including regulatory T cells, are normal. AKT phosphorylation can be readily observed in most WT T-cell compartments but not DP thymocytes in response to TCR activation. Thus, the PI3K-AKT pathway is crucial for the transition of intermediate single positive to DP thymocytes but is dispensable for apoptosis and maturation of developing thymocytes.

PTEN hamartoma tumor syndromes

The PTEN hamartoma tumor syndromes (PHTS) are a collection of rare clinical syndromes characterized by germline mutations of the tumor suppressor PTEN. These syndromes are driven by cellular overgrowth, leading to benign hamartomas in virtually any organ. Cowden syndrome (CS), the prototypic PHTS syndrome, is associated with increased susceptibility to breast, thyroid, and endometrial cancer. PTEN is located on chromosome 10q22-23 and negatively regulates the prosurvival PI3K/Akt/mTOR pathway through its lipid phosphatase activity. Loss of PTEN activates this pathway and leads to increased cellular growth, migration, proliferation, and survival. Clinical management of patients with PHTS, particularly those with CS, should include early and frequent screening, surveillance, and preventive care for associated malignancies. Concomitant with improved understanding of the biology of PTEN and the PI3K/Akt/mTOR pathway, inhibitors of this pathway are being developed as anticancer agents. These medications could have applications for patients with PHTS, for whom no medical options currently exist.

Strain-specific spontaneous and NNK-mediated tumorigenesis in Pten+/- mice

Pten is a negative regulator of the Akt pathway, and its inactivation is believed to be an etiological factor in many tumor types. Pten+/- mice are susceptible to a variety of spontaneous tumor types, depending on strain background. Pten+/- mice, in lung tumor-sensitive and -resistant background strains, were treated with a tobacco carcinogen, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), to determine whether allelic Pten deletion can cooperate with NNK in carcinogenesis in lung or other tissues. In lung tumor-resistant C57BL/6 Pten+/- or +/+ mice, NNK treatment did not lead to any lung tumors and did not increase the incidence or severity of tumors previously reported for this strain. In contrast, in a lung tumor-susceptible pseudo-A/J strain, there was a dose-dependent increase in lung tumor size in Pten+/- compared with +/+ mice, although there was no increase in multiplicity. No other tumor types were observed in pseudo-A/J Pten+/- mice regardless of NNK treatment. Lung tumors from these Pten+/- mice had K-ras mutations, retained Pten expression and had similar Akt pathway activation as lung tumors from +/+ mice. Therefore, deletion of a single copy of Pten does not substantially add to the lung tumor phenotype conferred by mutation of K-ras by NNK, and there is likely no selective advantage for loss of the second Pten allele in lung tumor initiation.

PTEN: a new guardian of the genome

The phosphatase and tensin homolog deleted on chromosome 10 (PTEN) tumor suppressor is a phosphatase that antagonizes the phosphoinositol-3-kinase/AKT signaling pathway and suppresses cell survival as well as cell proliferation. PTEN is the second most frequently mutated gene in human cancer after p53. Germline mutations of PTEN have been found in cancer susceptibility syndromes, such as Cowden syndrome, in which over 80% of patients have mutations of PTEN. Homozygous deletion of Pten causes embryonic lethality, suggesting that PTEN is essential for embryonic development. Mice heterozygous for Pten develop spontaneous tumors in a variety of organs comparable with the spectrum of its mutations in human cancer. The mechanisms of PTEN functions in tumor suppression are currently under intense investigation. Recent studies demonstrate that PTEN plays an essential role in the maintenance of chromosomal stability and that loss of PTEN leads to massive alterations of chromosomes. The tumor suppressor p53 is known as a guardian of the genome that mediates the cellular response to environmental stress, leading to cell cycle arrest or cell death. Through completely different mechanisms, PTEN also protects the genome from instability. Thus, we propose that PTEN is a new guardian of the genome. In this review, we will discuss new discoveries on the role of PTEN in tumor suppression and explore mechanisms by which PTEN maintains genomic stability.

The roles of PTEN in development, physiology and tumorigenesis in mouse models: a tissue-by-tissue survey

In 1997, PTEN (phosphatase and tensin homologue deleted on chromosome 10, 10q23.3) was identified as an important tumor suppressor gene that is inactivated in a wide variety of human cancers. Ever since, PTEN's function has been extensively studied, and huge progress has been made in understanding PTEN's role in normal physiology and disease. In this review, we will systematically summarize the important data that have been gained from gene inactivation studies in mice and will put these data into physiological context using a tissue-by-tissue approach. We will cover mice exhibiting complete and constitutive inactivation of Pten as well as a large number of strains in which Pten has been conditionally deleted in specific tissues. We hope to highlight not only the tumor suppressive function of Pten but also its roles in embryogenesis and in the maintenance of the normal physiological functions of many organ systems.

Genetic and phenotypic heterogeneity in the PTEN hamartoma tumour syndrome

Germline PTEN (Phosphatase and TENsin homologue deleted on chromosome TEN) mutations predispose to phenotypically diverse disorders that share several overlapping clinical features: Cowden syndrome, Bannayan-Riley-Ruvalcaba syndrome, Proteus syndrome and Proteus-like syndrome, collectively classified as PTEN hamartoma tumour syndrome (PHTS). The meticulous acquisition and documentation of PHTS phenotypic data at different levels and the profiling of the plethora of genetic changes in PTEN and other genes within the same or related pathways are important in resolving the challenge of discriminating heritable cancers from sporadic PHTS-mimicking clinical features. The characterization of PTEN and PTEN-related pathways from a multidisciplinary perspective underscores the importance of incorporating data from different -omics, which is crucial for the advancement of personalized medicine.

Recent advances in the genetic analysis of PTEN and PI3K innate immune properties

The role of the PI3-kinase pathway and its antagonist PTEN in the regulation of innate immune responses has only recently attracted the attention of the scientific community. The PI3K/PTEN signaling axis is most renowned for its critical involvement in the malignant transformation of cells leading to tumorigenesis. PI3K function in the regulation of innate immunity, either pro-inflammatory or anti-inflammatory, is still a controversial issue. Undoubtedly, PI3K serves as an essential pro-inflammatory signaling molecule to activate leukocytes, initiate migration and facilitate phagocytosis. Nevertheless, it is less clear how PI3K and PTEN modulate the amplitude of immune responses. Here, we review recent advances on the immune biology by means of reverse genetics analyzing the role of the PI3K/PTEN signaling cascade in innate immunity.

Functional integration of microRNAs into oncogenic and tumor suppressor pathways

A large body of evidence has documented abnormal microRNA (miRNA) expression patterns in diverse human malignancies. Given that miRNA expression is tightly regulated during development and cellular differentiation, aberrant miRNA expression in cancer cells is likely to be in part a consequence of the loss of normal cellular identity that accompanies malignant transformation. Nevertheless, it is now clear that miRNAs function as critical effectors of several canonical oncogenic and tumor suppressor pathways, including those controlled by Myc and p53. Gain- and loss-of-function of these factors in cancer cells contributes to miRNA dysregulation, directly influencing neoplastic phenotypes including cellular proliferation and apoptosis.

Regulation of T-cell responses by PTEN

The phosphoinositide 3-kinase (PI3K) signaling pathway plays a critical role in the development, activation, and homeostasis of T cells by modulating the expression of survival and mitogenic factors in response to a variety of stimuli. Ligation of the antigen receptor, costimulatory molecules, and cytokine receptors activate PI3K, resulting in the production of the lipid second messenger phosphatidylinositol-3,4,5-triphosphate (PIP(3)). A number of molecules help to regulate the activity of this pathway, including the lipid phosphatase PTEN (phosphatase and tensin homolog deleted on chromosome 10). By limiting the amount of PIP(3) available within the cell, PTEN directly opposes PI3K activity and influences the selection of developing thymocytes as well as the activation requirements of mature T cells. T cells with unchecked PI3K activity, as a result of PTEN deficiency, contribute to the development of both autoimmune disease and lymphoma. This review dissects our current understanding of PI3K and PTEN and discusses why appropriate balance of these molecules is necessary to maintain normal T-cell responses.

Loss of the SSeCKS/Gravin/AKAP12 gene results in prostatic hyperplasia

SSeCKS/Gravin/AKAP12 (SSeCKS) is a kinase scaffolding protein that encodes metastasis-suppressor activity through the suppression of Src-mediated oncogenic signaling and vascular endothelial growth factor expression. SSeCKS expression is down-regulated in Src- and Ras-transformed fibroblasts, in human cancer cell lines and in several types of human cancer, including prostate. Normal human and mouse prostates express abundant SSeCKS in secretory epithelial cells and, to a lesser extent, in the surrounding mesenchyme. Here, we show that the loss of SSeCKS results in prostatic hyperplasia in the anterior and ventral lobes as well as increased levels of apoptosis throughout the prostate. Dysplastic foci were observed less frequently but were associated with the loss of E-cadherin staining and the loss of high molecular weight cytokeratin-positive basal epithelial cells. SSeCKS-null prostate tissues expressed significantly higher relative levels of AKT(poS473) compared with wild-type controls, suggesting that SSeCKS attenuates phosphatidylinositol-3-OH kinase signaling. The data suggest that SSeCKS-null mice have increased susceptibility for oncogenic transformation in the prostate.

Important role of the LKB1-AMPK pathway in suppressing tumorigenesis in PTEN-deficient mice

The LKB1 tumour suppressor phosphorylates and activates AMPK (AMP-activated protein kinase) when cellular energy levels are low, thereby suppressing growth through multiple pathways, including inhibiting the mTORC1 (mammalian target of rapamycin complex 1) kinase that is activated in the majority of human cancers. Blood glucose-lowering Type 2 diabetes drugs also induce LKB1 to activate AMPK, indicating that these compounds could be used to suppress growth of tumour cells. In the present study, we investigated the importance of the LKB1-AMPK pathway in regulating tumorigenesis in mice resulting from deficiency of the PTEN (phosphatase and tensin homologue deleted on chromosome 10) tumour suppressor, which drives cell growth through overactivation of the Akt and mTOR (mammalian target of rapamycin) kinases. We demonstrate that inhibition of AMPK resulting from a hypomorphic mutation that decreases LKB1 expression does not lead to tumorigenesis on its own, but markedly accelerates tumour development in PTEN(+/-) mice. In contrast, activating the AMPK pathway by administration of metformin, phenformin or A-769662 to PTEN(+/-) mice significantly delayed tumour onset. We demonstrate that LKB1 is required for activators of AMPK to inhibit mTORC1 signalling as well as cell growth in PTEN-deficient cells. Our findings highlight, using an animal model relevant to understanding human cancer, the vital role that the LKB1-AMPK pathway plays in suppressing tumorigenesis resulting from loss of the PTEN tumour suppressor. They also suggest that pharmacological inhibition of LKB1 and/or AMPK would be undesirable, at least for the treatment of cancers in which the mTORC1 pathway is activated. Most importantly, our results demonstrate the potential of AMPK activators, such as clinically approved metformin, as anticancer agents, which will suppress tumour development by triggering a physiological signalling pathway that potently inhibits cell growth.

Tenets of PTEN tumor suppression

Since its discovery as the elusive tumor suppressor gene at the frequently mutated 10q23 locus, PTEN has been identified as lost or mutated in several sporadic and heritable tumor types. A decade of work has established that PTEN is a nonredundant phosphatase that is essential for regulating the highly oncogenic prosurvival PI3K/AKT signaling pathway. This review discusses emerging modes of PTEN function and regulation, and speculates about how manipulation of PTEN function could be used for cancer therapy.

Pten haploinsufficiency accelerates formation of high-grade astrocytomas

We previously reported that central nervous system (CNS) inactivation of Nf1 and p53 tumor suppressor genes in mice results in the development of low-grade to high-grade progressive astrocytomas. When the tumors achieve high grade, they are frequently accompanied by Akt activation, reminiscent of the frequent association of PTEN mutations in human high-grade glioma. In the present study, we introduced CNS heterozygosity of Pten into the Nf1/p53 astrocytoma model. Resulting mice had accelerated morbidity, shortened survival, and full penetrance of high-grade astrocytomas. Haploinsufficiency of Pten accelerated formation of grade 3 astrocytomas, whereas loss of Pten heterozygosity and Akt activation coincided with progression into grade 4 tumors. These data suggest that successive loss of each Pten allele may contribute to de novo formation of high-grade astrocytoma and progression into glioblastoma, respectively, thus providing insight into the etiology of primary glioblastoma. The presence of ectopically migrating neural stem/progenitor lineage cells in presymptomatic Pten-deficient mutant brains supports the notion that these tumors may arise from stem/progenitor cells.

Clinicopathological significance of PTEN loss and the phosphoinositide 3-kinase/Akt pathway in sporadic colorectal neoplasms: is PTEN loss predictor of local recurrence?

BACKGROUND

PTEN is a tumor-suppressor gene located on chromosome 10. Deficient PTEN expression leads to activation of the phosphoinositide 3-kinase (PI3K)/Akt (pAkt) signaling pathway, which may contribute to multiple human cancers. The relation between PTEN expression and Akt activation is still unclear in colorectal cancers and adenomatous polyps. Moreover, PTEN and pAkt expression in relation to demographic, tumoral, and outcome variables remains to be elucidated.

METHODS

PTEN and pAkt expression were evaluated in 76 primary colorectal cancers and 25 adenomatous colorectal polyp tissues using immunohistochemical staining on paraffin-embedded sections. PTEN and pAkt expression were compared with clinicopathologic features of colorectal cancers. The relationship between PTEN and pAkt expression was also investigated.

RESULTS

In colorectal cancers, pAkt expression was found to be significantly higher than polyps (P = .007). On the other hand, PTEN expression was significantly lower in polyps (P <.0001). In colorectal cancer patients, PTEN expression showed a negative correlation with young age, female sex, and left-sided (distal) tumors. On multivariate analysis, low PTEN expression (PTEN loss) was noted as an independent parameter for local recurrence (P = .024). There was significant association between pAkt expression and stage (P = .008), and preoperative serum carcinoembryonic antigen (CEA) levels (P = .017) in colorectal cancers. A negative correlation between PTEN and pAkt expression was found in colon cancer patients (P = .010), whereas no significiant association was found in adenomatous polyps (P = .403). No correlation of PTEN expression or pAkt expression was observed in Kaplan-Meier survival statistics and multivariate analyses for disease-free and overall survival.

CONCLUSIONS

The current study suggests that the PTEN loss-PI3K/pAkt pathway may play an important role in sporadic colon carcinogenesis and that reduced PTEN expression may predict relapse in colorectal cancer patients.

The protein phosphatase activity of PTEN regulates SRC family kinases and controls glioma migration

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is mutated or lost in 60% to 70% of advanced gliomas and is associated with malignant phenotypic changes such as migration, which contribute to the morbidity and mortality of this disease. Most of the tumor suppressor function of PTEN has been attributed to its ability to dephosphorylate the second messenger, phosphatidylinositol 3,4,5-triphosphate, resulting in the biological control of the phosphatidylinositol 3-kinase (PI3K)/AKT pathway. Despite recent work suggesting that the protein phosphatase activity of PTEN controls glioma cell migration, the mechanisms by which this occurs are unclear. Herein, we show using glioma cell lines (U87MG and U373MG) stably transfected with wild-type PTEN or catalytically altered mutants of PTEN that PTEN controls integrin-directed migration in a lipid phosphatase, PI3K/AKT-independent manner. Confirming this observation, we show that the stable overexpression of COOH-terminal Src kinase, the physiologic negative regulator of SRC family kinases (SFK), or treatment with the SFK inhibitor PP1 abrogates glioma migration. The results provide direct evidence that the downstream effect of the protein phosphatase activity of PTEN is to suppress SFK and FYN, and to regulate RAC-GTPase activity after alpha(v) integrin stimulation. Furthermore, studying vitronectin-directed migration using (a) Fyn small interfering RNA and (b) astrocytes from Fyn heterozygous (+/-) mice, Pten heterozygous (+/-) mice, Pten and Fyn double heterozygous (+/-) mice, or Fyn knockout (-/-) mice confirmed a role of FYN in alpha(v) integrin-mediated haptotaxis in glial cells. Our combined results provide direct biochemical and genetic evidence that PTEN's protein phosphatase activity controls FYN kinase function in glioma cells and regulates migration in a PI3K/AKT-independent manner.

Lymphoproliferative disease and autoimmunity in mice with increased miR-17-92 expression in lymphocytes

The genomic region encoding the miR-17-92 microRNA (miRNA) cluster is often amplified in lymphoma and other cancers, and cancer cells carrying this amplification have higher expression of miRNA in this cluster. Retroviral expression of miR-17-92 accelerates c-Myc-induced lymphoma development, but precisely how higher expression of miR-17-92 promotes lymphomagenesis remains unclear. Here we generated mice with higher expression of miR-17-92 in lymphocytes. These mice developed lymphoproliferative disease and autoimmunity and died prematurely. Lymphocytes from these mice showed more proliferation and less activation-induced cell death. The miR-17-92 miRNA suppressed expression of the tumor suppressor PTEN and the proapoptotic protein Bim. This mechanism probably contributed to the lymphoproliferative disease and autoimmunity of miR-17-92-transgenic mice and contributes to lymphoma development in patients with amplifications of the miR-17-92 coding region.

Antigen-induced Pten gene deletion in T cells exacerbates neuropathology in experimental autoimmune encephalomyelitis

The Pten tumor suppressor gene is critical for normal intrathymic development of T cells; however, its role in mature antigen-activated T cells is less well defined. A genetically crossed mouse line, Pten(fl/fl) GBC, in which Pten gene deletions could be primarily confined to antigen-activated CD8+ T cells, enabled us to evaluate the consequences of Pten loss on the course of experimental autoimmune encephalomyelitis. Compared with Pten(fl/fl) controls, myelin oligodendrocyte glycoprotein (MOG) peptide-immunized Pten(fl/fl) GBC mice developed more severe and protracted disease. This was accompanied by increased spinal cord white matter myelin basic protein depletion and axonal damage, as well as a striking persistence of macrophage and granzyme B-expressing cellular neuroinfiltrates in the chronic phase of the disease. This persistence may be explained by the observation that anti-CD3 activated Pten(fl/fl) GBC T cells were more resistant to proapoptotic stimuli. Consistent with the predicted consequences of Pten loss, purified CD8+ T cells from Pten(fl/fl) GBC mice displayed augmented proliferative responses to anti-T-cell receptor stimulation, and MOG-primed Pten(fl/fl) GBC T cells exhibited a reduced activation threshold to MOG peptide. Pten(fl/fl) GBC mice also developed atypical central nervous system disease, manifested by prominent cervical cord and forebrain involvement. Collectively, our findings indicate that the phosphatidylinositol 3-kinase signaling pathway is an essential regulator of CD8+ T-cell effector function in experimental autoimmune encephalomyelitis.

Pten inactivation accelerates oncogenic K-ras-initiated tumorigenesis in a mouse model of lung cancer

Phosphatase and tensin homologue deleted from chromosome 10 (Pten) is expressed aberrantly in non-small cell lung cancer cells, but the role of Pten in lung neoplasia has not been fully elucidated. In this study, we used a genetic approach to inactivate Pten in the bronchial epithelium of mice. Although, by itself, Pten inactivation had no discernible effect on bronchial epithelial histology, it accelerated lung tumorigenesis initiated by oncogenic K-ras, causing more rapid lethality than that induced by oncogenic K-ras alone (8 weeks versus 24 weeks of median duration of survival, respectively). Lung tumors arose in K-ras mutant, Pten-deficient mice that rapidly obstructed bronchial lumina and replaced alveolar spaces. Relative to K-ras mutant tumors, the K-ras mutant, Pten-deficient tumors exhibited more advanced histologic severity and more prominent inflammation and vascularity. Thus, Pten inactivation cooperated with oncogenic K-ras in promoting lung tumorigenesis.

Low expression of FHIT and PTEN correlates with malignancy of gastric carcinomas: tissue-array findings

To clarify the roles of FHIT (fragile histidine triad) and PTEN (phosphatase and tensin homology deleted from human chromosome 10) expression in the genesis and progression of gastric cancers, we examined expression of FHIT and PTEN on tissue microarray containing gastric normal mucosa (n=49), adenoma (n=49), noncancerous mucosa adjacent to carcinoma (n=84) and carcinoma (n=249) by immunohistochemistry. Their expression was compared with clinicopathologic parameters of tumors, including expression of p53 and cysteine protease protein 32 as well as survival time of patients with carcinoma. The results showed expression of FHIT and PTEN were lower in gastric carcinoma than those in normal mucosa, noncancerous mucosa adjacent to carcinoma and adenoma of the stomach (P<0.05). FHIT and PTEN expression showed a significantly negative association with depth of invasion, lymphatic invasion, and lymph node metastasis, liver metastasis, and Union Internationale Contre le Cancer staging of gastric carcinoma (P<0.05). Intestinal-type gastric carcinomas highly expressed FHIT and PTEN protein, compared with diffuse-type ones (P<0.05). Expression of FHIT and PTEN were positively related with expression of p53 and cysteine protease protein 32 in gastric carcinoma (P<0.05), as well as favorable prognosis of the patients with the tumors (P<0.05). There was positive relationship between FHIT and PTEN expression in gastric carcinoma (P<0.05). It was suggested that down-regulated expression of FHIT and PTEN contributed to gastric carcinogenesis possibly by involving in the imbalance between apoptosis and proliferation of cells. Their altered expression underlay the molecular basis of invasion, metastasis, differentiation of gastric carcinoma.

Portrait of PTEN: messages from mutant mice

PTEN is a tumor suppressor gene mutated in many human sporadic cancers and in hereditary cancer syndromes such as Cowden disease. The major substrate of PTEN is phosphatidylinositol-3,4,5-trisphosphate (PI(3,4,5)P3), a second messenger molecule produced following PI3K activation induced by a variety of stimuli. PI(3,4,5)P3 activates the serine-threonine kinase Akt, which is involved in antiapoptosis, proliferation and oncogenesis. In mice, heterozygosity for a null mutation of Pten (Pten(+/-)mice) frequently leads to the development of a variety of cancers and autoimmune disease. Homozygosity for the null mutation (Pten(-/-) mice) results in early embryonic lethality, precluding the functional analysis of Pten in adult tissues and organs. To investigate the physiological functions of Pten in viable mice, we and other groups have used the Cre-loxP system to generate various tissue-specific Pten mutations. The present review will summarize results obtained from the study of conditional mutant mice lacking Pten in specific tissues, and discuss the possible biological and molecular explanations for why Pten deficiency leads to tumorigenesis.