FOXO3a represses VEGF expression through FOXM1-dependent and -independent mechanisms in breast cancer

Forkhead box K2 modulates epirubicin and paclitaxel sensitivity through FOXO3a in breast cancer

The forkhead transcription factor FOXK2 has recently been implicated in cancer cell proliferation and survival, but a role in cancer chemotherapeutic drug resistance has hitherto not been explored. Here we demonstrate that FOXK2 has a central role in mediating the cytotoxic drug response in breast cancer. Clonogenic and cell viability assays showed that enhanced FOXK2 expression sensitizes MCF-7 breast cancer cells to paclitaxel or epirubicin treatment, whereas FOXK2 depletion by small interfering RNAs (siRNAs) confers drug resistance. Our data also showed that the activation of the tumour suppressor FOXO3a by paclitaxel and epirubicin is mediated through the induction of FOXK2, as depletion of FOXK2 by siRNA limits the induction of FOXO3a by these drugs in MCF-7 cells. Chromatin immunoprecipitation (ChIP) analysis showed that in response to drug treatment, FOXK2 accumulates and binds to the proximal FOXO3a promoter region in MCF-7 cells. Furthermore, we also uncovered that FOXK2 is deregulated and, therefore, can express at high levels in the nucleus of both the paclitaxel and epirubicin drug-resistant MCF-7 cells. Our results showed that ectopically overexpressed FOXK2 accumulates in the nuclei of drug-resistant MCF-7 cells but failed to be recruited to target genes, including FOXO3a. Crucially, we found that FOXO3a is required for the anti-proliferative and epirubicin-induced cytotoxic function of FOXK2 in MCF-7 cells by sulphorhodamine and clonogenic assays. The physiological importance of the regulation of FOXO3a by FOXK2 is further confirmed by the significant correlations between FOXO3a and FOXK2 expression in breast carcinoma patient samples. Further survival analysis also reveals that high nuclear FOXK2 expression significantly associates with poorer clinical outcome, particularly in patients who have received conventional chemotherapy, consistent with our finding that FOXK2 is deregulated in drug-resistant cells. In summary, our results suggest that paclitaxel and epirubicin target the FOXK2 to modulate their cytotoxicity and deregulated FOXK2 confers drug resistance.

FOXO3a mediates the cytotoxic effects of cisplatin in lung cancer cells

Cisplatin is one of the major chemotherapeutic agents used against different human cancers. A better understanding of the downstream cellular targets of cisplatin will provide information on its mechanism of action. FOXO3a is a member of the FOXO transcription factor family, which modulates the expression of genes involved in cell cycle arrest, apoptosis, and other cellular processes. In this study, we have investigated the effects of cisplatin in a panel of lung cancer cell lines. The results showed that cisplatin inhibited the proliferation of these lung cancer cell lines by inhibiting the PI3K/AKT pathway, with evidence of decreasing phosphorylation of PI3K and AKT under cisplatin treatment, and constitutively activating AKT1 could reduce cisplatin-induced cell apoptosis. More importantly, cisplatin significantly inhibited FOXO3a phosphorylation (at Thr32, AKT phosphorylation site) and induced FOXO3a nuclear accumulation, which in turn increased the expression of FOXO3a-dependent apoptotic protein Bim. Knockdown of FOXO3a expression using small interfering RNA attenuated cisplatin-induced apoptosis. Furthermore, activation of FOXO3a induced cell apoptosis irrespective of p53 status, whereas p53 may act as FOXO3a downstream molecules involved in cisplatin-induced cell apoptosis. Together, our findings suggested that FOXO3a is a relevant mediator of the cytotoxic effects of cisplatin in lung cancer cells.

HDAC2 selectively regulates FOXO3a-mediated gene transcription during oxidative stress-induced neuronal cell death

All neurodegenerative diseases are associated with oxidative stress-induced neuronal death. Forkhead box O3a (FOXO3a) is a key transcription factor involved in neuronal apoptosis. However, how FOXO3a forms complexes and functions in oxidative stress processing remains largely unknown. In the present study, we show that histone deacetylase 2 (HDAC2) forms a physical complex with FOXO3a, which plays an important role in FOXO3a-dependent gene transcription and oxidative stress-induced mouse cerebellar granule neuron (CGN) apoptosis. Interestingly, we also found that HDAC2 became selectively enriched in the promoter region of the p21 gene, but not those of other target genes, and inhibited FOXO3a-mediated p21 transcription. Furthermore, we found that oxidative stress reduced the interaction between FOXO3a and HDAC2, leading to an increased histone H4K16 acetylation level in the p21 promoter region and upregulated p21 expression in a manner independent of p53 or E2F1. Phosphorylation of HDAC2 at Ser 394 is important for the HDAC2-FOXO3a interaction, and we found that cerebral ischemia/reperfusion reduced phosphorylation of HDAC2 at Ser 394 and mitigated the HDAC2-FOXO3a interaction in mouse brain tissue. Our study reveals the novel regulation of FOXO3a-mediated selective gene transcription via epigenetic modification in the process of oxidative stress-induced cell death, which could be exploited therapeutically.

Identification of FOXM1 as a therapeutic target in B-cell lineage acute lymphoblastic leukaemia

Despite recent advances in the cure rate of acute lymphoblastic leukaemia (ALL), the prognosis for patients with relapsed ALL remains poor. Here we identify FOXM1 as a candidate responsible for an aggressive clinical course. We show that FOXM1 levels peak at the pre-B-cell receptor checkpoint but are dispensable for normal B-cell development. Compared with normal B-cell populations, FOXM1 levels are 2- to 60-fold higher in ALL cells and are predictive of poor outcome in ALL patients. FOXM1 is negatively regulated by FOXO3A, supports cell survival, drug resistance, colony formation and proliferation in vitro, and promotes leukemogenesis in vivo. Two complementary approaches of pharmacological FOXM1 inhibition-(i) FOXM1 transcriptional inactivation using the thiazole antibiotic thiostrepton and (ii) an FOXM1 inhibiting ARF-derived peptide-recapitulate the findings of genetic FOXM1 deletion. Taken together, our data identify FOXM1 as a novel therapeutic target, and demonstrate feasibility of FOXM1 inhibition in ALL.

The DEAD box protein p68: a crucial regulator of AKT/FOXO3a signaling axis in oncogenesis

Increased abundance of proto-oncogene AKT and reduced expression of tumor suppressor Forkhead box O3 (FOXO3a), the downstream target of AKT, is frequent in carcinogenesis. Mechanistic insights of AKT gene regulation are limited. DEAD box RNA helicase p68 is overexpressed in various cancers and acts as a transcriptional co-activator of several transcription factors, including β-catenin. Here, we report a novel mechanism of p68-mediated transcriptional activation of AKT, and its ensuing effect on FOXO3a, in colon carcinogenesis. Interestingly, we found that the expression of p68 and AKT exhibits strong positive correlation in normal and colon carcinoma patient samples. In addition, p68 increased both AKT messenger RNA (mRNA) and protein, enhanced AKT promoter activity in multiple colon cancer cell lines. Conversely, p68 knockdown led to reduced AKT mRNA and protein, diminished AKT promoter activity. Here, we demonstrated that p68 occupies AKT promoter with β-catenin as well as nuclear factor-κB (NF-κB)and cooperates with these in potentiating AKT transcription. Furthermore, p68 and FOXO3a expression followed inverse correlation in the same set of colon carcinoma samples. We observed that p68 significantly reduced FOXO3a protein level in an AKT-dependent manner. Studies in primary tumors and metastatic lung nodules generated in mice colorectal allograft model, using syngeneic cells stably expressing p68, corroborated our in vitro findings. Hence, a new mechanism of oncogenesis is attributed to p68 by upregulation of AKT and consequent nuclear exclusion and degradation of tumor suppressor FOXO3a.

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

Background

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

Methods

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

Results

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

Discussion

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

FoxM1 influences embryo implantation and is regulated by 17 beta-estradiol and progesterone in mouse uteri and endometrium cells

To be a successful implantation, endometrial receptivity should be established. Forkhead box M1 (FoxM1) is described as a major oncogenic transcription factor in tumor initiation, promotion, and progression. FoxM1 regulates the expression of lots of targeted genes important to cell differentiation, proliferation and apoptosis; cell-cycle progression; and tumor angiogenesis, migration, invasion, and metastasis. According to these functions, we believe that FoxM1 should also play an essential role in embryo implantation. To test our hypothesis, we observed the expression and distribution of FoxM1 during the early pregnancy of mouse. Then, we used Immunohistochemistry to examine the expression of FoxM1 induced by E2 and/or P4 in the ovariectomized mouse uterus and human endometrium cells. This study further investigated whether FoxM1 was an important factor in the implantation. Our results showed that FoxM1 expressed in the mouse uterus during early pregnancy (Day 1 to 5). The expression of FoxM1 gradually increased along pregnancy process; FoxM1 expression could be increased by E2. On the contrary, FoxM1 expression could be decreased by P4 and E2 plus P4. We also detected the proliferation of human endometrium cells. We found that E2 might promote cells proliferation, while P4 and E2 plus P4 inhibited cells proliferation; Inhibiting FoxM1 could interfere the embryo implantation of mouse. Amplification or inhibiting of FoxM1 in JAR cells can increase or decrease the adhesion rate to Rl95-2 and HEC-1A cells separately. Our data indicate that FoxM1 might play an important role during the process of mouse embryo implantation.

FOXM1: A key oncofoetal transcription factor in health and disease

Forkhead Box M1 (FOXM1) is a bona fide oncofoetal transcription factor, which orchestrates complex temporal and spatial gene expression throughout embryonic and foetal development as well as during adult tissue homeostasis and repair. Controlled FOXM1 expression and activity provides a balanced transcriptional programme to ensure proper growth and maturation during embryogenesis and foetal development as well as to manage appropriate homeostasis and repair of adult tissues. Conversely, deregulated FOXM1 upregulation likely affects cell migration, invasion, angiogenesis, stem cell renewal, DNA damage repair and cellular senescence, which impact tumour initiation, progression, metastasis, angiogenesis and drug resistance. A thorough understanding of the regulation and role of FOXM1 in health and in cancer should contribute to the development of better diagnostics and treatments for cancer as well as congenital disorders and other developmental diseases.

Effect of high-intensity exercise on aged mouse brain mitochondria, neurogenesis, and inflammation

In aged mice, we assessed how intensive exercise affects brain bioenergetics, inflammation, and neurogenesis-relevant parameters. After 8 weeks of a supra-lactate threshold treadmill exercise intervention, 21-month-old C57BL/6 mice showed increased brain peroxisome proliferator-activated receptor gamma coactivator-1α protein, mammalian target of rapamycin and phospho-mammalian target of rapamycin protein, citrate synthase messenger RNA, and mitochondrial DNA copy number. Hippocampal vascular endothelial growth factor A (VEGF-A) gene expression trended higher, and a positive correlation between VEGF-A and PRC messenger RNA levels was observed. Brain doublecortin, brain-derived neurotrophic factor, tumor necrosis factor-α, and CCL11 gene expression, as well as plasma CCL11 protein levels, were unchanged. Despite these apparent negative findings, a negative correlation between plasma CCL11 protein levels and hippocampal doublecortin gene expression was observed; further analysis indicated exercise may mitigate this relationship. Overall, our data suggest supra-lactate threshold exercise activates a partial mitochondrial biogenesis in aged mice, and a gene (VEGF-A) known to support neurogenesis. Our data are consistent with another study that found systemic inflammation in general, and CCL11 protein specifically, suppresses hippocampal neurogenesis. Our study supports the view that intense exercise above the lactate threshold may benefit the aging brain; future studies to address the extent to which exercise-generated lactate mediates the observed effects are warranted.

Genetics of breast cancer bone metastasis: a sequential multistep pattern

Bone metastasis accounts for the vast majority of breast cancer (BC) metastases, and is related to a high rate of morbidity and mortality. A number of seminal studies have uncovered gene expression signatures involved in BC development and bone metastasis; each of them points at a distinct step of the 'invasion-metastasis cascade'. In this review, we provide most recently discovered functions of sets of genes that are selected from widely accepted gene signatures that are implicate in BC progression and bone metastasis. We propose a possible sequential pattern of gene expression that may lead a benign primary breast tumor to get aggressiveness and progress toward bone metastasis. A panel of genes which primarily deal with features like DNA replication, survival, proliferation, then, angiogenesis, migration, and invasion has been identified. TGF-β, FGF, NFκB, WNT, PI3K, and JAK-STAT signaling pathways, as the key pathways involved in breast cancer development and metastasis, are evidently regulated by several genes in all three signatures. Epithelial to mesenchymal transition that is also an important mechanism in cancer stem cell generation and metastasis is evidently regulated by these genes. This review provides a comprehensive insight regarding breast cancer bone metastasis that may lead to a better understanding of the disease and take step toward better treatments.

FOXM1 and its oncogenic signaling in pancreatic cancer pathogenesis

Pancreatic cancer is a devastating disease with an overall 5-year survival rate less than 5%. Multiple signaling pathways are implicated in the pathogenesis of pancreatic cancer, such as Wnt/β-catenin, Notch, Hedgehog, hypoxia-inducible factor, signal transducer and activator of transcription, specificity proteins/Krüppel-like factors, and Forkhead box (FOX). Recently, increasing evidence has demonstrated that the transcription factor FOXM1 plays important roles in the initiation, progression, and metastasis of a variety of human tumors, including pancreatic cancer. In this review, we focus on the current understanding of the molecular pathogenesis of pancreatic cancer with a special focus on the function and regulation of FOXM1 and rationale for FOXM1 as a novel molecular target for pancreatic cancer prevention and treatment.

Twist1 promotes gastric cancer cell proliferation through up-regulation of FoxM1

Twist-related protein 1 (Twist1), also known as class A basic helix-loop-helix protein 38 (bHLHa38), has been implicated in cell lineage determination and differentiation. Previous studies demonstrate that Twist1 expression is up-regulated in gastric cancer with poor clinical outcomes. Besides, Twist1 is suggested to be involved in progression of human gastric cancer. However, its biological functions remain largely unexplored. In the present study, we show that Twist 1 overexpression leads to a significant up-regulation of FoxM1, which plays a key role in cell cycle progression in gastric cancer cells. In contrast, knockdown of Twist 1 reduces FoxM1 expression, suggesting that FoxM1 might be a direct transcriptional target of Twist 1. At the molecular level, we further reveal that Twist 1 could bind to the promoter region of FoxM1, and subsequently recruit p300 to induce FoxM1 mRNA transcription. Therefore, our results uncover a previous unknown Twist 1/FoxM1 regulatory pathway, which may help to understand the mechanisms of gastric cancer proliferation.

The transcription factor FOXM1 (Forkhead box M1): proliferation-specific expression, transcription factor function, target genes, mouse models, and normal biological roles

FOXM1 (Forkhead box M1) is a typical proliferation-associated transcription factor, which stimulates cell proliferation and exhibits a proliferation-specific expression pattern. Accordingly, both the expression and the transcriptional activity of FOXM1 are increased by proliferation signals, but decreased by antiproliferation signals, including the positive and negative regulation by protooncoproteins or tumor suppressors, respectively. FOXM1 stimulates cell cycle progression by promoting the entry into S-phase and M-phase. Moreover, FOXM1 is required for proper execution of mitosis. Accordingly, FOXM1 regulates the expression of genes, whose products control G1/S-transition, S-phase progression, G2/M-transition, and M-phase progression. Additionally, FOXM1 target genes encode proteins with functions in the execution of DNA replication and mitosis. FOXM1 is a transcriptional activator with a forkhead domain as DNA binding domain and with a very strong acidic transactivation domain. However, wild-type FOXM1 is (almost) inactive because the transactivation domain is repressed by three inhibitory domains. Inactive FOXM1 can be converted into a very potent transactivator by activating signals, which release the transactivation domain from its inhibition by the inhibitory domains. FOXM1 is essential for embryonic development and the foxm1 knockout is embryonically lethal. In adults, FOXM1 is important for tissue repair after injury. FOXM1 prevents premature senescence and interferes with contact inhibition. FOXM1 plays a role for maintenance of stem cell pluripotency and for self-renewal capacity of stem cells. The functions of FOXM1 in prevention of polyploidy and aneuploidy and in homologous recombination repair of DNA-double-strand breaks suggest an importance of FOXM1 for the maintenance of genomic stability and chromosomal integrity.

The Forkhead Box M1 protein regulates BRIP1 expression and DNA damage repair in epirubicin treatment

FOXM1 is implicated in genotoxic drug resistance but its role and mechanism of action remain unclear. Here, we establish that γH2AX foci, indicative of DNA double-strand breaks (DSBs), accumulate in a time-dependent manner in the drug-sensitive MCF-7 cells but not in the resistant counterparts in response to epirubicin. We find that FOXM1 expression is associated with epirubicin sensitivity and DSB repair. Ectopic expression of FOXM1 can increase cell viability and abrogate DSBs sustained by MCF-7 cells following epirubicin, owing to an enhancement in repair efficiency. Conversely, alkaline comet and γH2AX foci formation assays show that Foxm1-null cells are hypersensitive to DNA damage, epirubicin and γ-irradiation. Furthermore, we find that FOXM1 is required for DNA repair by homologous recombination (HR) but not non-homologous end joining (NHEJ), using HeLa cell lines harbouring an integrated direct repeat green fluorescent protein reporter for DSB repair. We also identify BRIP1 as a direct transcription target of FOXM1 by promoter analysis and chromatin-immunoprecipitation assay. In agreement, depletion of FOXM1 expression by small interfering RNA downregulates BRIP1 expression at the protein and mRNA levels in MCF-7 and the epirubicin-resistant MCF-7 Epi(R) cells. Remarkably, the requirement for FOXM1 for DSB repair can be circumvented by reintroduction of BRIP1, suggesting that BRIP1 is an important target of FOXM1 in DSB repair. Indeed, like FOXM1, BRIP1 is needed for HR. These data suggest that FOXM1 regulates BRIP1 expression to modulate epirubicin-induced DNA damage repair and drug resistance.

Forkhead box proteins: tuning forks for transcriptional harmony

Forkhead box (FOX) proteins are multifaceted transcription factors that are responsible for fine-tuning the spatial and temporal expression of a broad range of genes both during development and in adult tissues. This function is engrained in their ability to integrate a multitude of cellular and environmental signals and to act with remarkable fidelity. Several key members of the FOXA, FOXC, FOXM, FOXO and FOXP subfamilies are strongly implicated in cancer, driving initiation, maintenance, progression and drug resistance. The functional complexities of FOX proteins are coming to light and have established these transcription factors as possible therapeutic targets and putative biomarkers for specific cancers.

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.

Activation of protein kinase CK2 attenuates FOXO3a functioning in a PML-dependent manner: implications in human prostate cancer

Protein kinase CK2 (also known as Caseine Kinase II) is an ubiquitous Ser/Thr protein kinase present in both the nucleus and cytoplasm of cells, targeting several key enzymes, growth factor receptors, transcription factors and cytoskeletal proteins. It is not only a key player in regulating cellular growth and proliferation, but also behaves as a potent suppressor of apoptosis. CK2 has been frequently found to be deregulated (mostly hyperactivated) in all cancers, prostate cancer being prominent of them. In the recent past, tumor suppressor PML (promyelocytic leukemia) has been shown to be a target of phosphorylation by CK2. This phosphorylation promotes the ubiquitin-mediated proteasomal degradation of PML thereby effectively curbing its role as a tumor suppressor. Among many others, PML has also been established to mediate its tumor suppressive role by mitigating the inactivation of active AKT (pAKT) inside the nucleus by assembling a dephosphorylating platform for nuclear pAKT. One of the immediate consequences, of this inactivation is the stabilization of FOXO3a, another well-established tumor suppressor, inside the nucleus and its downstream activities. Here, we propose a novel signaling axis apexed by deregulated CK2, dismantling the association of PML and PHLPP2 (we also report PHLPP2 to be a novel interacting partner of PML inside the nucleus), ultimately leading to the inactivation and nuclear exclusion of FOXO3a, thereby downregulating p21/p27/Bim in which degradation of PML and the concomitant stabilization of pAKT plays a cardinal part.

FOX(M1) news--it is cancer

FOXM1 is an oncogenic transcription factor of the Forkhead family and it has a well-defined role in cell proliferation and cell-cycle progression. Expression of FOXM1 is excluded in quiescent or differentiated cells, but its level is highly elevated in proliferating and malignant cells. Overexpression of FOXM1 has been reported in more than 20 types of human cancer. In recent years, FOXM1 has been implicated in diverse cellular processes and also a growing body of experimental data has underlined the relevance of FOXM1 in tumorigenesis. Although FOXM1 is under the control of three major tumor suppressors (RB, p53, and p19(ARF)), it is still active in the majority of human cancers. The oncogenic potential of FOXM1 is mainly based on its ability to transcriptionally activate genes that are involved in different facets of cancer development. In this review, the contribution of FOXM1 to each of the hallmarks of cancer will be summarized and discussed.

FOXM1 (Forkhead box M1) in tumorigenesis: overexpression in human cancer, implication in tumorigenesis, oncogenic functions, tumor-suppressive properties, and target of anticancer therapy

FOXM1 (Forkhead box M1) is a typical proliferation-associated transcription factor and is also intimately involved in tumorigenesis. FOXM1 stimulates cell proliferation and cell cycle progression by promoting the entry into S-phase and M-phase. Additionally, FOXM1 is required for proper execution of mitosis. In accordance with its role in stimulation of cell proliferation, FOXM1 exhibits a proliferation-specific expression pattern and its expression is regulated by proliferation and anti-proliferation signals as well as by proto-oncoproteins and tumor suppressors. Since these factors are often mutated, overexpressed, or lost in human cancer, the normal control of the foxm1 expression by them provides the basis for deregulated FOXM1 expression in tumors. Accordingly, FOXM1 is overexpressed in many types of human cancer. FOXM1 is intimately involved in tumorigenesis, because it contributes to oncogenic transformation and participates in tumor initiation, growth, and progression, including positive effects on angiogenesis, migration, invasion, epithelial-mesenchymal transition, metastasis, recruitment of tumor-associated macrophages, tumor-associated lung inflammation, self-renewal capacity of cancer cells, prevention of premature cellular senescence, and chemotherapeutic drug resistance. However, in the context of urethane-induced lung tumorigenesis, FOXM1 has an unexpected tumor suppressor role in endothelial cells because it limits pulmonary inflammation and canonical Wnt signaling in epithelial lung cells, thereby restricting carcinogenesis. Accordingly, FOXM1 plays a role in homologous recombination repair of DNA double-strand breaks and maintenance of genomic stability, that is, prevention of polyploidy and aneuploidy. The implication of FOXM1 in tumorigenesis makes it an attractive target for anticancer therapy, and several antitumor drugs have been reported to decrease FOXM1 expression.

Trastuzumab-resistant cells rely on a HER2-PI3K-FoxO-survivin axis and are sensitive to PI3K inhibitors

The antibody trastuzumab is approved for treatment of patients with HER2 (ERBB2)-overexpressing breast cancer. A significant fraction of these tumors are either intrinsically resistant or acquire resistance rendering the drug ineffective. The development of resistance has been attributed to failure of the antibody to inhibit phosphoinositide 3-kinase (PI3K), which is activated by the HER2 network. Herein, we examined the effects of PI3K blockade in trastuzumab-resistant breast cancer cell lines. Treatment with the pan-PI3K inhibitor XL147 and trastuzumab reduced proliferation and pAKT levels, triggering apoptosis of trastuzumab-resistant cells. Compared with XL147 alone, the combination exhibited a superior antitumor effect against trastuzumab-resistant tumor xenografts. Furthermore, treatment with XL147 and trastuzumab reduced the cancer stem-cell (CSC) fraction within trastuzumab-resistant cells both in vitro and in vivo. These effects were associated with FoxO-mediated inhibition of transcription of the antiapoptosis gene survivin (BIRC5) and the CSC-associated cytokine interleukin-8. RNA interference-mediated or pharmacologic inhibition of survivin restored sensitivity to trastuzumab in resistant cells. In a cohort of patients with HER2-overexpressing breast cancer treated with trastuzumab, higher pretreatment tumor levels of survivin RNA correlated with poor response to therapy. Together, our results suggest that survivin blockade is required for therapeutic responses to trastuzumab and that by combining trastuzumab and PI3K inhibitors, CSCs can be reduced within HER2(+) tumors, potentially preventing acquired resistance to anti-HER2 therapy.

FoxO1 and FoxM1 transcription factors have antagonistic functions in neonatal cardiomyocyte cell-cycle withdrawal and IGF1 gene regulation

RATIONALE

In the mammalian heart, cardiomyocytes withdraw from the cell cycle and initiate hypertrophic growth soon after birth, but the transcriptional regulatory mechanisms that control these neonatal transitions are not well-defined.

OBJECTIVE

Forkhead family transcription factors have been implicated as positive (forkhead box [Fox] transcription factor M1) and negative (FoxO1 and FoxO3) regulators of cardiomyocyte proliferation prenatally, but their regulatory interactions and functions in neonatal cell-cycle withdrawal have not been reported previously. Potential regulators of Fox activity, including the metabolic indicator AMP-activated protein kinase (AMPK), and Fox transcriptional targets (p21, p27, insulin-like growth factor 1 [IGF1]) also were examined.

METHODS AND RESULTS

In cultured neonatal rat cardiomyocytes, AMPK activates FoxOs, and AMPK inhibition is sufficient to induce cell proliferation. In vivo, combined loss of FoxO1 and FoxO3 specifically in cardiomyocytes leads to delayed cell-cycle withdrawal and increased expression of IGF1 and FoxM1. Conversely, cardiomyocyte-specific loss of FoxM1 results in decreased neonatal cardiomyocyte cell proliferation, decreased expression of IGF1, and increased expression of cell-cycle inhibitors p21 and p27. IGF1 is a direct downstream target of cardiac Fox transcription factors, which is negatively regulated by FoxOs and positively regulated by FoxM1, dependent on AMPK activation status.

CONCLUSIONS

These data support a regulatory mechanism whereby the balance of FoxO and FoxM1 transcription factors integrates metabolic status, mediated by AMPK, and cell-cycle regulation, through competitive regulation of target genes, including IGF1, in neonatal cardiomyocytes.

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.

Targeting FOXM1 in cancer

Oncogenic transcription factor FOXM1 is overexpressed in the majority of human cancers. In addition, FOXM1 has been implicated in cell migration, invasion, angiogenesis and metastasis. The important role of FOXM1 in cancer affirms its significance for therapeutic intervention. Current data suggest that targeting FOXM1 in mono- or combination therapy may have promising therapeutic benefits for the treatment of cancer. However, challenges with the delivery of anti-FOXM1 siRNA to tumors and the absence of small molecules, which specifically inhibit FOXM1, are delaying the development of FOXM1 inhibitors as feasible anticancer drugs. In this review, we describe and summarize the efforts that have been made to target FOXM1 in cancer and the consequences of FOXM1 suppression in human cancer cells.

Tumour promoting and suppressing roles of the atypical MAP kinase signalling pathway ERK3/4-MK5

Perturbed action of signal transduction pathways, including the mitogen-activated protein (MAP) kinase pathways, is one of the hallmarks of many cancers. While the implication of the typical MAP kinase pathways ERK1/2-MEK1/2, p38MAPK and JNK is well established, recent findings illustrate that the atypical MAP kinase ERK3/4-MK5 may also be involved in tumorigenic processes. Remarkably, the ERK3/4-MK5 pathway seems to possess anti-oncogenic as well as pro-oncogenic properties in cell culture and aninal models. This review summarizes the mutations in the genes encoding ERK3, ERK4 and MK5 that have been detected in different cancers, reports aberrant expression levels of these proteins in human tumours, and discusses the mechanisms by which this pathway can induce senescence, stimulate angiogenesis and invasiveness.

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.