Forkhead protein FKHR and its phosphorylated form p-FKHR in human prostate cancer

Signalling transduction of O-GlcNAcylation and PI3K/AKT/mTOR-axis in prostate cancer

Hexosamine biosynthetic (HBP) and PI3K/AKT/mTOR pathways are found to predominate the proliferation and survival of prostate cancer cells. Both these pathways have their own specific intermediates to propagate the secondary signals in down-stream cascades and besides having their own structured network, also have shared interconnecting branches. These interconnections are either competitive or co-operative in nature depending on the microenvironmental conditions. Specifically, in prostate cancer HBP and mTOR pathways increases the expression and protein level of androgen receptor in order to support cancer cell proliferation, advancement and metastasis. Pharmacological inhibition of a single pathway is therefore insufficient to stop disease progression as the cancer cells manage to alter the signalling channel. This is one of the primary reasons for the therapeutic failure in prostate cancer and emergence of chemoresistance. Inhibition of these multiple pathways at their common junctures might prove to be of benefit in men suffering from an advanced disease state. Hence, a thorough understanding of these cellular intersecting points and their significance with respect to signal transduction mechanisms might assist in the rational designing of combinations for effective management of prostate cancer.

Proteomic Analysis of Cardioembolic and Large Artery Atherosclerotic Clots Using Reverse Phase Protein Array Technology Reveals Key Cellular Interactions Within Clot Microenvironments

Thrombus characteristics are dependent on clot composition, but identification of the etiology based on histological analysis has proved inconclusive. Identification of proteomic signatures may help to differentiate between clots of different etiologies such as cardioembolic, large artery atherosclerotic, and other known etiologies, information that could enhance an individualized medicine approach to secondary stroke prevention. In this study, total protein extracts from cardioembolic (n=25) and large artery atherosclerotic (n=23) thrombus specimens were arrayed in quadruplicate on nitrocellulose slides and immunostained for 31 proteins using a Dako Autostainer (Agilent Technologies, Inc., Santa Clara, USA). We quantified 31 proteins involved in platelet and/or endothelial function, inflammation, oxidative stress, and metabolism. Pathway analysis showed more heterogeneity and protein network interactions in the cardioembolic clots but no specific correlations with clot etiology. Reverse-phase protein arrays are a powerful tool for assessing cellular interactions within the clot microenvironment and may enhance understanding of clot formation and origination. This tool could be further explored to help in identifying stroke etiology in large vessel occlusion patients with embolic stroke of an undetermined source.

Prognostic implications of forkhead box protein O1 (FOXO1) and paired box 3 (PAX3) in epithelial ovarian cancer

BACKGROUND

Transcription factors forkhead box protein O1 (FOXO1) and paired box 3 (PAX3) have been reported to play important roles in various cancers. However, their role in epithelial ovarian cancer (EOC) has not been elucidated yet. Therefore, we evaluated the expression and clinical significance of FOXO1 and PAX3 in EOC.

METHODS

Immunohistochemical analyses of FOXO1 and PAX3 in 212 EOCs, 57 borderline ovarian tumors, 153 benign epithelial ovarian tumors, and 79 nonadjacent normal epithelial tissues were performed using tissue microarray. Various clinicopathological variables, including the survival of EOC patients, were compared. In addition, the effect of FOXO1 on cell growth was assessed in EOC cell lines.

RESULTS

FOXO1 and PAX3 protein expression levels were significantly higher in EOC tissues than in nonadjacent normal epithelial tissues, benign tissues, and borderline tumors (all p < 0.001). In EOC tissues, FOXO1 expression was positively correlated with PAX3 expression (Spearman's rho = 0.118, p = 0.149). Multivariate survival analysis revealed that high FOXO1 expression (hazard ratio = 2.77 [95% CI, 1.48-5.18], p = 0.001) could be an independent prognostic factor for overall survival. Most importantly, high expression of both FOXO1 and PAX3 showed a high hazard ratio (4.60 [95% CI, 2.00-10.55], p < 0.001) for overall survival. Also in vitro results demonstrated that knockdown of FOXO1 was associated with decreased cell viability, migration, and colony formation.

CONCLUSIONS

This study revealed that high expression of FOXO1/PAX3 is an indicator of poor prognosis in EOC. Our results suggest the promising potential of FOXO1 and PAX3 as prognostic and therapeutic markers. The possible link between biological functions of FOXO1 and PAX3 in EOC warrants further studies.

Forkhead box protein O1 (FOXO1) and paired box gene 3 (PAX3) overexpression is associated with poor prognosis in patients with cervical cancer

PURPOSE

Forkhead box protein O1 (FOXO1) and paired box gene 3 (PAX3) have been reported to play an imported role in human cancers, but their role in cervical cancer has not yet been clarified. In this study, we evaluated the functional role of FOXO1 in cervical cancer cells and investigated the expression and clinical significance of FOXO1 and PAX3 in cervical lesions.

METHODS

In vitro assessment of cell function by cell viability, migration, and invasion assays were performed on FOXO1-knockdown cervical cancer cells. Immunohistochemical (IHC) staining analyses of FOXO1 and PAX3 were performed with a tissue microarray (TMA). The clinical significance was evaluated by comparing the data with various clinicopathologic characteristics, including survival of patients with cervical cancer.

RESULTS

In vitro results revealed that knockdown of FOXO1 is associated with decreased cell viability (p < 0.001), migration (p < 0.001), and invasion (p < 0.05), supporting the oncogenic role of FOXO1 in cervical cancer. FOXO1 and PAX3 expression was significantly higher in CIN (both p < 0.001) and cancer tissue (both p < 0.001) than in normal tissue. Multivariate analysis indicated that FOXO1 expression (hazard ratio 4.01 [95% CI 1.22-13.10], p = 0.021) and an advanced FIGO stage (hazard ratio 3.89 [95% CI 1.35-11.19], p = 0.012) were independent prognostic factors for overall survival.

CONCLUSIONS

This study reveals increased FOXO1 and PAX3 expression in cervical cancers and indicates an oncogenic role of FOXO1 in cervical cancer cells that correlates with poor patient survival.

Progesterone Treatment Attenuates Glycolytic Metabolism and Induces Senescence in Glioblastoma

We examined the effect of progesterone treatments on glycolytic metabolism and senescence as possible mechanisms in controlling the growth of glioblastoma multiforme (GBM). In an orthotopic mouse model, after tumor establishment, athymic nude mice received treatment with progesterone or vehicle for 40 days. Compared to controls, high-dose progesterone administration produced a significant reduction in tumor size (~47%) and an increased survival rate (~43%) without any demonstrable toxicity to peripheral organs (liver, kidney). This was accompanied by a significant improvement in spontaneous locomotor activity and reduced anxiety-like behavior. In a follow-up in vitro study of U87MG-luc, U87dEGFR and U118MG tumor cells, we observed that high-dose progesterone inhibited expression of Glut1, which facilitated glucose transport into the cytoplasm; glyceraldehyde 3-phosphate dehydrogenase (GAPDH; a glycolysis enzyme); ATP levels; and cytoplasmic FoxO1 and Phospho-FoxO1, both of which control glycolytic metabolism through upstream PI3K/Akt/mTOR signaling in GBM. In addition, progesterone administration attenuated EGFR/PI3K/Akt/mTOR signaling, which is highly activated in grade IV GBM. High-dose progesterone also induced senescence in GBM as evidenced by changes in cell morphology and β-galactocidase accumulation. In conclusion, progesterone inhibits the modulators of glycolytic metabolism and induces premature senescence in GBM cells and this can help to reduce/slow tumor progression.

FOXO1 overexpression and loss of pSerine256-FOXO1 expression predicts clinical outcome in esophageal adenocarcinomas

The function of Forkhead box O 1 (FOXO1) and pSerine256-FOXO1 immunostaining in esophageal cancer is unclear. To clarify the prognostic role of nuclear FOXO1 and cytoplasmic pSerine256-FOXO1 immunostaining, a tissue microarray containing more than 600 esophageal cancers was analyzed. In non-neoplastic esophageal mucosae, FOXO1 expression was detectable in low and pSerine256-FOXO1 expression in high intensities. Increased FOXO1 and decreased pSerine256-FOXO1 expression were linked to advanced tumor stage and high UICC stage in esophageal adenocarcinomas (EACs) (tumor stage: p = 0.0209 and p < 0.0001; UICC stage: p = 0.0201 and p < 0.0001) and squamous cell carcinomas (ESCCs) (tumor stage: p = 0.0003 and p = 0.0016; UICC stage: p = 0.0026 and p = 0.0326). Additionally, overexpression of FOXO1 and loss of pSerine256-FOXO1 expression predicted shortened survival of patients with EACs (p = 0.0003 and p = 0.0133) but were unrelated to outcome in patients with ESCCs (p = 0.7785 and p = 0.8426). In summary, our study shows that overexpression of nuclear FOXO1 and loss of cytoplasmic pSerine256-FOXO1 expression are associated with poor prognosis in patients with EACs. Thus, evaluation of FOXO1 and pSerine256-FOXO1 protein expression - either alone or in combination with other markers - might be useful for prediction of clinical outcome in patients with EAC.

β-arrestin1-medieated inhibition of FOXO3a contributes to prostate cancer cell growth in vitro and in vivo

Recently, β-arrestin1 has been indicated as a prostate cancer promoter through promoting cell proliferation and epithelial to mesenchymal transition, but its underlying mechanism remains unclear. Here, our data revealed that β-arrestin1 could promote cell growth through inhibiting the transcriptional activity and expression of FOXO3a in prostate cancer cells in vitro and in vivo. We found that β-arrestin1 could promote the cell and tumor growth of prostate cancer, and β-arrestin1 expression represented a negative correlation with FOXO3a expression but not FOXO1 expression in prostate cancer cell lines and tissues. In addition, forced expression of β-arrestin1 induced a significant decrease of FOXO3a expression but had no clear effect on FOXO1 expression. Mechanistically, β-arrestin1 could interact with FOXO3a and MDM2, respectively, and promote the interaction between FOXO3a and MDM2, whereas it had no obvious interaction with FOXO1. Furthermore, β-arrestin1 could inhibit the transcriptional activity of FOXO3a via Akt and ERK1/2 pathways. Together, our results revealed a novel mechanism for β-arrestin1 in the regulation of the prostate cancer procession through inhibiting FOXO3a.

FOXO3a expression is associated with lymph node metastasis and poor disease-free survival in triple-negative breast cancer

Aims

Forkhead box O (FOXO) transcription factors, consisting of FOXO1, FOXO3a, FOXO4 and FOXO6, are involved in carcinogenesis and tumour progression. Recent studies have suggested that FOXOs act as tumour suppressors in a variety of human cancers. This study investigated the clinicopathological significance of FOXOs in triple-negative breast cancer (TNBC).

Methods

FOXO protein expressions were assessed by immunohistochemistry in 125 TNBC tissues. Correlations between FOXO protein expression and various clinicopathological parameters, including patients’ survival, were investigated. MDA-MB-468 cell line was used for in vitro cell proliferation and migration assay.

Results

FOXO1 protein expression was not observed in all 125 TNBC tissues. FOXO4 and FOXO6 protein expressions were detected in 11 (8.8%) and 14 (11.2%) TNBC tissues, respectively. Loss of FOXO4 expression was significantly associated with high histological grade (P=0.014, χ2 test), and TNBCs with positive FOXO6 expression correlated with high grade (P=0.020, χ2 test). FOXO3a expression was detected in 40 (32%) TNBC cases and correlated with adverse clinicopathological features, such as lymph node metastasis (P=0.021, χ2 test), perineural invasion (P=0.013, χ2 test) and higher Ki-67 proliferation index (P=0.048, t-test). Additionally, FOXO3a expression was significantly associated with poor disease-free survival (P=0.015, log-rank test). In the in vitro study, siRNA-mediated FOXO3a knockdown in the MDA-MB-468 cell line inhibited cell proliferation and migration.

Conclusion

Among FOXO members, FOXO3a may have a potential role in promoting tumour cell migration and proliferation and may serve as a prognostic biomarker and a potential therapeutic target for TNBC.

New Insights into Protein Kinase B/Akt Signaling: Role of Localized Akt Activation and Compartment-Specific Target Proteins for the Cellular Radiation Response

Genetic alterations driving aberrant activation of the survival kinase Protein Kinase B (Akt) are observed with high frequency during malignant transformation and cancer progression. Oncogenic gene mutations coding for the upstream regulators or Akt, e.g., growth factor receptors, RAS and phosphatidylinositol-3-kinase (PI3K), or for one of the three Akt isoforms as well as loss of the tumor suppressor Phosphatase and Tensin Homolog on Chromosome Ten (PTEN) lead to constitutive activation of Akt. By activating Akt, these genetic alterations not only promote growth, proliferation and malignant behavior of cancer cells by phosphorylation of various downstream signaling molecules and signaling nodes but can also contribute to chemo- and radioresistance in many types of tumors. Here we review current knowledge on the mechanisms dictating Akt’s activation and target selection including the involvement of miRNAs and with focus on compartmentalization of the signaling network. Moreover, we discuss recent advances in the cross-talk with DNA damage response highlighting nuclear Akt target proteins with potential involvement in the regulation of DNA double strand break repair.

Metformin inhibits estrogen-dependent endometrial cancer cell growth by activating the AMPK-FOXO1 signal pathway

Metformin is an oral biguanide commonly used for treating type II diabetes and has recently been reported to possess antiproliferative properties that can be exploited for the prevention and treatment of a variety of cancers. The mechanisms underlying this effect have not been fully elucidated. Our study shows a marked loss of AMP-activated protein kinase (AMPK) phosphorylation and nuclear human Forkhead box O1 (FOXO1) protein in estrogen-dependent endometrial cancer (EC) tumors compared to normal control endometrium. Metformin treatment suppressed EC cell growth in a time-dependent manner in vitro; this effect was cancelled by cotreatment with an AMPK inhibitor, compound C. Metformin decreased FOXO1 phosphorylation and increased FOXO1 nuclear localization in Ishikawa and HEC-1B cells, with non-significant increase in FOXO1 mRNA expression. Moreover, compound C blocked the metformin-induced changes of FOXO1 and its phosphorylation protein, suggesting that metformin upregulated FOXO1 activity by AMPK activation. Similar results were obtained after treatment with insulin. In addition, transfection with siRNA for FOXO1 cancelled metformin-inhibited cell growth, indicating that FOXO1 mediated metformin to inhibit EC cell proliferation. A xenograft mouse model further revealed that metformin suppressed HEC-1B tumor growth, accompanied by downregulated ki-67 and upregulated AMPK phosphorylation and nuclear FOXO1 protein. Taken together, these data provide a novel mechanism of antineoplastic effect for metformin through the regulation of FOXO1, and suggest that the AMPK-FOXO1 pathway may be a therapeutic target to the development of new antineoplastic drugs.

β-Arrestin2 Contributes to Cell Viability and Proliferation via the Down-Regulation of FOXO1 in Castration-Resistant Prostate Cancer

β-Arrestin2 has been identified to act as a corepressor of androgen receptor (AR) signaling by binding to AR and serving as a scaffold to affect the activity and expression of AR in androgen-dependent prostate cancer cells; however, little is known regarding its role in castration-resistant prostate cancer (CRPC) progression. Here, our data demonstrated that β-arrestin2 contributes to the cell viability and proliferation of CRPC via the downregulation of FOXO1 activity and expression. Mechanistically, in addition to its requirement for FOXO1 phosphorylation induced by IGF-1, β-arrestin2 could inhibit FOXO1 activity in an Akt-independent manner and delay FOXO1 dephosphorylation through the inhibition of PP2A phosphatase activity and the attenuation of the interaction between FOXO1 and PP2A. Furthermore, β-arrestin2 could downregulate FOXO1 expression via ubiquitylation and proteasomal degradation. Together, our results identified a novel role for β-arrestin2 in the modulation of the CRPC progress through FOXO1. Thus, the characterization of β-arrestin2 may represent an alternative therapeutic target for CRPC treatment.

Gene Signatures Stratify Computed Tomography Screening Detected Lung Cancer in High-Risk Populations

BACKGROUND

Although screening programmes of smokers have detected resectable early lung cancers more frequently than expected, their efficacy in reducing mortality remains debatable. To elucidate the biological features of computed tomography (CT) screening detected lung cancer, we examined the mRNA signatures on tumours according to the year of detection, stage and survival.

METHODS

Gene expression profiles were analysed on 28 patients (INT-IEO training cohort) and 24 patients of Multicentre Italian Lung Detection (MILD validation cohort). The gene signatures generated from the training set were validated on the MILD set and a public deposited DNA microarray data set (GSE11969). Expression of selected genes and proteins was validated by real-time RT-PCR and immunohistochemistry. Enriched core pathway and pathway networks were explored by GeneSpring GX10.

FINDINGS

A 239-gene signature was identified according to the year of tumour detection in the training INT-IEO set and correlated with the patients' outcomes. These signatures divided the MILD patients into two distinct survival groups independently of tumour stage, size, histopathological type and screening year. The signatures can also predict survival in the clinically detected cancers (GSE11969). Pathway analyses revealed tumours detected in later years enrichment of the PI3K/PTEN/AKT pathway, with up-regulation of PDPK1, ITGB1 and down-regulation of FOXO1A. Analysis of normal lung tissue from INT-IEO cohort produced signatures distinguishing patients with early from late detected tumours.

INTERPRETATION

The distinct pattern of "indolent" and "aggressive" tumour exists in CT-screening detected lung cancer according to the gene expression profiles. The early development of an aggressive phenotype may account for the lack of mortality reduction by screening observed in some cohorts.

Expression of ERG protein in prostate cancer: variability and biological correlates

Prostate cancer is the second leading cause of cancer-related death of men in the USA. The TMPRSS2/ERG (T/E) fusion gene is present in approximately 50% of prostate cancers and promotes tumor progression in vivo. The presence of the T/E fusion gene is strongly associated with the expression of ERG protein, but emerging evidence indicates a significant interfocal and intrafocal variability in the levels of ERG protein expression. We therefore analyzed ERG protein expression by image analysis to objectively quantitate the extent of such heterogeneity, and confirmed significant interfocal and intrafocal variability of ERG protein expression levels in cancer expressing ERG. To define the pathways associated with ERG and its variable expression in prostate cancer, we have analyzed the correlations of ERG expression, as evaluated by immunohistochemistry, with 46 key proteins associated with signal transduction, transcriptional control, and other processes using a large tissue microarray with more than 500 prostate cancers. We found a significant correlation of ERG expression with the markers of activation of the PI3K, MYC, and NFκB pathways, which had previously been linked directly or indirectly to ERG expression. We have also identified significant correlations with novel proteins that have not been previously linked to ERG expression, including serum response factor, the p160 coactivator SRC1, and Sprouty1. Notably, SKP2 only correlated with a high level of ERG protein expression. Thus ERG expression is variable in prostate cancer and is associated with activation of multiple pathways and proteins including several potentially targetable pathways.

Long‑term exposure to leptin enhances the growth of prostate cancer cells

Obesity correlates with an increased risk of developing prostate cancer (PCa) and leptin plays an important role in PCa progression. Since leptin is produced by adipocytes, the serum leptin level is higher in obese than in non-obese individuals. However, the effects of leptin remain controversial and unclear. The aim of the present study was to investigate the effect of leptin on PCa cell aggressiveness. Three human PCa cell lines (LNCaP, DU145 and PC-3) were treated with recombinant leptin for 28 days. Cell proliferation, migration, and invasion were estimated using the WST assay, a wound-healing assay, and a BD Matrigel invasion assay, respectively. The mechanism underlying the proliferative effect of leptin was investigated by cell transfections with small interfering RNA (siRNA) against the leptin receptor (ObR) or forkhead box O1 (FOXO1), and by immunocytochemistry. Long-term exposure of PCa cells to leptin enhanced their proliferation, migration and invasion. Leptin increased ObR expression and enhanced Akt phosphorylation constitutively. Leptin also increased the phosphorylation of FOXO1 via PI3K signaling and FOXO1 gene silencing enhanced PCa cell proliferation. Leptin induced the translocation of FOXO1 from the nucleus to the cytoplasm. Furthermore, the PI3K inhibitor, LY294002 suppressed this translocation. These results suggested that leptin regulated the subcellular localization of FOXO1 and induced Akt phosphorylation. Additionally, we revealed that leptin increased the expression of cyclin D1 and decreased the expression of p21 protein. In conclusion, long-term exposure to leptin increased the cell proliferation, migration, and invasion of PCa cells through inactivation of FOXO1. This inactivation resulted from exclusion of FOXO1 from the nucleus and its restriction to the cytoplasm through PI3K/Akt signaling. Our findings contribute to an understanding of the association between obesity and PCa aggressiveness.

miR-96 promotes cell proliferation and clonogenicity by down-regulating of FOXO1 in prostate cancer cells

The present study aimed to investigate the biological functions of miR-96 in the processes of proliferation and clonogenicity in the prostate cancer cells. miR-96 was identified to be markedly up-regulated in prostate cancer cell and cancer tissues compared with normal prostate cell and normal prostate tissues by microarray method and RT-PCR analysis. Down-regulation of miR-96 expression reduced the proliferation and colony formation ability of PC3 prostate cancer cells, while over-expression of miR-96 induced proliferation and colony formation ability of LNCaP prostate cancer cells. Forkhead box protein O1 (FOXO1) is key tumor suppressors and has been shown to play key roles in the regulation of diverse cellular processes, including cell proliferation, differentiation, cell cycle progression and apoptosis. The expression level of FOXO1 was strikingly up-regulated in PC3 cells after transfected with miR-96 inhibitor, and FOXO1 expression was down-regulated in LNCaP cells after transfected with miR-96 mimics. miR-96 may play a vital role in promoting cell proliferation in human prostate cancer cells. Inhibition of miR-96 caused expression increase of tumor suppressor gene FOXO1, thus manipulating miR-96 expression may be a promising approach in treatment of prostate cancer.

The antiapoptotic function of miR-96 in prostate cancer by inhibition of FOXO1

microRNAs (miRNAs) are small molecules that regulate gene expression posttranscriptionally. In a previous study, we identified miR-96 to be upregulated in prostate cancer specimens in comparison to normal adjacent tissue and to be an independent marker of biochemical relapse in a multivariate prediction model. Therefore, we investigated the functional role of miR-96 in prostate carcinogenesis. LNCaP and DU145 prostate cancer cells were transiently transfected with miR-96 precursors and phenotypic changes were analyzed. The miR-96 increased proliferation and impaired apoptosis induced by camptothecine in these cells. In silico target prediction analysis identified FOXO1 as potential pro-apoptotic miR-96 target. miR-96 was able to bind to both bindings sites in the FOXO1 3' UTR in a luciferase reporter gene assay. Overexpression of miR-96 in LNCaP cells resulted in a reduced FOXO1 expression. Overexpression of FOXO1 induced a strong apoptotic phenotype that was partially rescued by coexpression of miR-96. RT-qPCR and immunohistochemistry of 69 prostate cancer specimens revealed a downregulation of FOXO1 and an inverse correlation of miR-96 and FOXO1 protein expression. In conclusion, we show that miR-96 can regulate apoptosis in prostate cancer, by inhibiting the FOXO1 transcription factor.

Deregulation of FoxO3a accelerates prostate cancer progression in TRAMP mice

BACKGROUND

Forkhead box, class "O" (FoxO) transcription factors are involved in multiple signaling pathways and possess tumor suppressor functions. Loss of PTEN and activation of PI3K/Akt is frequently observed in prostate cancer, which may potentially inactivate FoxO activity. We therefore investigated the role of FoxO transcription factors in prostate cancer progression, in particular FoxO3a, in transgenic adenocarcinoma of the mouse prostate (TRAMP) mice, which mimics progressive forms of human disease.

METHODS

Prostate cancer progression in TRAMP mice was followed from 8 to 28 weeks. Expression patterns of Akt, FoxO1a, FoxO3a, FoxO4, and their phosphorylated form, DNA binding activity and downstream signaling molecules during different stages of disease progression were examined by immunoblotting, immunoprecipitation, enzyme-linked immunoabsorbant assay (ELISA), and immunohistochemistry. Inhibition of FoxO3a activity was attained by using FoxO3a peptide treatment to TRAMP mice.

RESULTS

In TRAMP mice, FoxO3a activity is negatively regulated by Akt/PKB through post-translational modification. Progressive increase in Akt activation during prostate cancer progression led to increase phosphorylation of FoxO3a and binding with 14-3-3, which potentially affected its transcriptional activity in age-specific manner. Furthermore, blocking FoxO3a activity resulted in accelerated prostate cancer progression in these mice, which was associated with the loss of cell cycle control and increased proliferation and survival markers.

CONCLUSIONS

Restoration of FoxO3a activity represents an attractive therapeutic target in the chemoprevention and possibly in inhibition of progression of prostate cancer.

Apigenin inhibits prostate cancer progression in TRAMP mice via targeting PI3K/Akt/FoxO pathway

Forkhead box O (FoxO) transcription factors play an important role as tumor suppressor in several human malignancies. Disruption of FoxO activity due to loss of phosphatase and tensin homolog and activation of phosphatidylinositol-3 kinase (PI3K)/Akt are frequently observed in prostate cancer. Apigenin, a naturally occurring plant flavone, exhibits antiproliferative and anticarcinogenic activities through mechanisms, which are not fully defined. In the present study, we show that apigenin suppressed prostate tumorigenesis in transgenic adenocarcinoma of the mouse prostate (TRAMP) mice through the PI3K/Akt/FoxO-signaling pathway. Apigenin-treated TRAMP mice (20 and 50 μg/mouse/day, 6 days/week for 20 weeks) exhibited significant decrease in tumor volumes of the prostate as well as completely abolished distant organ metastasis. Apigenin treatment resulted in significant decrease in the weight of genitourinary apparatus (P < 0.0001), dorsolateral (P < 0.0001) and ventral prostate (P < 0.028), compared with the control group. Apigenin-treated mice showed reduced phosphorylation of Akt (Ser473) and FoxO3a (Ser253), which correlated with its increased nuclear retention and decreased binding of FoxO3a with 14-3-3. These events lead to reduced proliferation as assessed by Ki-67 and cyclin D1, along with upregulation of FoxO-responsive proteins BIM and p27/Kip1. Complementing in vivo results, similar observations were noted in human prostate cancer LNCaP and PC-3 cells after apigenin treatment. Furthermore, binding of FoxO3a with p27/Kip1 was markedly increased after 10 and 20 μM apigenin treatment resulting in G0/G1-phase cell cycle arrest, which was consistent with the effects elicited by PI3K/Akt inhibitor, LY294002. These results provide convincing evidence that apigenin effectively suppressed prostate cancer progression, at least in part, by targeting the PI3K/Akt/FoxO-signaling pathway.

High cytoplasmic FOXO1 and pFOXO1 expression in astrocytomas are associated with worse surgical outcome

FOXO1 is at a convergence point of receptor tyrosine kinase (RTK) signaling, which is one of the three core pathways implicated in glioblastoma. It was recently shown that FOXO1 can effectively induce glioma cell death and inhibit tumor growth through cell cycle arrest and apoptosis. We therefore evaluated FOXO1 and pFOXO1 protein expression in 181 primary astrocytoma samples and 16 normal brain samples. Astrocytoma samples expressed higher cytoplasmic FOXO1 and pFOXO1 than normal brain samples. Nuclear pFOXO1 level was significantly higher than nuclear FOXO1 in astrocytomas. High cytoplasmic FOXO1 expression was associated with older onset age (P = 0.001) and higher WHO grade (P = 0.001). The trend was also observed between cytoplasmic pFOXO1 expression and WHO grade although not significant. Univariate survival analysis showed that both high cytoplasmic FOXO1 and pFOXO1 expression indicated a significantly shorter median overall survival and progression-free survival. Multivariate survival analysis revealed cytoplasmic FOXO1 expression, cytoplasmic pFOXO1 expression, WHO grade, gender, extent of resection and radiotherapy to be independent prognostic factors for overall survival and progression-free survival. Thus, our data suggested that cytoplasmic FOXO1 and pFOXO1 expression may serve as valuable prognostic variables in astrocytomas and may have significant implications for the development and application of targeted therapy.

Expression of FOXO1 is associated with GATA3 and Annexin-1 and predicts disease-free survival in breast cancer

PURPOSE

To determine the prognostic value of FOXO1, GATA3 and Annexin-1 expression in breast cancer.

METHODS

Tissue microarray and individual paraffin tissue slides from 131 patients were used for the study. The association of FOXO1, GATA3 and Annexin-1 expression with clinicopathological features of breast cancer and disease outcome was examined in retrospective samples. Kaplan-Meier survival curves and Cox regression with multivariate analysis were used for assessing the relative risk (RR) and disease-free survival (DFS). The expression of FOXO1, GATA3 and Annexin-1 were determined by immunohistochemistry and the association among the three proteins was analyzed by Logistic regression analysis.

RESULTS

The nuclear expression of FOXO1 was observed in most of the normal breast tissues and 51.3% of the malignant breast tissues. GATA3 and Annexin-1 were expressed at 73% and 24.6% respectively in breast cancer tissues. The expression of FOXO1, GATA3 and Annexin-1 were all inversely correlated with lymph node-positive tumors. Both FOXO1 and Annexin-1 expression were also inversely associated with HER2-overexpressing tumors. FOXO1 expression was significantly associated with both GATA3 and Annexin-1 expression. In addition, Multivariate analyses confirm that only FOXO1 levels independently predict DFS.

CONCLUSION

FOXO1 expression in breast cancer is regulated by the PI3K/Akt pathway. The expression of FOXO1 is also associated with GATA3 and/or Annexin-1. Restoring or targeting FOXO1 to the cell nucleus in breast cancer tissues may improve response to therapy and disease outcome. Further clinical studies are warranted to test this hypothesis.

FOXO1 inhibits Runx2 transcriptional activity and prostate cancer cell migration and invasion

Prostate cancer patients with regional lymph node involvement at radical prostatectomy often experience disease progression to other organs, with the bone as the predominant site. The transcription factor Runx2 plays an important role in bone formation and prostate cancer cell migration, invasion, and metastasis. Here we showed that the forkhead box O (FOXO1) protein, a key downstream effector of the tumor suppressor PTEN, inhibits the transcriptional activity of Runx2 in prostate cancer cells. This inhibition was enhanced by PTEN but diminished by active Akt. FOXO1 bound to Runx2 in vitro and in vivo and suppressed Runx2's activity independent of its transcriptional function. FOXO1 inhibited Runx2-promoted migration of prostate cancer cells, whereas silencing of endogenous FOXO1 enhanced prostate cancer cell migration in a Runx2-dependent manner. Forced expression of FOXO1 also inhibited Runx2-promoted prostate cancer cell invasion. Finally, we found that expression of PTEN and the level of FOXO1 in the nucleus is inversely correlated with expression of Runx2 in a cohort of prostate cancer specimens from patients with lymph node and bone metastasis. These data reveal FOXO1 as a critical negative regulator of Runx2 in prostate cancer cells. Inactivation of FOXO1 due to frequent loss of PTEN in prostate cancer cells may leave the oncogenic activities of Runx2 unchecked, thereby driving promiscuous expression of Runx2 target genes involved in cell migration and invasion and favoring prostate cancer progression.

Activation of NF-{kappa}B by TMPRSS2/ERG Fusion Isoforms through Toll-Like Receptor-4

The TMPRSS2/ERG (T/E) fusion gene is present and thought to be an oncogenic driver of approximately half of all prostate cancers. Fusion of the androgen-regulated TMPRSS2 promoter to the ERG oncogene results in constitutive high level expression of ERG which promotes prostate cancer invasion and proliferation. Here, we report the characterization of multiple alternatively spliced T/E fusion gene isoforms which have differential effects on invasion and proliferation. We found that T/E fusion gene isoforms differentially increase NF-κB-mediated transcription, which may explain in part the differences in biological activities of the T/E fusion isoforms. This increased activity is due to phosphorylation of NF-κB p65 on Ser536. Tissue microarray immunochemistry revealed that p65 phospho-Ser536 is present in the majority of prostate cancers where it is associated with ERG protein expression. The T/E fusion gene isoforms differentially increase expression of a number of NF-κB associated genes including PAR1, CCL2, FOS, TLR3, and TLR4 (Toll-like receptor). TLR4 activation is known to promote p65 Ser536 phosphorylation and knockdown of TLR4 with shRNA decreases Ser536 phosphorylation in T/E fusion gene expressing cells. TLR4 can be activated by proteins in the tumor microenvironment and lipopolysacharide from Gram (-) bacteria. Our findings suggest that bacterial infection of the prostate and/or endogenous microenvironment proteins may promote progression of high-grade prostatic intraepithelial neoplasia and/or prostate cancers that express the T/E fusion gene, where the NF-κB pathway might be targeted as a rational therapeutic approach.

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.

Coordinate regulation of FOXO1 by miR-27a, miR-96, and miR-182 in breast cancer cells

The FOXO1 transcription factor orchestrates the regulation of genes involved in the apoptotic response, cell cycle checkpoints, and cellular metabolism. FOXO1 is a putative tumor suppressor, and the expression of this gene is dysregulated in some cancers, including prostate and endometrial cancers. However, the molecular mechanism resulting in aberrant expression of human FOXO1 in cancer cells is poorly understood. We show here that FOXO1 mRNA is down-regulated in breast tumor samples as compared with normal breast tissue. Silencing of the microRNA processing enzymes, Drosha and Dicer, led to an increase in FOXO1 expression. We also identified functional and specific microRNA target sites in the FOXO1 3'-untranslated region for miR-27a, miR-96, and miR-182, microRNAs that have previously been linked to oncogenic transformation. The three microRNAs, miR-27a, miR-96 and miR-182, were observed to be highly expressed in MCF-7 breast cancer cells, in which the level of FOXO1 protein is very low. Antisense inhibitors to each of these microRNAs led to a significant increase in endogenous FOXO1 expression and to a decrease in cell number in a manner that was blocked by FOXO1 siRNA. Overexpression of FOXO1 resulted in decreased cell viability because of inhibition of cell cycle traverse and induction of cell death. We have identified a novel mechanism of FOXO1 regulation, and targeting of FOXO1 by microRNAs may contribute to transformation or maintenance of an oncogenic state in breast cancer cells.

Role of sirtuin histone deacetylase SIRT1 in prostate cancer. A target for prostate cancer management via its inhibition?

Prostate cancer (PCa) is a major age-related malignancy, and according to estimates from the American Cancer Society, a man's chance of developing this cancer significantly increases with increasing age, from 1 in 10,149 by age 39 to 1 in 38 by age 59 to 1 in 7 by age 70. Therefore, it is important to identify the causal connection between mechanisms of aging and PCa. Employing in vitro and in vivo approaches, in this study, we tested the hypothesis that SIRT1, which belongs to the Sir2 (silent information regulator 2) family of sirtuin class III histone deacetylases, is overexpressed in PCa, and its inhibition will have antiproliferative effects in human PCa cells. Our data demonstrated that SIRT1 was significantly overexpressed in human PCa cells (DU145, LNCaP, 22Rnu1, and PC3) compared with normal prostate epithelial cells (PrEC) at protein, mRNA, and enzymatic activity levels. SIRT1 was also found to be overexpressed in human PCa tissues compared with adjacent normal prostate tissue. Interestingly, our data demonstrated that SIRT1 inhibition via nicotinamide and sirtinol (at the activity level) as well as via short hairpin RNA-mediated RNA interference (at the genetic level) resulted in a significant inhibition in the growth and viability of human PCa cells while having no effect on normal prostate epithelial cells. Further, we found that inhibition of SIRT1 caused an increase in FOXO1 acetylation and transcriptional activation in PCa cells. Our data suggested that SIRT1, via inhibiting FOXO1 activation, could contribute to the development of PCa. We suggest that SIRT1 could serve as a target toward developing novel strategies for PCa management.

Role of sirtuin histone deacetylase SIRT1 in prostate cancer. A target for prostate cancer management via its inhibition?

Prostate cancer (PCa) is a major age-related malignancy, and according to estimates from the American Cancer Society, a man's chance of developing this cancer significantly increases with increasing age, from 1 in 10,149 by age 39 to 1 in 38 by age 59 to 1 in 7 by age 70. Therefore, it is important to identify the causal connection between mechanisms of aging and PCa. Employing in vitro and in vivo approaches, in this study, we tested the hypothesis that SIRT1, which belongs to the Sir2 (silent information regulator 2) family of sirtuin class III histone deacetylases, is overexpressed in PCa, and its inhibition will have antiproliferative effects in human PCa cells. Our data demonstrated that SIRT1 was significantly overexpressed in human PCa cells (DU145, LNCaP, 22Rnu1, and PC3) compared with normal prostate epithelial cells (PrEC) at protein, mRNA, and enzymatic activity levels. SIRT1 was also found to be overexpressed in human PCa tissues compared with adjacent normal prostate tissue. Interestingly, our data demonstrated that SIRT1 inhibition via nicotinamide and sirtinol (at the activity level) as well as via short hairpin RNA-mediated RNA interference (at the genetic level) resulted in a significant inhibition in the growth and viability of human PCa cells while having no effect on normal prostate epithelial cells. Further, we found that inhibition of SIRT1 caused an increase in FOXO1 acetylation and transcriptional activation in PCa cells. Our data suggested that SIRT1, via inhibiting FOXO1 activation, could contribute to the development of PCa. We suggest that SIRT1 could serve as a target toward developing novel strategies for PCa management.