The PTEN/PI3K pathway governs normal vascular development and tumor angiogenesis

Inhibition of phosphatidylinositol 3-kinase/Akt signaling attenuates hypoxia-induced pulmonary artery remodeling and suppresses CREB depletion in arterial smooth muscle cells

Hypoxia-induced pulmonary hypertension is characterized by progressive remodeling of the pulmonary artery (PA) system and loss of the transcription factor, cAMP response element binding protein (CREB) in PA smooth muscle cells (SMCs). Previous in vitro studies suggested that platelet-derived growth factor, a mitogen produced in the hypoxic arterial wall, elicits loss of CREB in medial SMCs via the PI3K/Akt pathway. These events trigger switching of SMCs from a quiescent, contractile phenotype to a proliferative, migratory, dedifferentiated, and synthetic phenotype, which contributes to PA thickening. Here, we investigated whether inhibition of PI3K or Akt could attenuate arterial remodeling in the lung and prevent CREB loss in PA medial SMCs in rats subjected to chronic hypoxia. Inhibition of either enzyme-blunted hypoxia-induced PA remodeling and SMC CREB depletion and diminished SMC proliferation and collagen deposition. Inhibition of Akt, but not PI3K, suppressed muscularization of distal arterioles and blunted right ventricular hypertrophy. Interestingly, mean PA pressure was elevated equally by hypoxia in untreated and inhibitor-treated groups but was normalized acutely by the Rho kinase inhibitor, Fasudil. We conclude that PI3K and Akt inhibitors can attenuate hypoxia-induced PA remodeling and SMC CREB depletion but fail to block the development of pulmonary hypertension because of their inability to repress Rho kinase-mediated vasoconstriction.

HDAC inhibitor DWP0016 activates p53 transcription and acetylation to inhibit cell growth in U251 glioblastoma cells

Here we report a hydroacid named DWP0016, which exhibited HDAC inhibition and induced p53 acetylation in U251 glioblastoma cells. DWP0016 effectively inhibited the cell growth of U251 cells and other four carcinoma cell lines but did not affect the normal cells. Cell cycle distribution analysis showed DWP0016 arrested at G1 phase cell cycle dose-dependently in U251 cells. DWP0016 induced caspase-dependent and independent apoptosis in U251 cells, which was identified by flow cytometry analysis, caspases activity analysis, Western blotting assay, and caspases inhibition. Mechanisms research suggested that DWP0016 activated transcription and acetylation of tumor suppressor p53. DWP0016 regulated p300, CBP, and PCAF to facilitate p53 acetylation at lys382 in U251 cells. In addition, activation of p53 by DWP0016 promoted PUMA to catalyze mitochondrial pathway. Besides, siRNA assay indicated p53 was the key gene to induce growth inhibition, cell cycle arrest, and apoptosis in DWP0016 treated U251 cells. Conclusively, our results show DWP0016 is a potent HDAC inhibitor and the anti-tumor activity is consistent with its intended p53 activation mechanisms. These findings indicate the promising antitumor potential of DWP0016 for further glioblastoma treatment applications.

Ablation of Arg1 in hematopoietic cells improves respiratory function of lung parenchyma, but not that of larger airways or inflammation in asthmatic mice

Asthma is a chronic inflammatory disease of the small airways, with airway hyperresponsiveness (AHR) and inflammation as hallmarks. Recent studies suggest a role for arginase in asthma pathogenesis, possibly because arginine is the substrate for both arginase and NO synthase and because NO modulates bronchial tone and inflammation. Our objective was to investigate the importance of increased pulmonary arginase 1 expression on methacholine-induced AHR and lung inflammation in a mouse model of allergic asthma. Arginase 1 expression in the lung was ablated by crossing Arg1(fl/fl) with Tie2Cre(tg/-) mice. Mice were sensitized and then challenged with ovalbumin. Lung function was measured with the Flexivent. Adaptive changes in gene expression, chemokine and cytokine secretion, and lung histology were quantified with quantitative PCR, ELISA, and immunohistochemistry. Arg1 deficiency did not affect the allergic response in lungs and large-airway resistance, but it improved peripheral lung function (tissue elastance and resistance) and attenuated adaptive increases in mRNA expression of arginine-catabolizing enzymes Arg2 and Nos2, arginine transporters Slc7a1 and Slc7a7, chemokines Ccl2 and Ccl11, cytokines Tnfa and Ifng, mucus-associated epithelial markers Clca3 and Muc5ac, and lung content of IL-13 and CCL11. However, expression of Il4, Il5, Il10, and Il13 mRNA; lung content of IL-4, IL-5, IL-10, TNF-α, and IFN-γ protein; and lung pathology were not affected. Correlation analysis showed that Arg1 ablation disturbed the coordinated pulmonary response to ovalbumin challenges, suggesting arginine (metabolite) dependence of this response. Arg1 ablation in the lung improved peripheral lung function and affected arginine metabolism but had little effect on airway inflammation.

Complex dural arteriovenous fistula in Bannayan-Riley-Ruvalcaba syndrome

In this paper the authors report the case of a complex dural arteriovenous fistula (dAVF) with high-risk features in a 14-year-old girl with Bannayan-Riley-Ruvalcaba syndrome (BRRS), a phosphatase and tensin homolog-associated syndrome, presenting with signs and symptoms of increased intracranial pressure (ICP) that had previously been attributed to pseudotumor cerebri. This fistula was obliterated following 2 stages of embolization, and the patient experienced immediate symptomatic improvement. At the 2-month follow-up evaluation, the fistula remained angiographically occluded, and her symptoms continue to improve. This is the third reported case of an intracranial dAVF in a patient with BRRS. Because high-risk dAVFs can result in devastating morbidity, early detection with vascular imaging is crucial for patients with BRRS presenting with signs of increased ICP. Goals of treatment should include complete fistula obliteration whenever possible.

Adipose tissue insulin sensitivity and macrophage recruitment: Does PI3K pick the pathway?

In the United States, obesity is a burgeoning health crisis, with over 30% of adults and nearly 20% of children classified as obese. Insulin resistance, a common metabolic complication associated with obesity, significantly increases the risk of developing metabolic diseases such as hypertension, coronary heart disease, stroke, type 2 diabetes, and certain cancers. With the seminal finding that obese adipose tissue harbors cytokine secreting immune cells, obesity-related research over the past decade has focused on understanding adipocyte–macrophage crosstalk and its impact on systemic insulin sensitivity. Indeed, adipose tissue has emerged as a central mediator of obesity- and diet-induced insulin resistance. In this mini-review, we focus on a potential role of adipose tissue phosphoinositide 3-kinase (PI3K) as a point of convergence of cellular signaling pathways that integrates nutrient sensing and inflammatory signaling to regulate tissue insulin sensitivity.

Associations of the PTEN -9C>G polymorphism with insulin sensitivity and central obesity in Chinese

BACKGROUND

Phosphatase and tensin homolog on chromosome 10 gene (PTEN) is known as a tumor-suppressor gene. Previous studies demonstrated that PTEN dysfunction affects the function of insulin. However, investigations of PTEN single nucleotide polymorphisms (SNPs) and IR-related disease associations are limited. The aim of the present study was to investigate whether its polymorphism could be involved in the risk of metabolic syndrome (MetS).

METHODS

The genotype frequency of PTEN -9C>G polymorphism was determined by using a Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS) method in 530 subjects with MetS and 202 healthy control subjects of the Han Ethnic Chinese population in a case-control analysis.

RESULTS

The PTEN -9C>G polymorphism was not associated with MetS or its hyperglycemia, hypertension and hypertriglyceridemia components. In the control individuals aged <60 years or ≥60 years, the CG genotype individuals had lower insulin sensitivity than CC individuals (P<0.05). In the <60-year-old MetS group and normal glucose tolerance (NGT) subgroup, the CG individuals had lower insulin sensitivity and higher waist circumference (WC) and waist-height-ratio (WHtR) than CC individuals (P<0.05). Multiple linear regression analysis showed that the PTEN polymorphism (P=0.001) contributed independently to 4.2% (adjusted R(2)) of insulin sensitivity variance (estimated by Matsuda ISI), while age (P=0.004), gender (P=0.000) and the PTEN polymorphism (P=0.032) contributed independently to 5.6% (adjusted R(2)) of WHtR variance.

CONCLUSIONS

The CG genotype of PTEN -9C>G polymorphism was not associated with MetS and some of its components as well. However, it may not only decrease insulin sensitivity in the healthy control and MetS in pre-elderly or NGT subjects, but may also increase the risk of central obesity among these MetS individuals.

Selective inactivation of PTEN in smooth muscle cells synergizes with hypoxia to induce severe pulmonary hypertension

Background

Pulmonary vascular remodeling in pulmonary hypertension (PH) is characterized by increased vascular smooth muscle cell (SMC) and adventitial fibroblast proliferation, small vessel occlusion, and inflammatory cell accumulation. The underlying molecular mechanisms driving progression remain poorly defined. We have focused on loss of the phosphatase PTEN in SMCs as a major driver of pathological vascular remodeling. Our goal was to define the role of PTEN in human PH and in hypoxia‐induced PH using a mouse model with inducible deletion of PTEN in SMCs.

Methods and Results

Staining of human biopsies demonstrated enhanced inactive PTEN selectively in the media from hypertensive patients compared to controls. Mice with induced deletion of PTEN in SMCs were exposed to normoxia or hypoxia for up to 4 weeks. Under normoxia, SMC PTEN depletion was sufficient to induce features of PH similar to those observed in wild‐type mice exposed to chronic hypoxia. Under hypoxia, PTEN depletion promoted an irreversible progression of PH characterized by increased pressure, extensive pulmonary vascular remodeling, formation of complex vascular lesions, and increased macrophage accumulation associated with synergistic increases in proinflammatory cytokines and proliferation of both SMCs and nonSMCs.

Conclusions

Chronic inactivation of PTEN selectively in SMC represents a critical mediator of PH progression, leading to cell autonomous events and increased production of factors correlated to proliferation and recruitment of adventitial and inflammatory cells, resulting in irreversible progression of the disease.

Loss of Pten promotes angiogenesis and enhanced vegfaa expression in zebrafish

Angiogenesis, the emergence of vessels from an existing vascular network, is pathologically associated with tumor progression and is of great interest for therapeutic intervention. PTEN is a frequently mutated tumor suppressor and has been linked to the progression of many types of tumors, including hemangiosarcomas in zebrafish. Here, we report that mutant zebrafish embryos lacking functional Pten exhibit enhanced angiogenesis, accompanied by elevated levels of phosphorylated Akt (pAkt). Inhibition of phosphoinositide 3-kinase (PI3K) by LY294002 treatment and application of sunitinib, a widely used anti-angiogenic compound, suppressed enhanced angiogenesis in Pten mutants. Vegfaa has a crucial role in angiogenesis and vegfaa expression was upregulated in embryos lacking functional Pten. Interestingly, vegfaa expression was also upregulated in hemangiosarcomas from haploinsufficient adult zebrafish Pten mutants. Elevated vegfaa expression in mutant embryos lacking functional Pten was suppressed by LY294002. Surprisingly, sunitinib treatment dramatically enhanced vegfaa expression in Pten mutant embryos, which might account for tumor relapse in human patients who are treated with sunitinib. Combined treatment with suboptimal concentrations of sunitinib and LY294002 rescued enhanced angiogenesis in pten mutant embryos without the dramatic increase in vegfaa expression, suggesting a new approach for therapeutic intervention in VEGFR-signaling-dependent tumors.

Concomitant loss of EAF2/U19 and Pten synergistically promotes prostate carcinogenesis in the mouse model

Multiple genetic alterations are associated with prostate carcinogenesis. Tumor-suppressor genes phosphatase and tensin homolog deleted on chromosome 10 (Pten) and androgen upregulated gene 19 (U19), which encodes ELL-associated factor 2 (EAF2), are frequently inactivated or downregulated in advanced prostate cancers. Previous studies showed that EAF2 knockout caused tumors in multiple organs and prostatic intraepithelial neoplasia (PIN) in mice. However, EAF2-knockout mice did not develop prostate cancer even at 2 years of age. To further define the roles of EAF2 in prostate carcinogenesis, we crossed the Pten+/- and EAF2+/- mice in the C57/BL6 background to generate EAF2-/-Pten+/-, Pten+/-, EAF2-/- and wild-type mice. The prostates from virgin male mice with the above four genotypes were analyzed at 7 weeks, 19 weeks and 12 months of age. Concomitant loss of EAF2 function and inactivation of one Pten allele induced spontaneous prostate cancer in 33% of the mice. Prostatic tissues from intact EAF2-/- Pten+/- mice exhibited higher levels of phospho-Akt, -p44/42 and microvessel density. Moreover, phospho-Akt remained high after castration. Consistently, there was a synergistic increase in prostate epithelial proliferation in both intact and castrated EAF2-/-Pten+/- mice. Using laser-capture microdissection coupled with real-time reverse transcription-PCR, we confirmed that co-downregulation of EAF2 and Pten occurred in >50% clinical prostate cancer specimens with Gleason scores of 8-9 (n=11), which is associated with poor prognosis. The above findings together demonstrated synergistic functional interactions and clinical relevance of concurrent EAF2 and Pten downregulation in prostate carcinogenesis.

Postoperative dural arteriovenous fistula in a patient with Cowden disease: a case report

We report the case of a 37-year-old male with Cowden disease that caused a gradual neurological deficit because of rupture of a brain stem cavernous hemangioma. Removal of the hemangioma and hematoma was performed with an infrafacial triangle approach. Nine months after the operation, magnetic resonance imaging showed abnormal vessels on the cerebellar surface. Digital subtraction angiography showed a dural arteriovenous fistula (dAVF) from part of the meningeal artery to the ectatic inferior vermian vein with cortical reflux. After embolization, surgical obliteration of the dAVF was performed. Surgical findings showed neovascularization in the thickened dura, in which dural vessels shunted to cerebellar vessels through adhesion between the dura mater and cerebellar surface. Therefore, the thickened dura was removed with the cerebellar surface. This case suggests that postoperative angiogenesis may cause arteriovenous fistula in patients with Cowden disease.

Phosphoproteomic analysis implicates the mTORC2-FoxO1 axis in VEGF signaling and feedback activation of receptor tyrosine kinases

The vascular endothelial growth factor (VEGF) signaling pathway plays a pivotal role in normal development and also represents a major therapeutic target for tumors and intraocular neovascular disorders. The VEGF receptor tyrosine kinases promote angiogenesis by phosphorylating downstream proteins in endothelial cells. We applied a large-scale proteomic approach to define the VEGF-regulated phosphoproteome and its temporal dynamics in human umbilical vein endothelial cells and then used siRNA (small interfering RNA) screens to investigate the function of a subset of these phosphorylated proteins in VEGF responses. The PI3K (phosphatidylinositol 3-kinase)-mTORC2 (mammalian target of rapamycin complex 2) axis emerged as central in activating VEGF-regulated phosphorylation and increasing endothelial cell viability by suppressing the activity of the transcription factor FoxO1 (forkhead box protein O1), an effect that limited cellular apoptosis and feedback activation of receptor tyrosine kinases. This FoxO1-mediated feedback loop not only reduced the effectiveness of mTOR inhibitors at decreasing protein phosphorylation and cell survival but also rendered cells more susceptible to PI3K inhibition. Collectively, our study provides a global and dynamic view of VEGF-regulated phosphorylation events and implicates the mTORC2-FoxO1 axis in VEGF receptor signaling and reprogramming of receptor tyrosine kinases in human endothelial cells.

MicroRNA control of vascular endothelial growth factor signaling output during vascular development

The regulated response of endothelial cells to signals in their environment is not only critical for the de novo formation of primordial vascular networks during early development (ie, vasculogenesis), but is also required for the subsequent growth and remodeling of new blood vessels from preexisting ones (ie, angiogenesis). Vascular endothelial growth factors (Vegfs) and their endothelial cell-specific receptors play a crucial role in nearly all aspects of blood vessel growth. How the outputs from these pathways affect and coordinate endothelial behavior is an area of intense research. Recently, numerous studies have highlighted roles for microRNAs in modulating Vegf signaling output in several different contexts. In this review, we will provide an overview of how small RNAs regulate multiple aspects of the Vegf signaling pathway. In particular, we highlight areas where identification of microRNAs and their targets has provided new insight into the role of downstream effectors in modulating Vegf output during development. As Vegf plays a broad role in multiple aspects of endothelial biology and has become a target for therapeutic manipulation of pathological blood vessel growth, microRNAs that affect Vegf signaling output will undoubtedly be major targets of clinical value.

Regulation of angiogenesis by PI3K signaling networks

Phosphoinositide 3-kinases (PI3Ks) are an evolutionary conserved family of lipid kinases that control cell growth, metabolism and survival. By generating lipid second messengers that interact with specialized lipid-binding domains found in a wide spectrum of signaling molecules, PI3Ks instigate signaling through a network of downstream effector pathways. Genetic studies in zebrafish and mice revealed the critical importance of intact PI3K signaling in the endothelium and provided first insights into how individual PI3K isoforms are utilized to control vascular development and function. Here, we review the myriad roles of PI3Ks in the endothelium and the mechanisms through which they couple environmental signals with specific steps of angiogenic vessel growth.

Stable tumor vessel normalization with pO₂ increase and endothelial PTEN activation by inositol trispyrophosphate brings novel tumor treatment

Tumor hypoxia is a characteristic of cancer cell growth and invasion, promoting angiogenesis, which facilitates metastasis. Oxygen delivery remains impaired because tumor vessels are anarchic and leaky, contributing to tumor cell dissemination. Counteracting hypoxia by normalizing tumor vessels in order to improve drug and radio therapy efficacy and avoid cancer stem-like cell selection is a highly challenging issue. We show here that inositol trispyrophosphate (ITPP) treatment stably increases oxygen tension and blood flow in melanoma and breast cancer syngeneic models. It suppresses hypoxia-inducible factors (HIFs) and proangiogenic/glycolysis genes and proteins cascade. It selectively activates the tumor suppressor phosphatase and tensin homolog (PTEN) in vitro and in vivo at the endothelial cell (EC) level thus inhibiting PI3K and reducing tumor AKT phosphorylation. These mechanisms normalize tumor vessels by EC reorganization, maturation, pericytes attraction, and lowering progenitor cells recruitment in the tumor. It strongly reduces vascular leakage, tumor growth, drug resistance, and metastasis. ITPP treatment avoids cancer stem-like cell selection, multidrug resistance (MDR) activation and efficiently enhances chemotherapeutic drugs activity. These data show that counteracting tumor hypoxia by stably restoring healthy vasculature is achieved by ITPP treatment, which opens new therapeutic options overcoming hypoxia-related limitations of antiangiogenesis-restricted therapies. By achieving long-term vessels normalization, ITPP should provide the adjuvant treatment required in order to overcome the subtle definition of therapeutic windows for in vivo treatments aimed by the current strategies against angiogenesis-dependent tumors.

p55PIK-PI3K stimulates angiogenesis in colorectal cancer cell by activating NF-κB pathway

Vascular growth factor (VEGF) is an important mediator of angiogenesis. PI3K plays essential roles in angiogenesis; however, the mechanisms and specific functions of individual isoforms of PI3K members in tumor angiogenesis regulation are still not fully understood. In this study, we evaluate the role of p55PIK, a PI3K regulatory subunit encoded by PIK3R3 gene, in tumor angiogenesis. We reported that overexpression of p55PIK in cancer cells up-regulated HIF-1α expression and increased VEGF expression. Furthermore, overexpression of p55PIK increased tumor angiogenesis in vivo and in vitro. Moreover, data indicated enhanced HIF-1α expression by p55PIK-PI3K depended on its ability to activate NF-кB signaling pathways, especially to increase the phosphorylation of p65 subunits of NF-κB. Our study suggested that p55PIK-PI3K was essential in regulating cancer cell-mediated angiogenesis and contributed to tumor growth and that the p55PIK provides a potential and specific target for new anti-angiogenesis drug development.

Mesodermal Pten inactivation leads to alveolar capillary dysplasia- like phenotype

Alveolar capillary dysplasia (ACD) is a congenital, lethal disorder of the pulmonary vasculature. Phosphatase and tensin homologue deleted from chromosome 10 (Pten) encodes a lipid phosphatase controlling key cellular functions, including stem/progenitor cell proliferation and differentiation; however, the role of PTEN in mesodermal lung cell lineage formation remains unexamined. To determine the role of mesodermal PTEN in the ontogeny of various mesenchymal cell lineages during lung development, we specifically deleted Pten in early embryonic lung mesenchyme in mice. Pups lacking Pten died at birth, with evidence of failure in blood oxygenation. Analysis at the cellular level showed defects in angioblast differentiation to endothelial cells and an accompanying accumulation of the angioblast cell population that was associated with disorganized capillary beds. We also found decreased expression of Forkhead box protein F1 (Foxf1), a gene associated with the ACD human phenotype. Analysis of human samples for ACD revealed a significant decrease in PTEN and increased activated protein kinase B (AKT). These studies demonstrate that mesodermal PTEN has a key role in controlling the amplification of angioblasts as well as their differentiation into endothelial cells, thereby directing the establishment of a functional gas exchange interface. Additionally, these mice could serve as a murine model of ACD.

Stimulus-dependent phosphorylation of profilin-1 in angiogenesis

Angiogenesis, the formation of new blood vessels, is fundamental to development and post-injury tissue repair. Vascular endothelial growth factor (VEGF)-A guides and enhances endothelial cell migration to initiate angiogenesis. Profilin-1 (Pfn-1) is an actin-binding protein that enhances actin filament formation and cell migration, but stimulus-dependent regulation of Pfn-1 has not been observed. Here, we show that VEGF-A-inducible phosphorylation of Pfn-1 at Tyr 129 is critical for endothelial cell migration and angiogenesis. Chemotactic activation of VEGF receptor kinase-2 (VEGFR2) and Src induces Pfn-1 phosphorylation in the cell leading edge, promoting Pfn-1 binding to actin and actin polymerization. Conditional endothelial knock-in of phosphorylation-deficient Pfn1(Y129F) in mice reveals that Pfn-1 phosphorylation is critical for angiogenesis in response to wounding and ischaemic injury, but not for developmental angiogenesis. Thus, VEGFR2/Src-mediated phosphorylation of Pfn-1 bypasses canonical, multistep intracellular signalling events to initiate endothelial cell migration and angiogenesis, and might serve as a selective therapeutic target for anti-angiogenic therapy.

VEGF receptor signaling in vertebrate development

The secreted glycoprotein vascular endothelial growth factor A (VEGF or VEGFA) affects many different cell types and modifies a wide spectrum of cellular behaviors in tissue culture models, including proliferation, migration, differentiation and survival. The versatility of VEGF signaling is reflected in the complex composition of its cell surface receptors and their ability to activate a variety of different downstream signaling molecules. A major challenge for VEGF research is to determine which of the specific signaling pathways identified in vitro control development and homeostasis of tissues containing VEGF-responsive cell types in vivo.

PTEN hamartoma of soft tissue: a distinctive lesion in PTEN syndromes

PTEN hamartoma tumor syndrome (PHTS) presents in a spectrum that encompasses the eponymous disorders Cowden and Bannayan-Riley-Ruvalcaba. Herein, we delineate the distinctive histopathology of a predominantly intramuscular lesion in PHTS, often called "arteriovenous malformation," because of certain imaging and histopathologic features. Cases were identified by review of lesions resected from patients with PHTS registered at our Vascular Anomalies Center and of unusual intramuscular vascular anomalies in our pathology database from 1985 to 2008. Thirty-four patients with this lesion were identified: 20 had a clinical diagnosis of, or were suspected to have, PHTS (genetically confirmed in 16). In 4 patients without clinical manifestations of PHTS, 2 had PTEN mutations, 1 did not, and in 1 the mutation was intronic. In the remaining 10, there was insufficient clinical information to fully assess whether they had manifestations of PHTS. Lesions manifested by 15 years of age, normally with pain and swelling, and were most often located in the lower extremity. The major mass was usually intramuscular, but often there were fascial and subcutaneous components and not infrequently a cutaneous vascular stain. Magnetic resonance imaging generally showed an infiltrative soft tissue lesion involving the muscle, fascia, and subcutis with frequently enlarged, serpiginous vessels, small arteriovenous fistulae with disproportionately dilated draining veins, and a prominent adipocytic component. Some lesions involved contiguous muscles, and 20% were multifocal. Resected specimens ranged in size from 1.2 to 25 cm; in 1 patient, amputation was necessary. Histopathologically, these unencapsulated masses, often with a nodular appearance at scanning magnification, consisted of: (1) a variable admixture of mature adipocytic and dense and/or myxoid fibrous tissues (50% to 90% of surface area); (2) a vascular component (10% to 50% of surface area) with: (a) clusters of venous channels, some with excessively and irregularly muscularized complex walls and lumens, and others with thin walls resembling pulmonary alveoli, (b) tortuous, thick-walled arteries with concentric muscular hyperplasia and relatively small lumens, (c) numerous small vessels (arteries, veins, and indeterminate channels), and (d) occasional arteriovenous communications; (3) lymphoid follicles (50%); (4) foci of bone (20%); and (5) hypertrophic nerves with "onion bulb" proliferation of periaxonal spindled cells (9%). We designate this disorganized overgrowth of essentially mesenchymal elements as PTEN hamartoma of soft tissue. It differs from other vascular and connective tissue lesions that occur in patients with PHTS. PTEN hamartoma of soft tissue is histopathologically distinctive, and its identification should prompt a thorough investigation for PHTS.

Identification of DNA repair pathways that affect the survival of ovarian cancer cells treated with a poly(ADP-ribose) polymerase inhibitor in a novel drug combination

Floxuridine (5-fluorodeoxyuridine, FdUrd), a U.S. Food and Drug Administration-approved drug and metabolite of 5-fluorouracil, causes DNA damage that is repaired by base excision repair (BER). Thus, poly(ADP-ribose) polymerase (PARP) inhibitors, which disrupt BER, markedly sensitize ovarian cancer cells to FdUrd, suggesting that this combination may have activity in this disease. It remains unclear, however, which DNA repair and checkpoint signaling pathways affect killing by these agents individually and in combination. Here we show that depleting ATR, BRCA1, BRCA2, or RAD51 sensitized to ABT-888 (veliparib) alone, FdUrd alone, and FdUrd + ABT-888 (F+A), suggesting that homologous recombination (HR) repair protects cells exposed to these agents. In contrast, disabling the mismatch, nucleotide excision, Fanconi anemia, nonhomologous end joining, or translesion synthesis repair pathways did not sensitize to these agents alone (including ABT-888) or in combination. Further studies demonstrated that in BRCA1-depleted cells, F+A was more effective than other chemotherapy+ABT-888 combinations. Taken together, these studies 1) identify DNA repair and checkpoint pathways that are important in ovarian cancer cells treated with FdUrd, ABT-888, and F+A, 2) show that disabling HR at the level of ATR, BRCA1, BRCA2, or RAD51, but not Chk1, ATM, PTEN, or FANCD2, sensitizes cells to ABT-888, and 3) demonstrate that even though ABT-888 sensitizes ovarian tumor cells with functional HR to FdUrd, the effects of this drug combination are more profound in tumors with HR defects, even compared with other chemotherapy + ABT-888 combinations, including cisplatin + ABT-888.

COUP-TFII is a major regulator of cell cycle and Notch signaling pathways

Chicken ovalbumin upstream promoter transcription factor (COUP-TF)II has been shown to play a major role in endothelial cell growth and regulation of the Notch signaling pathway to confer vein identity. However, the underlying mechanisms for COUP-TFII regulation in these pathways remain to be defined. Here we employed a genomic approach by using microarray analysis to identify downstream targets in human umbilical vein endothelial cells (HUVEC) cells and found the expression of many genes in the cell cycle pathway and Notch signaling pathway are significantly altered in the COUP-TFII-depleted cells. The expression of E2F transcription factor 1 (E2F1), a key transcription factor that regulates the expression of cell cycle regulators, is reduced in the absence of COUP-TFII. Using chromatin immunoprecipitation experiments, we showed that COUP-TFII directly regulates the expression of E2F1 through tethering to the Sp1 binding sites in the promoter of E2F1 to modulate cell proliferation. In addition, we also demonstrate that Foxc1 and Np-1, two upstream genes of Notch signaling and Hey2, a downstream effector of Notch signaling, are direct targets of COUP-TFII. Furthermore, COUP-TFII suppresses the expression of EphrinB2, an arterial marker, while enhancing the expression of ephrin receptor B4, a venous marker, supporting our in vivo findings that COUP-TFII regulates vein identity by suppressing the Notch signal pathway.

Testosterone improves the transition of primary oocytes in artificial maturation eels (Anguilla japonica) by altering ovarian PTEN expression

In mammals, androgens appear to enhance the development of primary ovarian follicles, but PI3K (phosphoinositide 3-kinases) pathway is well recognized as one of the critical pathways in early follicular development. Roles of the PI3K were revealed by deletion of PTEN (phosphatase and tensin homolog on chromosome 10). PTEN is demonstrated to play an important role in the early stage of follicle development. In the Japanese eel, two forms of PTEN have been cloned, but what their functions on the development of early ovarian follicles are still not clear. The natural blockage and inducible of ovarian development was a benefit to address this question in the eel. Testosterone (T) shows to ameliorate the early ovarian development in the eel. The aims of this study were to elucidate the two forms of PTEN by cellular and physiological criteria and to study the effects of T on the ovarian PTEN production in the exogenous pituitary extracts-stimulated eel. Our results suggested that two forms of PTEN are existing in the Japanese eel, and eel ovarian development corresponded to the decrease in ovarian PTEN expression, vice versa. In addition, the supplement of T on eel early ovarian development can be attributed to its PTEN inhibitor role.

New insights into PTEN regulation mechanisms and its potential function in targeted therapies

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a tumor suppressor gene of phosphatased activity. Its low or lacking expression closely relates with tumor progress and poor prognosis. The regulation and function ascribed to PTEN have become more diverse since its discovery as a putative phosphatase mutated in many human tumors. PTEN function is positively and negatively regulated at the transcriptional level, as well as post-translationally by phosphorylation, oxidation and acetylation. Deregulation of PTEN is implicated in other human diseases in addition to cancers, including diabetes and obesity, modulation of PTEN level has widespread therapeutic applications to those tumorigenesis and non-tumor diseases. This review will summarize the new points on the regulation of PTEN and briefly discuss the potential therapeutic role of PTEN in some diseases.

PI3K signaling in the regulation of branching morphogenesis

Branching morphogenesis drives the formation of epithelial organs including the mammary gland, lung, kidney, salivary gland and prostate. Branching at the cellular level also drives development of the nervous and vascular systems. A variety of signaling pathways are orchestrated together to establish the pattern of these branched organs. The phosphoinositide 3-kinase (PI3K) signaling network is of particular interest because of the diverse outcomes it generates, including proliferation, motility, growth, survival and cell death. Here, we focus on the role of the PI3K pathway in the development of branched tissues. Cultured cells, explants and transgenic mice have revealed that the PI3K pathway is critical for the regulation of cell proliferation, apoptosis and motility during branching of tissues.

Roles of Polo-like kinase 3 in suppressing tumor angiogenesis

Angiogenesis is essential for promoting growth and metastasis of solid tumors by ensuring blood supply to the tumor mass. Targeting angiogenesis is therefore an attractive approach to therapeutic intervention of cancer. Tumor angiogenesis is a process that is controlled by a complex network of molecular components including sensors, signaling transducers, and effectors, leading to cellular responses under hypoxic conditions. Positioned at the center of this network are the hypoxia-inducible factors (HIFs). HIF-1 is a major transcription factor that consists of two subunits, HIF-1α and HIF-1β. It mediates transcription of a spectrum of gene targets whose products are essential for mounting hypoxic responses. HIF-1α protein level is very low in the normoxic condition but is rapidly elevated under hypoxia. This dramatic change in the cellular HIF-1α level is primarily regulated through the proteosome-mediated degradation process. In the past few years, scientific progress has clearly demonstrated that HIF-1α phosphorylation is mediated by several families of protein kinases including GSK3β and ERKs both of which play crucial roles in the regulation of HIF-1α stability. Recent research progress has identified that Polo-like kinase 3 (Plk3) phosphorylates HIF-1α at two previously unidentified serine residues and that the Plk3-mediated phosphorylation of these residues results in destabilization of HIF-1α. Plk3 has also recently been found to phosphorylate and stabilize PTEN phosphatase, a known regulator of HIF-1α and tumor angiogenesis. Given the success of targeting protein kinases and tumor angiogenesis in anti-cancer therapies, Plk3 could be a potential molecular target for the development of novel and effective therapeutic agents for cancer treatment.

Combination testing of cediranib (AZD2171) against childhood cancer models by the pediatric preclinical testing program

BACKGROUND

Cediranib (AZD2171) is a potent small molecule inhibitor of vascular endothelial growth factor (VEGF) receptors. Cediranib has demonstrated single agent activity in several adult cancers and is being studied in combination with standard cytotoxic agents in multiple disease settings.

PROCEDURES

Cediranib was tested in vivo against six childhood tumor xenograft models (four sarcomas, one glioblastoma, one neuroblastoma) alone or combined with cyclophosphamide (two models), vincristine (three models) or cisplatin (one model), each administered at its maximum tolerated dose, or rapamycin (six models).

RESULTS

The combination of cediranib with standard cytotoxic agents was superior to the cytotoxic agent used alone for a single xenograft (one of the three xenografts evaluated for the vincristine-cediranib combination). The cediranib-cyclophosphamide combination was inferior to single agent cyclophosphamide in time to event for both models studied and was significantly inferior for one of the models. Cediranib combined with rapamycin was superior to each of the agents used alone in two of the six models and was determined to be additive or supra-additive with rapamycin in four models, although the effects were not large.

CONCLUSIONS

Cediranib combined with cytotoxic chemotherapy agents demonstrated little or no benefit (and in one case was significantly inferior) compared to chemotherapy alone for the six pediatric cancer xenografts studied. By contrast, the combination of cediranib with rapamycin was additive or supra-additive in four of the six models in terms of prolongation of time to event, though tumor regressions were not observed for this combination.

Both p110α and p110β isoforms of PI3K can modulate the impact of loss-of-function of the PTEN tumour suppressor

The PI3K (phosphoinositide 3-kinase) pathway is commonly activated in cancer as a consequence of inactivation of the tumour suppressor PTEN (phosphatase and tensin homologue deleted on chromosome 10), a major negative regulator of PI3K signalling. In line with this important role of PTEN, mice that are heterozygous for a PTEN-null allele (PTEN+/− mice) spontaneously develop a variety of tumours in multiple organs. PTEN is a phosphatase with selectivity for PtdIns(3,4,5)P3, which is produced by the class I isoforms of PI3K (p110α, p110β, p110γ and p110δ). Previous studies indicated that PTEN-deficient cancer cell lines mainly depend on p110β, and that p110β, but not p110α, controls mouse prostate cancer development driven by PTEN loss. In the present study, we investigated whether the ubiquitously expressed p110α can also functionally interact with PTEN in cancer. Using genetic mouse models that mimic systemic administration of p110α- or p110β-selective inhibitors, we confirm that inactivation of p110β, but not p110α, inhibits prostate cancer development in PTEN+/− mice, but also find that p110α inactivation protects from glomerulonephritis, pheochromocytoma and thyroid cancer induced by PTEN loss. This indicates that p110α can modulate the impact of PTEN loss in disease and tumourigenesis. In primary and immortalized mouse fibroblast cell lines, both p110α and p110β controlled steady-state PtdIns(3,4,5)P3 levels and Akt signalling induced by heterozygous PTEN loss. In contrast, no correlation was found in primary mouse tissues between PtdIns(3,4,5)P3 levels, PI3K/PTEN genotype and cancer development. Taken together, our results from the present study show that inactivation of either p110α or p110β can counteract the impact of PTEN inactivation. The potential implications of these findings for PI3K-targeted therapy of cancer are discussed.

Dehydrocostuslactone suppresses angiogenesis in vitro and in vivo through inhibition of Akt/GSK-3β and mTOR signaling pathways

The traditional Chinese medicine component dehydrocostuslactone (DHC) isolated from Saussurea costus (Falc.) Lipschitz, has been shown to have anti-cancer activity. Angiogenesis is an essential process in the growth and progression of cancer. In this study, we demonstrated, for the first time, the anti-angiogenic mechanism of action of DHC to be via the induction of cell cycle progression at the G0/G1 phase due to abrogation of the Akt/glycogen synthase kinase-3β (GSK-3β)/cyclin D1 and mTOR signaling pathway. First, we demonstrated that DHC has an anti-angiogenic effect in the matrigel-plug nude mice model and an inhibitory effect on human umbilical vein endothelial cell (HUVEC) proliferation and capillary-like tube formation in vitro. DHC caused G0/G1 cell cycle arrest, which was associated with the down-regulation of cyclin D1 expression, leading to the suppression of retinoblastoma protein phosphorylation and subsequent inhibition of cyclin A and cdk2 expression. With respect to the molecular mechanisms underlying the DHC-induced cyclin D1 down-regulation, this study demonstrated that DHC significantly inhibits Akt expression, resulting in the suppression of GSK-3β phosphorylation and mTOR expression. These effects are capable of regulating cyclin D1 degradation, but they were significantly reversed by constitutively active myristoylated (myr)-Akt. Furthermore, the abrogation of tube formation induced by DHC was also reversed by overexpression of Akt. And the co-treatment with LiCl and DHC significantly reversed the growth inhibition induced by DHC. Taken together, our study has identified Akt/GSK-3β and mTOR as important targets of DHC and has thus highlighted its potential application in angiogenesis-related diseases, such as cancer.

Novel 5'TOPmRNAs regulated by ribosomal S6 kinase are important for cardiomyocyte development: S6 kinase suppression limits cardiac differentiation and promotes pluripotent cells toward a neural lineage

Moving stem cells from bench to bedside has been a challenging task. Undermining this task is comprehending and optimizing the underlying regulatory mechanisms that drive differentiation of stem cells into desired cell and tissue types. Here we present evidence that ribosomal S6 kinase (S6K) is among the proteins upregulated as embryonic stem cells (ESCs) and human induced pluripotent stem cells differentiate into beating cardiomyocytes. We hypothesized that S6K plays a pivotal role in cardiomyogenesis, primarily because it regulates the translation of 3 cardiac-involved genes recently shown to have 5' terminal oligopyrimidine (5'TOP) sequences: connexin 43 (Cx43), desmoplakin (Dsp), and phosphatase and tensin homolog (PTEN). Along with another independent laboratory, we confirmed that S6K is indeed upregulated in beating ESC-derived cardiomyocytes compared to the surrounding nonbeating, differentiated cells. S6K short interfering RNA-transfected stem cell cultures indicate that inhibition of S6K strongly hinders development of cardiomyocyte beating and translation of Cx43, Dsp, and PTEN; these cardiac 5'TOP mRNAs were only properly translated in cells with S6K, supporting our hypothesis. An unexpected discovery took the role of S6K one step further: S6K-knockdown stem cell cultures developed significantly more neurons than seen in embryoid bodies subjected to a typical cardiac differentiation protocol. These results introduced the novel idea that in addition to its critical cardiac roles, S6K may be a significant factor that prevents stem cells from pursuing a neuronal pathway. Overall, results have indicated the necessity of S6K for normal stem cell cardiomyogenesis, as well as lowered S6K expression for stem cell neurogenesis.

The PTEN and Myotubularin phosphoinositide 3-phosphatases: linking lipid signalling to human disease

Two classes of lipid phosphatases selectively dephosphorylate the 3 position of the inositol ring of phosphoinositide signaling molecules: the PTEN and the Myotubularin families. PTEN dephosphorylates PtdIns(3,4,5)P(3), acting in direct opposition to the Class I PI3K enzymes in the regulation of cell growth, proliferation and polarity and is an important tumor suppressor. Although there are several PTEN-related proteins encoded by the human genome, none of these appear to fulfill the same functions. In contrast, the Myotubularins dephosphorylate both PtdIns(3)P and PtdIns(3,5)P(2), making them antagonists of the Class II and Class III PI 3-kinases and regulators of membrane traffic. Both phosphatase groups were originally identified through their causal mutation in human disease. Mutations in specific myotubularins result in myotubular myopathy and Charcot-Marie-Tooth peripheral neuropathy; and loss of PTEN function through mutation and other mechanisms is evident in as many as a third of all human tumors. This chapter will discuss these two classes of phosphatases, covering what is known about their biochemistry, their functions at the cellular and whole body level and their influence on human health.

An introduction to phosphoinositides

Phosphoinositides (PIs) are minor components of cellular membranes that play critical regulatory roles in several intracellular functions. This chapter describes the main enzymes regulating the turnover of each of the seven PIs in mammalian cells and introduces to some of their intracellular functions and to some evidences of their involvement in human diseases. Due to the complex interrelation between the distinct PIs and the plethora of functions that they can regulate inside a cell, this chapter is not meant to be a comprehensive coverage of all aspects of PI signalling but rather an introduction to this complex signalling field. For more details of their regulation/functions and extensive description of their intracellular roles, more detailed reviews are suggested on each single topic.

PI3K/AKT/mTOR Pathway in Angiogenesis

The phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) pathway is activated in the majority of human cancers. This pathway is known to play a key role in numerous cellular functions including proliferation, adhesion, migration, invasion, metabolism, and survival, but in the current review we focus on its role in angiogenesis. PI3K activation may occur via RAS mutation, loss of phosphatase and tensin homolog (PTEN), or by increased expression of growth factor receptors such as epidermal growth factor receptor. There is a connection between the PI3K pathway and angiogenesis. Hypoxia leads to HIF-1α stabilization and is a major stimulus for increased vascular endothelial growth factor (VEGF) production by tumor cells. However, activation of the PI3K/AKT pathway in tumor cells can also increase VEGF secretion, both by hypoxia-inducible factor 1 (HIF-1) dependent and independent mechanisms. The PI3K/AKT pathway also modulates the expression of other angiogenic factors such as nitric oxide and angiopoietins. Numerous inhibitors targeting the PI3K/AKT/mTOR pathway have been developed, and these agents have been shown to decrease VEGF secretion and angiogenesis. The effect of these inhibitors on tumor vasculature can be difficult to predict. The vasculature of tumors is aberrant, leading to sluggish bloodflow and elevated interstitial blood pressure, which can be perpetuated by the high levels of VEGF. Hence, decreasing VEGF expression can paradoxically lead to vascular normalization and improved bloodflow in some tumors. In addition to its importance in cancer, the PI3K pathway also plays an essential role in the formation of normal blood vessels during development. Embryos with kinase-dead p110α catalytic subunit of PI3K develop vascular defects. Stimulation of endothelial cells by VEGF leads to activation of the PI3K pathway within these cells, which is important for cell migration. Sustained endothelial activation of AKT1 has been shown to induce the formation of structurally abnormal blood vessels that recapitulate the aberrations of tumor vessels. Hence, the PI3K pathway plays an important role in regulating angiogenesis both in normal tissues and in cancers.

Ablation of 3-phosphoinositide-dependent protein kinase 1 (PDK1) in vascular endothelial cells enhances insulin sensitivity by reducing visceral fat and suppressing angiogenesis

The phosphatidylinositol 3-kinase signaling pathway in vascular endothelial cells is important for systemic angiogenesis and glucose metabolism. In this study, we addressed the precise role of the 3-phosphoinositide-dependent protein kinase 1 (PDK1)-regulated signaling network in endothelial cells in vivo, using vascular endothelial PDK1 knockout (VEPDK1KO) mice. Surprisingly, VEPDK1KO mice manifested enhanced glucose tolerance and whole-body insulin sensitivity due to suppression of their hepatic glucose production with no change in either peripheral glucose disposal or even impaired vascular endothelial function at 6 months of age. When mice were fed a standard diet at 6 months of age and a high-fat diet at 3 months of age, hypertrophy of epididymal adipose tissues was inhibited, adiponectin mRNA was significantly increased, and mRNA of MCP1, leptin, and TNFα was decreased in the white adipose tissue of VEPDK1KO mice in comparison with controls. Consequently, both the circulating adiponectin levels and the activity of hepatic AMP-activated protein kinase were significantly increased, subsequently enhancing whole-body insulin sensitivity and energy expenditure with increased hepatic fatty acid oxidation in VEPDK1KO mice. These results provide the first in vivo evidence that lowered angiogenesis through the deletion of PDK1 signaling not only interferes with the growth of adipose tissue but also induces increased energy expenditure due to amelioration of the adipocytokine profile. This demonstrates an unexpected role of PDK1 signaling in endothelial cells on the maintenance of proper glucose homeostasis through the regulation of adipocyte development.

Transforming growth factor-β-induced endothelial-to-mesenchymal transition is partly mediated by microRNA-21

OBJECTIVE

MicroRNAs are a class of small ribonucleotides regulating gene/protein targets by transcript degradation or translational inhibition. Transforming growth factor-β (TGF-β) is involved in cardiac fibrosis partly by stimulation of endothelial-to-mesenchymal transition (EndMT). Here, we investigated whether microRNA (miR)-21, a microRNA enriched in fibroblasts and involved in general fibrosis, has a role in cardiac EndMT.

METHODS AND RESULTS

TGF-β treatment of endothelial cells significantly increased miR-21 expression and induced EndMT characterized by suppression of endothelial and increase of fibroblast markers. Overexpression of miR-21 alone also stimulated EndMT. Importantly, miR-21 blockade by transfection of specific microRNA inhibitors partly prevented TGF-β-induced EndMT. Mechanistically, miR-21 silenced phosphatase and tensin homolog in endothelial cells, resulting in activation of the Akt-pathway. Akt inhibition partly restored TGF-β-mediated loss of endothelial markers during EndMT. In vivo, pressure overload of the left ventricle led to increased expression of miR-21 in sorted cardiac endothelial cells, which displayed molecular and phenotypic signs of EndMT. This was attenuated by treatment of mice subjected to left ventricular pressure overload with an antagomir against miR-21.

CONCLUSIONS

TGF-β-mediated EndMT is regulated at least in part by miR-21 via the phosphatase and tensin homolog/Akt pathway. In vivo, antifibrotic effects of miR-21 antagonism are partly mediated by blocking EndMT under stress conditions.

Environmental impact on vascular development predicted by high-throughput screening

BACKGROUND

Understanding health risks to embryonic development from exposure to environmental chemicals is a significant challenge given the diverse chemical landscape and paucity of data for most of these compounds. High-throughput screening (HTS) in the U.S. Environmental Protection Agency (EPA) ToxCast™ project provides vast data on an expanding chemical library currently consisting of > 1,000 unique compounds across > 500 in vitro assays in phase I (complete) and Phase II (under way). This public data set can be used to evaluate concentration-dependent effects on many diverse biological targets and build predictive models of prototypical toxicity pathways that can aid decision making for assessments of human developmental health and disease.

OBJECTIVE

We mined the ToxCast phase I data set to identify signatures for potential chemical disruption of blood vessel formation and remodeling.

METHODS

ToxCast phase I screened 309 chemicals using 467 HTS assays across nine assay technology platforms. The assays measured direct interactions between chemicals and molecular targets (receptors, enzymes), as well as downstream effects on reporter gene activity or cellular consequences. We ranked the chemicals according to individual vascular bioactivity score and visualized the ranking using ToxPi (Toxicological Priority Index) profiles.

RESULTS

Targets in inflammatory chemokine signaling, the vascular endothelial growth factor pathway, and the plasminogen-activating system were strongly perturbed by some chemicals, and we found positive correlations with developmental effects from the U.S. EPA ToxRefDB (Toxicological Reference Database) in vivo database containing prenatal rat and rabbit guideline studies. We observed distinctly different correlative patterns for chemicals with effects in rabbits versus rats, despite derivation of in vitro signatures based on human cells and cell-free biochemical targets, implying conservation but potentially differential contributions of developmental pathways among species. Follow-up analysis with antiangiogenic thalidomide analogs and additional in vitro vascular targets showed in vitro activity consistent with the most active environmental chemicals tested here.

CONCLUSIONS

We predicted that blood vessel development is a target for environmental chemicals acting as putative vascular disruptor compounds (pVDCs) and identified potential species differences in sensitive vascular developmental pathways.

Multiple, recurrent, refractory vascular malformations as the primary presenting feature of a PTEN mutation

Complete history and physical examinations are very important in patients with a vascular anomaly. This brief report highlights the case of a five-year-old male who presented with recurrent arteriovenous malformations of the hand and forearm. The patient also demonstrated additional clinical and diagnostic imaging features consistent with a PTEN Hamartoma-Tumor syndrome. The prompt identification of individuals with this condition is important, given the more locally aggressive nature to the malformations and the increased potential for future malignant disease. The etiology and clinical features associated with PTEN Hamartoma-Tumor syndromes are reviewed in this case.

Targeting PI3K signaling as a therapeutic approach for colorectal cancer

Survival times of patients with colorectal cancer (CRC) have increased over the past decade, primarily as a result of treatment with combinations of conventional cytotoxic agents. Because CRC is commonly associated with mutations in genes that control growth factor signaling, therapies are being developed to target the products of these genes; individualized treatment might also be guided by specific mutations in tumors and by new biomarkers. Currently, targeted therapies confer limited clinical benefit; better drugs are therefore needed. Genomic studies indicate that phosphoinositide 3-kinase (PI3K) signaling is one of the most frequently deregulated pathways in several human cancers, including CRC. PI3K signaling has an important role in cancer cell proliferation, survival, motility, and metabolism and therefore could be an attractive therapeutic target. We review PI3K signaling in CRC and discuss current therapeutic approaches.

Clinical significance of expression of PTEN, Akt and pAkt in hepatocellular carcinoma

AIM: To explore the expression of phosphatase and tensin homology deleted on chromosome ten (PTEN), Akt and pAkt proteins in hepatocellular carcinoma (HCC) and to elucidate their clinical significance.

METHODS: Immunohistochemical analysis was performed to detect the expression of PTEN, Akt and pAkt proteins in 78 specimens of hepatocellular carcinoma and 21 specimens of normal liver tissues. The relationship of their expression with clinicopathological and prognostic parameters was analyzed.

RESULTS: The rate of PTEN overexpression was significantly lower in HCC than in normal liver tissue (42.3% vs 90.5%, P < 0.05), while the rates of Akt and pAkt overexpression were significantly higher in HCC than in normal liver tissue (66.7% vs 33.3%; 43.6% vs 9.5%, both P < 0.05). PTEN expression was correlated with tumor size, cancer embolus of the portal vein, tumor invasion, lymph node metastasis and TNM stage. Akt and pAkt expression was correlated with tumor size, invasion, lymph node metastasis and TNM stage. PTEN expression was negatively correlated with Akt (r = -0.385, P = 0.000) and pAkt (r =- 0.334, P = 0.003) expression in HCC. Patients with low PTEN expression or high Akt and pAkt expression had a significantly worse survival time than those with high PTEN expression or low Akt and pAkt expression (P = 0.000). A multivariate analysis based on the COX regression model demonstrated that TNM stage and pAkt expression were independent prognostic factors for HCC.

CONCLUSION: The expression of PTEN, Akt and pAkt proteins is closely related to the malignant biological behavior of HCC. pAkt can be used as a key factor for predicting prognosis in HCC patients.

Autophagy process is associated with anti-neoplastic function

Autophagy is a highly conserved process of cellular degradation, which is present in yeast, plants, and mammals. Under normal physiological conditions, autophagy acts to maintain cellular homeostasis and regulate the turnover of organelles. In response to cellular stresses, autophagy prevents the accumulation of impaired proteins and organelles, which serves to inhibit carcinogenesis. On this basis, it is widely accepted that most tumor suppressors, such as beclin 1 associated proteins, forkhead box class O (FoxO) family proteins, multiple mammalian target of Rapamycin (mTOR) inactivators, and nuclear p53 play a role in inducing autophagy. Here, we focus on how the process of autophagy is associated with anti-neoplastic function.

Apoptosis regulator through modulating IAP expression (ARIA) controls the PI3K/Akt pathway in endothelial and endothelial progenitor cells

Endothelial and endothelial progenitor cells (ECs and EPCs) play a fundamental role in angiogenesis that is essential for numerous physiological and pathological processes. The phosphatase and tensin homolog (PTEN)/ phosphoinositide 3-kinase (PI3K) pathway has been implicated in angiogenesis, but the mechanism in the regulation of this pathway in ECs and EPCs is poorly understood. Here we show that ARIA (apoptosis regulator through modulating IAP expression), a transmembrane protein that we recently identified, regulates the PTEN/PI3K pathway in ECs and EPCs and controls developmental and postnatal angiogenesis in vivo. We found that ARIA is abundantly expressed in EPCs and regulates their angiogenic functions by modulating PI3K/Akt/endothelial nitric oxide synthase (eNOS) signaling. Genetic deletion of ARIA caused nonfatal bleeding during embryogenesis, in association with increased small vessel density and altered expression of various vascular growth factors including angiopoietins and VEGF receptors. Postnatal neovascularization induced by critical limb ischemia was substantially enhanced in ARIA-null mice, in conjunction with more bone marrow (BM)-derived ECs detected in ischemic muscles. Administration of PI3K or NO synthase inhibitor completely abolished the enhanced neovascularization in ARIA(-/-) mice. Mechanistically, we identified that ARIA interacts with PTEN at the intracellular domain independently of the PTEN phosphorylation in its C-terminal tail. Overexpressed ARIA increased PTEN in the membrane fraction, whereas ARIA-silencing reduced the membrane-associated PTEN, resulting in modified PI3K/Akt signaling. Taken together, our findings establish a previously undescribed mode of regulation of the PTEN/PI3K/Akt pathway by ARIA, and reveal a unique mechanism in the control of angiogenesis. These functions of ARIA might offer a unique therapeutic potential.

Open cascades as simple solutions to providing ultrasensitivity and adaptation in cellular signaling

Cell signaling is achieved predominantly by reversible phosphorylation-dephosphorylation reaction cascades. Up until now, circuits conferring adaptation have all required the presence of a cascade with some type of closed topology: negative-feedback loop with a buffering node, or incoherent feed-forward loop with a proportioner node. In this paper--using Goldbeter and Koshland-type expressions--we propose a differential equation model to describe a generic, open signaling cascade that elicits an adaptation response. This is accomplished by coupling N phosphorylation-dephosphorylation cycles unidirectionally, without any explicit feedback loops. Using this model, we show that as the length of the cascade grows, the steady states of the downstream cycles reach a limiting value. In other words, our model indicates that there are a minimum number of cycles required to achieve a maximum in sensitivity and amplitude in the response of a signaling cascade. We also describe for the first time that the phenomenon of ultrasensitivity can be further subdivided into three sub-regimes, separated by sharp stimulus threshold values: OFF, OFF-ON-OFF, and ON. In the OFF-ON-OFF regime, an interesting property emerges. In the presence of a basal amount of activity, the temporal evolution of early cycles yields damped peak responses. On the other hand, the downstream cycles switch rapidly to a higher activity state for an extended period of time, prior to settling to an OFF state (OFF-ON-OFF). This response arises from the changing dynamics between a feed-forward activation module and dephosphorylation reactions. In conclusion, our model gives the new perspective that open signaling cascades embedded in complex biochemical circuits may possess the ability to show a switch-like adaptation response, without the need for any explicit feedback circuitry.

VEGF-mediated PI3K class IA and PKC signaling in cardiomyogenesis and vasculogenesis of mouse embryonic stem cells

VEGF-, phosphoinositide 3-kinase (PI3K)- and protein kinase C (PKC)-regulated signaling in cardiac and vascular differentiation was investigated in mouse ES cells and in ES cell-derived Flk-1⁺ cardiovascular progenitor cells. Inhibition of PI3K by wortmannin and LY294002, disruption of PI3K catalytic subunits p110α and p110δ using short hairpin RNA (shRNA), or inhibition of p110α with compound 15e and of p110δ with IC-87114 impaired cardiac and vascular differentiation. By contrast, TGX-221, an inhibitor of p110β, and shRNA knockdown of p110β were without significant effects. Antagonists of the PKC family, i.e. bisindolylmaleimide-1 (BIM-1), GÖ 6976 (targeting PKCα/βII) and rottlerin (targeting PKCδ) abolished vasculogenesis, but not cardiomyogenesis. Inhibition of Akt blunted cardiac as well as vascular differentiation. VEGF induced phosphorylation of PKCα/βII and PKCδ but not PKCζ. This was abolished by PI3K inhibitors and the VEGFR-2 antagonist SU5614. Furthermore, phosphorylation of Akt and phosphoinositide-dependent kinase-1 (PDK1) was blunted upon inhibition of PI3K, but not upon inhibition of PKC by BIM-1, suggesting that activation of Akt and PDK1 by VEGF required PI3K but not PKC. In summary, we demonstrate that PI3K catalytic subunits p110α and p110δ are central to cardiovasculogenesis of ES cells. Akt downstream of PI3K is involved in both cardiomyogenesis and vasculogenesis, whereas PKC is involved only in vasculogenesis.

A critical role for GRP78/BiP in the tumor microenvironment for neovascularization during tumor growth and metastasis

Glucose-regulated protein 78 (GRP78)/BiP is a multifunctional protein which plays a major role in endoplasmic reticulum (ER) protein processing, protein quality control, maintaining ER homeostasis, and controlling cell signaling and viability. Previously, using a transgene-induced mammary tumor model, we showed that Grp78 heterozygosity impeded cancer growth through suppression of tumor cell proliferation and promotion of apoptosis and the Grp78(+/-) mice exhibited dramatic reduction (70%) in the microvessel density (MVD) of the endogenous mammary tumors, while having no effect on the MVD of normal organs. This observation suggests that GRP78 may critically regulate the function of the host vasculature within the tumor microenvironment. In this article, we interrogated the role of GRP78 in the tumor microenvironment. In mouse tumor models in which wild-type (WT), syngeneic mammary tumor cells were injected into the host, we showed that Grp78(+/-) mice suppressed tumor growth and angiogenesis during the early phase but not during the late phase of tumor growth. Growth of metastatic lesions of WT, syngeneic melanoma cells in the Grp78(+/-) mice was potently suppressed. We created conditional heterozygous knockout of GRP78 in the host endothelial cells and showed severe reduction of tumor angiogenesis and metastatic growth, with minimal effect on normal tissue MVD. Furthermore, knockdown of GRP78 expression in immortalized human endothelial cells showed that GRP78 is a critical mediator of angiogenesis by regulating cell proliferation, survival, and migration. Our findings suggest that concomitant use of current chemotherapeutic agents and novel therapies against GRP78 may offer a powerful dual approach to arrest cancer initiation, progression, and metastasis.

PTEN loss in the continuum of common cancers, rare syndromes and mouse models

PTEN is among the most frequently inactivated tumour suppressor genes in sporadic cancer. PTEN has dual protein and lipid phosphatase activity, and its tumour suppressor activity is dependent on its lipid phosphatase activity, which negatively regulates the PI3K-AKT-mTOR pathway. Germline mutations in PTEN have been described in a variety of rare syndromes that are collectively known as the PTEN hamartoma tumour syndromes (PHTS). Cowden syndrome is the best-described syndrome within PHTS, with approximately 80% of patients having germline PTEN mutations. Patients with Cowden syndrome have an increased incidence of cancers of the breast, thyroid and endometrium, which correspond to sporadic tumour types that commonly exhibit somatic PTEN inactivation. Pten deletion in mice leads to Cowden syndrome-like phenotypes, and tissue-specific Pten deletion has provided clues to the role of PTEN mutation and loss in specific tumour types. Studying PTEN in the continuum of rare syndromes, common cancers and mouse models provides insight into the role of PTEN in tumorigenesis and will inform targeted drug development.

PTEN's regulation of VEGF and VEGFR1 expression and its clinical significance in myeloid leukemia

Phosphatase and tensin homolog (PTEN) acts as a novel tumor suppressor gene. PTEN protein plays an important role in regulating proliferation, apoptosis, invasion, and migration of many cancer cells. PTEN also modulates angiogenesis mediated by vascular endothelial growth factor (VEGF) via down-regulating PI3K/Akt pathway in many solid tumors. However, the effects of PTEN on VEGF and VEGFR1 (FLT1)-mediated angiogenesis, migration, invasion of leukemia cells, and its clinical significance are still unknown in myeloid leukemia. Therefore, we investigated the effect of PTEN on PI3K/Akt and VEGF/FLT1 pathways by transfecting wild-type PTEN gene to induce high expression of wild-type PTEN gene and protein in chronic myelogenous leukemia cell line K562 cells. We also observed the correlation between the expression levels of PTEN and VEGF/FLT1 and its clinical significance in myeloid leukemia patients. We found that the expression reconstitution of wild-type PTEN had significant effect on inhibiting proliferation, migration, and invasion abilities of K562 cells via down-regulation of Akt phosphorylation and inhibition of VEGF/FLT1 expression. In myeloid leukemia patients, a negative correlation was found between the expression level of PTEN mRNA and that of VEGF and FLT1 mRNA. Down-regulation of PTEN expression accompanied by up-regulation of VEGF and FLT1 mRNA indicated a higher tendency of extramedullary disease in acute myeloid leukemia patients. In conclusion, PTEN could modulate the function of VEGF/VEGFR signaling pathway down-regulation of Akt phosphorylation and that PTEN would be a candidate target to be addressed for inhibiting angiogenesis along with the treatment of myeloid leukemia.