RNA Interference–Mediated Depletion of Phosphoinositide 3-Kinase Activates Forkhead Box Class O Transcription Factors and Induces Cell Cycle Arrest and Apoptosis in Breast Carcinoma Cells

The Anticancer Effects of Marine Carotenoid Fucoxanthin through Phosphatidylinositol 3-Kinase (PI3K)-AKT Signaling on Triple-Negative Breast Cancer Cells

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer that lacks specific targets such as estrogen, progesterone, and HER2 receptors. TNBC affects one in eight women in the United States, making up 15-20% of breast cancer cases. Patients with TNBC can develop resistance to chemotherapy over time, leading to treatment failure. Therefore, finding other options like natural products is necessary for treatment. The advantages of using natural products sourced from plants as anticancer agents are that they are less toxic, more affordable, and have fewer side effects. These products can modulate several cellular processes of the tumor microenvironment, such as proliferation, migration, angiogenesis, cell cycle arrest, and apoptosis. The phosphatidyl inositol 3-kinase (PI3K)-AKT signaling pathway is an important pathway that contributes to the survival and growth of the tumor microenvironment and is associated with these cellular processes. This current study examined the anticancer effects of fucoxanthin, a marine carotenoid isolated from brown seaweed, in the MDA-MB-231 and MDA-MB-468 TNBC cell lines. The methods used in this study include a cytotoxic assay, PI3K-AKT signaling pathway PCR arrays, and Wes analysis. Fucoxanthin (6.25 µM) + TNF-α (50 ng/mL) and TNF-α (50 ng/mL) showed no significant effect on cell viability compared to the control in both MDA-MB-231 and MDA-MB-468 cells after a 24 h treatment period. PI3K-AKT signaling pathway PCR array studies showed that in TNF-α-stimulated (50 ng/mL) MDA-MB-231 and MDA-MB-468 cells, fucoxanthin (6.25 µM) modulated the mRNA expression of 12 genes, including FOXO1, RASA1, HRAS, MAPK3, PDK2, IRS1, EIF4EBP1, EIF4B, PTK2, TIRAP, RHOA, and ELK1. Additionally, fucoxanthin significantly downregulated the protein expression of IRS1, EIF4B, and ELK1 in MDA-MB-231 cells, and no change in the protein expression of EIF4B and ELK1 was shown in MDA-MB-468 cells. Fucoxanthin upregulated the protein expression of RHOA in both cell lines. The modulation of the expression of genes and proteins of the PI3K-AKT signaling pathway may elucidate fucoxanthin's effects in cell cycle progression, apoptotic processes, migration, and proliferation, which shows that PI3K-AKT may be the possible molecular mechanism for fucoxanthin's effects. In conclusion, the results obtained in this study elucidate fucoxanthin's molecular mechanisms and indicate that fucoxanthin may be considered a promising candidate for breast cancer-targeted therapy.

Valproic acid treatment attenuates cisplatin-induced kidney injury by suppressing proximal tubular cell damage

Cisplatin treatment is effective against several types of carcinomas. However, it frequently leads to kidney injury, which warrants effective prevention methods. Sodium valproic acid is a prophylactic drug candidate with a high potential for clinical application against cisplatin-induced kidney injury. Therefore, in this study, we aimed to elucidate the mechanism underlying the prophylactic effect of valproic acid on cisplatin-induced kidney injury in a mouse model and HK2 and PODO cells with cisplatin-induced toxicity. In the mouse model of cisplatin-induced kidney injury, various renal function parameters and tubular damage scores were worsened by cisplatin, but they were significantly improved upon combination with valproic acid. No difference was observed in cisplatin accumulation between the cisplatin-treated and valproic acid-treated groups in whole blood and the kidneys. The mRNA expression levels of proximal tubular damage markers, apoptosis markers, and inflammatory cytokines significantly increased in the cisplatin group 72 h after cisplatin administration but significantly decreased upon combination with valproic acid. In HK2 cells, a human proximal tubular cell line, the cisplatin-induced decrease in cell viability was significantly suppressed by co-treatment with valproic acid. Valproic acid may inhibit cisplatin-induced kidney injury by suppressing apoptosis, inflammatory responses, and glomerular damage throughout the kidneys by suppressing proximal tubular cell damage. However, prospective controlled trials need to evaluate these findings before their practical application.

Identification of Potential Therapeutic Genes and Pathways in Phytoestrogen Emodin Treated Breast Cancer Cell Lines via Network Biology Approaches

Phytoestrogens have been investigated for their potential anti-tumorigenic effects in various cancers including breast cancer. Emodin being a phytoestrogen shows anti-carcinogenic properties especially in estrogen receptor positive (ER+) breast cancers. The aim of this study is to identify the molecular mechanism and related biological pathways in both (ER+) MCF-7 and (ER-) MDA-MB-231 breast cancer cell lines upon Emodin treatment via microarray analysis in order to find out therapeutic biomarkers. In both cell lines, first differentially expressed genes were identified, then gene ontology and functional pathway enrichment analyses were performed. Genes regulated through multiple pathways were studied together with literature and a gene cluster was determined for each cell line. Further GeneMANIA and STRING databases were used to study the interactions within the related gene clusters. The results showed that, the genes which are related to cell cycle were significantly regulated in both cell lines. Also, Forkhead Box O1-related genes were found to be prominent in MCF-7 cells. In MDA-MB-231 cells, spindle attachment checkpoint mechanism-related genes were regulated, remarkably. As a result, novel gene regulations reported in this study in response to Emodin will give more information about its metabolism and antiproliferative effect, especially in ER + cells.

Metabolism of Reactive Oxygen Species in Osteosarcoma and Potential Treatment Applications

Background: The present study was designed to explore the underlying role of hypoxia-inducible factor 1α (HIF-1α) in reactive oxygen species (ROS) formation and apoptosis in osteosarcoma (OS) cells induced by hypoxia. Methods: In OS cells, ROS accumulated and apoptosis increased within 24 h after exposure to low HIF-1α expression levels. A co-expression analysis showed that HIF was positively correlated with Forkhead box class O1 (FoxO1) expression and negatively correlated with CYP-related genes from the National Center for Biotechnology Information’s Gene Expression Omnibus (NCBI GEO) datasets. Hypoxia also considerably increased HIF-1α and FoxO1 expression. Moreover, the promoter region of FoxO1 was directly regulated by HIF-1α. We inhibited HIF-1α via siRNA and found that the ROS accumulation and apoptosis induced by hypoxia in OS cells decreased. In this study, a murine xenograft model of BALB-c nude mice was adopted to test tumour growth and measure the efficacy of 2-ME + As₂O₃ treatment. Results: Ad interim knockdown of HIF-1α also inhibited manganese-dependent superoxide dismutase (MnSOD), catalase and sestrin 3 (Sesn3) expression in OS cells. Furthermore, hypoxia-induced ROS formation and apoptosis in OS cells were associated with CYP450 protein interference and were ablated by HIF-1α silencing via siRNA. Conclusions: Our data reveal that HIF-1α inhibits ROS accumulation by directly regulating FoxO1 in OS cells, which induces MnSOD, catalase and Sesn3 interference, thus resulting in anti-oxidation effects. The combination of an HIF-1α inhibitor (2-mercaptoethanol,2-ME) and ROS inducer (arsenous oxide, As₂O₃) can prohibit proliferation and migration and promote apoptosis in MG63 cells in vitro while inhibiting tumour growth in vivo.

FOXO1 Negates the Cooperative Action of FOXL2C134W and SMAD3 in CYP19 Expression in HGrC1 Cells by Sequestering SMAD3

Adult granulosa cell tumor (aGCT) is a rare type of ovarian cancer characterized by estrogen excess. Interestingly, only the single somatic mutation FOXL2 ^C134W was found across virtually all aGCTs. We previously reported that FOXL2^C134W stimulates CYP19 transcription synergistically with SMAD3, leading to elevated estradiol synthesis in a human granulosa cell line (HGrC1). This finding suggested a key role for FOXL2^C134W in causing the typical estrogen overload in patients with aGCTs. We have now investigated the effect of FOXO1, a tumor suppressor, on CYP19 activation by FOXL2^C134W in the presence of SMAD3. Intriguingly, FOXO1 antagonized the positive, synergistic effect of FOXL2^C134W and SMAD3 on CYP19 transcription. Similar to FOXL2^C134W, FOXO1 binds SMAD3 but not the proximal FOXL2^C134W binding site (-199 bp) of the CYP19 promoter identified in our earlier studies. The results of a competitive binding assay suggested a possible underlying mechanism in which FOXO1 sequesters SMAD3 away from FOXL2^C134W, thereby negating the cooperative action of FOXL2^C134W and SMAD3 in inducing CYP19 expression. To our knowledge, this study is the first to demonstrate the ability of FOXO1 to restore an altered CYP19 expression by FOXL2^C134W and SMAD3 and provides insight as to why FOXO1 deficiency promotes GCT development in mice.

Piperlongumine-induced nuclear translocation of the FOXO3A transcription factor triggers BIM-mediated apoptosis in cancer cells

The transcription factor forkhead box O 3A (FOXO3A) is a tumor suppressor that promotes cell cycle arrest and apoptosis. Piperlongumine (PL), a plant alkaloid, is known to selectively kill tumor cells while sparing normal cells. However, the mechanism of PL-induced cancer cell death is not fully understood. We report here that an association of FOXO3A with the pro-apoptotic protein BIM (also known as BCL2-like 11, BCL2L11) has a direct and specific function in PL-induced cancer cell death. Using HeLa cells stably expressing a FOXO3A-GFP fusion protein and several other cancer cell lines, we found that PL treatment induces FOXO3A dephosphorylation and nuclear translocation and promotes its binding to the BIM gene promoter, resulting in the up-regulation of BIM in the cancer cell lines. Accordingly, PL inhibited cell viability and caused intrinsic apoptosis in a FOXO3A-dependent manner. Of note, siRNA-mediated FOXO3A knockdown rescued the cells from PL-induced cell death. In vivo, the PL treatment markedly inhibited xenograft tumor growth, and this inhibition was accompanied by the activation of the FOXO3A-BIM axis. Moreover, PL promoted FOXO3A dephosphorylation by inhibiting phosphorylation and activation of Akt, a kinase that phosphorylates FOXO3A. In summary, our findings indicate that PL activates the FOXO3A-BIM apoptotic axis by promoting dephosphorylation and nuclear translocation of FOXO3A via Akt signaling inhibition. These findings uncover a critical mechanism underlying the effects of PL on cancer cells.

Goserelin promotes the apoptosis of epithelial ovarian cancer cells by upregulating forkhead box O1 through the PI3K/AKT signaling pathway

Gonadotropins, including luteinizing hormone (LH) and follicle stimulating hormone (FSH), are conducive to the growth of ovarian cancer based on the ‘gonadotropin theory’ and are regulated by gonadotropin-releasing hormone (GnRH). The present study was carried out to investigate the effect of goserelin, a GnRH agonist, on the apoptosis of epithelial ovarian cancer (EOC) cells and the underlying in vitro and in vivo mechanisms. Through flow cytometry, Hoechst staining and TUNEL staining, we demonstrated that goserelin promoted the apoptosis of EOC cells both in vitro and in vivo. Through human apoptosis gene PCR array, we verified that the promotion of EOC cell apoptosis by goserelin was linked to the upregulation of members of the tumor necrosis factor (TNF) and TNF receptor superfamilies, which have been identified as downstream targets of forkhead box O1 (FOXO1). Goserelin enhanced FOXO1 expression, and siRNA-mediated knockdown of FOXO1 abrogated the induction of apoptosis by goserelin. Moreover, goserelin decreased AKT activity, and FOXO1 upregulation by goserelin was dependent on the phosphatidylinositol 3-kinase (PI3K)/AKT pathway. In vivo, the expression of key factors in the PI3K/AKT/FOXO1 pathway was consistent with that observed in vitro. In conclusion, our data suggested that goserelin may promote EOC cell apoptosis by upregulating FOXO1 through the PI3K/AKT signaling pathway. We believe that GnRH agonists may be potential antitumor agents, and key factors in the PI3K/AKT-FOXO1 pathway may also be novel therapeutic targets for the treatment of EOC.

FOXO Signaling Pathways as Therapeutic Targets in Cancer

Many transcription factors play a key role in cellular differentiation and the delineation of cell phenotype. Transcription factors are regulated by phosphorylation, ubiquitination, acetylation/deacetylation and interactions between two or more proteins controlling multiple signaling pathways. These pathways regulate different physiological processes and pathological events, such as cancer and other diseases. The Forkhead box O (FOXO) is one subfamily of the fork head transcription factor family with important roles in cell fate decisions and this subfamily is also suggested to play a pivotal functional role as a tumor suppressor in a wide range of cancers. During apoptosis, FOXOs are involved in mitochondria-dependent and -independent processes triggering the expression of death receptor ligands like Fas ligand, TNF apoptosis ligand and Bcl‑X_L, bNIP3, Bim from Bcl-2 family members. Different types of growth factors like insulin play a vital role in the regulation of FOXOs. The most important pathway interacting with FOXO in different types of cancers is the PI3K/AKT pathway. Some other important pathways such as the Ras-MEK-ERK, IKK and AMPK pathways are also associated with FOXOs in tumorigenesis. Therapeutically targeting the FOXO signaling pathway(s) could lead to the discovery and development of efficacious agents against some cancers, but this requires an enhanced understanding and knowledge of FOXO transcription factors and their regulation and functioning. This review focused on the current understanding of cell biology of FOXO transcription factors which relates to their potential role as targets for the treatment and prevention of human cancers. We also discuss drugs which are currently being used for cancer treatment along with their target pathways and also point out some potential drawbacks of those drugs, which further signifies the need for development of new drug strategies in the field of cancer treatment.

Protection against β-amyloid-induced neurotoxicity by naturally occurring Z-ligustilide through the concurrent regulation of p38 and PI3-K/Akt pathways

Alzheimer's disease (AD) is primarily characterized by the progressive loss of functional neurons in the brain. Therefore, compounds with neuroprotective property may have therapeutic value in treating AD. Z-ligustilide (Z-LIG) is an essential oil originally isolated from umbelliferous plants. In the current study, the neuroprotective effects and underlying mechanisms of Z-LIG against fibrillar aggregates of Aβ_25-35 and Aβ_1-42-induced neurotoxicity were investigated in both SH-SY5Y cells and differentiated PC12 cells. Z-LIG at 1-30 μM provided an effective neuroprotection, as evidenced by the increase in cell viability, as well as the decrease in LDH release and intracellular accumulation of reactive oxygen species. Additionally, Z-LIG markedly blocked Aβ fibrils-induced condensed nuclei and sub-G1 accumulation suggestive of apoptosis. Furthermore, Z-LIG substantially reversed the activation of phosphorylated p38 and the inhibition of phosphorylated Akt caused by Aβ_25-35. LY294002, the specific inhibitor of PI3-K, significantly abrogated the protein expression of up-regulated phosphorylated Akt offered by Z-LIG. Most importantly, siRNA-mediated knockdown of PI3-K and p38 significantly abolished the neuroprotective effects of Z-LIG. The results taken together indicate that Z-LIG protects against Aβ fibrils-induced neurotoxicity possibly through the inhibition of p38 and activation of PI3-K/Akt signaling pathways concurrently. Z-LIG might be a potential candidate for further preclinical study aimed at the prevention and treatment of AD.

FOXO transcription factors in cancer development and therapy

The forkhead box O (FOXO) transcription factors are considered as tumor suppressors that limit cell proliferation and induce apoptosis. FOXO gene alterations have been described in a limited number of human cancers, such as rhabdomyosarcoma, leukemia and lymphoma. In addition, FOXO proteins are inactivated by major oncogenic signals such as the phosphatidylinositol-3 kinase pathway and MAP kinases. Their expression is also repressed by micro-RNAs in multiple cancer types. FOXOs are mediators of the tumor response to various therapies. However, paradoxical roles of FOXOs in cancer progression were recently described. FOXOs contribute to the maintenance of leukemia-initiating cells in acute and chronic myeloid leukemia. These factors may also promote invasion and metastasis of subsets of colon and breast cancers. Resistance to treatment was also ascribed to FOXO activation in multiple cases, including targeted therapies. In this review, we discuss the complex role of FOXOs in cancer development and response to therapy.

Methylseleninic acid promotes antitumour effects via nuclear FOXO3a translocation through Akt inhibition

Selenium supplement has been shown in clinical trials to reduce the risk of different cancers including lung carcinoma. Previous studies reported that the antiproliferative and pro-apoptotic activities of methylseleninic acid (MSA) in cancer cells could be mediated by inhibition of the PI3K pathway. A better understanding of the downstream cellular targets of MSA will provide information on its mechanism of action and will help to optimize its use in combination therapies with PI3K inhibitors. For this study, the effects of MSA on viability, cell cycle, metabolism, apoptosis, protein and mRNA expression, and reactive oxygen species production were analysed in A549 cells. FOXO3a subcellular localization was examined in A549 cells and in stably transfected human osteosarcoma U2foxRELOC cells. Our results demonstrate that MSA induces FOXO3a nuclear translocation in A549 cells and in U2OS cells that stably express GFP-FOXO3a. Interestingly, sodium selenite, another selenium compound, did not induce any significant effects on FOXO3a translocation despite inducing apoptosis. Single strand break of DNA, disruption of tumour cell metabolic adaptations, decrease in ROS production, and cell cycle arrest in G1 accompanied by induction of apoptosis are late events occurring after 24h of MSA treatment in A549 cells. Our findings suggest that FOXO3a is a relevant mediator of the antiproliferative effects of MSA. This new evidence on the mechanistic action of MSA can open new avenues in exploiting its antitumour properties and in the optimal design of novel combination therapies. We present MSA as a promising chemotherapeutic agent with synergistic antiproliferative effects with cisplatin.

Pterostilbine, an active component of blueberries, sensitizes colon cancer cells to 5-fluorouracil cytotoxicity

Although colorectal cancer (CRC) treatment with 5-fluorouracil (5-FU) is the first line of therapy for this debilitating disease, treatment effectiveness is often hampered by the development of drug resistance and toxicity at high doses. ER-β can play an important role in CRC development and possibly in its response to therapy. Pterostilbene (PT) possesses antioxidant and anticancer effects that are mediated by ER-β. In the current study, we test the hypothesis that PT sensitizes colon cancer cells to 5-FU and we examine the underlying mechanism(s) by which PT exerts its cytotoxic effects in CRC cells. Our data indicate that PT exhibited a more potent cytotoxic effect in Caco-2 compared to HCT-116 cells. PT/5-FU co-treatment was more effective in Caco-2 cells. Our data indicate that ER-β is expressed at higher levels in Caco-2 cells and its levels are further boosted with PT treatment. PT significantly suppressed Akt and ERK phosphorylations, and enhanced FOXO-1 and p27^kip1 levels in Caco-2 cells. PT also induced a significant increase in Caco-2 cells at pre-G phase coupled with increased Bax/Bcl-2 ratio and PARP cleavage. These results provide a rationale for novel combination treatment strategies, especially for patients with 5-FU-resistant tumors expressing ER-β protein.

Effects of PTEN on the proliferation and apoptosis of colorectal cancer cells via the phosphoinositol-3-kinase/Akt pathway

Colorectal cancer (CRC) is one of the most common type of malignancy with a poor prognosis, due to a high frequency of metastasis and tumor recurrence. It has been reported that deletion and/or mutation of the PTEN gene can be involved in the pathogenesis of many types of cancers through the activation of the PI3K/Akt signaling pathway. Immunohistochemical staining was conducted to detect PTEN expression in CRC, adenomas and normal tissues. For the measurement of cell proliferation, CCK-8 was used. Apoptotic cells were quantified using FACS. Immunohistochemical staining results demonstrated that the expression of PTEN gradually decreased from normal colorectal mucosa, to colon hyperplastic polyps, adenomas, and ultimately primary colorectal adenocarcinomas. Upregulation of PTEN expression inhibited the proliferation of LoVo and SW480 cells, inducing G1 phase arrest and reducing the number of cells in the S phase. LoVo and SW480 cells with upregulated PTEN were sensitive to apoptosis induced by 5-FU. In addition, upregulation of PTEN inhibited the activity of Akt and activated the FoxO transcription factor. This is the first report of a gradual decrease in expression of PTEN from normal colon epithelial tissue to colon hyperplastic polyps, colorectal adenomas and finally CRC. Upregulation of PTEN inhibited the activity of the Akt pathway and regulated downstream genes involved in the cell cycle. These results suggest that inhibition of CRC cell proliferation and cell cycle arrest by PTEN are closely related to PI3K/Akt/FoxO.

Evaluating the evidence for targeting FOXO3a in breast cancer: a systematic review

Background

Tumour cells show greater dependency on glycolysis so providing a sufficient and rapid energy supply for fast growth. In many breast cancers, estrogen, progesterone and epidermal growth factor receptor-positive cells proliferate in response to growth factors and growth factor antagonists are a mainstay of treatment. However, triple negative breast cancer (TNBC) cells lack receptor expression, are frequently more aggressive and are resistant to growth factor inhibition. Downstream of growth factor receptors, signal transduction proceeds via phosphatidylinositol 3-kinase (PI3k), Akt and FOXO3a inhibition, the latter being partly responsible for coordinated increases in glycolysis and apoptosis resistance. FOXO3a may be an attractive therapeutic target for TNBC. Therefore we have undertaken a systematic review of FOXO3a as a target for breast cancer therapeutics.

Methods

Articles from NCBI were retrieved systematically when reporting primary data about FOXO3a expression in breast cancer cells after cytotoxic drug treatment.

Results

Increased FOXO3a expression is common following cytotoxic drug treatment and is associated with apoptosis and cell cycle arrest. There is some evidence that metabolic enzyme expression is also altered and that this effect is also elicited in TNBC cells. FOXO3a expression serves as a positive prognostic marker, especially in estrogen (ER) receptor positive cells.

Discussion

FOXO3a is upregulated by a number of receptor-dependent and -independent anti-cancer drugs and associates with apoptosis. The identification of microRNA that regulate FOXO3a directly suggest that it offers a tangible therapeutic target that merits wider evaluation.

The differential susceptibilities of MCF-7 and MDA-MB-231 cells to the cytotoxic effects of curcumin are associated with the PI3K/Akt-SKP2-Cip/Kips pathway

Background

The mechanism underlying the differential cytotoxicity of curcumin in various cancer types, however, remains largely unclear. The aims of this study is to examine the concentration- and time-related effects of curcumin on two different breast cancer cells, MCF-7 and MDA-MB-231, and investigated the functional changes induced by curcumin treatment, as well as their relationship to the PI3K/Akt-SKP2-Cip/Kips pathway.

Methods

First, WST-1 and clonogenic assay were performed to determine the cytotoxicity of curcumin in MCF-7 and MDA-MB-231 cells. Then, the expression of CDK interacting protein/Kinase inhibitory protein (Cip/Kips) members (p27, p21 and p57) and S-phase kinase-associated protein-2 (SKP2) was investigated by QRT PCR and Western Blotting. Curcumin’s effect on PI3K (phosphatidylinositol 3-kinase) /Akt and its substrates Foxo1 and Foxo3a were then studied by Western Blotting. Small interfering RNAs (siRNAs) targeting SKP2 was used to explore the relationship between SKP2 and Cip/Kips members. Finally, WST-1 assay was tested to explore the concomitant treatment with curcumin and the inhibition of PKB or SKP2 signaling on curcumin sensitivity in MCF-7 and MDA-MB-231 cells.

Results

We demonstrated MCF-7 and MDA-MB-231 cells exhibited differential responses to curcumin by WST-1 and clonogenic assay (MDA-MB-231 cells was sensitive, and MCF-7 cells was resistant), which were found to be related to the differential curcumin-mediated regulation of SKP2-Cip/Kips (p21 and p27 but not p57) signaling. The differential cellular responses were further linked to the converse effects of curcumin on PI3K/Akt and its substrates Foxo1 and Foxo3a. Importantly, PI3K inhibitor wortmannin could counteract both curcumin-induced phosphorylation of Akt and up-regulation of SKP2 in MCF-7 cells. Subsequent WST-1 assay demonstrated concomitant treatment with curcumin and wortmannin or SKP2 siRNA not only further augmented curcumin sensitivity in MDA-MB-231 cells but also overcame curcumin resistance in MCF-7 cells.

Conclusions

Our study established PI3K/Akt-SKP2-Cip/Kips signaling pathway is involved in the mechanism of action of curcumin and revealed that the discrepant modulation of this pathway by curcumin is responsible for the differential susceptibilities of these two cell types to curcumin.

Sphingomyelin Synthase 1 Regulates Neuro-2a Cell Proliferation and Cell Cycle Progression Through Modulation of p27 Expression and Akt Signaling

Sphingomyelin synthase (SMS) is a key enzyme involved in the generation of sphingomyelin (SM) and regulation of cell growth and survival. However, the effects of SMS on neuronal cell proliferation and cell cycle progression are not completely elucidated. In this study, we examined the direct effects of SMS1 in regulating cell cycle progression and proliferation of Neuro-2a cells that exhibit neuronal characteristics. Neuro-2a cells transfected with SMS-specific small hairpin RNA (shRNA) expressed significantly lower levels of SMS1. RNA interference-mediated depletion of SMS1 in Neuro-2a cells caused a significant decrease in SM levels. Decreased SMS1 levels resulted in reduced proliferation rate and morphological changes including neurite-like outgrowth. Also, silencing of SMS1 induced cell cycle arrest as shown by the increased percentage of cells in G0/G1 and decreased proportion of cells in S phase. These changes were accompanied by upregulation of cyclin-dependent kinase inhibitor p27 and decreased levels of cyclin D1 and phospho-Akt. Nuclear accumulation of p27 was also evident in SMS1-deficient cells. Furthermore, loss of SMS1 inhibited the migratory potential of Neuro-2a cells in association with decreased levels of matrix metalloproteinases. These results indicate that SMS1 plays an important role in mediating the key signaling pathways that are involved in the tight coordination of multiple cellular activities, including neuronal cell proliferation, cell cycle progression, and migration, and therefore may have significant implications in neurodegenerative diseases.

Romidepsin (FK228) and its analogs directly inhibit phosphatidylinositol 3-kinase activity and potently induce apoptosis as histone deacetylase/phosphatidylinositol 3-kinase dual inhibitors

Activation of phosphatidylinositol 3-kinase (PI3K) signaling is involved in carcinogenesis and cancer progression. The PI3K inhibitors are considered candidate drugs for cancer treatment. Here, we describe a drug screening system for novel PI3K inhibitors using Saccharomyces cerevisiae strains with deleterious mutations in the ATP-binding cassette transporter genes, because wild-type S. cerevisiae uses drug efflux pumps for reducing intracellular drug concentrations. By screening the chemical library of the Screening Committee of Anticancer Drugs, we identified the histone deacetylase (HDAC) inhibitor romidepsin (FK228) and its novel analogs. In vitro PI3K activity assays confirmed that these compounds directly inhibit PI3K activity at μM-range concentrations. FK-A5 analog was the most potent inhibitor. Western blotting revealed that these compounds inhibit phosphorylation of protein kinase B and downstream signaling components. Molecular modeling of the PI3K-FK228 complex indicated that FK228 binds to the ATP-binding pocket of PI3K. At μM-range concentrations, FK228 and FK-A5 show potent cytotoxicity, inducing apoptosis even in HDAC inhibitor-resistant cells. Furthermore, HDAC/PI3K dual inhibition by FK228 and FK-A5 at μM-range concentrations potentiates the apoptosis induction, mimicking the effect of combining specific HDAC and PI3K inhibitors. In this study, we showed that FK228 and its analogs directly inhibit PI3K activity and induce apoptosis at μM-range concentrations, similar to HDAC/PI3K dual inhibition. In future, optimizing the potency of FK228 and its analogs against PI3K may contribute to the development of novel HDAC/PI3K dual inhibitors for cancer treatment.

Ligand-free estrogen receptor activity complements IGF1R to induce the proliferation of the MCF-7 breast cancer cells

Background

Ligand-dependent activation of the estrogen receptor (ER) as well as of the insulin-like growth factor type 1 (IGF1R) induces the proliferation of luminal breast cancer cells. These two pathways cooperate and are interdependent. We addressed the question of the mechanisms of crosstalk between the ER and IGF1R.

Methods

We evaluated the mitogenic effects of estradiol (E2; agonist ligand of ER) and of insulin (a ligand of IGF1R) in the MCF-7 cells by flow cytometry and by analyzing the cell levels of cell cycle-related proteins (immunoblotting) and mRNA (RT-QPCR). To verify the requirement for the kinase activity of Akt (a downstream target of IGF1R) in the mitogenic action of estradiol, we used shRNA strategy and shRNA-resistant expression vectors.

Results

The activation of the ER by E2 is unable to induce the cell cycle progression when the phosphatidyl inositol-3 kinase (PI3K)/Akt signaling is blocked by a chemical inhibitor (LY 294002) or by shRNA targeting Akt1 and Akt2. shRNA-resistant Akt wild-type constructs efficiently complemented the mitogenic signaling activity of E2 whereas constructs with inactivated kinase function did not. In growth factor-starved cells, the residual PI3K/Akt activity is sufficient to complement the mitogenic action of E2. Conversely, when ER function is blocked by the antiestrogen ICI 182780, IGF1R signaling is intact but does not lead to efficient reinitiation of the cell cycle in quiescent, growth factor-starved MCF-7 cells. The basal transcription-promoting activity of ligand-free ER in growth factor-starved cells is sufficient to complement the mitogenic action of the IGF1R-dependent signaling.

Conclusions

The basal ER activity in the absence of ligand is sufficient to allow efficient mitogenic action of IGF1R agonists and needs to be blocked to prevent the cell cycle progression.

PI3K/AKT and ERK regulate retinoic acid-induced neuroblastoma cellular differentiation

Neuroblastoma, the most common extra-cranial solid tumor in infants and children, is characterized by a high rate of spontaneous remissions in infancy. Retinoic acid (RA) has been known to induce neuroblastoma differentiation; however, the molecular mechanisms and signaling pathways that are responsible for RA-mediated neuroblastoma cell differentiation remain unclear. Here, we sought to determine the cell signaling processes involved in RA-induced cellular differentiation. Upon RA administration, human neuroblastoma cell lines, SK-N-SH and BE(2)-C, demonstrated neurite extensions, which is an indicator of neuronal cell differentiation. Moreover, cell cycle arrest occurred in G1/G0 phase. The protein levels of cyclin-dependent kinase inhibitors, p21 and p27(Kip), which inhibit cell proliferation by blocking cell cycle progression at G1/S phase, increased after RA treatment. Interestingly, RA promoted cell survival during the differentiation process, hence suggesting a potential mechanism for neuroblastoma resistance to RA therapy. Importantly, we found that the PI3K/AKT pathway is required for RA-induced neuroblastoma cell differentiation. Our results elucidated the molecular mechanism of RA-induced neuroblastoma cellular differentiation, which may be important for developing novel therapeutic strategy against poorly differentiated neuroblastoma.

Inhibitors of phosphatidylinositol 3'-kinases promote mitotic cell death in HeLa cells

The phosphatidylinositol 3-kinase (PI3K) pathway plays an important role in many biological processes, including cell cycle progression, cell growth, survival, actin rearrangement and migration, and intracellular vesicular transport. However, the involvement of the PI3K pathway in the regulation of mitotic cell death remains unclear. In this study, we treated HeLa cells with the PI3K inhibitors, 3-methyladenine (3-MA, as well as a widely used autophagy inhibitor) and wortmannin to examine their effects on cell fates using live cell imaging. Treatment with 3-MA decreased cell viability in a time- and dose-dependent manner and was associated with caspase-3 activation. Interestingly, 3-MA-induced cell death was not affected by RNA interference-mediated knockdown (KD) of beclin1 (an essential protein for autophagy) in HeLa cells, or by deletion of atg5 (an essential autophagy gene) in mouse embryonic fibroblasts (MEFs). These data indicate that cell death induced by 3-MA occurs independently of its ability to inhibit autophagy. The results from live cell imaging studies showed that the inhibition of PI3Ks increased the occurrence of lagging chromosomes and cell cycle arrest and cell death in prometaphase. Furthermore, PI3K inhibitors promoted nocodazole-induced mitotic cell death and reduced mitotic slippage. Overexpression of Akt (the downstream target of PI3K) antagonized PI3K inhibitor-induced mitotic cell death and promoted nocodazole-induced mitotic slippage. These results suggest a novel role for the PI3K pathway in regulating mitotic progression and preventing mitotic cell death and provide justification for the use of PI3K inhibitors in combination with anti-mitotic drugs to combat cancer.

[Effect of Integrin α5β1-mediated ERK signal pathway on proliferation and migration of A549 cells]

背景与目的

近年研究显示整合素α5β1作为整合素家族的重要部分与非小细胞肺癌的转移性、浸润性和低分化趋向密切相关。本研究应用整合素α5/β1 siRNA双链及ERK抑制剂PD98095干预人肺癌细胞A549，探讨整合素α5β1蛋白表达对A549细胞生长和迁移能力的影响及其细胞内信号转导机制。

方法

实验分为未转染组、脂质体组、整合素α5β1 siRNA转染组和PD98095组四组。采用免疫印迹（Western blot）和逆转录-聚合酶链反应（RT-PCR）检测A549中整合素α5β1蛋白和mRNA表达水平，Western blot检测A549中ERK1/2、MMP-9和caspase-3蛋白水平，四甲基偶氮唑盐比色（MT）法和Annexin-V FITC PI双染色法检测A549增殖和凋亡。

结果

整合素α5/β1 siRNA双链在抑制α5/β1蛋白和mRNA表达的同时，可以下调ERK的mRNA和蛋白表达，并抑制其磷酸化水平。整合素α5/β1 siRNA双链和PD98059均可以明显抑制A549细胞的增殖，促进细胞凋亡和细胞内caspase-3蛋白表达，并抑制细胞内MMP-9蛋白表达。

结论

整合素α5β1可能通过介导的ERK信号转导通路参与了A549细胞的增殖和迁移调控。

Glycogen synthase kinase 3 beta: can it be a target for oral cancer

Despite progress in treatment approaches for oral cancer, there has been only modest improvement in patient outcomes in the past three decades. The frequent treatment failure is due to the failure to control tumor recurrence and metastasis. These failures suggest that new targets should be identified to reverse oral epithelial dysplastic lesions. Recent developments suggest an active role of glycogen synthase kinase 3 beta (GSK3 β) in various human cancers either as a tumor suppressor or as a tumor promoter. GSK3β is a Ser/Thr protein kinase, and there is emerging evidence that it is a tumor suppressor in oral cancer. The evidence suggests a link between key players in oral cancer that control transcription, accelerated cell cycle progression, activation of invasion/metastasis and anti-apoptosis, and regulation of these factors by GSK3β. Moreover, the major upstream kinases of GSK3β and their oncogenic activation by several etiological agents of oral cancer support this hypothesis. In spite of all this evidence, a detailed analysis of the role of GSK3β in oral cancer and of its therapeutic potential has yet to be conducted by the scientific community. The focus of this review is to discuss the multitude of roles of GSK3β, its possible role in controlling different oncogenic events and how it can be targeted in oral cancer.

Phosphoinositide 3-kinase mediates CD40 ligand-induced oxidative stress and endothelial dysfunction via Rac1 and NADPH oxidase 2

OBJECTIVES

CD40 ligand (CD40L) has been implicated as an inducer of reactive oxygen species (ROS) generation in endothelial cells, but definitive evidence for this and the in vivo relevance haves not been demonstrated fully. We thus investigated whether phosphoinositide 3-kinase (PI3K) was linked to ROS generation and endothelial reactivity in response to CD40L.

METHODS AND RESULTS

CD40L treatment activated PI3K activity by regulating the association between PI3K p85 and the CD40 receptor. CD40L exposure also stimulated the GTPase Rac1, which is known to activate NADPH oxidases, and enhanced ROS formation, whereas PI3K inhibition or depletion by small interfering RNA (siRNA) prevented these responses. Subsequently, PI3K overexpression activated Rac1 and increased ROS generation. These responses were not observed in the presence of inactive Rac1 or siRNA against the NADPH oxidase subunit NOX2. Protein kinase Czeta mediates PI3K-regulated NADPH oxidase activation by promoting cellular p47phox translocation. Importantly, PI3K inhibition prevented CD40L-mediated ROS generation and endothelial dysfunction in a mouse model. In summary, PI3K mediates CD40L-induced ROS production and subsequent endothelial dysfunction.

CONCLUSIONS

Targeting PI3K may provide a new therapeutic approach in diseases associated with oxidative stress and endothelial dysfunction.

Akt2 inhibition enables the forkhead transcription factor FoxO3a to have a repressive role in estrogen receptor alpha transcriptional activity in breast cancer cells

Estrogen receptor alpha (ER) and the insulin-like growth factor I receptor (IGF-IR) pathways are engaged in a functional cross talk in breast cancer, promoting tumor progression and increased resistance to anticancer treatments and radiotherapy. Here, we introduce new mechanisms through which proteins of the IGF-I/IGF-IR signaling pathway may regulate ER function in the absence of ligand. Our results indicate that in ER-positive breast cancer cells, Akt2 modulates ER transcriptional activity at multiple levels, including (i) the regulation of ER expression and its nuclear retention and (ii) the activation of one of its downstream targets, the Forkhead transcription factor FoxO3a. FoxO3a colocalizes and coprecipitates with ER in the nucleus, where it binds to Forkhead-responsive sequences on the ER target pS2/TFF-1 promoter; in addition, FoxO3a silencing leads to an increase of ER transcriptional activity, suggesting a repressive role of the Forkhead transcription factor in ER function. Moreover, 17beta-estradiol upregulates FoxO3a levels, which could represent the basis for an ER-mediated homeostatic mechanism. These findings provide further evidence of the importance of mediators of the growth factor signaling in ER regulation, introducing the Akt2/FoxO3a axis as a pursuable target in therapy for ER-positive breast cancer.

The PI3K/Akt/FOXO3a/p27Kip1 signaling contributes to anti-inflammatory drug-suppressed proliferation of human osteoblasts

Akt has been reported to suppress p27(Kip1) promoter activity through Forkhead box O (FOXO) in different kinds of cells. Previous studies indicated that anti-inflammatory drugs up-regulated p27(Kip1), and this effect might play an important role in anti-inflammatory drug-induced cell cycle arrest of human osteoblasts (hOBs). In this study, we hypothesized that these drugs might increase p27(Kip1) expression in hOBs by altering the Akt/FOXO signaling. We tested this hypothesis by examining the influences of three anti-inflammatory drugs on the levels and/or activities of Akt, FOXO and p27(Kip1) as well as the relationship between these factors and proliferation of hOBs. We tested the effects of indomethacin (10(-5) and 10(-4)M), celecoxib (10(-6) and 10(-5)M), and dexamethasone (10(-7) and 10(-6)M) using PI3K inhibitor, LY294002 (10(-5)M) as the basis of comparison. The three drugs suppressed the canonical level of phosphorylated Akt in hOBs. This was accompanied by elevated FOXO3a level and increased promoter activity, mRNA expression and protein level of p27(Kip1). Furthermore, the anti-inflammatory drugs suppressed the EGF-induced increases in proliferation, phosphorylation, and nucleus translocation of Akt. Simultaneously, they suppressed EGF-induced decreases of FOXO3a nucleus accumulation and p27(Kip1) mRNA expression. On the other hand, FOXO silencing significantly attenuated the drug-induced up-regulation of p27(Kip1) and suppression of proliferation in hOBs. To the best of our knowledge, this study represents the first to demonstrate that Akt/FOXO3a/p27(Kip1) pathway contributes to suppression of hOB proliferation by anti-inflammatory drugs. We suggest that anti-inflammatory drugs suppress hOB proliferation, at least partly, through inactivating Akt, activating FOXO3a, and eventually up-regulating p27(Kip1) expression.

Deregulation of FOXO3A during prostate cancer progression

Forkhead box transcription factor FOXO3A, an important regulator of cellular function, is thought to act as a tumor suppressor. We studied whether alterations in FOXO3A activity occur in prostate tumorigenesis. Our studies demonstrate that FOXO3A activity is negatively regulated by Akt/PKB through posttranslational modifications. In prostate cancer cells, Akt activation causes increased accumulation of FOXO3A and its binding chaperone protein 14-3-3 in the cytosol. Higher levels of FOXO3A in the cytosol correlated with phosphorylation at Ser253, which accounted for its nuclear exclusion. Dominant negative Akt approach in PC-3 cells increased FOXO3A accumulation in the nucleus, causing upregulation of the downstream target, MnSOD. Conversely, stable DU145-Akt over-expressing cells exhibited decreased FOXO3A levels in the nucleus. Similar findings were noted in prostate tumor specimens, in which marked cytoplasmic accumulation of FOXO3A and 14-3-3 in prostate tumors was observed with increasing Gleason grade, in contrast to exclusively nuclear accumulation in benign prostate cells. These findings correlate with decreased FOXO3A DNA binding activity along with down-modulation of FOXO3A transcriptional activity with increasing tumor grade. Our findings demonstrate that tumor associated alterations and redistribution of FOXO3A are frequent events in the etiology of prostate cancer.

PIK3CA and PIK3CB inhibition produce synthetic lethality when combined with estrogen deprivation in estrogen receptor-positive breast cancer

Several phosphoinositide 3-kinase (PI3K) catalytic subunit inhibitors are currently in clinical trial. We therefore sought to examine relationships between pharmacologic inhibition and somatic mutations in PI3K catalytic subunits in estrogen receptor (ER)-positive breast cancer, in which these mutations are particularly common. RNA interference (RNAi) was used to determine the effect of selective inhibition of PI3K catalytic subunits, p110alpha and p110beta, in ER(+) breast cancer cells harboring either mutation (PIK3CA) or gene amplification (PIK3CB). p110alpha RNAi inhibited growth and promoted apoptosis in all tested ER(+) breast cancer cells under estrogen deprived-conditions, whereas p110beta RNAi only affected cells harboring PIK3CB amplification. Moreover, dual p110alpha/p110beta inhibition potentiated these effects. In addition, treatment with the clinical-grade PI3K catalytic subunit inhibitor BEZ235 also promoted apoptosis in ER(+) breast cancer cells. Importantly, estradiol suppressed apoptosis induced by both gene knockdowns and BEZ235 treatment. Our results suggest that PI3K inhibitors should target both p110alpha and p110beta catalytic subunits, whether wild-type or mutant, and be combined with endocrine therapy for maximal efficacy when treating ER(+) breast cancer.

Calpain small-1 modulates Akt/FoxO3A signaling and apoptosis through PP2A

Here, we show that FoxO3A transcription factor is upregulated upon calpain small-1 (CAPNS1) depletion both in mouse embryonic fibroblasts (MEFs) and in the human mammary carcinoma cell line MCF-7. On starvation, CAPNS1 depletion is associated with a higher rate of FoxO3A dephosphorylation and translocation to the nucleus and to a sharper increase in the levels of p27Kip1 and Bim, the products of two FoxO target genes. Notably, FoxO3A depletion in CAPNS1-/- MEFs reduces both the induction of Bim and apoptosis. Both okadaic acid treatment and silencing of the protein phosphatase 2A (PP2A) catalytic subunit can partially reduce starvation-induced FoxO3A activation and apoptosis in CAPNS1-/- fibroblasts. PP2A associates more tightly with Akt in CAPNS1 knockout cells, indicating that PP2A is involved in calpain-mediated FoxO regulation. Finally, we show that PP2A regulatory subunits B56 alpha and gamma are in vitro substrates of calpain, and calpain regulates B56 alpha stability in vivo, suggesting a direct role of calpain in the regulation of PP2A function. In conclusion, for the first time we report that CAPNS1 interferes with PP2A-Akt interaction consequently affecting FoxO3A-dependent cell death. Calpain inhibition might therefore be exploited as a tool to induce apoptosis in tumors sensitive to FoxO activation.

Combination of vitamin E and selenium causes an induction of apoptosis of human prostate cancer cells by enhancing Bax/Bcl-2 ratio

BACKGROUND

The Selenium and Vitamin E Chemoprevention Trial (SELECT) is aimed at determining the usefulness of a combination of vitamin E and selenium for Prostate cancer (PCa) prevention in humans. The aim of this study is to evaluate the efficacy and mechanistic basis of this combination.

METHODS

We determined the effect of vitamin E (+-alpha-tocopheryl succinate, VES) and selenium (methylselenic acid, MSA), alone and in combination, on the proliferation of LNCaP, DU145, and PC-3 cells as well as normal prostate PrEC cells. We also determined the involvement of Bcl-2 family proteins as a mechanism of the biological effects of vitamin E and selenium combination.

RESULTS

VES or MSA alone led to a modest inhibition in the viability and growth of PCa cells. However, a combination of these two agents resulted in a dramatic increase in growth inhibition of PCa cells. Interestingly, VES and/or MSA were not found to have any effect on the growth or viability of normal PrEC cells. VES and MSA treatment to human PCa cells resulted in (i) induction of apoptosis, (ii) increase in Bax, Bak, and Bid proteins, and (iii) decrease in Bcl-2 protein. Furthermore, Bax knockdown via shRNA and Bcl-2 overexpression via Bcl-2 plasmid resulted in a rescue of PCa cells from apoptosis.

CONCLUSIONS

Our study suggested that vitamin E and selenium combination may be more effective than either of these agents alone. Further, our data demonstrated a causal connection between Bax and Bcl-2 modulation and induction of apoptosis by VES and MSA combination.

Forkhead transcription factor FOXO subfamily is essential for reactive oxygen species-induced apoptosis

Intracellular accumulation of reactive oxygen species is implicated in the pathogenesis of cancer and other diseases by disturbing proper cell cycle control or cell survival. Here, we show that the expression and phosphorylation of FOXO is drastically affected by H(2)O(2) treatment, resulting in drastic induction of luteal cell apoptosis. Western blot analysis revealed that FOXO1a accumulated preferentially in the nucleus upon ROS stimuli, resulting in the transactivation of IRS promoter activity driven by H(2)O(2)-activated FOXO1a. Because ROS-induced cell death was suppressed by co-transfection of a FOXO3a mutant that lacks the activation-domain of transcription, transactivation of pro-apoptotic genes by FOXO was necessary to cause ROS-induced apoptosis. In fact, expression of several pro-apoptotic genes, such as Bim and BCL-6 was induced in H(2)O(2)-stimulated cells, and was blocked by co-transfection of dominant-negative type FOXO3a mutant. These findings indicate that FOXO is a key regulator of ROS-induced apoptosis in mammalian cells.

Multiple roles of FOXO transcription factors in mammalian cells point to multiple roles in cancer

The FOXO family of transcription factors has been implicated in several cellular processes including cell cycle arrest, cell death and protection from stress stimuli. FOXO function is influenced by multiple signaling pathways. Many of these pathways are known to be misregulated in cancer. Perturbation of FOXO function leads to uncontrolled cell proliferation and accumulation of DNA damage. It is becoming clear that active FOXO proteins play an important role in keeping cells in check and inactivation of FOXO proteins is associated with characteristics of cancer cells. FOXO proteins may represent new therapeutic targets for a broad spectrum of cancers.