Y box-binding protein 1 induces resistance to oncogenic transformation by the phosphatidylinositol 3-kinase pathway

Y-Box Binding Protein 1: Unraveling the Multifaceted Role in Cancer Development and Therapeutic Potential

Y-box binding protein 1 (YBX1), a member of the Cold Shock Domain protein family, is overexpressed in various human cancers and is recognized as an oncogenic gene associated with poor prognosis. YBX1's functional diversity arises from its capacity to interact with a broad range of DNA and RNA molecules, implicating its involvement in diverse cellular processes. Independent investigations have unveiled specific facets of YBX1's contribution to cancer development. This comprehensive review elucidates YBX1's multifaceted role in cancer across cancer hallmarks, both in cancer cell itself and the tumor microenvironment. Based on this, we proposed YBX1 as a potential target for cancer treatment. Notably, ongoing clinical trials addressing YBX1 as a target in breast cancer and lung cancer have showcased its promise for cancer therapy. The ramp up in in vitro research on targeting YBX1 compounds also underscores its growing appeal. Moreover, the emerging role of YBX1 as a neural input is also proposed where the high level of YBX1 was strongly associated with nerve cancer and neurodegenerative diseases. This review also summarized the up-to-date advanced research on the involvement of YBX1 in pancreatic cancer.

YB-1 Is a Novel Target for the Inhibition of α-Adrenergic-Induced Hypertrophy

Cardiac hypertrophy resulting from sympathetic nervous system activation triggers the development of heart failure. The transcription factor Y-box binding protein 1 (YB-1) can interact with transcription factors involved in cardiac hypertrophy and may thereby interfere with the hypertrophy growth process. Therefore, the question arises as to whether YB-1 influences cardiomyocyte hypertrophy and might thereby influence the development of heart failure. YB-1 expression is downregulated in human heart biopsies of patients with ischemic cardiomyopathy (n = 8), leading to heart failure. To study the impact of reduced YB-1 in cardiac cells, we performed small interfering RNA (siRNA) experiments in H9C2 cells as well as in adult cardiomyocytes (CMs) of rats. The specificity of YB-1 siRNA was analyzed by a miRNA-like off-target prediction assay identifying potential genes. Testing three high-scoring genes by transfecting cardiac cells with YB-1 siRNA did not result in downregulation of these genes in contrast to YB-1, whose downregulation increased hypertrophic growth. Hypertrophic growth was mediated by PI3K under PE stimulation, as well by downregulation with YB-1 siRNA. On the other hand, overexpression of YB-1 in CMs, caused by infection with an adenovirus encoding YB-1 (AdYB-1), prevented hypertrophic growth under α-adrenergic stimulation with phenylephrine (PE), but not under stimulation with growth differentiation factor 15 (GDF15; n = 10-16). An adenovirus encoding the green fluorescent protein (AdGFP) served as the control. YB-1 overexpression enhanced the mRNA expression of the Gq inhibitor regulator of G-protein signaling 2 (RGS2) under PE stimulation (n = 6), potentially explaining its inhibitory effect on PE-induced hypertrophic growth. This study shows that YB-1 protects cardiomyocytes against PE-induced hypertrophic growth. Like in human end-stage heart failure, YB-1 downregulation may cause the heart to lose its protection against hypertrophic stimuli and progress to heart failure. Therefore, the transcription factor YB-1 is a pivotal signaling molecule, providing perspectives for therapeutic approaches.

A TLR/CD44 axis regulates T cell trafficking in experimental and human multiple sclerosis

In the pathogenesis of autoimmune disorders, the modulation of leukocytes' trafficking plays a central role, still poorly understood. Here, we focused on the effect of TLR2 ligands in trafficking of T helper cells through reshuffling of CD44 isoforms repertoire. Concurrently, strain background and TLR2 haplotype affected Wnt/β-catenin signaling pathway and expression of splicing factors. During EAE, mCD44 v9- v 10 was specifically enriched in the forebrain and showed an increased ability to bind stably to osteopontin. Similarly, we observed that hCD44 v7 was highly enriched in cells of cerebrospinal fluid from MS patients with active lesions. Moreover, TLRs engagement modulated the composition of CD44 variants also in human T helper cells, supporting the hypothesis that pathogens or commensals, through TLRs, in turn modulate the repertoire of CD44 isoforms, thereby controlling the distribution of lesions in the CNS. The interference with this mechanism(s) represents a potential tool for prevention and treatment of autoimmune relapses and exacerbations.

YB1 Is a Major Contributor to Health Disparities in Triple Negative Breast Cancer

Simple Summary

Triple negative breast cancer (TNBC) is a devastating disease that affects many women, due to the lack of FDA-approved targeted therapy. In the absence of cell surface receptors ER, PR, and Her2 that can be targeted with hormonal and antibody treatments, cytotoxic chemotherapy remains the major course of treatment, with a dismal response and rapid recurrence due to the acquisition of resistance. TNBC is also twice as more prevalent in African American (AA) when compared to Caucasian American (CA) women. This study investigated the role of the YB1 gene in the disparities in TNBC between AA and CA women. We found that YB1 is highly expressed in TNBC tumors of AA origin when compared to CAs. Increased expression levels and activity of YB1 correlates with poor disease outcomes, resistance to chemotherapy, and the activation of the cancer stem cell (CSC) phenotype, with higher levels in AA than in CA TNBC tumors. More importantly, we found that the targeted inhibition of the expression and activity of YB1 significantly inhibited the oncogenic behavior of AA tumors through sensitization to chemotherapy and inhibition of CSCs. Our study is the first to show that YB1 activity may be a major biological contributor to the health disparities in TNBC, and that development of therapies that specifically target YB1 could reduce these disparities.

Abstract

Triple negative breast cancer (TNBC) is the most aggressive amongst all breast cancer (BC) subtypes. While TNBC tumors represent less than 20% of all BC subtypes, they are responsible for the most BC-related deaths. More significantly, when considering TNBC incidence across all racial/ethnic groups, TNBC accounts for less than 20% of all BCs. However, in non-Hispanic black women, the incidence rate of TNBC is more than 40%, which may be a contributing factor to the higher BC-related death rate in this population. These disparities remain strong even after accounting for differences in socioeconomic status, healthcare access, and lifestyle factors. Increased evidence now points to biological mechanisms that are intrinsic to the tumor that contribute to disparate TNBC disease burdens. Here, we show that YB1, a multifunction gene, plays a major role in the TNBC disparities between African American (AA) and Caucasian American (CA) women. We show in three independent TNBC tumors cohorts, that YB1 is significantly highly expressed in AA TNBC tumors when compared to CAs, and that increased levels of YB1 correlate with poor survival of AA patients with TNBC. We used a combination of genetic manipulation of YB1 and chemotherapy treatment, both in vitro and in animal models of TNBC to show that YB1 oncogenic activity is more enhanced in TNBC cell lines of AA origin, by increasing their tumorigenic and aggressive behaviors, trough the activation of cancer stem cell phenotype and resistance to chemotherapeutic treatments.

The roles of Y-box-binding protein (YB)-1 and C-X-C motif chemokine ligand 14 (CXCL14) in the progression of prostate cancer via extracellular-signal-regulated kinase (ERK) signaling

The cold-shock protein Y-box-binding protein (YB)-1 regulates the expression of various chemokines and their receptors at the transcriptional level. Expression of the orphan chemokine CXCL14 is repressed by EGF induced signaling. The possible links between EGF-mediated YB-1 and CXCL14 as well as the functions of critical kinase pathways in the progression of prostate cancer have remained unexplored. Here we examined the correlation between YB-1 and CXCL14, and the ERK/AKT/mTOR pathways in prostate cancer. Knockdown of YB-1 decreased cyclinD1 expression with an upregulation of cleaved-PARP in human prostate cancer cells. EGF treatment upregulated phospho-YB-1 expression in a time-dependent manner, while treatment with an ERK inhibitor completely silenced its expression in prostate cancer cells. EGF treatment stimulates CyclinD1 and YB-1 phosphorylation in an ERK-dependent pathway. Positive and negative regulation of YB-1 and CXCL14 was observed after EGF treatment in prostate cancer cells, respectively. EGF rescues cell cycle and apoptosis via the AKT and ERK pathways. Furthermore, YB-1 silencing induces G1 arrest and apoptosis, while knockdown of CXCL14 facilitates cell growth and inhibits apoptosis in prostate cancer cells. YB-1 and CXCL14 were inversely correlated in prostate cancer cells and tissues. A significant association between poor overall survival and High YB-1 expression was observed in human prostate cancer patients. In conclusion, our data reveal the functional relationship between YB-1 and CXCL14 in EGF mediated ERK signaling, and YB-1 expression is a significant prognostic marker to predict prostate cancer.

Blocking Y-Box Binding Protein-1 through Simultaneous Targeting of PI3K and MAPK in Triple Negative Breast Cancers

Simple Summary

Triple-negative breast cancer (TNBC) is associated with the high rates of relapse and metastasis and poor survival. YB-1 is overexpressed in TNBC tumor tissues. In the present study, we demonstrated that S102 phosphorylation of YB-1 in TNBC cell lines depend on the mutation status of the components of the MAPK/ERK and PI3K/Akt pathways. Simultaneous targeting of MEK and PI3K was found to be the most effective approach to block YB-1 phosphorylation and to inhibit YB-1 dependent cell proliferation. YBX1 knockout was sufficient to block TNBC tumor growth.

Abstract

The multifunctional protein Y-box binding protein-1 (YB-1) regulates all the so far described cancer hallmarks including cell proliferation and survival. The MAPK/ERK and PI3K/Akt pathways are also the major pathways involved in cell growth, proliferation, and survival, and are the frequently hyperactivated pathways in human cancers. A gain of function mutation in KRAS mainly leads to the constitutive activation of the MAPK pathway, while the activation of the PI3K/Akt pathway occurs either through the loss of PTEN or a gain of function mutation of the catalytic subunit alpha of PI3K (PIK3CA). In this study, we investigated the underlying signaling pathway involved in YB-1 phosphorylation at serine 102 (S102) in KRAS(G13D)-mutated triple-negative breast cancer (TNBC) MDA-MB-231 cells versus PIK3CA(H1047R)/PTEN(E307K) mutated TNBC MDA-MB-453 cells. Our data demonstrate that S102 phosphorylation of YB-1 in KRAS-mutated cells is mainly dependent on the MAPK/ERK pathway, while in PIK3CA/PTEN-mutated cells, YB-1 S102 phosphorylation is entirely dependent on the PI3K/Akt pathway. Independent of the individual dominant pathway regulating YB-1 phosphorylation, dual targeting of MEK and PI3K efficiently inhibited YB-1 phosphorylation and blocked cell proliferation. This represents functional crosstalk between the two pathways. Our data obtained from the experiments, applying pharmacological inhibitors and genetic approaches, shows that YB-1 is a key player in cell proliferation, clonogenic activity, and tumor growth of TNBC cells through the MAPK and PI3K pathways. Therefore, dual inhibition of these two pathways or single targeting of YB-1 may be an effective strategy to treat TNBC.

YB-1 Knockdown Inhibits the Proliferation of Mesothelioma Cells through Multiple Mechanisms

Y-box binding protein-1 (YB-1) is a multifunctional oncoprotein that has been shown to regulate proliferation, invasion and metastasis in a variety of cancer types. We previously demonstrated that YB-1 is overexpressed in mesothelioma cells and its knockdown significantly reduces tumour cell proliferation, migration, and invasion. However, the mechanisms driving these effects are unclear. Here, we utilised an unbiased RNA-seq approach to characterise the changes to gene expression caused by loss of YB-1 knockdown in three mesothelioma cell lines (MSTO-211H, VMC23 and REN cells). Bioinformatic analysis showed that YB-1 knockdown regulated 150 common genes that were enriched for regulators of mitosis, integrins and extracellular matrix organisation. However, each cell line also displayed unique gene expression signatures, that were differentially enriched for cell death or cell cycle control. Interestingly, deregulation of STAT3 and p53-pathways were a key differential between each cell line. Using flow cytometry, apoptosis assays and single-cell time-lapse imaging, we confirmed that MSTO-211H, VMC23 and REN cells underwent either increased cell death, G1 arrest or aberrant mitotic division, respectively. In conclusion, this data indicates that YB-1 knockdown affects a core set of genes in mesothelioma cells. Loss of YB-1 causes a cascade of events that leads to reduced mesothelioma proliferation, dependent on the underlying functionality of the STAT3/p53-pathways and the genetic landscape of the cell.

Reducing Hypothalamic Stem Cell Senescence Protects against Aging-Associated Physiological Decline

Age-dependent loss of hypothalamic neural stem cells (htNSCs) is important for the pathological consequences of aging; however, it is unclear what drives the senescence of htNSCs. Here, we report that a long non-coding RNA, Hnscr, is abundantly expressed in the htNSCs of young mice but decreases markedly in middle-aged mice. We show that depletion of Hnscr is sufficient to drive the senescence of htNSCs and aging-like phenotypes in mice. Mechanistically, Hnscr binds to Y-box protein 1 (YB-1) to prevent its degradation and thus the attenuation of transcription of the senescence marker gene p16^INK4A. Through molecular docking, we discovered that a naturally occurring small compound, theaflavin 3-gallate, can mimic the activity of Hnscr. Treatment of middle-aged mice with theaflavin 3-gallate reduced the senescence of htNSCs while improving aging-associated pathology. These results point to a mediator of the aging process and one that can be pharmacologically targeted to improve aging-related outcomes.

Y-box proteins combine versatile cold shock domains and arginine-rich motifs (ARMs) for pleiotropic functions in RNA biology

Y-box proteins are single-strand DNA- and RNA-binding proteins distinguished by a conserved cold shock domain (CSD) and a variable C-terminal domain organized into alternating short modules rich in basic or acidic amino acids. A huge literature depicts Y-box proteins as highly abundant, staggeringly versatile proteins that interact with all mRNAs and function in most forms of mRNA-specific regulation. The mechanisms by which Y-box proteins recognize mRNAs are unclear, because their CSDs bind a jumble of diverse elements, and the basic modules in the C-terminal domain are considered to bind nonspecifically to phosphates in the RNA backbone. A survey of vertebrate Y-box proteins clarifies the confusing names for Y-box proteins, their domains, and RNA-binding motifs, and identifies several novel conserved sequences: first, the CSD is flanked by linkers that extend its binding surface or regulate co-operative binding of the CSD and N-terminal and C-terminal domains to proteins and RNA. Second, the basic modules in the C-terminal domain are bona fide arginine-rich motifs (ARMs), because arginine is the predominant amino acid and comprises 99% of basic residues. Third, conserved differences in AA (amino acid) sequences between isoforms probably affect RNA-binding specificity. C-terminal ARMs connect with many studies, demonstrating that ARMs avidly bind sites containing specific RNA structures. ARMs crystallize insights into the under-appreciated contributions of the C-terminal domain to site-specific binding by Y-box proteins and difficulties in identifying site-specific binding by the C-terminal domain. Validated structural biology techniques are available to elucidate the mechanisms by which YBXprot (Y-box element-binding protein) CSDs and ARMs identify targets.

Crosstalk between Akt signaling and cold shock proteins in mediating invasive cell phenotypes

Cold shock proteins are up-regulated by cellular stress and orchestrate inflammatory responses, cell proliferation, and differentiation. Enhanced cold shock protein expression promotes malignant cell transformation; up-regulation is detected in most cancers and associated with poor prognosis. Akt1, a serine/threonine kinase, is a potent oncogene, which activates pro-proliferative and anti-apoptotic signaling pathways, and phosphorylates the cold shock domain. Unexpectedly, chicken-YB-1 abrogates PI3K-Akt-dependent oncogenic cell transformation in embryonic fibroblasts. Here, we addressed the question whether chicken and human Y-box binding protein-1 (YB-1) act differently on cell transformation, and how a related protein, DNA-binding protein-A (DbpA) behaves in comparison. NIH3T3 cells were transduced with lentiviral vectors encoding for myristoylated (constitutive active) Akt1, YB-1, DbpA, or shRNA targeting YB-1 expression. Colony formation assays showed that human YB-1 acts similar to chicken on Akt-dependent cell transformation. This activity was not titratable. Given the correlation of nuclear YB-1 and upregulated DbpA expression in a series of clear cell renal cell carcinomas (n = 40) the colony formation assay was extended to include ectopic DbpA expression. DbpA alone prominently induced cell transformation, which was enhanced when constitutive active Akt1 or concomitant YB-1 expression was present. Notably, co-expression of DbpA together with YB-1 abrogated the repressive effect on Akt1 signaling observed with YB-1 alone. Macroscopically, some colonies yielded a remarkable “invasive” phenotype. Thus, cold shock proteins may convey profound anti- and pro-oncogenic effects on Akt-dependent cell transformation. DbpA is able to overcome the anti-oncogenic effects seen with combined YB-1 and Akt signaling in an in vitro model of colonial growth.

The tumor-associated YB-1 protein: new player in the circadian control of cell proliferation

Correct spatial and temporal control of cell proliferation is of fundamental importance for tissue homeostasis. Its deregulation has been associated with several pathological conditions. In common with almost every aspect of plant and animal biology, cell proliferation is dominated by day-night rhythms generated by the circadian clock. However, our understanding of the crosstalk between the core clock and cell cycle control mechanisms remains incomplete. In this study, using zebrafish as a vertebrate model system, we show that the nuclear localization of the Y-box binding protein 1 (YB-1), a regulator of cyclin expression and a hallmark of certain cancers, is robustly regulated by the circadian clock. We implicate clock-controlled changes in YB-1 SUMOylation as one of the mechanisms regulating its periodic nuclear entry at the beginning of the light phase. Furthermore, we demonstrate that YB-1 nuclear protein is able to downregulate cyclin A2 mRNA expression in zebrafish via its direct interaction with the cyclin A2 promoter. Thus, by acting as a direct target of cyclic posttranslational regulatory mechanisms, YB-1 serves as one bridge between the circadian clock and its cell cycle control.

YBX1 at the crossroads of non-coding transcriptome, exosomal, and cytoplasmic granular signaling

YBX1 (Y box binding protein 1) is an RNA-/DNA-binding multifunctional protein harboring the classical cold shock protein (CSD) domain, an A/P domain, and a long C-terminal domain with alternating positively and negatively charged amino acids. It is a well-established oncogenic transcriptional factor, and regulates apoptosis, translation, cell proliferation, mRNA splicing, repair, differentiation, and stress response. The non-coding transcriptome has added yet another layer of complexity to the YBX1-mediated master regulation of cellular functions. Interestingly, YBX1 has been shown to localize to cytoplasmic granules such as P granules and stress granules. These granules regulate the non-coding transcriptome profile as well as mRNA translation and degradation. In this review, we discuss the recent findings on YBX1 signaling as mediated by various classes of non-coding RNAs, and on the functions of YBX1 at P granules, stress granules, exosomes, and mitochondria. YBX1 is a well-established target for cancer therapy and understanding its functions at organelles and ncRNA transcriptomes will shed new insights for devising organelle based anti-cancer therapies.

Role of Y Box Protein-1 in cancer: As potential biomarker and novel therapeutic target

The Y-box binding protein (YB-1) is known to be a multifunctional transcription and translation factor during expression of several proteins. It is a vital oncoprotein that regulates cancer cell progression and proliferation. YB-1 is over-expressed in various human cancers such as breast cancer, colon cancer, lung cancer, gastric cancer, oesophageal cancer and glioblastoma. Nuclear expression of YB-1 is found to be associated with multidrug resistance and cancer cell progression. YB-1 is reported to regulate many cellular signalling pathways in different types of cancer proliferation. Knowledge about nuclear localization and nuclear level expression of YB-1 in different cancers has been correlated with prospective prognosis of cancer. This review discusses the prospects of YB-1 as a potential biomarker as well as therapeutic target in lieu of their role during cancer progression and multidrug resistance.

Etoposide enhances antitumor efficacy of MDR1-driven oncolytic adenovirus through autoupregulation of the MDR1 promoter activity

Conditionally replicating adenoviruses (CRAds), or oncolytic adenoviruses, such as E1B55K-deleted adenovirus, are attractive anticancer agents. However, the therapeutic efficacy of E1B55K-deleted adenovirus for refractory solid tumors has been limited. Environmental stress conditions may induce nuclear accumulation of YB-1, which occurs in multidrug-resistant and adenovirus-infected cancer cells. Overexpression and nuclear localization of YB-1 are associated with poor prognosis and tumor recurrence in various cancers. Nuclear YB-1 transactivates the multidrug resistance 1 (MDR1) genes through the Y-box. Here, we developed a novel E1B55K-deleted adenovirus driven by the MDR1 promoter, designed Ad5GS3. We tested the feasibility of using YB-1 to transcriptionally regulate Ad5GS3 replication in cancer cells and thereby to enhance antitumor efficacy. We evaluated synergistic antitumor effects of oncolytic virotherapy in combination with chemotherapy. Our results show that adenovirus E1A induced E2F-1 activity to augment YB-1 expression, which shut down host protein synthesis in cancer cells during adenovirus replication. In cancer cells infected with Ad5WS1, an E1B55K-deleted adenovirus driven by the E1 promoter, E1A enhanced YB-1 expression, and then further phosphorylated Akt, which, in turn, triggered nuclear translocation of YB-1. Ad5GS3 in combination with chemotherapeutic agents facilitated nuclear localization of YB-1 and, in turn, upregulated the MDR1 promoter activity and enhanced Ad5GS3 replication in cancer cells. Thus, E1A, YB-1, and the MDR1 promoter form a positive feedback loop to promote Ad5GS3 replication in cancer cells, and this regulation can be further augmented when chemotherapeutic agents are added. In the in vivo study, Ad5GS3 in combination with etoposide synergistically suppressed tumor growth and prolonged survival in NOD/SCID mice bearing human lung tumor xenografts. More importantly, Ad5GS3 exerted potent oncolytic activity against clinical advanced lung adenocarcinoma, which was associated with elevated levels of nuclear YB-1 and cytoplasmic MDR1 expression in the advanced tumors. Therefore, Ad5GS3 may have therapeutic potential for cancer treatment, especially in combination with chemotherapy. Because YB-1 is expressed in a broad spectrum of cancers, this oncolytic adenovirus may be broadly applicable.

Akt-mediated phosphorylation controls the activity of the Y-box protein MSY3 in skeletal muscle

BACKGROUND

The Y-box protein MSY3/Csda represses myogenin transcription in skeletal muscle by binding a highly conserved cis-acting DNA element located just upstream of the myogenin minimal promoter (myogHCE). It is not known how this MSY3 activity is controlled in skeletal muscle. In this study, we provide multiple lines of evidence showing that the post-translational phosphorylation of MSY3 by Akt kinase modulates the MSY3 repression of myogenin.

METHODS

Skeletal muscle and myogenic C2C12 cells were used to study the effects of MSY3 phosphorylation in vivo and in vitro on its sub-cellular localization and activity, by blocking the IGF1/PI3K/Akt pathway, by Akt depletion and over-expression, and by mutating potential MSY3 phosphorylation sites.

RESULTS

We observed that, as skeletal muscle progressed from perinatal to postnatal and adult developmental stages, MSY3 protein became gradually dephosphorylated and accumulated in the nucleus. This correlated well with the reduction of phosphorylated active Akt. In C2C12 myogenic cells, blocking the IGF1/PI3K/Akt pathway using LY294002 inhibitor reduced MSY3 phosphorylation levels resulting in its accumulation in the nuclei. Knocking down Akt expression increased the amount of dephosphorylated MSY3 and reduced myogenin expression and muscle differentiation. MSY3 phosphorylation by Akt in vitro impaired its binding at the MyogHCE element, while blocking Akt increased MSY3 binding activity. While Akt over-expression rescued myogenin expression in MSY3 overexpressing myogenic cells, ablation of the Akt substrate, (Ser126 located in the MSY3 cold shock domain) promoted MSY3 accumulation in the nucleus and abolished this rescue. Furthermore, forced expression of Akt in adult skeletal muscle induced MSY3 phosphorylation and myogenin derepression.

CONCLUSIONS

These results support the hypothesis that MSY3 phosphorylation by Akt interferes with MSY3 repression of myogenin circuit activity during muscle development. This study highlights a previously undescribed Akt-mediated signaling pathway involved in the repression of myogenin expression in myogenic cells and in mature muscle. Given the significance of myogenin regulation in adult muscle, the Akt/MSY3/myogenin regulatory circuit is a potential therapeutic target to counteract muscle degenerative disease.

YB-1 overexpression promotes a TGF-β1-induced epithelial-mesenchymal transition via Akt activation

The Y-box binding protein-1 (YB-1) is a transcription/translation regulatory protein, and the expression thereof is associated with cancer aggressiveness. In the present study, we explored the regulatory effects of YB-1 during the transforming growth factor-β1 (TGF-β1)-induced epithelial-to-mesenchymal transition (EMT) in lung adenocarcinoma cells. Downregulation of YB-1 increased E-cadherin promoter activity, and upregulation of YB-1 decreased promoter activity, suggesting that the YB-1 level may be correlated with the EMT. TGF-β1 induced YB-1 expression, and TGF-β1 translocated cytosolic YB-1 into the nucleus. YB-1 overexpression promoted TGF-β1-induced downregulation of epithelial markers, upregulation of mesenchymal markers, and cell migration. Moreover, YB-1 overexpression enhanced the expression of E-cadherin transcriptional repressors via TGF-β1-induced Akt activation. Our findings afford new insights into the role played by YB-1 in the TGF-β1 signaling pathway.

Y-box binding protein 1--a prognostic marker and target in tumour therapy

Y-box binding protein 1 (YB-1) is a multifunctional protein involved in various cellular processes including both transcriptional and translational regulation of target gene expression. Significantly increased YB-1 levels have been reported in a number of human malignancies and shown to be associated with poor prognosis and disease recurrence. Indeed, YB-1 can act as a versatile oncoprotein playing an important role in tumour cell proliferation and progression. Consequently, YB-1 not only proves to be a good prognostic tumour marker, but also may be a promising emerging molecular target for the development of new therapeutical strategies. In this review, we discuss both the role of YB-1 in cancer and specifically in malignant melanoma as well as possible translations into the clinics derived thereof.

Roles of YB-1 under arsenite-induced stress: translational activation of HSP70 mRNA and control of the number of stress granules

BACKGROUND

When cells become stressed, they form stress granules (SGs) and show an increase of the molecular chaperone HSP70. The translational regulator YB-1 is a component of SGs, but it is unclear whether it contributes to the translational induction of HSP70 mRNA. Here we examined the roles of YB-1 in SG assembly and translational regulation of HSP70 mRNA under arsenite-induced stress.

METHOD

Using arsenite-treated NG108-15 cells, we examined whether YB-1 was included in SGs with GluR2 mRNA, a target of YB-1, and investigated the interaction of YB-1 with HSP70 mRNA and its effect on translation of the mRNA. We also investigated the distribution of these mRNAs to SGs or polysomes, and evaluated the role of YB-1 in SG assembly.

RESULTS

Arsenite treatment reduced the translation level of GluR2 mRNA; concomitantly, YB-1-bound HSP70 mRNA was increased and its translation was induced. Sucrose gradient analysis revealed that the distribution of GluR2 mRNA was shifted from heavy-sedimenting to much lighter fractions, and also to SG-containing non-polysomal fractions. Conversely, HSP70 mRNA was shifted from the non-polysomal to polysome fractions. YB-1 depletion abrogated the arsenite-responsive activation of HSP70 synthesis, but SGs harboring both mRNAs were still assembled. The number of SGs was increased by YB-1 depletion and decreased by its overexpression.

CONCLUSION

In arsenite-treated cells, YB-1 mediates the translational activation of HSP70 mRNA and also controls the number of SGs through inhibition of their assembly.

GENERAL SIGNIFICANCE

Under stress conditions, YB-1 exerts simultaneous but opposing actions on the regulation of translation via SGs and polysomes.

JNK1/2 Activation by an Extract from the Roots of Morus alba L. Reduces the Viability of Multidrug-Resistant MCF-7/Dox Cells by Inhibiting YB-1-Dependent MDR1 Expression

Cancer cells acquire anticancer drug resistance during chemotherapy, which aggravates cancer disease. MDR1 encoded from multidrug resistance gene 1 mainly causes multidrug resistance phenotypes of different cancer cells. In this study, we demonstrate that JNK1/2 activation by an extract from the root of Morus alba L. (White mulberry) reduces doxorubicin-resistant MCF-7/Dox cell viability by inhibiting YB-1 regulation of MDR1 gene expression. When MCF-7 or MCF-7/Dox cells, where MDR1 is highly expressed were treated with an extract from roots or leaves of Morus alba L., respectively, the root extract from the mulberry (REM) but not the leaf extract (LEM) reduced cell viabilities of both MCF-7 and MCF-7/Dox cells, which was enhanced by cotreatment with doxorubicin. REM but not LEM further inhibited YB-1 nuclear translocation and its regulation of MDR1 gene expression. Moreover, REM promoted phosphorylation of c-Jun NH2-terminal kinase 1/2 (JNK1/2) and JNK1/2 inhibitor, SP600125 and rescued REM inhibition of both MDR1 expression and viabilities in MCF-7/Dox cells. Consistently, overexpression of JNK1, c-Jun, or c-Fos inhibited YB-1-dependent MDR1 expression and reduced viabilities in MCF-7/Dox cells. In conclusion, our data indicate that REM-activated JNK-cJun/c-Fos pathway decreases the viability of MCF-7/Dox cells by inhibiting YB-1-dependent MDR1 gene expression. Thus, we suggest that REM may be useful for treating multidrug-resistant cancer cells.

Mutual regulation between Raf/MEK/ERK signaling and Y-box-binding protein-1 promotes prostate cancer progression

PURPOSE

Y-box-binding protein-1 (YB-1) is known to conduct various functions related to cell proliferation, anti-apoptosis, epithelial-mesenchymal transition, and castration resistance in prostate cancer. However, it is still unknown how YB-1 affects cancer biology, especially its correlations with the mitogen-activated protein kinase (MAPK) signaling pathway. Therefore, we aimed to examine the interaction between YB-1 and the MAPK pathway in prostate cancer.

EXPERIMENTAL DESIGN

Quantitative real-time PCR, Western blotting, and co-immunoprecipitation assay were conducted in prostate cancer cells. YB-1, phosphorylated YB-1 (p-YB-1), and ERK2 protein expressions in 165 clinical specimens of prostate cancer were investigated by immunohistochemistry. YB-1, p-YB-1, and ERK2 nuclear expressions were compared with clinicopathologic characteristics and patient prognoses.

RESULTS

EGF upregulated p-YB-1, whereas MEK inhibitor (U0126, PD98059) decreased p-YB-1. Inversely, silencing of YB-1 using siRNA decreased the expression of ERK2 and phosphorylated MEK, ERK1/2, and RSK. Furthermore, YB-1 interacted with ERK2 and Raf-1 and regulated their expressions, through the proteasomal pathway. Immunohistochemical staining showed a significant correlation among the nuclear expressions of YB-1, p-YB-1, and ERK2. The Cox proportional hazards model revealed that high ERK2 expression was an independent prognostic factor [HR, 7.947; 95% confidence interval (CI), 3.527-20.508; P<0.0001].

CONCLUSION

We revealed the functional relationship between YB-1 and MAPK signaling and its biochemical relevance to the progression of prostate cancer. In addition, ERK2 expression was an independent prognostic factor. These findings suggest that both the ERK pathway and YB-1 may be promising molecular targets for prostate cancer diagnosis and therapeutics.

MAPK and PI3K/AKT mediated YB-1 activation promotes melanoma cell proliferation which is counteracted by an autoregulatory loop

Y-box binding protein 1 (YB-1) is an oncogenic transcription and translation factor and is overexpressed in several types of cancer. Our previous data showed that YB-1 is upregulated and translocated to the nucleus during melanoma progression and that YB-1 is an important transcription factor regulating proliferation, survival, migration, invasion and chemosensitivity of melanoma cells. It has been suggested that YB-1 is activated and translocated to the nucleus after S102-phosphorylation in the DNA binding domain. In this study, we show that activation of YB-1 by S102-phosphorylation and nuclear translocation is increased during melanoma progression using a human tissue microarray with 100 melanocytic lesions. Furthermore, we analysed the mechanisms governing the expression and activity of YB-1 in melanoma cells. We show that the PI3K/AKT and p53 signalling, growth factors and chemotherapeutic agents increase YB-1 promoter activity. This, however, resulted in no or only modest increase in YB-1 protein expression. We show that the MAPK and PI3K/AKT signalling pathways, both activated in melanoma cells, as well as p53 overexpression increase YB-1 S102-phosphorylation, whereas NFκB signalling inhibits phosphorylation. Overexpression of YB-1 in melanoma cells inhibits translation efficiency and by this proliferation and survival of melanoma cells indicating that there is an autoregulatory loop restricting YB-1 protein expression. These data suggest that there is a tightly regulated feedback mechanism regulating YB-1 expression and activation, necessary for proper cell cycle progression of melanoma cells.

Y-box-binding protein 1 (YB-1) and its functions

This review describes the structure and functions of Y-box binding protein 1 (YB-1) and its homologs. Interactions of YB-1 with DNA, mRNAs, and proteins are considered. Data on the participation of YB-1 in DNA reparation and transcription, mRNA splicing and translation are systematized. Results on interactions of YB-1 with cytoskeleton components and its possible role in mRNA localization are discussed. Data on intracellular distribution of YB-1, its redistribution between the nucleus and the cytoplasm, and its secretion and extracellular functions are summarized. The effect of YB-1 on cell differentiation, its involvement in extra- and intracellular signaling pathways, and its role in early embryogenesis are described. The mechanisms of regulation of YB-1 expression in the cell are presented. Special attention is paid to the involvement of YB-1 in oncogenic cell transformation, multiple drug resistance, and dissemination of tumors. Both the oncogenic and antioncogenic activities of YB-1 are reviewed. The potential use of YB-1 in diagnostics and therapy as an early cancer marker and a molecular target is discussed.

Ribonucleoprotein Y-box-binding protein-1 regulates mitochondrial oxidative phosphorylation (OXPHOS) protein expression after serum stimulation through binding to OXPHOS mRNA

Mitochondria play key roles in essential cellular functions, such as energy production, metabolic pathways and aging. Growth factor-mediated expression of the mitochondrial OXPHOS (oxidative phosphorylation) complex proteins has been proposed to play a fundamental role in metabolic homoeostasis. Although protein translation is affected by general RNA-binding proteins, very little is known about the mechanism involved in mitochondrial OXPHOS protein translation. In the present study, serum stimulation induced nuclear-encoded OXPHOS protein expression, such as NDUFA9 [NADH dehydrogenase (ubiquinone) 1α subcomplex, 9, 39 kDa], NDUFB8 [NADH dehydrogenase (ubiquinone) 1β subcomplex, 8, 19 kDa], SDHB [succinate dehydrogenase complex, subunit B, iron sulfur (Ip)] and UQCRFS1 (ubiquinol-cytochrome c reductase, Rieske iron-sulfur polypeptide 1), and mitochondrial ATP production, in a translation-dependent manner. We also observed that the major ribonucleoprotein YB-1 (Y-box-binding protein-1) preferentially bound to these OXPHOS mRNAs and regulated the recruitment of mRNAs from inactive mRNPs (messenger ribonucleoprotein particles) to active polysomes. YB-1 depletion led to up-regulation of mitochondrial function through induction of OXPHOS protein translation from inactive mRNP release. In contrast, YB-1 overexpression suppressed the translation of these OXPHOS mRNAs through reduced polysome formation, suggesting that YB-1 regulated the translation of mitochondrial OXPHOS mRNAs through mRNA binding. Taken together, our findings suggest that YB-1 is a critical factor for translation that may control OXPHOS activity.

Formation of amyloid-like fibrils by Y-box binding protein 1 (YB-1) is mediated by its cold shock domain and modulated by disordered terminal domains

YB-1, a multifunctional DNA- and RNA-binding nucleocytoplasmic protein, is involved in the majority of DNA- and mRNA-dependent events in the cell. It consists of three structurally different domains: its central cold shock domain has the structure of a β-barrel, while the flanking domains are predicted to be intrinsically disordered. Recently, we showed that YB-1 is capable of forming elongated fibrils under high ionic strength conditions. Here we report that it is the cold shock domain that is responsible for formation of YB-1 fibrils, while the terminal domains differentially modulate this process depending on salt conditions. We demonstrate that YB-1 fibrils have amyloid-like features, including affinity for specific dyes and a typical X-ray diffraction pattern, and that in contrast to most of amyloids, they disassemble under nearly physiological conditions.

Phosphatidylinositol 3-kinase: the oncoprotein

The catalytic and regulatory subunits of class I phosphoinositide 3-kinase (PI3K) have oncogenic potential. The catalytic subunit p110α and the regulatory subunit p85 undergo cancer-specific gain-of-function mutations that lead to enhanced enzymatic activity, ability to signal constitutively, and oncogenicity. The β, γ, and δ isoforms of p110 are cell-transforming as overexpressed wild-type proteins. Class I PI3Ks have the unique ability to generate phosphoinositide 3,4,5 trisphosphate (PIP(3)). Class II and class III PI3Ks lack this ability. Genetic and cell biological evidence suggests that PIP(3) is essential for PI3K-mediated oncogenicity, explaining why class II and class III enzymes have not been linked to cancer. Mutational analysis reveals the existence of at least two distinct molecular mechanisms for the gain of function seen with cancer-specific mutations in p110α; one causing independence from upstream receptor tyrosine kinases, the other inducing independence from Ras. An essential component of the oncogenic signal that is initiated by PI3K is the TOR (target of rapamycin) kinase. TOR is an integrator of growth and of metabolic inputs. In complex with the raptor protein (TORC1), it controls cap-dependent translation, and this function is essential for PI3K-initiated oncogenesis.

YB-1 binds to GluR2 mRNA and CaM1 mRNA in the brain and regulates their translational levels in an activity-dependent manner

The translational regulator YB-1 binds to mRNAs. In the brain, YB-1 is prominently expressed from the prenatal stage until the first week after birth, being associated with polysomes and distributed in neuronal dendrites, but its expression declines to a much lower level thereafter. It is therefore of interest to identify the mRNAs whose translation is controlled by YB-1 in the postnatal growing brain. In this study we found that YB-1 interacted with the mRNAs for glutamate receptor subunit 2 (GluR2) and calmodulin1 (CaM1) in both brain and NG108-15 cells. Overexpression or knockdown of YB-1 altered the levels of these proteins significantly in cultured cells without any change in their mRNA levels. When the cells were treated with neurotransmitters, translation of these proteins was induced within a short time, and a change in the amount of YB-1 on its target mRNAs was observed in the heavy-sedimenting polysome fractions on a sucrose gradient. Depletion of YB-1 expression by siRNA abrogated the translational activation. Furthermore, in the brain of kainic acid-treated mice, the distribution of YB-1 was shifted to much heavier fractions associated with polysomes within 30 min to 1 h after the treatment, and the distribution returned to lighter fractions within the following 2 h. The protein levels of GluR2 and CaM1 were also increased transiently when the distribution of YB-1 on the gradient changed. These results suggest that in the brain of growing mice, YB-1 binds to GluR2 and CaM1 mRNAs and regulates their translation in an activity-dependent manner.

Phosphatidylinositol 3-kinase: the oncoprotein

The catalytic and regulatory subunits of class I phosphoinositide 3-kinase (PI3K) have oncogenic potential. The catalytic subunit p110α and the regulatory subunit p85 undergo cancer-specific gain-of-function mutations that lead to enhanced enzymatic activity, ability to signal constitutively, and oncogenicity. The β, γ, and δ isoforms of p110 are cell-transforming as overexpressed wild-type proteins. Class I PI3Ks have the unique ability to generate phosphoinositide 3,4,5 trisphosphate (PIP(3)). Class II and class III PI3Ks lack this ability. Genetic and cell biological evidence suggests that PIP(3) is essential for PI3K-mediated oncogenicity, explaining why class II and class III enzymes have not been linked to cancer. Mutational analysis reveals the existence of at least two distinct molecular mechanisms for the gain of function seen with cancer-specific mutations in p110α; one causing independence from upstream receptor tyrosine kinases, the other inducing independence from Ras. An essential component of the oncogenic signal that is initiated by PI3K is the TOR (target of rapamycin) kinase. TOR is an integrator of growth and of metabolic inputs. In complex with the raptor protein (TORC1), it controls cap-dependent translation, and this function is essential for PI3K-initiated oncogenesis.

Mitochondrial helicases and mitochondrial genome maintenance

Helicases are essential enzymes that utilize the energy of nucleotide hydrolysis to drive unwinding of nucleic acid duplexes. Helicases play roles in all aspects of DNA metabolism including DNA repair, DNA replication and transcription. The subcellular locations and functions of several helicases have been studied in detail; however, the roles of specific helicases in mitochondrial biology remain poorly characterized. This review presents important recent advances in identifying and characterizing mitochondrial helicases, some of which also operate in the nucleus.

Akt-mediated regulation of NFkappaB and the essentialness of NFkappaB for the oncogenicity of PI3K and Akt

The serine/threonine kinase Akt (cellular homolog of murine thymoma virus akt8 oncogene), also known as PKB (protein kinase B), is activated by lipid products of phosphatidylinositol 3-kinase (PI3K). Akt phosphorylates numerous protein targets that control cell survival, proliferation and motility. Previous studies suggest that Akt regulates transcriptional activity of the nuclear factor-kappaB (NFkappaB) by inducing phosphorylation and subsequent degradation of inhibitor of kappaB (IkappaB). We show here that NFkappaB-driven transcription increases in chicken embryonic fibroblasts (CEF) transformed by myristylated Akt (myrAkt). Accordingly, both a dominant negative mutant of Akt and Akt inhibitors repress NFkappaB-dependent transcription. The degradation of the IkappaB protein is strongly enhanced in Akt-transformed cells, and the loss of NFkappaB activity by introduction of a super-repressor of NFkappaB, IkappaBSR, interferes with PI3K- and Akt-induced oncogenic transformation of CEF. The phosphorylation of the p65 subunit of NFkappaB at serine 534 is also upregulated in Akt-transformed cells. Our data suggest that the stimulation of NFkappaB by Akt is dependent on the phosphorylation of p65 at S534, mediated by IKK (IkappaB kinase) alpha and beta. Akt phosphorylates IKKalpha on T23, and this phosphorylation event is a prerequisite for the phosphorylation of p65 at S534 by IKKalpha and beta. Our results demonstrate two separate functions of the IKK complex in NFkappaB activation in cells with constitutive Akt activity: the phosphorylation and consequent degradation of IkappaB and the phosphorylation of p65. The data further support the conclusion that NFkappaB activity is essential for PI3K- and Akt-induced oncogenic transformation.

HSP60 interacts with YB-1 and affects its polysome association and subcellular localization

YB-1 is a DNA/RNA-binding protein which, in the cytoplasm, associates with polysomes and regulates translation. However, YB-1 has a novel nuclear localization signal, and its nuclear accumulation is correlated with cancer induction. Here we designated the amino-acid sequence as YB-NLS and demonstrated that YB-NLS is necessary for the nuclear translocation of overexpressed YB-1 in NG108-15 cells. In addition, we found that a heat shock protein, HSP60, binds to YB-NLS in the cytoplasm. Interestingly, when HSP60 expression was repressed, an increase of polysome-associated YB-1 was observed in heavy-sedimenting fractions on a sucrose gradient. Overexpression of HSP60 resulted in a decrease of YB-1 in the heavy-sedimenting fractions and suppression of YB-NLS activity. Furthermore, the NLS-deleted YB-1 was apparently associated with the heavy-sedimenting polysomes. These results suggest that HSP60 interacts with YB-1 at the YB-NLS region and acts as a regulator of polysome association and the subcellular distribution of YB-1.

RNA-binding specificity of Y-box protein 1

Y-box protein 1 (YB-1) is a multifunctional DNA/RNA-binding protein that regulates transcription and translation. The specificity of YB-1's RNA binding and its consequences are unknown. Because expression and subcellular localization of YB-1 have been reported to be important in breast cancer, we determined the specificity and functional impact of YB-1 mRNA-binding in MCF7 breast cancer cells. We used YB-1 antibodies to immunoprecipitate YB-1 and microarray profiling to compare YB-1-bound and total poly(A) RNA. We demonstrated that YB-1 mRNA-binding was preferential. Transcript sequences significantly associated with this binding had high GC content. Selected YB-1 mRNA-binding targets were confirmed by QRT-PCR. However, downregulation of YB-1 levels by siRNA did not affect their RNA or protein expression. Thus, YB-1 has RNA-binding specificity; however, YB-1 binding does not necessarily regulate the stability or translation of its mRNA targets. Further study is needed to determine the functional consequences of selective YB-1 mRNA binding.

General RNA-binding proteins have a function in poly(A)-binding protein-dependent translation

The interaction between the poly(A)-binding protein (PABP) and eukaryotic translational initiation factor 4G (eIF4G), which brings about circularization of the mRNA, stimulates translation. General RNA-binding proteins affect translation, but their role in mRNA circularization has not been studied before. Here, we demonstrate that the major mRNA ribonucleoprotein YB-1 has a pivotal function in the regulation of eIF4F activity by PABP. In cell extracts, the addition of YB-1 exacerbated the inhibition of 80S ribosome initiation complex formation by PABP depletion. Rabbit reticulocyte lysate in which PABP weakly stimulates translation is rendered PABP-dependent after the addition of YB-1. In this system, eIF4E binding to the cap structure is inhibited by YB-1 and stimulated by a nonspecific RNA. Significantly, adding PABP back to the depleted lysate stimulated eIF4E binding to the cap structure more potently if this binding had been downregulated by YB-1. Conversely, adding nonspecific RNA abrogated PABP stimulation of eIF4E binding. These data strongly suggest that competition between YB-1 and eIF4G for mRNA binding is required for efficient stimulation of eIF4F activity by PABP.

YB-1 promotes microtubule assembly in vitro through interaction with tubulin and microtubules

Background

YB-1 is a major regulator of gene expression in eukaryotic cells. In addition to its role in transcription, YB-1 plays a key role in translation and stabilization of mRNAs.

Results

We show here that YB-1 interacts with tubulin and microtubules and stimulates microtubule assembly in vitro. High resolution imaging via electron and atomic force microscopy revealed that microtubules assembled in the presence of YB-1 exhibited a normal single wall ultrastructure and indicated that YB-1 most probably coats the outer microtubule wall. Furthermore, we found that YB-1 also promotes the assembly of MAPs-tubulin and subtilisin-treated tubulin. Finally, we demonstrated that tubulin interferes with RNA:YB-1 complexes.

Conclusion

These results suggest that YB-1 may regulate microtubule assembly in vivo and that its interaction with tubulin may contribute to the control of mRNA translation.

Constitutively active Rheb induces oncogenic transformation

Rheb (Ras-homolog enriched in brain) is a component of the phosphatidylinositol 3-kinase (PI3K) target of rapamycin (TOR) signaling pathway, functioning as a positive regulator of TOR. Constitutively active mutants of Rheb induce oncogenic transformation in cell culture. The transformed cells are larger and contain more protein than their normal counterparts. They show constitutive phosphorylation of the ribosomal protein S6 kinase and the eukaryotic initiation factor 4E-binding protein 1, two downstream targets of TOR. The TOR-specific inhibitor rapamycin strongly interferes with transformation induced by constitutively active Rheb, suggesting that TOR activity is essential for the oncogenic effects of mutant Rheb. Rheb-induced transformation is also dependent on a C-terminal farnesylation signal that mediates localization to a cellular membrane. An engineered N-terminal myristylation signal can substitute for the farnesylation. Immunofluorescence localizes wild-type and mutant Rheb to vesicular structures in the cytoplasm, overlapping with the endoplasmic reticulum.

mTOR signalling in human cancer

Inhibitors of mTOR, the mammalian target of rapamycin, have been extensively studied in clinical trials for cancer treatment. Results have been promising, mostly in certain lymphomas, but in solid tumours the results have been generally less encouraging. However, recent results, particularly in renal cell carcinoma, have provided renewed interest in the role of mTOR inhibitors in solid tumours. A rational, and potentially more successful, development of these agents (i.e., RAD001, temsirolimus and AP23573) likely relies in a deeper knowledge of mTOR signalling in cancer, both at the preclinical and clinical levels. These would allow a better selection of patients more likely to respond to the use of biologically active doses of the agents and the development of mechanistically based combinations with other agents. The goal of this review is to provide an update on the complex signalling of mTOR in cancer and on the biological effects of mTOR inhibitors in cancer cells.

Phosphorylation by Akt disables the anti-oncogenic activity of YB-1

The Y box-binding protein 1 (YB-1) is a DNA/RNA-binding protein that regulates mRNA transcription and translation. It is a major component of free messenger ribonucleoprotein particles and, at higher concentrations, blocks protein synthesis. In chicken embryo fibroblasts, overexpression of YB-1 confers a specific resistance to oncogenic cellular transformation by phosphoinositide 3-kinase (PI3K) or Akt/PKB. Recent studies have identified YB-1 as a direct substrate of Akt. The functional significance of Akt-mediated phosphorylation remains largely unknown. We generated YB-1 mutants in the Akt phosphorylation consensus sequence to explore the effect of phosphorylated YB-1 in PI3K-induced transformation. In contrast to wild-type YB-1, the phosphomimetic S99E mutant no longer interferes with cellular transformation. This mutant has reduced affinity for the cap of mRNAs and fails to inhibit cap-dependent translation. The data suggest that phosphorylation by Akt disables the inhibitory activity of YB-1 and thereby enhances the translation of transcripts that are necessary for oncogenesis. Overexpression of wild-type YB-1 overrides inactivation by Akt and maintains inhibition of protein synthesis and resistance to transformation.

YB-1 is a Transcription/Translation Factor that Orchestrates the Oncogenome by Hardwiring Signal Transduction to Gene Expression

The Y-box Binding Protein-1 (YB-1) is a highly conserved oncogenic transcription/translation factor that is expressed in cancers affecting adults and children. It is now believed that YB-1 plays a causal role in the development of cancer given recent work showing that its expression drives the tumorigenesis in the mammary gland. In human breast cancers, YB-1 is associated with rapidly proliferating tumors that are highly aggressive. Moreover, expression of YB-1 promotes the growth of breast cancer cell lines both in monolayer and anchorage independent conditions. The involvement of YB-1 in breast cancer pathogenesis has made it a putative therapeutic target; however, the mechanism(s) that regulate YB-1 are poorly understood. This review first describes the oncogenic properties of YB-1 in cancer. It also highlights the importance of YB-1 in hardwiring signal transduction pathways to the regulation of genes involved in the development of cancer.

Mechanisms of translational deregulation in human tumors and therapeutic intervention strategies

Analysis of the recurrent genetic aberrations present in human tumors provides insight into how normal cells escape appropriate proliferation and survival cues. Commonly mutated genes encode proteins that monitor DNA damage (e.g., p53), proteins that regulate the cell cycle (such as Rb), and proteins that regulate signal transduction pathways (such as APC, PTEN and Ras). Analysis of the relevant targets and downstream events of these genes in normal and tumor cells will clearly highlight important pathways for tumorigenesis. However, more infrequent mutations are also informative in defining events critical for the process of tumorigenesis, and often delineate important pathways lying downstream of commonly mutated oncogenes and tumor suppressors. Together, these studies have led to the conclusion that deregulated protein synthesis plays an important role in human cancer. This review will discuss the evidence implicating mRNA translation as an important downstream consequence of signal transduction pathways initiated by mutated oncogenes and tumor suppressors, as well as additional genetic findings implicating the importance of global and specific translational control in human cancer. It will also discuss therapeutic strategies that take advantage of differences in translational regulation between normal and tumor cells.

The increased expression of Y box-binding protein 1 in melanoma stimulates proliferation and tumor invasion, antagonizes apoptosis and enhances chemoresistance

In previous studies we identified the transcription/translation factor Y-box-binding protein (YB-1) as a gene that is upregulated in primary melanoma and melanoma metastases when compared to benign melanocytic nevi. To analyze whether YB-1 expression correlates with melanoma progression in vitro and in vivo, we performed expression analysis on melanoma cell lines representing different stages of melanoma progression and on tissues of melanocytic nevi, primary melanoma and melanoma metastases. Our data indicate that compared to benign melanocytes YB-1 expression is increased in melanoma cells in vitro and in vivo and that YB-1 is translocated into the nucleus in invasive and metastatic melanoma cells. To reveal the functional role of YB-1 in melanoma progression we achieved a stable downregulation of YB-1 using shRNA in metastatic melanoma cells. Interestingly, YB-1 downregulation resulted in a pronounced reduced rate of proliferation and an increased rate of apoptotic cell death. In addition, migration and invasion of melanoma cells in monolayer and in a three-dimensional skin reconstruct in vitro was significantly reduced. These effects were accompanied by downregulation of genes involved in proliferation, survival and migration/invasion of melanoma cells such as MMP-2, bcl-2, Cyclin D1, p53 and p16INK4A. Furthermore, melanoma cells with a reduced YB-1 expression showed a decreased resistance to the chemotherapeutic agents cisplatin and etoposide. These data suggest that YB-1 is involved in malignant transformation of melanocytes and contributes to the stimulation of proliferation, tumor invasion, survival and chemoresistance. Thus, YB-1 may be a promising molecular target in melanoma therapy.

YB-1 Is Important for an Early Stage Embryonic Development

The eukaryotic Y-box-binding protein-1 (YB-1) is involved in the transcriptional and translational control of many biological processes, including cell proliferation. In clinical studies, the cellular level of YB-1 closely correlates with tumor growth and prognosis. To understand the role of YB-1 in vivo, especially in the developmental process, we generated YB-1 knock-out mice, which are embryonic lethal and exhibit exencephaly associated with abnormal patterns of cell proliferation within the neuroepithelium. beta-Actin expression and F-actin formation were reduced in the YB-1 null embryo and YB-1(-/-) mouse embryonic fibroblasts, suggesting that the neural tube defect is caused by abnormal cell morphology and actin assembly within the neuroepithelium. Fibroblasts derived from YB-1(-/-) embryos demonstrated reduced growth and cell density. A colony formation assay showed that YB-1(-/-) mouse embryonic fibroblasts failed to undergo morphological transformation and remained contact-inhibited in culture. These results demonstrate that YB-1 is involved in early mouse development, including neural tube closure and cell proliferation.

mTOR and cancer therapy

Proteins regulating the mammalian target of rapamycin (mTOR), as well as some of the targets of the mTOR kinase, are overexpressed or mutated in cancer. Rapamycin, the naturally occurring inhibitor of mTOR, along with a number of recently developed rapamycin analogs (rapalogs) consisting of synthetically derived compounds containing minor chemical modifications to the parent structure, inhibit the growth of cell lines derived from multiple tumor types in vitro, and tumor models in vivo. Results from clinical trials indicate that the rapalogs may be useful for the treatment of subsets of certain types of cancer. The sporadic responses from the initial clinical trials, based on the hypothesis of general translation inhibition of cancer cells are now beginning to be understood owing to a more complete understanding of the dynamics of mTOR regulation and the function of mTOR in the tumor microenvironment. This review will summarize the preclinical and clinical data and recent discoveries of the function of mTOR in cancer and growth regulation.

Akt-mediated YB-1 phosphorylation activates translation of silent mRNA species

YB-1 is a broad-specificity RNA-binding protein that is involved in regulation of mRNA transcription, splicing, translation, and stability. In both germinal and somatic cells, YB-1 and related proteins are major components of translationally inactive messenger ribonucleoprotein particles (mRNPs) and are mainly responsible for storage of mRNAs in a silent state. However, mechanisms regulating the repressor activity of YB-1 are not well understood. Here we demonstrate that association of YB-1 with the capped 5' terminus of the mRNA is regulated via phosphorylation by the serine/threonine protein kinase Akt. In contrast to its nonphosphorylated form, phosphorylated YB-1 fails to inhibit cap-dependent but not internal ribosome entry site-dependent translation of a reporter mRNA in vitro. We also show that similar to YB-1, Akt is associated with inactive mRNPs and that activated Akt may relieve translational repression of the YB-1-bound mRNAs. Using Affymetrix microarrays, we found that many of the YB-1-associated messages encode stress- and growth-related proteins, raising the intriguing possibility that Akt-mediated YB-1 phosphorylation could, in part, increase production of proteins regulating cell proliferation, oncogenic transformation, and stress response.

Phosphoinositide 3-kinase: from viral oncoprotein to drug target

The catalytic subunit p110alpha of the phosphoinositide 3-kinase (PI3K) and the serine-threonine protein kinase Akt have been extensively studied as retroviral oncoproteins. The experimental tools developed with the retroviral vectors are now being applied to PI3K mutations in human cancer. The most frequently occurring mutants of p110alpha are oncogenic in vitro and in vivo, show gain of enzymatic function, activate Akt, and their oncogenic activity is sensitive to rapamycin. The related isoforms p110beta, gamma and delta induce oncogenic transformation as wild-type proteins. Mutated p110alpha proteins are ideal drug targets. Identification of small molecule inhibitors that specifically target these mutant proteins is a realistic and urgent goal.

YB-1 represses AP1-dependent gene transactivation and interacts with an AP-1 DNA sequence

Involvement of the AP-1 (activator protein-1) transcription factor has been demonstrated previously in the regulation of cell proliferation and cell-cycle progression, in the control of cell migration, invasion and metastasis, and in signal transduction, stress responsiveness, DNA replication and DNA repair. YB-1 (Y-box-binding protein-1) has also been implicated in many of these processes. However, the mechanism by which YB-1 mediates these processes is poorly understood. In the present study, we report that overexpression of a transfected gene encoding YB-1 in human HeLa cervical carcinoma cells significantly represses the transactivation of a minimal AP-1 reporter construct in response to the tumour promoter PMA. YB-1 also represses mRNA expression and PMA-induced promoter transactivation of the endogenous AP-1 target gene encoding matrix metalloproteinase-12 (metalloelastase). YB-1 transrepression of both the minimal and matrix metalloproteinase-12 promoter reporter constructs is dependent on the AP-1 sequence. To identify new nuclear proteins that bind specifically to the AP-1 DNA-binding site, we devised a DNA-affinity-chromatography-based assay termed NAPSTER (nucleotide-affinity preincubation specificity test of recognition) and discovered a 49 kDa protein from human cancer cells that binds in a sequence-specific manner to the AP-1 DNA sequence. By tandem MS fragmentation sequencing analyses we determined that p49 is a YB-1. Immunoblotting of the NAPSTER-purified p49 protein using anti-YB-1 antibodies confirmed YB-1 binding to the AP-1 DNA sequence, as did gel mobility-supershift assays using YB-1 antibodies. This is the first report of YB-1 transrepression and interaction at the AP-1 DNA-binding site.

Oncogenic PI3K deregulates transcription and translation

There have long been indications of a role for PI3K (phosphatidylinositol 3-kinase) in cancer pathogenesis. Experimental data document a requirement for deregulation of both transcription and translation in PI3K-mediated oncogenic transformation. The recent discoveries of cancer-specific mutations in PIK3CA, the gene that encodes the catalytic subunit p110alpha of PI3K, have heightened the interest in the oncogenic potential of this lipid kinase and have made p110alpha an ideal drug target.

Transcription factors and drug resistance

Intrinsic or acquired resistance to anticancer agents is a major obstacle to the success of chemotherapy. Anticancer agents are known to modulate signal transduction pathways and alter expression of genes that play an important role in drug resistance. Emerging evidence suggests that the complexity of genomic response against anticancer agents arise from elaborate gene expression by multiple transcription factors. Here, we briefly describe the development of solid tumours and the appearance of drug-resistant cells. We also review what is known of the transcription factors that are involved in resistance to drugs, particularly cisplatin.

Significance of the Y-box proteins in human cancers

Y-box proteins belong to the cold shock domain family of proteins that are known to be involved in both transcriptional and translational control. Here, we give a brief overview of the structure, regulation and physiological functions of the Y-box proteins. This is followed by examining the role of Y-box protein 1 (YB-1), the most extensively studied of the Y-box protein in tumorigenesis, and its clinicopathological significance. YB-1 has the potential to be a prognostic marker and predictor of chemoresistance in human cancers.