FOXO3a induces differentiation of Bcr-Abl-transformed cells through transcriptional down-regulation of Id1

Functional analyses of miRNA-146b-5p during myogenic proliferation and differentiation in chicken myoblasts

Background

In the poultry and livestock industries, precise genetic information is crucial for improving economic traits. Thus, functional genomic studies help to generate faster, healthier, and more efficient animal production. Chicken myoblast cells, which are required for muscle development and regeneration, are particularly important because chicken growth is closely related to muscle mass.

Results

In this study, we induced expression of microRNA-146b-5p mediated by the piggyBac transposon system in primary chicken myoblast (pCM) cells. Subsequently, we analyzed and compared the proliferation and differentiation capacity and also examined the expression of related genes in regular pCM (rpCM) cells and pCM cells overexpressing miRNA-146b-5p (pCM-146b OE cells). pCM-146b OE cells showed increased proliferation and upregulated gene expression related to cell proliferation. In addition, next-generation sequencing analyses were performed to compare global gene expression patterns between rpCM cells and pCM-146b OE cells. We found that the higher proliferation in pCM-146b OE cells was the result of upregulation of gene sets related to the cell cycle. Moreover, miRNA-146b-5p overexpression had inhibitory effects on myotube differentiation in pCM cells.

Conclusions

Collectively these results demonstrate that miR-146b-5p is closely related to the proliferation and differentiation of chicken myogenic cells as a modulator of post-transcription.

ID1 Mediates Escape from TGFβ Tumor Suppression in Pancreatic Cancer

TGFβ is an important tumor suppressor in pancreatic ductal adenocarcinoma (PDA), yet inactivation of TGFβ pathway components occurs in only half of PDA cases. TGFβ cooperates with oncogenic RAS signaling to trigger epithelial-to-mesenchymal transition (EMT) in premalignant pancreatic epithelial progenitors, which is coupled to apoptosis owing to an imbalance of SOX4 and KLF5 transcription factors. We report that PDAs that develop with the TGFβ pathway intact avert this apoptotic effect via ID1. ID1 family members are expressed in PDA progenitor cells and encode components of a set of core transcriptional regulators shared by PDAs. PDA progression selects against TGFβ-mediated repression of ID1. The sustained expression of ID1 uncouples EMT from apoptosis in PDA progenitors. AKT signaling and mechanisms linked to low-frequency genetic events converge on ID1 to preserve its expression in PDA. Our results identify ID1 as a crucial node and potential therapeutic target in PDA. SIGNIFICANCE: Half of PDAs escape TGFβ-induced tumor suppression without inactivating the TGFβ pathway. We report that ID1 expression is selected for in PDAs and that ID1 uncouples TGFβ-induced EMT from apoptosis. ID1 thus emerges as a crucial regulatory node and a target of interest in PDA.This article is highlighted in the In This Issue feature, p. 1.

The roles of FOX proteins in virus-associated cancers

Forkhead box (FOX) proteins play a crucial role in regulating the expression of genes involved in multiple biological processes, such as metabolism, development, differentiation, proliferation, apoptosis, migration, invasion, and longevity. Deregulation of FOX proteins is commonly associated with cancer initiation, progression, and chemotherapeutic drug resistance in many human tumors. FOX proteins deregulate through genetic events and the perturbation of posttranslational modification. The purpose of the present review is to describe the deregulation of FOX proteins by oncoviruses. Oncoviruses utilize various mechanisms to deregulate FOX proteins, including alterations in posttranslational modifications, cellular localization independently of posttranslational modifications, virus-encoded miRNAs, activation or suppression of a series of cell signaling pathways. This deregulation can affect proliferation, metastasis, chemotherapy resistance, and immunosuppression in virus-induced cancers and help to chronic viral infection, development of gluconeogenic responses, and inflammation. Since the PI3K/Akt/mTOR signaling pathway is the upstream FOXO, suppressing it can cause FOXO function to return, and this can be one of the reasons for patients to recover from the infection of the viruses used to treat these inhibitors. Hence, FOX proteins could serve as prognosis markers and target therapy specifically in cancers caused by oncoviruses.

Novel combined Ato-C treatment synergistically suppresses proliferation of Bcr-Abl-positive leukemic cells in vitro and in vivo

Chronic myelogenous leukemia (CML) accounts for 15-20% of all leukemias affecting adults. Despite recent advances in the development of specific Bcr-Abl tyrosine kinase inhibitors (TKIs), some CML patients suffer from relapse due to TKI resistance. Here, we assessed the efficacy of a novel combinatorial arsenic trioxide (ATO) and cisplatin (CDDP) treatment (Ato-C) in human Bcr-Abl-positive leukemic cells. Combination index analyses revealed that a synergistic interaction of ATO and CDDP elicits a wide range of effects in K562, KU-812, MEG-A2, and KCL-22 cells. Notably, Ato-C synergistically enhanced apoptosis and decreased the survival of both acquired TKI-resistant CML cells and the cells expressing mutant Bcr-Abl^T315I. In addition, Ato-C dramatically decreased the phosphorylation level of forkhead transcription factor FOXO1/3a and STAT5 as well as c-Myc protein level. Interestingly, results of gene set enrichment analysis showed that Ato-C significantly downregulates the expression of MYC- and/or E2F1-target genes. Furthermore, Ato-C significantly suppressed the proliferation of MEG-A2-derived tumor when compared with that following monotherapy in vivo. Collectively, these results suggest that combined Ato-C treatment could be a promising alternative to the current therapeutic regime in CML.

FOXO1 promotes resistance of non-Hodgkin lymphomas to anti-CD20-based therapy

Diminished overall survival rate of non-Hodgkin lymphoma (NHL) patients treated with a combination regimen of rituximab, cyclophosphamide, doxorubicin, vincristine and prednisone (R-CHOP) has been recently linked to recurrent somatic mutations activating FOXO1. Despite of the clinical relevance of this finding, the molecular mechanism driving resistance to R-CHOP therapy remains largely unknown. Herein, we investigated the potential role of FOXO1 in the therapeutic efficacy of rituximab, the only targeted therapy included in the R-CHOP regimen. We found CD20 transcription is negatively regulated by FOXO1 in NHL cell lines and in human lymphoma specimens carrying activating mutations of FOXO1. Furthermore, both the expression of exogenous mutants of FOXO1 and the inhibition of AKT led to FOXO1 activation in lymphoma cells, increased binding to MS4A1 promoter and diminished CD20 expression levels. In contrast, a disruption of FOXO1 with CRISPR/Cas9 genome-editing (sgFOXO1) resulted in CD20 upregulation, improved the cytotoxicity induced by rituximab and the survival of mice with sgFOXO1 tumors. Accordingly, pharmacological inhibition of FOXO1 activity in primary samples upregulated surface CD20 levels. Importantly, FOXO1 was required for the downregulation of CD20 levels by the clinically tested inhibitors of BTK, SYK, PI3K and AKT. Taken together, these results indicate for the first time that the AKT-unresponsive mutants of FOXO1 are important determinant of cell response to rituximab-induced cytotoxicity, and suggest that the genetic status of FOXO1 together with its transcriptional activity need further attention while designing anti-CD20 antibodies based regimens for the therapy of pre-selected lymphomas.

FOXO3a promotes gastric cancer cell migration and invasion through the induction of cathepsin L

Forkhead box O3A (FOXO3a) is an important transcription factor involved in various human cancers. However, the role of FOXO3a in regulating the invasion and metastasis of gastric cancer cells has not been clarified. Here, we report that FOXO3a overexpression promoted migration and invasion of gastric cancer cells by upregulating cathepsin L. FOXO3a knockdown suppressed migration and invasion and also downregulated cathepsin L expression in gastric cancer cells. Silencing cathepsin L in these cells suppressed FOXO3a overexpression-induced cell migration and invasion. Mechanistic studies revealed that FOXO3a increased cathepsin L promoter activation, and cathepsin L overexpression repressed E-cadherin expression, causing gastric cancer cells to undergo epithelial-mesenchymal transition (EMT). Our data reveal a previously unexplored function of FOXO3a in gastric cancer invasion by regulating proteins involved in extracellular matrix (ECM) degradation and EMT. We suggest that FOXO3a may be of prognostic value and a potential therapeutic target in blocking tumor metastasis.

FOXM1 facilitates gastric cancer cell migration and invasion by inducing Cathepsin D

Forkhead box M1 (FOXM1) has been reported as a vital transcription factor in different human malignancies. To date, the mechanisms of FOXM1 in modulating the invasion and metastasis of gastric cancer cells have not been elucidated. In the present study, we found that overexpression of FOXM1 prompted cell migration and invasion of gastric cancer, and increased the expression of Cathepsin D (Cath-D). However, FOXM1 siRNA repressed cell migration and invasion, and also decreased the expression of Cath-D in gastric cancer cells. Blocking of Cath-D repressed FOXM1 overexpression-mediated cell migration and invasion. Mechanically, FOXM1 facilitated the activation of Cath-D promoter. Furthermore, overexpression of Cath-D affected the expression of E-cadherin, leading to epithelial-mesenchymal transition (EMT) of gastric cancer cells. In conclusion, this study demonstrated that FOXM1 promotes gastric cancer cell migration and invasion through inducing expression of Cath-D in gastric cancer. Thus, FOXM1 may be recommended as a potential therapeutic target for gastric cancer patients.

FOXO transcription factors at the interface of metabolism and cancer

Diabetes refers to a group of metabolic diseases characterized by impaired insulin signalling and high blood glucose. A growing body of epidemiological evidence links diabetes to several types of cancer but the underlying molecular mechanisms are poorly understood. The signalling cascade connecting insulin and FOXO proteins provides a compelling example for a conserved pathway at the interface between insulin signalling and cancer. FOXOs are transcription factors that orchestrate programs of gene expression known to control a variety of processes in response to cellular stress. Genes regulated by this family of proteins are involved in the regulation of cellular energy production, oxidative stress resistance and cell viability and proliferation. Accordingly, FOXO factors have been shown to play an important role in the suppression of tumour growth and in the regulation of metabolic homeostasis. There is emerging evidence that deregulation of FOXO factors might account for the association between insulin resistance-related metabolic disorders and cancer.

siRNA-mediated knockdown of ID1 disrupts Nanog- and Oct-4-mediated cancer stem cell-likeness and resistance to chemotherapy in gastric cancer cells

DNA-binding protein inhibitor ID-1 (ID1) serves an essential role in tumor progression, and the self-renewal and pluripotency of embryonic stem cells. However, the effect of ID1 on the stemness and cancer stem cell (CSC)-like properties of gastric adenocarcinoma cells remains to be elucidated. In the present study, effective ID1 knockdown was achieved in gastric cancer (GC) cells using small interfering RNA, and the self-renewal ability and cisplatin (DDP) sensitivity of GC cells was subsequently examined. ID1 knockdown in the MKN-28 and MGC-803 cell lines was demonstrated to significantly suppress colony formation (P=0.005 in MKN-28 and P=0.001 in MGC-803), tumor spheroid formation (P=0.021 in MKN-28 and P=0.037 in MGC-803), cell proliferation (P=0.028 in MKN-28 and P=0.001 in MGC-803) and migration (P=0.002 in MKN-28 and P=0.015 in MGC-803). To the best of our knowledge, the present study revealed for the first time that ID1 knockdown suppresses the expression of the key CSC-associated factors Nanog and octamer-binding protein 4 (Oct-4). It was further demonstrated that ID1 knockdown sensitized GC cells to DDP. In conclusion, knockdown of ID1 attenuates the stem cell like-properties of self-renewal in normal GC cells, potentially through the targeting of Nanog and Oct-4, and subsequently decreases cell proliferation and resistance to DDP. The results of the present study suggest that ID1 functions as an oncogene in GC and regulates the stem cell like-properties of gastric cancer cells by targeting Nanog and Oct-4.

ID1 upregulation and FoxO3a downregulation by Epstein-Barr virus-encoded LMP1 in Hodgkin's lymphoma

Cancer-initiating cells (CICs) are specialized cells that have the ability to self-renew and are multipotent. We recently demonstrated that Forkhead box O3a (FoxO3a)-expressing cells exhibited a CIC-like potential in Hodgkin's lymphoma (HL). A proportion of HL patients are infected with Epstein-Barr virus (EBV). EBV-encoded latent membrane protein (LMP) 1 downregulates FoxO3a, suggesting that FoxO3a expression may be abolished in EBV-positive HL. Inhibitors of DNA-binding (ID) proteins are highly conserved transcription factors mediating stem cell functions. To the best of our knowledge, no study has investigated possible associations among ID1, FoxO3a and LMP1 expression in HL to date. We immunohistochemically evaluated the expression of the three abovementioned factors in HL patients. The ID1 expression level was inversely correlated with that of FoxO3a (P=0.00035). LMP1-positive HL cells abundantly expressed ID1 (P=0.029), but not FoxO3a (P=0.00085). Thus, our previous observation that FoxO3a may serve as a marker of CICs may not be applicable in EBV-positive HL patients, but rather ID1 may be a candidate CIC marker in this type of HL.

AKT isoforms modulate Th1-like Treg generation and function in human autoimmune disease

Foxp3(+) regulatory T cells (Tregs) exhibit plasticity, which dictates their function. Secretion of the inflammatory cytokine IFNγ, together with the acquisition of a T helper 1 (Th1)-like effector phenotype as observed in cancer, infection, and autoimmune diseases, is associated with loss of Treg suppressor function through an unknown mechanism. Here, we describe the signaling events driving the generation of human Th1-Tregs. Using a genome-wide gene expression approach and pathway analysis, we identify the PI3K/AKT/Foxo1/3 signaling cascade as the major pathway involved in IFNγ secretion by human Tregs. Furthermore, we describe the opposing roles of AKT isoforms in Th1-Treg generation ex vivo Finally, we employ multiple sclerosis as an in vivo model with increased but functionally defective Th1-Tregs. We show that the PI3K/AKT/Foxo1/3 pathway is activated in ex vivo-isolated Tregs from untreated relapsing-remitting MS patients and that blockade of the pathway inhibits IFNγ secretion and restores the immune suppressive function of Tregs. These data define a fundamental pathway regulating the function of human Tregs and suggest a novel treatment paradigm for autoimmune diseases.

Inhibitor of Differentiation/DNA Binding 1 (ID1) Inhibits Etoposide-induced Apoptosis in a c-Jun/c-Fos-dependent Manner

ID1 (inhibitor of differentiation/DNA binding 1) acts an important role in metastasis, tumorigenesis, and maintenance of cell viability. It has been shown that the up-regulation of ID1 is correlated with poor prognosis and the resistance to chemotherapy of human cancers. However, the underlying molecular mechanism remains elusive. Here, we determined for the first time that up-regulating ID1 upon etoposide activation was mediated through AP-1 binding sites within theID1promoter and confirmed that ID1 enhanced cell resistance to DNA damage-induced apoptosis in esophageal squamous cell carcinoma cells. Ablation of c-Jun/c-Fos or ID1 expression enhanced etoposide-mediated apoptosis through increasing activity of caspase 3 and PARP cleavage. Moreover, c-Jun/c-Fos and ID1 were positively correlated in human cancers. More importantly, simultaneous high expression of ID1 and c-Jun or c-Fos was correlated with poor survival in cancer patients. Collectively, we demonstrate the importance of c-Jun/c-Fos-ID1 signaling pathway in chemoresistance of esophageal cancer cells and provide considerable insight into understanding the underlying molecular mechanisms in esophageal squamous cell carcinoma cell biology.

The antiproliferative activity of kinase inhibitors in chronic myeloid leukemia cells is mediated by FOXO transcription factors

Chronic myeloid leukemia (CML) is initiated and maintained by the tyrosine kinase BCR-ABL which activates a number of signal transduction pathways, including PI3K/AKT signaling and consequently inactivates FOXO transcription factors. ABL-specific tyrosine kinase inhibitors (TKIs) induce minimal apoptosis in CML progenitor cells, yet exert potent antiproliferative effects, through as yet poorly understood mechanisms. Here, we demonstrate that in CD34+ CML cells, FOXO1 and 3a are inactivated and relocalized to the cytoplasm by BCR-ABL activity. TKIs caused a decrease in phosphorylation of FOXOs, leading to their relocalization from cytoplasm (inactive) to nucleus (active), where they modulated the expression of key FOXO target genes, such as Cyclin D1, ATM, CDKN1C, and BCL6 and induced G1 arrest. Activation of FOXO1 and 3a and a decreased expression of their target gene Cyclin D1 were also observed after 6 days of in vivo treatment with dasatinib in a CML transgenic mouse model. The over-expression of FOXO3a in CML cells combined with TKIs to reduce proliferation, with similar results seen for inhibitors of PI3K/AKT/mTOR signaling. While stable expression of an active FOXO3a mutant induced a similar level of quiescence to TKIs alone, shRNA-mediated knockdown of FOXO3a drove CML cells into cell cycle and potentiated TKI-induced apoptosis. These data demonstrate that TKI-induced G1 arrest in CML cells is mediated through inhibition of the PI3K/AKT pathway and reactivation of FOXOs. This enhanced understanding of TKI activity and induced progenitor cell quiescence suggests that new therapeutic strategies for CML should focus on manipulation of this signaling network. Stem Cells2014;32:2324–2337

Inhibition of Ras-mediated signaling pathways in CML stem cells

BACKGROUND

Chronic myeloid leukemia (CML) is a clonal myeloproliferative disorder characterized by the presence of the BCR-ABL1 oncoprotein in cells with a hematopoietic stem cell (HSC) origin. BCR-ABL1 tyrosine kinase activity leads to constitutive activation of Ras, which in turn acts as a branch point to initiate multiple downstream signaling pathways governing proliferation, self-renewal, differentiation and apoptosis. As aberrant regulation of these cellular processes causes transformation and disease progression particularly in advanced stages of CML, investigation of these signaling pathways may uncover new therapeutic targets for the selective eradication of CML stem cells. Transcription factors play a crucial role in unbalancing the Ras signaling network and have recently been investigated as potential modulators in this regard. In this review, we first briefly summarize the Ras-associated molecular pathways that are involved in the regulation of CML stem cell properties. Next we discuss the relevance of Ras-associated transcription factors as nuclear targets in combination treatment strategies for CML.

CONCLUSIONS

A closer investigation of the influence of Ras-mediated signaling pathways on CML progression to blast crisis is warranted to uncover new directions for targeted therapies, particularly in cases that are resistant to current tyrosine kinase inhibitors.

Insulin-like growth factor--phosphatidylinositol 3 kinase signaling in canine cortisol-secreting adrenocortical tumors

Background

Hypercortisolism is a common endocrine disorder in dogs, caused by a cortisol‐secreting adrenocortical tumor (AT) in approximately 15% of cases. In adrenocortical carcinomas of humans, activation of the phosphatidylinositol 3 kinase (PI3K) signaling pathway by insulin‐like growth factor (IGF) signaling represents a promising therapeutic target.

Objectives

To investigate the involvement of PI3K signaling in the pathogenesis of ATs in dogs and to identify pathway components that may hold promise as future therapeutic targets or as prognostic markers.

Animals

Analyses were performed on 36 canine cortisol‐secreting ATs (11 adenomas and 25 carcinomas) and 15 normal adrenal glands of dogs.

Methods

mRNA expression analysis was performed for PI3K target genes, PI3K inhibitor phosphatase and tensin homolog (PTEN), IGFs, IGF receptors, IGF binding proteins and epidermal growth factor receptors. Mutation analysis was performed on genes encoding PTEN and PI3K catalytic subunit (PIK3CA).

Results

Target gene expression indicated PI3K activation in carcinomas, but not in adenomas. No amino acid‐changing mutations were detected in PTEN or PIK3CA and no significant alterations in IGF‐II or IGFR1 expression were detected. In carcinomas, ERBB2 expression tended to be higher than in normal adrenal glands, and higher expression of inhibitor of differentiation 1 and 2 (ID1 and ID2) was detected in carcinomas with recurrence within 2.5 years after adrenalectomy.

Conclusions and Clinical Importance

Based on these results, ERBB2 might be a promising therapeutic target in ATs in dogs, whereas ID1 and 2 might be valuable as prognostic markers and therapeutic targets.

Spred2 modulates the erythroid differentiation induced by imatinib in chronic myeloid leukemia cells

Differentiation induction is currently considered as an alternative strategy for treating chronic myelogenous leukemia (CML). Our previous work has demonstrated that Sprouty-related EVH1 domainprotein2 (Spred2) was involved in imatinib mediated cytotoxicity in CML cells. However, its roles in growth and lineage differentiation of CML cells remain unknown. In this study, we found that CML CD34⁺ cells expressed lower level of Spred2 compared with normal hematopoietic progenitor cells, and adenovirus mediated restoration of Spred2 promoted the erythroid differentiation of CML cells. Imatinib could induce Spred2 expression and enhance erythroid differentiation in K562 cells. However, the imatinib induced erythroid differentiation could be blocked by Spred2 silence using lentiviral vector PLKO.1-shSpred2. Spred2 interference activated phosphorylated-ERK (p-ERK) and inhibited erythroid differentiation, while ERK inhibitor, PD98059, could restore the erythroid differentiation, suggesting Spred2 regulated the erythroid differentiation partly through ERK signaling. Furthermore, Spred2 interference partly restored p-ERK level leading to inhibition of erythroid differentiation in imatinib treated K562 cells. In conclusion, Spred2 was involved in erythroid differentiation of CML cells and participated in imatinib induced erythroid differentiation partly through ERK signaling.

Genome-wide identification of FoxO-dependent gene networks in skeletal muscle during C26 cancer cachexia

BACKGROUND

Evidence from cachectic cancer patients and animal models of cancer cachexia supports the involvement of Forkhead box O (FoxO) transcription factors in driving cancer-induced skeletal muscle wasting. However, the genome-wide gene networks and associated biological processes regulated by FoxO during cancer cachexia are unknown. We hypothesize that FoxO is a central upstream regulator of diverse gene networks in skeletal muscle during cancer that may act coordinately to promote the wasting phenotype.

METHODS

To inhibit endogenous FoxO DNA-binding, we transduced limb and diaphragm muscles of mice with AAV9 containing the cDNA for a dominant negative (d.n.) FoxO protein (or GFP control). The d.n.FoxO construct consists of only the FoxO3a DNA-binding domain that is highly homologous to that of FoxO1 and FoxO4, and which outcompetes and blocks endogenous FoxO DNA binding. Mice were subsequently inoculated with Colon-26 (C26) cells and muscles harvested 26 days later.

RESULTS

Blocking FoxO prevented C26-induced muscle fiber atrophy of both locomotor muscles and the diaphragm and significantly spared force deficits. This sparing of muscle size and function was associated with the differential regulation of 543 transcripts (out of 2,093) which changed in response to C26. Bioinformatics analysis of upregulated gene transcripts that required FoxO revealed enrichment of the proteasome, AP-1 and IL-6 pathways, and included several atrophy-related transcription factors, including Stat3, Fos, and Cebpb. FoxO was also necessary for the cancer-induced downregulation of several gene transcripts that were enriched for extracellular matrix and sarcomere protein-encoding genes. We validated these findings in limb muscles and the diaphragm through qRT-PCR, and further demonstrate that FoxO1 and/or FoxO3a are sufficient to increase Stat3, Fos, Cebpb, and the C/EBPβ target gene, Ubr2. Analysis of the Cebpb proximal promoter revealed two bona fide FoxO binding elements, which we further establish are necessary for Cebpb promoter activation in response to IL-6, a predominant cytokine in the C26 cancer model.

CONCLUSIONS

These findings provide new evidence that FoxO-dependent transcription is a central node controlling diverse gene networks in skeletal muscle during cancer cachexia, and identifies novel candidate genes and networks for further investigation as causative factors in cancer-induced wasting.

Spontaneous presence of FOXO3-specific T cells in cancer patients

In the present study, we describe forkhead box O3 (FOXO3)-specific, cytotoxic CD8⁺ T cells existent among peripheral-blood mononuclear cells (PBMCs) of cancer patients. FOXO3 immunogenicity appears specific, as we did not detect reactivity toward FOXO3 among T cells in healthy individuals. FOXO3 may naturally serve as a target antigen for tumor-reactive T cells as it is frequently over-expressed in cancer cells. In addition, expression of FOXO3 plays a critical role in immunosuppression mediated by tumor-associated dendritic cells (TADCs). Indeed, FOXO3-specific cytotoxic T lymphocytes (CTLs) were able to specifically recognize and kill both FOXO3-expressing cancer cells as well as dendritic cells. Thus, FOXO3 was processed and presented by HLA-A2 on the cell surface of both immune cells and cancer cells. As FOXO3 programs TADCs to become tolerogenic, FOXO3 signaling thereby comprises a significant immunosuppressive mechanism, such that FOXO3 targeting by means of specific T cells is an attractive clinical therapy to boost anticancer immunity. In addition, the natural occurrence of FOXO3-specific CTLs in the periphery suggests that these T cells hold a function in the complex network of immune regulation in cancer patients.

FoxO3a and disease progression

The Forkhead box O (FoxO) family has recently been highlighted as an important transcriptional regulator of crucial proteins associated with the many diverse functions of cells. So far, FoxO1, FoxO3a, FoxO4 and FoxO6 proteins have been identified in humans. Although each FoxO family member has its own role, unlike the other FoxO families, FoxO3a has been extensively studied because of its rather unique and pivotal regulation of cell proliferation, apoptosis, metabolism, stress management and longevity. FoxO3a alteration is closely linked to the progression of several types of cancers, fibrosis and other types of diseases. In this review, we will examine the function of FoxO3a in disease progression and also explore FoxO3a’s regulatory mechanisms. We will also discuss FoxO3a as a potential target for the treatment of several types of disease.

Targeting forkhead box transcription factors FOXM1 and FOXO in leukemia (Review)

Deregulation of forkhead box (FOX) proteins has been found in many genetic diseases and malignancies including leukemia. Leukemia is a common neoplastic disease of the blood or bone marrow characterized by the presence of immature leukocytes and is one of the leading causes of death due to cancer. Forkhead transcription factors, FOXM1 and FOXO family members (FOXOs), are important mediators in leukemia development. Aberrant expression of FOXM1 and FOXOs results in leukemogenesis. Usually the expression of FOXM1 is upregulated, whereas the expression of FOXOs is downregulated due to phosphorylation, nuclear exclusion and degradation in leukemia. On the one hand, FOXOs are bona fide tumor suppressors, on the other hand, active FOXOs maintain leukemia stem cells and stimulate drug resistance genes, contributing to leukemogenesis. FOXM1 and FOXOs have been proven to be potential targets for the development of leukemia therapeutics. They are also valuable diagnostic and prognostic markers in leukemia for clinical applications. This review summarizes the present knowledge concerning the molecular mechanisms by which FOXM1 and FOXOs modulate leukemogenesis and leukemia development, the clinical relevance of these FOX proteins in leukemia and related areas that warrant further investigation.

ID proteins regulate diverse aspects of cancer progression and provide novel therapeutic opportunities

The inhibitor of differentiation (ID) proteins are helix-loop-helix transcriptional repressors with established roles in stem cell self-renewal, lineage commitment, and niche interactions. While deregulated expression of ID proteins in cancer was identified more than a decade ago, emerging evidence has revealed a central role for ID proteins in neoplastic progression of multiple tumor types that often mirrors their function in physiological stem and progenitor cells. ID proteins are required for the maintenance of cancer stem cells, self-renewal, and proliferation in a range of malignancies. Furthermore, ID proteins promote metastatic dissemination through their role in remodeling the tumor microenvironment and by promoting tumor-associated endothelial progenitor cell proliferation and mobilization. Here, we discuss the latest findings in this area and the clinical opportunities that they provide.

Transcription factor binding site analysis identifies FOXO transcription factors as regulators of the cutaneous wound healing process

The search for significantly overrepresented and co-occurring transcription factor binding sites in the promoter regions of the most differentially expressed genes in microarray data sets could be a powerful approach for finding key regulators of complex biological processes. To test this concept, two previously published independent data sets on wounded human epidermis were re-analyzed. The presence of co-occurring transcription factor binding sites for FOXO1, FOXO3 and FOXO4 in the majority of the promoter regions of the most significantly differentially expressed genes between non-wounded and wounded epidermis implied an important role for FOXO transcription factors during wound healing. Expression levels of FOXO transcription factors during wound healing in vivo in both human and mouse skin were analyzed and a decrease for all FOXOs in human wounded skin was observed, with FOXO3 having the highest expression level in non wounded skin. Impaired re-epithelialization was found in cultures of primary human keratinocytes expressing a constitutively active variant of FOXO3. Conversely knockdown of FOXO3 in keratinocytes had the opposite effect and in an in vivo mouse model with FOXO3 knockout mice we detected significantly accelerated wound healing. This article illustrates that the proposed approach is a viable method for identifying important regulators of complex biological processes using in vivo samples. FOXO3 has not previously been implicated as an important regulator of wound healing and its exact function in this process calls for further investigation.

The ID proteins: master regulators of cancer stem cells and tumour aggressiveness

Inhibitor of DNA binding (ID) proteins are transcriptional regulators that control the timing of cell fate determination and differentiation in stem and progenitor cells during normal development and adult life. ID genes are frequently deregulated in many types of human neoplasms, and they endow cancer cells with biological features that are hijacked from normal stem cells. The ability of ID proteins to function as central 'hubs' for the coordination of multiple cancer hallmarks has established these transcriptional regulators as therapeutic targets and biomarkers in specific types of human tumours.

SMAD7 antagonizes key TGFβ superfamily signaling in mouse granulosa cells in vitro

Transforming growth factor β (TGFβ) superfamily signaling is essential for female reproduction. Dysregulation of the TGFβ signaling pathway can cause reproductive diseases. SMA and MAD (mothers against decapentaplegic) (SMAD) proteins are downstream signaling transducers of the TGFβ superfamily. SMAD7 is an inhibitory SMAD that regulates TGFβ signalingin vitro. However, the function of SMAD7 in the ovary remains poorly defined. To determine the signaling preference and potential role of SMAD7 in the ovary, we herein examined the expression, regulation, and function of SMAD7 in mouse granulosa cells. We showed that SMAD7 was expressed in granulosa cells and subject to regulation by intraovarian growth factors from the TGFβ superfamily. TGFB1 (TGFβ1), bone morphogenetic protein 4, and oocyte-derived growth differentiation factor 9 (GDF9) were capable of inducingSmad7expression, suggesting a modulatory role of SMAD7 in a negative feedback loop. Using a small interfering RNA approach, we further demonstrated that SMAD7 was a negative regulator of TGFB1. Moreover, we revealed a link between SMAD7 and GDF9-mediated oocyte paracrine signaling, an essential component of oocyte–granulosa cell communication and folliculogenesis. Collectively, our results suggest that SMAD7 may function during follicular development via preferentially antagonizing and/or fine-tuning essential TGFβ superfamily signaling, which is involved in the regulation of oocyte–somatic cell interaction and granulosa cell function.

Functional characterization of Foxp3-specific spontaneous immune responses

Tumor-infiltrating CD4+CD25+ regulatory T cells (Tregs) are associated with an impaired prognosis in several cancers. The transcription factor forkhead box P3 (Foxp3) is generally expressed in Tregs. Here, we identify and characterize spontaneous cytotoxic immune responses to Foxp3-expressing cells in peripheral blood of healthy volunteers and cancer patients. These immune responses were directed against a HLA-A2-restricted peptide epitope derived from Foxp3. Foxp3-reactive T cells were characterized as cytotoxic CD8+ T cells. These cells recognized dendritic cells incubated with recombinant Foxp3 protein indicating that this protein was indeed internalized, processed and cross-presented in the context of HLA-A2. More importantly, however, Foxp3-specific T cells were able to specifically recognize Tregs. Similarly, Foxp3+ malignant T cells established from a Cutaneous T-cell lymphomas (CTCL) patient were readily killed by the Foxp3-specific cytotoxic T lymphocytes. The spontaneous presence of Foxp3-specific cytotoxic T-cell responses suggest a general role of such T cells in the complex network of immune regulation as such responses may eliminate Tregs, that is, suppression of the suppressors. Consequently, induction of Foxp3-specific cytotoxic T-cell responses appears as an attractive tool to boost spontaneous or therapeutically provoked immune responses, for example, for the therapy of cancer.

Role and regulation of the forkhead transcription factors FOXO3a and FOXM1 in carcinogenesis and drug resistance

The FOXO3a and FOXM1 forkhead transcription factors are key players in cancer initiation, progression, and drug resistance. Recent research shows that FOXM1 is a direct transcriptional target of FOXO3a, a vital downstream effector of the PI3K-AKT-FOXO signaling cascade. In addition, FOXM1 and FOXO3a also antagonize each other's activity by competitively binding to the same target genes, which are involved in chemotherapeutic drug sensitivity and resistance. Understanding the role and regulation of the FOXO-FOXM1 axis will provide insight into chemotherapeutic drug action and resistance in patients, and help to identify novel therapeutic approaches as well as diagnostic and predictive biomarkers.

Genome-wide analysis of FOXO3 mediated transcription regulation through RNA polymerase II profiling

Forkhead box O (FOXO) transcription factors are key players in diverse cellular processes affecting tumorigenesis, stem cell maintenance and lifespan. To gain insight into the mechanisms of FOXO-regulated target gene expression, we studied genome-wide effects of FOXO3 activation. Profiling RNA polymerase II changes shows that FOXO3 regulates gene expression through transcription initiation. Correlative analysis of FOXO3 and RNA polymerase II ChIP-seq profiles demonstrates FOXO3 to act as a transcriptional activator. Furthermore, this analysis reveals a significant part of FOXO3 gene regulation proceeds through enhancer regions. FOXO3 binds to pre-existing enhancers and further activates these enhancers as shown by changes in histone acetylation and RNA polymerase II recruitment. In addition, FOXO3-mediated enhancer activation correlates with regulation of adjacent genes and pre-existence of chromatin loops between FOXO3 bound enhancers and target genes. Combined, our data elucidate how FOXOs regulate gene transcription and provide insight into mechanisms by which FOXOs can induce different gene expression programs depending on chromatin architecture.

Role of the forkhead transcription factor FOXO-FOXM1 axis in cancer and drug resistance

The forkhead transcription factors FOXO and FOXM1 have pivotal roles in tumorigenesis and in mediating chemotherapy sensitivity and resistance. Recent research shows that the forkhead transcription factor FOXM1 is a direct transcriptional target repressed by the forkhead protein FOXO3a, a vital downstream effector of the PI3K-AKT-FOXO signaling pathway. Intriguingly, FOXM1 and FOXO3a also compete for binding to the same gene targets, which have a role in chemotherapeutic drug action and sensitivity. An understanding of the role and regulation of the FOXO-FOXM1 axis will impact directly on our knowledge of chemotherapeutic drug action and resistance in patients, and provide new insights into the design of novel therapeutic strategy and reliable biomarkers for prediction of drug sensitivity.

The Interface between BCR-ABL-Dependent and -Independent Resistance Signaling Pathways in Chronic Myeloid Leukemia

Chronic myeloid leukemia (CML) is a clonal hematopoietic disorder characterized by the presence of the Philadelphia chromosome which resulted from the reciprocal translocation between chromosomes 9 and 22. The pathogenesis of CML involves the constitutive activation of the BCR-ABL tyrosine kinase, which governs malignant disease by activating multiple signal transduction pathways. The BCR-ABL kinase inhibitor, imatinib, is the front-line treatment for CML, but the emergence of imatinib resistance and other tyrosine kinase inhibitors (TKIs) has called attention for additional resistance mechanisms and has led to the search for alternative drug treatments. In this paper, we discuss our current understanding of mechanisms, related or unrelated to BCR-ABL, which have been shown to account for chemoresistance and treatment failure. We focus on the potential role of the influx and efflux transporters, the inhibitor of apoptosis proteins, and transcription factor-mediated signals as feasible molecular targets to overcome the development of TKIs resistance in CML.

A specific role for phosphoinositide 3-kinase and AKT in osteoblasts?

The phosphoinositide 3-kinase and AKT (protein kinase B) signaling pathway (PI3K/AKT) plays a central role in the control of cell survival, growth, and proliferation throughout the body. With regard to bone, and particularly in osteoblasts, there is an increasing amount of evidence that the many signaling molecules exert some of their bone-specific effects in part via selectively activating some of the generic effects of the PI3K/AKT pathway in osteoblasts. There is further data demonstrating that PI3K/AKT has the capacity to specifically cross-talk with other signaling pathways and transcriptional networks controlling bone cells' development in order to fine-tune the osteoblast phenotype. There is also evidence that perturbations in the PI3K/AKT pathway may well be responsible for certain bone pathologies. In this review, we discuss some of these findings and suggest that the PI3K/AKT pathway is a central nexus in the extensive network of extracellular signaling pathways that control the osteoblast.

Deciphering the role of forkhead transcription factors in cancer therapy

Forkhead O transcription factors (FOXO) are critical for the regulation of cell cycle arrest, cell death, and DNA damage repair. Inactivation of FOXO proteins may be associated with tumorigenesis, including breast cancer, prostate cancer, glioblastoma, rhabdomyosarcoma, and leukemia. Accumulated evidence shows that activation of oncogenic pathways such as phosphoinositide-3-kinase/AKT/IKK or RAS/mitogen-activated protein kinase suppresses FOXO transcriptional activity through the phosphorylation of FOXOs at different sites that ultimately leads to nuclear exclusion and degradation of FOXOs. In addition, posttranslational modifications of FOXOs such as acetylation, methylation and ubiquitination also contribute to modulating FOXO3a functions. Several anti-cancer drugs like paclitaxel, imatinib, and doxorubicin activate FOXO3a by counteracting those oncogenic pathways which restrain FOXOs functions. In this review, we will illustrate the regulation of FOXOs and reveal potential therapeutics that target FOXOs for cancer treatment.

FOXM1: From cancer initiation to progression and treatment

The Forkhead box protein M1 (FOXM1) transcription factor is a regulator of myriad biological processes, including cell proliferation, cell cycle progression, cell differentiation, DNA damage repair, tissue homeostasis, angiogenesis and apoptosis. Elevated FOXM1 expression is found in cancers of the liver, prostate, brain, breast, lung, colon, pancreas, skin, cervix, ovary, mouth, blood and nervous system, suggesting it has an integral role in tumorigenesis. Recent research findings also place FOXM1 at the centre of cancer progression and drug sensitivity. In this review the involvement of FOXM1 in various aspects of cancer, in particular its role and regulation within the context of cancer initiation, progression, and cancer drug response, will be summarised and discussed.

Characterization of intracellular translocation of Forkhead transcription factor O (FoxO) members induced by NGF in PC12 cells

Nuclear translocation of Forkhead transcription factors of the O class (FoxOs) is important for the action of growth factors. However it is not known if all members of the FOXO family have the same translocation properties. We examined the effects of nerve growth factor (NGF) on nuclear/cytoplasmic shuttling of FoxO1, FoxO3a and FoxO6 in PC12 cells and determined their translocation kinetics. Our data demonstrated that NGF could induce the nuclear exclusion of FoxO1-GFP and FoxO3a-GFP in PC12 cells with different properties, but had no effect on FoxO6-GFP's nuclear localization and FoxO6-GFP showed an exclusive nuclear localization. Translocat ould be blocked by K252a and LY294002 but not by PD98059. Moreover, FoxO3a returned to cytoplasm at a higher rate than FoxO1 after NGF stimulation and it was more sensitive than FoxO1 to NGF stimulation.

The extending network of FOXO transcriptional target genes

The evolutionarily conserved Forkhead box O (FOXO) family of transcription factors regulates multiple transcriptional targets involved in various cellular processes, including proliferation, stress resistance, apoptosis, and metabolism. Target gene regulation appears to be controlled in a cell-type-specific manner due to association of FOXO isoforms with specific cofactors. Many of the cellular processes modulated by FOXO are themselves deregulated in tumorigenesis, and deletion of Foxo genes has demonstrated that these transcription factors function as tumor suppressors. Our understanding of the regulation of FOXO activity, and defining specific transcriptional targets, may provide clues to the molecular mechanisms controlling cell fate decisions. In this review we describe the functional consequences of FOXO activation based on our current knowledge of transcriptional targets.

Sense and sensitivity: FOXO and ROS in cancer development and treatment

Forkhead box O (FOXO) transcription factors are at the center of an emerging paradigm that links longevity, cell fate, and tumor development. Key to these processes is the ability of FOXO to regulate, and be regulated by, oxidative stress. Perturbation of the mechanisms that tightly couple reactive oxygen species (ROS) production, oxidative stress signaling, and FOXO activity to the subsequent cellular response is a pivotal step in cancer development and progression. Consequently, the ROS-FOXO pathway is a major therapeutic target in cancer, not only as it mediates the cellular response to chemotherapy, but also because it underpins drug resistance. As the intimate and reciprocal relation between FOXO and ROS is being unravelled, new opportunities arise to develop more-effective cancer treatments that circumvent resistance to the conventional cytotoxic drugs.

Expressions of forkhead class box O 3a on crushed rat sciatic nerves and differentiated primary Schwann cells

Forkhead box-containing protein, class O 3 a (FOXO3a), an Akt downstream target, plays an important role in peripheral nervous system. FOXO3a shares the ability to be inhibited and translocated from the nucleus on phosphorylation by proteins such as Akt/PKB in the PI3K signaling pathway. To elucidate the expression and possible function of FOXO3a in lesion and repair, we performed an acute sciatic nerve crush model and studied differential expressions of FOXO3a. We observed that expressions of FOXO3a in Schwann cells (SCs) of the peripheral nervous system and cAMP-induced differentiation were dynamically regulated. Western blot analysis showed FOXO3a level significantly decreased post injury. Moreover, Immunofluorescence double labeling suggested the changes were striking especially in SCs. In vitro, Western blot analysis showed that the expression of FOXO3a was decreased in cAMP-induced differentiated primary SCs. The FOXO3a siRNA-transfected SCs treated by cAMP promote differentiation of SCs through the PI3K/Akt pathway. The results indicate that FOXO3a plays an important role during differentiation of SCs.

Dual blocking of mTor and PI3K elicits a prodifferentiation effect on glioblastoma stem-like cells

Glioblastoma, the most intractable cerebral tumor, is highly lethal. Recent studies suggest that cancer stem-like cells (CSLCs) have the capacity to repopulate tumors and mediate radio- and chemoresistance, implying that future therapies may need to turn from the elimination of rapidly dividing, but differentiated, tumor cells to specifically targeting the minority of tumor cells that repopulate the tumor. However, the mechanism by which glioblastoma CSLCs maintain their immature stem-like state or, alternatively, become committed to differentiation is poorly understood. Here, we show that the inactivation of mammalian target of rapamycin (mTor) by the mTor inhibitor rapamycin or knockdown of mTor reduced sphere formation and the expression of neural stem cell (NSC)/progenitor markers in CSLCs of the A172 glioblastoma cell line. Interestingly, combination treatment with rapamycin and LY294002, a phosphatidylinositol 3-kinase (PI3K) inhibitor, not only reduced the expression of NSC/progenitor markers more efficiently than single-agent treatment, but also increased the expression of βIII-tubulin, a neuronal differentiation marker. Consistent with these results, a dual PI3K/mTor inhibitor, NVP-BEZ235, elicited a prodifferentiation effect on A172 CSLCs. Moreover, A172 CSLCs, which were induced to undergo differentiation by pretreatment with NVP-BEZ235, exhibited a significant decrease in their tumorigenicity when transplanted either subcutaneously or intracranially. Importantly, similar results were obtained when patient-derived glioblastoma CSLCs were used. These findings suggest that the PI3K/mTor signaling pathway is critical for the maintenance of glioblastoma CSLC properties, and targeting both mTor and PI3K of CSLCs may be an effective therapeutic strategy in glioblastoma.

The biological effects of C/EBPalpha in K562 cells depend on the potency of the N-terminal regulatory region, not on specificity of the DNA binding domain

The transcription factor C/EBPα is more potent than C/EBPβ in inducing granulocitic differentiation and inhibiting BCR/ABL-expressing cells. We took a "domain swapping" approach to assess biological effects, modulation of gene expression, and binding to C/EBPα-regulated promoters by wild-type and chimeric C/EBPα/C/EBPβ proteins. Wild-type and N-C/EBPα+ C/EBPβ-DBD induced transcription of the granulocyte-colony stimulating factor receptor (G-CSFR) gene, promoted differentiation, and suppressed proliferation of K562 cells vigorously; instead, wild-type C/EBPβ and N-C/EBPβ+C/EBPα-DBD had modest effects, although they bound the G-CSFR promoter like wild-type C/EBPα and N-C/EBPα+C/EBPβ-DBD. Chimeric proteins consisting of the TAD of VP16 and the DBD of C/EBPα or C/EBPβ inhibited proliferation and induced differentiation of K562 cells as effectively as wild-type C/EBPα. Gene expression profiles induced by C/EBPα resembled those modulated by N-C/EBPα+C/EBPβ-DBD, whereas C/EBPβ induced a pattern similar to that of N-C/EBPβ+C/EBPα-DBD. C/EBPα activation induced changes in the expression of more cell cycle- and apoptosis-related genes than the other proteins and enhanced Imatinib-induced apoptosis of K562 cells. Expression of FOXO3a, a novel C/EBPα-regulated gene, was required for apoptosis but not for differentiation induction or proliferation inhibition of K562 cells.

Upregulation of Id1 by Epstein-Barr virus-encoded LMP1 confers resistance to TGFbeta-mediated growth inhibition

Background

Epstein-Barr virus (EBV)-encoded LMP1 protein is commonly expressed in nasopharyngeal carcinoma (NPC). LMP1 is a prime candidate for driving tumourigenesis given its ability to activate multiple signalling pathways and to alter the expression and activity of variety of downstream targets. Resistance to TGFβ-mediated cytostasis is one of the growth transforming effects of LMP1. Of the downstream targets manipulated by LMP1, the induction of Id1 and inactivation of Foxo3a appear particularly relevant to LMP1-mediated effects. Id1, a HLH protein is implicated in cell transformation and plays a role in cell proliferation, whilst Foxo3a, a transcription factor controls cell integrity and homeostasis by regulating apoptosis. The mechanism(s) by which LMP1 induces these effects have not been fully characterised.

Results

In this study, we demonstrate that the ability of LMP1 to induce the phosphorylation and inactivation of Foxo3a is linked to the upregulation of Id1. Furthermore, we show that the induction of Id1 is essential for the transforming function of LMP1 as over-expression of Id1 increases cell proliferation, attenuates TGFβ-SMAD-mediated transcription and renders cells refractory to TGFβ-mediated cytostasis. Id1 silencing in LMP1-expressing epithelial cells abolishes the inhibitory effect of LMP1 on TGFβ-mediated cell growth arrest and reduces the ability of LMP1 to attenuate SMAD transcriptional activity. In response to TGFβ stimulation, LMP1 does not abolish SMAD phosphorylation but inhibits p21 protein expression. In addition, we found the induction of Id1 in LMP1-expressing cells upon stimulation by TGFβ. We provide evidence that LMP1 suppresses the transcriptional repressor ATF3, possibly leading to the TGFβ-induced Id1 upregulation.

Conclusion

The current data provide novel information regarding the mechanisms by which LMP1 suppresses TGFβ-induced cytostasis, highlighting the importance of Id1 in LMP1 mediated cell transformation

FoxOs cooperatively regulate diverse pathways governing neural stem cell homeostasis

The PI3K-AKT-FoxO pathway is integral to lifespan regulation in lower organisms and essential for the stability of long-lived cells in mammals. Here, we report the impact of combined FoxO1, 3, and 4 deficiencies on mammalian brain physiology with a particular emphasis on the study of the neural stem/progenitor cell (NSC) pool. We show that the FoxO family plays a prominent role in NSC proliferation and renewal. FoxO-deficient mice show initial increased brain size and proliferation of neural progenitor cells during early postnatal life, followed by precocious significant decline in the NSC pool and accompanying neurogenesis in adult brains. Mechanistically, integrated transcriptomic, promoter, and functional analyses of FoxO-deficient NSC cultures identified direct gene targets with known links to the regulation of human brain size and the control of cellular proliferation, differentiation, and oxidative defense. Thus, the FoxO family coordinately regulates diverse genes and pathways to govern key aspects of NSC homeostasis in the mammalian brain.

Caspases and p53 modulate FOXO3A/Id1 signaling during mouse neural stem cell differentiation

Neural stem cells (NSCs) differentiate into neurons and glia, and a large percentage undergoes apoptosis. The engagement and activity of apoptotic pathways may favor either cell death or differentiation. In addition, Akt represses differentiation by up-regulating the inhibitor of differentiation 1 (Id1), through phosphorylation of its repressor FOXO3A. The aim of this study was to investigate the potential cross-talk between apoptosis and proliferation during mouse NSC differentiation. We determined the time of neurogenesis and gliogenesis using neuronal beta-III tubulin and astroglial GFAP to confirm that both processes occurred at approximately 3 and 8 days, respectively. p-Akt, p-FOXO3A, and Id1 were significantly reduced throughout differentiation. Caspase-3 processing, p53 phosphorylation, and p53 transcriptional activation increased at 3 days of differentiation, with no evidence of apoptosis. Importantly, in cells exposed to the pancaspase inhibitor z-VAD.fmk, p-FOXO3A and Id1 were no longer down-regulated, p53 phosphorylation and transcriptional activation were reduced, while neurogenesis and gliogenesis were significantly delayed. The effect of siRNA-mediated silencing of p53 on FOXO3A/Id1 was similar to that of z-VAD.fmk only at 3 days of differentiation. Interestingly, caspase inhibition further increased the effect of p53 knockdown during neurogenesis. In conclusion, apoptosis-associated factors such as caspases and p53 temporally modulate FOXO3A/Id1 signaling and differentiation of mouse NSCs.

Differential regulation of E-cadherin and alpha-smooth muscle actin by BMP 7 in human renal proximal tubule epithelial cells and its implication in renal fibrosis

Chronic kidney diseases are characterized by progressive tubulointerstitial fibrosis, and TGFbeta1 plays a crucial role in its development. Bone morphogenic protein 7 (BMP 7), another member of the TGF superfamily, antagonized the profibrotic effects of TGFbeta1, including epithelial mesenchymal transition and E-cadherin loss, in the previous studies from animal models. We investigated the effect of BMP 7 on TGFbeta1-mediated E-cadherin loss in two different transformed human adult proximal tubule epithelia. We found that BMP 7 not only failed to prevent TGFbeta1-mediated E-cadherin loss but itself downregulated E-cadherin levels and that it had an additive effect with TGFbeta1 in inducing E-cadherin loss. The downregulation of E-cadherin by BMP 7 was mediated through the Smad1/5 pathway. BMP 7-mediated E-cadherin loss was not followed by de novo alpha-smooth muscle actin (alpha-SMA) expression (a marker of myofibroblastic phenotype), which was due to the concurrent induction of Inhibitor of DNA binding 1 (Id1, a basic helix loop helix class transcriptional regulator) through a non-Smad pathway. Concurrent treatment of BMP 7 and TGFbeta1 prevented TGFbeta1-mediated alpha-SMA induction. In summary, our results suggest that E-cadherin loss, the key feature of epithelial mesenchymal transition, will not necessarily be followed by total phenotype change; rather, cells may undergo some loss of phenotypic marker in a ligand-dependent manner and participate in reparative processes. The inhibition of de novo expression of alpha-SMA could explain the antifibrotic effect of BMP 7. Id1 might play a crucial role in maintaining proximal tubule epithelial cell phenotype and its signaling regulation could be a potential therapeutic target.

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.

A new fork for clinical application: targeting forkhead transcription factors in cancer

Forkhead O transcription factors (FOXO) play a pivotal role in the regulation of a myriad of cellular functions including cell cycle arrest, cell death, and protection from stress stimuli. Activation of cell survival pathways such as phosphoinositide-3-kinase/AKT/IKK or RAS/mitogen-activated protein kinase are known to phosphorylate FOXOs at different sites which cause FOXOs nuclear exclusion and degradation, resulting in the suppression of FOXO's transcriptional activity. Perturbation of FOXO's function leads to deregulated cell proliferation and accumulation of DNA damage, resulting in diseases such as cancer. Emerging evidence shows that active FOXO proteins are crucial for keeping cells in check; and inactivation of FOXO proteins is associated with tumorigenesis, including breast cancer, prostate cancer, glioblastoma, rhabdomyosarcoma, and leukemia. Moreover, clinically used drugs like paclitaxel, imatinib, and doxorubicin have been shown to achieve their therapeutic effects through activation of FOXO3a and FOXO3a targets. In this review, we will focus the novel functions of FOXOs revealed in recent studies and further highlight FOXOs as new therapeutic targets in a broad spectrum of cancers.

Regulation of B-cell proliferation and differentiation by pre-B-cell receptor signalling

The pre-B-cell receptor (pre-BCR) is expressed following the productive recombination of the immunoglobulin heavy chain gene. Signals through the pre-BCR are required for initiating diverse processes in pre-B cells, including proliferation and recombination of the light chain gene, which eventually lead to the differentiation of pre-B cells to immature B cells. However, the molecular mechanisms by which the pre-BCR promotes these processes remain largely unresolved. Recent findings suggest that forkhead box O (FOXO) transcription factors connect pre-BCR signalling to the activation of the recombination machinery. In this Review, we discuss how FOXO transcription factors are regulated by the pre-BCR to allow the progression of the cell cycle and the recombination of the light chain gene.