PTEN augments staurosporine-induced apoptosis in PTEN-null Ishikawa cells by downregulating PI3K/Akt signaling pathway

A review of natural products and small-molecule therapeutics acting on central nervous system malignancies: Approaches for drug development, targeting pathways, clinical trials, and challenges

In 2021, the World Health Organization released the fifth edition of the central nervous system (CNS) tumor classification. This classification uses histopathology and molecular pathogenesis to group tumors into more biologically and molecularly defined entities. The prognosis of brain cancer, particularly malignant tumors, has remained poor worldwide, approximately 308,102 new cases of brain and other CNS tumors were diagnosed in the year 2020, with an estimated 251,329 deaths. The cost and time-consuming nature of studies to find new anticancer agents makes it necessary to have well-designed studies. In the present study, the pathways that can be targeted for drug development are discussed in detail. Some of the important cellular origins, signaling, and pathways involved in the efficacy of bioactive molecules against CNS tumorigenesis or progression, as well as prognosis and common approaches for treatment of different types of brain tumors, are reviewed. Moreover, different study tools, including cell lines, in vitro, in vivo, and clinical trial challenges, are discussed. In addition, in this article, natural products as one of the most important sources for finding new chemotherapeutics were reviewed and over 700 reported molecules with efficacy against CNS cancer cells are gathered and classified according to their structure. Based on the clinical trials that have been registered, very few of these natural or semi-synthetic derivatives have been studied in humans. The review can help researchers understand the involved mechanisms and design new goal-oriented studies for drug development against CNS malignancies.

Granulosa cells undergo BPA-induced apoptosis in a miR-21-independent manner

Bisphenol A (BPA) is a harmful endocrine disrupting compound that alters not only classical cellular mechanisms but also epigenetic mechanisms. Evidence suggests that BPA-induced changes in microRNA expression can explain, in part, the changes observed at both the molecular and cellular levels. BPA is toxic to granulosa cells (GCs) as it can activate apoptosis, which is known to contribute to increased follicular atresia. miR-21 is a crucial antiapoptotic regulator in GCs, yet the exact function in a BPA toxicity model remains unclear. BPA was found to induce bovine GC apoptosis through the activation of several intrinsic factors. BPA reduced live cells counts, increased late apoptosis/necrosis, increased apoptotic transcripts (BAX, BAD, BCL-2, CASP-9, HSP70), increased the BAX/Bcl-2 ratio and HSP70 at the protein level, and induced caspase-9 activity at 12 h post-exposure. miR-21 inhibition increased early apoptosis and, while it did not influence transcript levels or caspase-9 activity, it did elevate the BAX/Bcl-2 protein ratio and HSP70 in the same manner as BPA. Overall, this study shows that miR-21 plays a molecular role in regulating intrinsic mitochondrial apoptosis; however, miR-21 inhibition did not make the cells more sensitive to BPA. Therefore, apoptosis induced by BPA in bovine GCs is miR-21 independent.

Alkaloids exhibit a meaningful function as anticancer agents by restraining cellular signaling pathways

Alkaloids are nitrogen-containing organic compounds widely found in natural products, which play an essential role in clinical treatment. Cellular signaling pathways in tumors are a series of enzymatic reaction pathways that convert extracellular signals into intracellular signals to produce biological effects. The ordered function of cell signaling pathways is essential for tumor cell proliferation, differentiation, and programmed death. This review describes the antitumor progression mediated by various alkaloids after inhibiting classical signaling pathways; related studies are systematically retrieved and collected through PubMed. We selected the four currently most popular pathways for discussion and introduced the molecular mechanisms mediated by alkaloids in different signaling pathways, including the NF-kB signaling pathway, PI3K/AKT signaling pathway, MAPK signaling pathway, and P53 signaling pathway. The research progress of alkaloids related to tumor signal transduction pathways and the realization of alkaloids as cancer prevention drugs by targeting signal pathways remains.

Integrative Analysis of lncRNAs in Kidney Cancer to Discover A New lncRNA (LINC00847) as A Therapeutic Target for Staphylococcal Enterotoxin tst Gene

Objective

Bacterial toxin can cause cell death through induction of apoptosis in cancer cell lines as well as changes in the expression patterns of long non-coding RNAs (lncRNAs) and genes. In the present study, the effect of tst gene on ACHN cell lines was reported along with proposing a novel pathway of apoptosis in kidney cancer.

Materials and Methods

In this experimental study, effective lncRNAs and genes were predicted from different criteria for renal cell carcinoma (RCC) by bioinformatics methods and lncRNA-miRNA-mRNA interaction was constructed; then the effect of Staphylococcus aureus tst gene on induction of apoptosis pathways on ACHN and HDF cell lines was investigated.

Results

After creation of lncRNA-miRNA-mRNA interaction, changes in expression levels of lncRNA LINC00847 (P=0.0024) and PTEN gene (P=0.0027) were identified, as potential apoptosis biomarkers for kidney cancer, after treating ACHN cell line by pCDNA3.1 (+)-tst compared to the empty vector. In contrast, there was no statistically significant difference in DICER1 expression levels in ACHN-tst cell (P≥0.05). In addition, transfection by pcDNA3.1 (+)-tst could increase ACHN cell apoptosis level (P<0.0001) compared to the pcDNA3.1 (+) group; but no significant effect was observed on normal cells.

Conclusion

It is suggested that lncRNA LINC00847, discovered in this study, could provide a new landscape for researches aimed to determine relationship between functional lncRNA and RCC pathways. pcDNA3.1 (+)-tst was found to increase apoptosis in the transfected cells.

PDK1 regulates the survival of the developing cortical interneurons

Inhibitory interneurons are critical for maintaining the excitatory/inhibitory balance. During the development cortical interneurons originate from the ganglionic eminence and arrive at the dorsal cortex through two tangential migration routes. However, the mechanisms underlying the development of cortical interneurons remain unclear. 3-Phosphoinositide-dependent protein kinase-1 (PDK1) has been shown to be involved in a variety of biological processes, including cell proliferation and migration, and plays an important role in the neurogenesis of cortical excitatory neurons. However, the function of PDK1 in interneurons is still unclear. Here, we reported that the disruption of Pdk1 in the subpallium achieved by crossing the Dlx5/6-Cre-IRES-EGFP line with Pdk1^fl/fl mice led to the severely increased apoptosis of immature interneurons, subsequently resulting in a remarkable reduction in cortical interneurons. However, the tangential migration, progenitor pools and cell proliferation were not affected by the disruption of Pdk1. We further found the activity of AKT-GSK3β signaling pathway was decreased after Pdk1 deletion, suggesting it might be involved in the regulation of the survival of cortical interneurons. These results provide new insights into the function of PDK1 in the development of the telencephalon.

Shikonin Attenuates Acetaminophen-Induced Hepatotoxicity by Upregulation of Nrf2 through Akt/GSK3β Signaling

Acetaminophen (APAP) overdose-induced acute liver damage is mostly due to overwhelmingly increased oxidative stress. Nuclear factor-erythroid 2-related factor2 (Nrf2) plays an important role in alleviating APAP hepatic toxicity. Shikonin (SHK) enhances Nrf2 in multiple lines of normal cells. Nevertheless, whether SHK protects against APAP-induced liver toxicity remains undefined. This study found SHK defended APAP-induced liver toxicity, as well as reversed the levels of serum alanine/aspartate aminotransferases (ALT/AST), liver myeloperoxidase (MPO) activity, and reactive oxygen species (ROS), while it enhanced the liver glutathione (GSH) level in APAP-treated mice. SHK rescued the cell viability and GSH depletion, but neutralized oxidative stress in APAP-treated human normal liver L-02 cells. Mechanically, SHK increased Nrf2 expression in the exposure of APAP at the protein level but not at the mRNA level. Inhibition of Nrf2 blocked the SHK effect in APAP-treated hepatocytes. Furthermore, SHK improved Nrf2 stability through stimulating PI3K/Akt pathway, thus inhibiting GSK-3β. In vivo studies confirmed the close correlation of liver protection of SHK against APAP and Akt/GSK-3β/Nrf2 pathway. In conclusion, this study reveals that SHK prevents APAP hepatotoxicity by upregulation of Nrf2 via PI3K/Akt/GSK-3β pathway. Therefore, SHK may be a promising candidate against APAP-induced liver injury.

Functional miRNAs in breast cancer drug resistance

Owing to improved early surveillance and advanced therapy strategies, the current death rate due to breast cancer has decreased; nevertheless, drug resistance and relapse remain obstacles on the path to successful systematic treatment. Multiple mechanisms responsible for drug resistance have been elucidated, and miRNAs seem to play a major part in almost every aspect of cancer progression, including tumorigenesis, metastasis, and drug resistance. In recent years, exosomes have emerged as novel modes of intercellular signaling vehicles, initiating cell–cell communication through their fusion with target cell membranes, delivering functional molecules including miRNAs and proteins. This review particularly focuses on enumerating functional miRNAs involved in breast cancer drug resistance as well as their targets and related mechanisms. Subsequently, we discuss the prospects and challenges of miRNA function in drug resistance and highlight valuable approaches for the investigation of the role of exosomal miRNAs in breast cancer progression and drug resistance.

Staurosporine suppresses survival of HepG2 cancer cells through Omi/HtrA2-mediated inhibition of PI3K/Akt signaling pathway

Staurosporine, which is an inhibitor of a broad spectrum of protein kinases, has shown cytotoxicity on several human cancer cells. However, the underlying mechanism is not well understood. In this study, we examined whether and how this compound has an inhibitory action on phosphatidylinositol 3-kinase (PI3K)/Akt pathway in vitro using HepG2 human hepatocellular carcinoma cell line. Cell viability and apoptosis were determined using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and terminal deoxyribonucleotidyl transferase–mediated dUTP-digoxigenin nick end labeling (TUNEL) assay, respectively. Glutathione S-transferase (GST) pull-down assay and co-immunoprecipitation were performed to detect protein–protein interactions. Small interfering RNA (siRNA) was used to silence the expression of targeted protein. We found that staurosporine significantly decreased cell viability and increased cell apoptosis in a concentration- and time-dependent manner in HepG2 cancer cells, along with the decreased expressions of PDK1 protein and Akt phosphorylation. Staurosporine was also found to enhance Omi/HtrA2 release from mitochondria. Furthermore, Omi/HtrA2 directly bound to PDK1. Pharmacological and genetic inhibition of Omi/HtrA2 restored protein levels of PDK1 and protected HepG2 cancer cells from staurosporine-induced cell death. In addition, staurosporine was found to activate autophagy. However, inhibition of autophagy exacerbated cell death under concomitant treatment with staurosporine. Taken together, our results indicate that staurosporine induced cytotoxicity response by inhibiting PI3K/Akt signaling pathway through Omi/HtrA2-mediated PDK1 degradation, and the process provides a novel mechanism by which staurosporine produces its therapeutic effects.

Lysophosphatidic Acid Inhibits Apoptosis Induced by Cisplatin in Cervical Cancer Cells

Cervical cancer is the second most common cause of cancer death in women worldwide. Lysophosphatidic acid (LPA) level has been found significantly increased in the serum of patients with ovarian, cervical, and colon cancers. LPA level in cervical cancer patients is significantly higher than in healthy controls. LPA receptors were found highly expressed in cervical cancer cells, suggesting LPA may play a role in the development of cervical cancer. The aim of this study is to investigate the effect of LPA on the apoptosis induced by cisplatin (DDP) in cervical cancer cell line and the underlying changes in signaling pathways. Our study found that cisplatin induced apoptosis of Hela cell through inhibiting expression of Bcl-2, upregulating the expression of Bax, Fas-L, and the enzyme activity of caspase-3 (p < 0.05); LPA significantly provided protection against the apoptosis induced by cisplatin by inhibiting the above alterations in apoptotic factor caused by cisplatin (p < 0.05). Moreover, PI3K/AKT pathway was found to be important for the LPA antiapoptosis effect, and administration of PI3K/AKT partially reversed the LPA-mediated protection against cisplatin-induced apoptosis (p < 0.05). These findings have shed new lights on the LPA bioactivity in cervical cancer cells and pointed to a possible sensitization scheme through combined administration of PI3K inhibitor and cisplatin for better treatment of cervical cancer patients, especially those with elevated LPA levels.

Potential protection of 2,3,5,4'-tetrahydroxystilbene-2-O-β-D-glucoside against staurosporine-induced toxicity on cultured rat hippocampus neurons

The present study explored the effect of 2,3,5,4'-tetrahydroxystilbene-2-O-β-d-glucoside (THSG) on the staurosporine (STS)-induced toxicity in cultured rat hippocampal neurons. The results showed that administration of 200μM of THSG significantly protected against 0.3μM of STS-induced apoptosis in cultured rat hippocampal neurons tested by methyl thiazolyl tetrazolium (MTT) and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assays. Furthermore, when the Akt signaling pathway was blocked by LY294002, an inhibitor of Phosphatidyl Inositol 3-kinase (PI3K), the protective effects of THSG against STS-induced neurotoxicity were abrogated. We further examined the involvement of PI3K/Akt signaling pathway in THSG protection against STS-induced cytotoxicity on cultured neurons and found that administration of THSG significantly inhibited the STS-induced decreases in the content of phosphorylated AKt (p-Akt). Moreover, we found that THSG rescued the down-regulation of B cell lymphoma/lewkmia-2 (Bcl2) and pro-caspase-3 (pro-Csp3) caused by STS in the neurons. These results indicate that THSG protect the cultured rat hippocampal neurons against STS-induced cytotoxicity and the PI3K/Akt signaling and mitochondrial apoptotic pathways are involved in the THSG-induced protective effects.

Rapid estrogen signaling negatively regulates PTEN activity through phosphorylation in endometrial cancer cells

Hyperestrogenicity is a risk factor for endometrial cancer. 17β-estradiol (E2) is known to stimulate both genomic and nongenomic estrogen receptor-α (ERα) actions in a number of reproductive tissues. However, the contributions of transcription-independent ERα signaling on normal and malignant endometrium are not fully understood. Phosphatase and tensin homolog (PTEN) is a tumor suppressor that decreases cellular mitosis primarily through negative regulation of the phosphoinositide 3-kinase/AKT signaling axis. PTEN levels are elevated during the E2 dominated, mitotically active, proliferative phase of the menstrual cycle, indicating possible hormonal regulation of PTEN in the uterus. In order to determine if rapid E2 signaling regulates PTEN, we used ERα-positive, PTEN-positive, endometrial cells. We show that cytosolic E2/ERα signaling leads to increased phosphorylation of PTEN at key regulatory residues. Importantly, E2 stimulation decreased PTEN lipid phosphatase activity and caused consequent increases in phospho-AKT. We further demonstrate that cytosolic ERα forms a complex with PTEN in an E2-dependent manner, and that ERα constitutively complexes with protein kinase2-α (CK2α), a kinase previously shown to phosphorylate the C-terminal tail of PTEN. These results provide mechanistic support for an E2-dependent, ERα cytosolic signaling complex that negatively regulates PTEN activity through carboxy terminus phosphorylation. Using an animal model, we show that sustained E2 signaling results in increased phospho-PTEN (S380, T382, and T383), total PTEN, and phospho-AKT (S473). Taken together, we provide a novel mechanism in which transcription-independent E2/ERα signaling may promote a pro-tumorigenic environment in the endometrium.

PI3K/Akt pathway restricts epithelial adhesion of Dr + Escherichia coli by down-regulating the expression of decay accelerating factor

The urogenital microbial infection in pregnancy is an important cause of maternal and neonatal morbidity and mortality. Uropathogenic Escherichia coli strains which express Dr fimbriae (Dr+) are associated with unique gestational virulence and they utilize cell surface decay accelerating factor (DAF or CD55) as one of the cellular receptor before invading the epithelial cells. Previous studies in our laboratory established that nitric oxide reduces the rate of E. coli invasion by delocalizing the DAF protein from cell surface lipid rafts and down-regulating its expression. The phosphoinositide 3-kinase/protein kinase B (PI3K/Akt) cell signal pathway plays an important role in host-microbe interaction because many bacteria including E. coli activate this pathway in order to establish infection. In the present study, we showed that the PI3K/Akt pathway negatively regulated the expression of DAF on the epithelial cell surface and thus inhibited the adhesion of Dr(+) E. coli to epithelial cells. Initially, using two human cell lines Ishikawa and HeLa which differ in constitutive activity of PI3K/Akt, we showed that DAF levels were associated with the PI3K/Akt pathway. We then showed that the DAF gene expression was up-regulated and the Dr(+) E. coli adhesion increased after the suppression of PI3K/Akt pathway in Ishikawa cells using inhibitor LY294002, and a plasmid which allowed the expression of PI3K/Akt regulatory protein PTEN. The down-regulation of PTEN protein using PTEN-specific siRNA activated the PI3K/Akt pathway, down-regulated the DAF, and decreased the adhesion of Dr(+) E. coli. We conclude that the PI3K/Akt pathway regulated the DAF expression in a nitric oxide independent manner.

Combined PTEN Mutation and Protein Expression Associate with Overall and Disease-Free Survival of Glioblastoma Patients

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a tumor suppressor commonly inactivated in glioblastoma multiforme (GBM), but the prognostic significance of PTEN remains controversial. Here, we demon- strate significant prognostic value of combined PTEN mutation and expression for the survival of patients with GBM on the basis of analysis of large-scale cancer genomic data. PTEN nonsense mutations associated with sig- nificantly shorter disease-free survival and overexpression of PTEN protein linked to shorter disease-free and overall survival of patients with GBM. PTEN nonsense mutations correlated with decreased p53 and Gata3 protein levels and increased genomic instability in human GBM tissues. Expression of nonsense PTEN mutant decreased p53 and Gata3 levels, producing increased DNA damage both in vitro and in vivo. Mice carrying xenograft tumors with nonsense PTEN mutant displayed significantly shorter survival. Our data demonstrated the prognostic value of combined PTEN mutation and protein expression for patients with GBM and highlighted distinct biologic effects of nonsense and missense mutations of PTEN.

Overexpression of PTEN suppresses lipopolysaccharide-induced lung fibroblast proliferation, differentiation and collagen secretion through inhibition of the PI3-K-Akt-GSK3beta pathway

Background

Abnormal and uncontrolled proliferation of lung fibroblasts may contribute to pulmonary fibrosis. Lipopolysaccharide (LPS) can induce fibroblast proliferation and differentiation through activation of phosphoinositide3-Kinase (PI3-K) pathway. However, the detail mechanism by which LPS contributes to the development of lung fibrosis is not clearly understood. To investigate the role of phosphatase and tensin homolog (PTEN), a PI3-K pathway suppressor, on LPS-induced lung fibroblast proliferation, differentiation, collagen secretion and activation of PI3-K, we transfected PTEN overexpression lentivirus into cultured mouse lung fibroblasts with or without LPS treatment to evaluate proliferation by MTT and Flow cytometry assays. Expression of PTEN, alpha-smooth muscle actin (alpha-SMA), glycogen synthase kinase 3 beta (GSK3beta) and phosphorylation of Akt were determined by Western-blot or real-time RT-PCR assays. The PTEN phosphorylation activity was measured by a malachite green-based assay. The content of C-terminal propeptide of type I procollagen (PICP) in cell culture supernatants was examined by ELISA.

Results

We found that overexpression of PTEN effectively increased expression and phosphatase activity of PTEN, and concomitantly inhibited LPS-induced fibroblast proliferation, differentiation and collagen secretion. Phosphorylation of Akt and GSK3beta protein expression levels in the LPS-induced PTEN overexpression transfected cells were significantly lower than those in the LPS-induced non-transfected cells, which can be reversed by the PTEN inhibitor, bpV(phen).

Conclusions

Collectively, our results show that overexpression and induced phosphatase activity of PTEN inhibits LPS-induced lung fibroblast proliferation, differentiation and collagen secretion through inactivation of PI3-K-Akt-GSK3beta signaling pathways, which can be abrogated by a selective PTEN inhibitor. Thus, expression and phosphatase activity of PTEN could be a potential therapeutic target for LPS-induced pulmonary fibrosis. Compared with PTEN expression level, phosphatase activity of PTEN is more crucial in affecting lung fibroblast proliferation, differentiation and collagen secretion.

2,3-Diaryl-2H-1-benzopyran derivatives interfere with classical and non-classical estrogen receptor signaling pathways, inhibit Akt activation and induce apoptosis in human endometrial cancer cells

OBJECTIVES

The present study was undertaken to explore the mechanism of anti-proliferative action of benzopyran compound D1 (2-[piperidinoethoxyphenyl]-3-phenyl-2H-benzopyran) and its hydroxy-(D2) and methoxy-(D3) derivatives in Ishikawa and human primary endometrial adenocarcinoma cells.

METHODS

Transcriptional activation assays were performed using luciferase reporter system and cell viability was determined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT). The stage of cell cycle was determined by flow-cytometry and real time analysis of cyclinE1 and cdc2 genes. The apoptotic effects were measured by AnnexinV/PI staining and TUNEL. The expression of PCNA, cyclinD1, pAkt, XIAP, cleaved caspase-9, -3, PARP, Bax and Bcl2 were determined by immunoblotting. The caspase-3 activity and mitochondrial membrane potential were measured by colorimetric assay.

RESULTS

All three compounds inhibited E(2)-induced ERE- and AP-1-mediated transactivation and proliferation in endometrial adenocarcinoma cells dose-dependently. Compound D1 caused the arrest of cells in the G(2) phase while D2 and D3 caused arrest in G(1) phase of the cell cycle. All compounds interfered with Akt activation, decreased XIAP expression leading to an increased cleavage of caspase-9, -3, PARP, increased Bax/Bcl2 ratio and caspase-3 activity.

CONCLUSION

Findings suggest that benzopyran derivatives inhibit cellular proliferation via modulating ER-dependent classical and non-classical signaling mechanisms, interfere with Akt activation and induce apoptosis via intrinsic pathway in endometrial adenocarcinoma cells.

An integrative genomic analysis revealed the relevance of microRNA and gene expression for drug-resistance in human breast cancer cells

Background

Acquisition of drug-resistance in cancer has led to treatment failure, however, their mechanisms have not been clarified yet. Recent observations indicated that aberrant expressed microRNA (miRNA) caused by chromosomal alterations play a critical role in the initiation and progression of cancer. Here, we performed an integrated genomic analysis combined with array-based comparative hybridization, miRNA, and gene expression microarray to elucidate the mechanism of drug-resistance.

Results

Through genomic approaches in MCF7-ADR; a drug-resistant breast cancer cell line, our results reflect the unique features of drug-resistance, including MDR1 overexpression via genomic amplification and miRNA-mediated TP53INP1 down-regulation. Using a gain of function study with 12 miRNAs whose expressions were down-regulated and genome regions were deleted, we show that miR-505 is a novel tumor suppressive miRNA and inhibits cell proliferation by inducing apoptosis. We also find that Akt3, correlate inversely with miR-505, modulates drug sensitivity in MCF7-ADR.

Conclusion

These findings indicate that various genes and miRNAs orchestrate to temper the drug-resistance in cancer cells, and thus acquisition of drug-resistance is intricately controlled by genomic status, gene and miRNA expression changes.

Effect of gamma-synuclein silencing on apoptotic pathways in retinal ganglion cells

gamma-Synuclein (Syn G) is highly expressed in retinal ganglion cells and the loss of these cells in glaucoma is associated with significant reduction of the intracellular Syn G level. However, a causative relationship between these two events has not been established. Here we show that the knockdown of Syn G results in a decreased viability of the immortalized retinal ganglion cells (RGC-5). The Syn G silencing reduces phosphorylation of serine 112 (Ser112) in Bad protein, a member of the Bcl-2 family that plays a critical role in apoptotic cell death signaling. Our gene expression analysis data suggests that changes in Bad phosphorylation status may be caused by a coordinated shift in activities of kinases controlling Bad phosphorylation and phosphatases catalyzing its dephosphorylation. Moreover, increased phosphorylation of Bad-sequestering protein 14-3-3 detected in these cells is also pro-apoptotic. These results suggest that the homeostatic level of Syn G in RGC-5 cells is required for transcriptional regulation of protein kinases and phosphatases, controlling phosphorylation of Bad and 14-3-3. Lowering Syn G causes Bad dephosphorylation, dissociation from phosphorylated 14-3-3, and translocation to mitochondria where it initiates apoptotic death cascade.

Loss of tuberous sclerosis complex-2 function and activation of mammalian target of rapamycin signaling in endometrial carcinoma

PURPOSE

The involvement of phosphatase and tensin homologue deleted on chromosome ten (PTEN) in endometrial carcinoma has implicated phosphatidylinositol 3-kinase signaling and mammalian target of rapamycin (mTOR) activation in this disease. Understanding the extent of mTOR involvement and the mechanism responsible for activation is important, as mTOR inhibitors are currently being evaluated in clinical trials for endometrial carcinoma. Although tuberous sclerosis complex 2 (TSC2) is the "gatekeeper" for mTOR activation, little is known about defects in the TSC2 tumor suppressor or signaling pathways that regulate TSC2, such as LKB1/AMP-activated protein kinase, in the development of endometrial carcinoma.

EXPERIMENTAL DESIGN

We determined the frequency of mTOR activation in endometrial carcinoma (primary tumors and cell lines) and investigated PTEN, LKB1, and TSC2 defects as underlying cause(s) of mTOR activation, and determined the ability of rapamycin to reverse these signaling defects in endometrial carcinoma cells.

RESULTS

Activation of mTOR was a consistent feature in endometrial carcinomas and cell lines. In addition to PTEN, loss of TSC2 and LKB1 expression occurred in a significant fraction of primary tumors (13% and 21%, respectively). In tumors that retained TSC2 expression, phosphorylation of tuberin at S939 was observed with a high frequency, indicating that mTOR repression by TSC2 had been relieved via AKT phosphorylation of this tumor suppressor. In PTEN-null and LKB1-null endometrial carcinoma cell lines with functional inactivation of TSC2, phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin and LY294002 were able to inhibit AKT and mTOR signaling and reverse TSC2 phosphorylation. In contrast, although rapamycin inhibited mTOR signaling, it did not relieve phosphorylation of TSC2 at S939.

CONCLUSIONS

Inactivation of TSC2 via loss of expression or phosphorylation occurred frequently in endometrial carcinoma to activate mTOR signaling. High-frequency mTOR activation supports mTOR as a rational therapeutic target for endometrial carcinoma. However, whereas rapamycin and its analogues may be efficacious at inhibiting mTOR activity, these drugs do not reverse the functional inactivation of TSC2 that occurs in these tumors.

Models representing type I and type II human endometrial cancers: Ishikawa H and Hec50co cells

OBJECTIVE

Endometrial cancer models are critical to the advancement of investigation, and Ishikawa H and Hec50co cells have been used as research tools. The purpose of these studies is to verify the degree to which these commonly used cell models share the molecular characteristics of the two major in vivo endometrial cancer subtypes, I and II.

METHODS

The studies reported include an analysis of pathologic features, tumor suppressor mutations, detailed karyotyping, and cell cycle regulation.

RESULTS

Ishikawa H cells are hormone responsive and have lost PTEN expression. In addition they have lost RB1 expression due to a deletion in exon 9. Hec50co cells have lost p53 expression due to a deletion at the junction of exon 6 and intron 6-7. Compared to Ishikawa H cells, Hec50co cells harbor many more chromosomal rearrangements (29 versus seven), and the doubling time is more rapid. The percent of cells in each phase of the cell cycle is reported and linked to cell cycle regulators.

CONCLUSION

We present extensive data indicating that Ishikawa H cells are excellent models for type I endometrial cancers, and Hec50co cells faithfully replicate the molecular characteristics of type II endometrial cancers. These studies allow testing of new therapeutic regimens using appropriate cell models.

PI3K is negatively regulated by PIK3IP1, a novel p110 interacting protein

Signaling initiated by Class Ia phosphatidylinositol-3-kinases (PI3Ks) is essential for cell proliferation and survival. We discovered a novel protein we call PI3K interacting protein 1 (PIK3IP1) that shares homology with the p85 regulatory PI3K subunit. Using a variety of in vitro and cell based assays, we demonstrate that PIK3IP1 directly binds to the p110 catalytic subunit and down modulates PI3K activity. Our studies suggest that PIK3IP1 is a new type of PI3K regulator.

PTEN augments doxorubicin-induced apoptosis in PTEN-null Ishikawa cells

To investigate whether PTEN can augment doxorubicin-induced apoptosis in PTEN-null Ishikawa cells. We previously demonstrated that Ishikawa cells do not possess functional PTEN protein because of protein truncations. Clones expressing the steady-state level of the PTEN protein from PTEN-null Ishikawa cells have been established and were used in this study. Doxorubicin is a commonly used anticancer drug in endometrial carcinoma. The cytotoxic effect of doxorubicin was evaluated using the methyl thiazoleterazolium (MTT) assay. We used the Hoechst 33258 staining to confirm the induction of apoptosis. Immunoprecipitation and Western blot analysis were performed to evaluate the effects of doxorubicin on phosphorylation of Bcl-2 antagonist of cell death (Bad) and protein kinase B (Akt/PKB). Doxorubicin induced death of all cell lines in a dose-dependent manner, but the death was more significant in PTEN-expressing clones than in parent Ishikawa cells. A low concentration of doxorubicin (0.1 muM) did not affect apoptosis in PTEN-null Ishikawa cells, but it induced apoptosis in PTEN-expressing clones. A high concentration (1 microM) induced apoptosis in all cell lines, but the percentages of apoptotic cells were higher in PTEN-expressing clones than in parent Ishikawa cells. In the clones, phospho-Akt/PKB and phospho-Bad (Ser-136) were downregulated. Doxorubicin reduced the levels of phospho-Akt/PKB and phospho-Bad (Ser-136) in all the cell lines, but the reduction was most significant in the PTEN-expressing clones. Our present results indicate that PTEN transfection significantly enhances doxorubicin chemosensitivity through effective induction of apoptosis by downregulation of the PI3K/Akt/PKB signaling pathway in Ishikawa cells.

Ubiquitous calpains promote both apoptosis and survival signals in response to different cell death stimuli

The mu- and m-calpain proteases have been implicated in both pro- or anti-apoptotic functions. Here we compared cell death responses and apoptotic or survival signaling pathways in primary mouse embryonic fibroblasts (MEFs) derived from wild type or capn4 knock-out mice which lack both mu- and m-calpain activities. Capn4(-/-) MEFs displayed resistance to puromycin, camptothecin, etoposide, hydrogen peroxide, ultraviolet light, and serum starvation, which was consistent with pro-apoptotic roles for calpain. In contrast, capn4(-/-) MEFs were more susceptible to staurosporine (STS) and tumor necrosis factor alpha-induced cell death, which provided evidence for anti-apoptotic signaling roles for calpain. Bax activation, release of cytochrome c, and activation of caspase-9 and caspase-3 all correlated with the observed cell death responses of wild type or capn4(-/-) MEFs to the various challenges, suggesting that calpain might play distinct roles in transducing different death signals to the mitochondria. There was no evidence that calpain cleaved Bcl-2 family member proteins that regulate mitochondrial membrane permeability including Bcl-2, Bcl-xl, Bad, Bak, Bid, or Bim. However, activation of the phosphatidylinositol 3 (PI3)-kinase/Akt survival signaling pathway was compromised in capn4(-/-) MEFs under all challenges regardless of the cell death outcome, and blocking Akt activation using the PI3-kinase inhibitor LY294002 abolished the protective effect of calpain to STS challenge. We conclude that the anti-apoptotic function of calpain in tumor necrosis factor alpha- and STS-challenged cells relates to a novel role in activating the PI3-kinase/Akt survival pathway.

PTEN is involved in the signal transduction pathway of contact inhibition in endometrial cells

PTEN is involved in the regulation of normal cellular functions in addition to its well-known role as a tumor suppressor. In the present study, we have shown that stable transfection of the PTEN gene into PTEN-mutated endometrial carcinoma cells leads to contact inhibition accompanied by a decreased level of phosphorylated-Akt (p-Akt) expression, an increase in p27(Kip1), and a decrease in beta-catenin. PTEN-induced cells with contact inhibition exhibit G0-G1 cell-cycle arrest, and the Ki-67 labeling index is reduced. These changes are canceled by transfection of a double-stranded short-interfering RNA against the PTEN gene. Normal endometrial stromal cells increase their PTEN expression when reaching confluence; this is followed by changes in the expression of Akt-related proteins in the same way as in tumor cells. These results indicate that PTEN, p-Akt, p27, and beta-catenin are involved in the signal transduction of contact inhibition and suggest that PTEN may, in part, control the proliferation of endometrial carcinoma cells through the induction of contact inhibition.

The complexity of PTEN: mutation, marker and potential target for therapeutic intervention

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is a phosphatase that removes phosphates primarily from lipids. It has also been called mutated in multiple advanced cancers 1 and transforming growth factor-beta regulated epithelial cell-enriched phosphatase 1. The best described substrate of PTEN is phosphatidyliniositol (3,4,5)-tris-phosphate [PtdIns(3,4,5)P3]. PTEN removes the phosphate in PtdIns(3,4,5)P(3) to generate PtdIns(4,5)P(2). PTEN serves to counter-balance the effects of phosphoinositide 3' kinase, which normally adds a phosphate to PtdIns(4,5)P(2) to generate PtdIns(3,4,5)P(3). PtdIns(3,4,5)P(3) recruits kinases such as phosphoinositide-dependent kinase 1, which in turn phosphorylate Akt, which phosphorylates other downstream proteins involved in regulation of apoptosis and cell-cycle progression. PTEN removal of the phosphate from PtdIns(3,4,5)P(3) inhibits this pathway by preventing localisation of proteins with pleckstrin homology domains to the cell membrane. Alterations of the PTEN gene are associated with cancer and other diseases. Novel therapeutic approaches have been developed to counteract the deletion/mutation of PTEN in human cancer. This review will discuss the role of PTEN in signal transduction and cancer as well as pharmacological approaches to combat PTEN loss in human cancer.

Apoptosis defects and chemotherapy resistance: molecular interaction maps and networks

Intrinsic (innate) and acquired (adaptive) resistance to chemotherapy critically limits the outcome of cancer treatments. For many years, it was assumed that the interaction of a drug with its molecular target would yield a lethal lesion, and that determinants of intrinsic drug resistance should therefore be sought either at the target level (quantitative changes or/and mutations) or upstream of this interaction, in drug metabolism or drug transport mechanisms. It is now apparent that independent of the factors above, cellular responses to a molecular lesion can determine the outcome of therapy. This review will focus on programmed cell death (apoptosis) and on survival pathways (Bcl-2, Apaf-1, AKT, NF-kappaB) involved in multidrug resistance. We will present our molecular interaction mapping conventions to summarize the AKT and IkappaB/NF-kappaB networks. They complement the p53, Chk2 and c-Abl maps published recently. We will also introduce the 'permissive apoptosis-resistance' model for the selection of multidrug-resistant cells.

Akt plays a central role in sarcomagenesis induced by Kaposi's sarcoma herpesvirus-encoded G protein-coupled receptor

We have recently engineered an in vivo endothelial cell-specific retroviral gene transfer system and found that a single Kaposi's sarcoma (KS)-associated herpesvirus/human herpesvirus 8 gene encoding a G protein-coupled receptor (vGPCR), is sufficient to induce KS-like tumors in mice. By using this system, we show here that the Akt signaling pathway plays a central role in vGPCR oncogenesis. Indeed, a constitutively active Akt was sufficient to induce benign hemangiomas in mice, whereas heterozyogosity for PTEN (the phosphatase and tension homologue deleted on chromosome 10), modestly enhancing basal Akt activity, dramatically enhanced vGPCR sarcomagenesis. Examination of KS biopsies from AIDS patients revealed active Akt as a prominent feature, supportive of a role for Akt in human Kaposi's sarcomagenesis. By using a vGPCR agonist-dependent mutant, we further establish constitutive activity as a requirement for vGPCR sarcomagenesis, validating targeted inhibition of key vGPCR signaling pathways as an approach for preventing its oncogenic potential. These observations prompted us to explore the efficacy of inhibiting Akt activation as a molecular approach to KS treatment. Pharmacological inhibition of the Akt pathway with the chemotherapeutic agent 7-hydroxystaurosporine prevented proliferation of vGPCR-expressing endothelial cells in vitro and inhibited their tumorigenic potential in vivo. Both were associated with a decrease in Akt activity. These results identify Akt as an essential player in vGPCR sarcomagenesis and demonstrate the therapeutic potential of drugs targeting this pathway in the treatment of KS.

Activation of the PI3K/Akt pathway and chemotherapeutic resistance

The resistance of many types of cancer to conventional chemotherapies is a major factor undermining successful cancer treatment. In this review, the role of a signal transduction pathway comprised of the lipid kinase, phosphatidylinositol 3-kinase (PI3K), and the serine/threonine kinase, Akt (or PKB), in chemotherapeutic resistance will be explored. Activation of this pathway plays a pivotal role in essential cellular functions such as survival, proliferation, migration and differentiation that underlie the biology of human cancer. Akt activation also contributes to tumorigenesis and tumor metastasis, and as shown most recently, resistance to chemotherapy. Modulating Akt activity is now a commonly observed endpoint of chemotherapy administration or administration of chemopreventive agents. Studies performed in vitro and in vivo combining small molecule inhibitors of the PI3K/Akt pathway with standard chemotherapy have been successful in attenuating chemotherapeutic resistance. As a result, small molecules designed to specifically target Akt and other components of the pathway are now being developed for clinical use as single agents and in combination with chemotherapy to overcome therapeutic resistance. Specifically inhibiting Akt activity may be a valid approach to treat cancer and increase the efficacy of chemotherapy.

Participation of various kinases in staurosporine induced apoptosis of RAW 264.7 cells

Staurosporine induced apoptosis of RAW 264.7 cells, a mouse macrophage-like cell line, as determined by DNA fragmentation, the increase of annexin V-stained cells, and the cleavage of poly(ADP-ribose)polymerase (PARP), a substrate of caspase. Analysis of the increase in the percentage of sub-G(1) cells revealed that the DNA fragmentation occurred in a time- and concentration-dependent manner at 0.021-2.1 microM of staurosporine. Staurosporine induced phosphorylation of p38 mitogen-activated protein kinase (MAPK) but suppressed spontaneous phosphorylation of p44/42 MAPK. The p38 MAPK inhibitor SB203580, the MAPK/extracellular signal-regulated kinase kinase inhibitor PD98059 and the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 potentiated the staurosporine-induced PARP cleavage and DNA fragmentation. The protein kinase A (PKA) inhibitor H-89 potentiated the staurosporine-induced DNA fragmentation without potentiating the PARP cleavage. In contrast, the protein kinase C (PKC) inhibitor Ro-31-8425 suppressed the PARP cleavage and DNA fragmentation. These findings suggested that staurosporine induces apoptosis via the caspase cascade in RAW 264.7 cells. The staurosporine-induced apoptosis is positively regulated by PKC, negatively regulated by p38 MAPK, p44/42 MAPK and PI3K via the caspase cascade, and negatively regulated by PKA without regulation of caspase activation.