Seiji Naito

Twist promotes tumor cell growth through YB-1 expression

YB-1 controls gene expression through both transcriptional and translational mechanisms and is involved in various biological activities such as brain development, chemoresistance, and tumor progression. We have previously shown that YB-1 is overexpressed in cisplatin-resistant cells and is involved in resistance against DNA-damaging agents. Structural analysis of the YB-1 promoter reveals that several E-boxes may participate in the regulation of YB-1 expression. Here, we show that the E-box-binding transcription factor Twist is overexpressed in cisplatin-resistant cells and that YB-1 is a target gene of Twist. Silencing of either Twist or YB-1 expression induces G(1) phase cell cycle arrest of tumor cell growth. Significantly, reexpression of YB-1 led to increase colony formation when Twist expression was down-regulated by small interfering RNA. However, cotransfection of Twist expression plasmid could not increase colony formation when YB-1 expression was down-regulated. Collectively, these data suggest that YB-1 is a major downstream target of Twist. Both YB-1 and Twist expression could induce tumor progression, promoting cell growth and driving oncogenesis in various cancers. Thus, both YB-1 and Twist may represent promising molecular targets for cancer therapy.

Programmed Cell Death Protein 4 Down-regulates Y-Box Binding Protein-1 Expression via a Direct Interaction with Twist1 to Suppress Cancer Cell Growth

Programmed cell death protein 4 (PDCD4) has recently been shown to be involved in both transcription and translation, and to regulate cell growth. However, the mechanisms underlying PDCD4 function are not well understood. In this study, we show that PDCD4 interacts directly with the transcription factor Twist1 and leads to reduced cell growth through the down-regulation of the Twist1 target gene Y-box binding protein-1 (YB-1). PDCD4 interacts with the DNA binding domain of Twist1, inhibiting its DNA binding ability and YB-1 expression. Immunohistochemical analysis showed that an inverse correlation between nuclear PDCD4 and YB-1 expression levels was observed in 37 clinical prostate cancer specimens. Growth suppression by PDCD4 expression was completely recovered by either Twist1 or YB-1 expression. Moreover, PDCD4-overexpressing cells are sensitive to cisplatin and paclitaxel but not to etoposide or 5-fluorouracil. In summary, PDCD4 negatively regulates YB-1 expression via its interaction with Twist1 and is involved in cancer cell growth and chemoresistance.

Twist and p53 reciprocally regulate target genes via direct interaction

Twist is basic helix-loop-helix transcription factor that binds to E-boxes in gene promoters. Twist possesses an oncogenic function by interfering with the tumor suppressor function of p53. Using a membrane pull-down assay, we found that Twist directly interacts with p53 and that this interaction underlies the inhibitory effects on p53 target gene expression. Twist interacted with the DNA-binding domain of p53 and suppressed the DNA-binding activity of p53. Transcriptional activation of the p21 promoter by p53 was significantly repressed by the expression of Twist. On the other hand, p53 interacted with the N-terminal domain of Twist and repressed Twist-dependent YB-1 promoter activity. Importantly, we found that p53-dependent growth suppression was canceled by the expression of either Twist or YB-1. Thus, our data suggest that Twist inhibits p53 function via a direct interaction with p53.

Clusterin Mediates TGF-β–Induced Epithelial–Mesenchymal Transition and Metastasis via Twist1 in Prostate Cancer Cells

TGF-β promotes epithelial-mesenchymal transition (EMT) and induces clusterin (CLU) expression, linking these genes to cancer metastasis. CLU is a pleiotropic molecular chaperone that confers survival and proliferative advantage to cancer cells. However, the molecular mechanisms by which TGF-β regulates CLU expression and CLU affects metastasis remain unknown. In this study, we report that the transcription factor Twist1 mediates TGF-β-induced CLU expression. By binding to E-boxes in the distal promoter region of CLU gene, Twist1 regulated basal and TGF-β-induced CLU transcription. In addition, CLU reduction reduced TGF-β induction of the mesenchymal markers, N-cadherin and fibronectin, thereby inhibiting the migratory and invasive properties induced by TGF-β. Targeted inhibition of CLU also suppressed metastasis in an in vivo model. Taken together, our findings indicate that CLU is an important mediator of TGF-β-induced EMT, and suggest that CLU suppression may represent a promising therapeutic option for suppressing prostate cancer metastatic progression.

Castration resistance of prostate cancer cells caused by castration-induced oxidative stress through Twist1 and androgen receptor overexpression

There are few successful therapies for castration-resistant prostate cancer (CRPC). Recently, CRPC has been thought to result from augmented androgen/androgen receptor (AR) signaling pathway, for most of which AR overexpression has been observed. In this study, Twist1, a member of basic helix-loop-helix transcription factors as well as AR was upregulated in response to hydrogen peroxide, and the response to which was abolished by an addition of N-acetyl-L-cysteine and Twist1 knockdown. In addition, castration-resistant LNCaP derivatives and hydrogen peroxide-resistant LNCaP derivatives exhibited a similar phenotype to each other. Then, both castration and AR knockdown increased intracellular reactive oxygen species level. Moreover, Twist1 was shown to regulate AR expression through binding to E-boxes in AR promoter region. Silencing of Twist1 suppressed cell growth of AR-expressing LNCaP cells as well as castration-resistant LNCaP derivatives by inducing cell-cycle arrest at G1 phase and cellular apoptosis. These findings indicated that castration-induced oxidative stress may promote AR overexpression through Twist1 overexpression, which could result in a gain of castration resistance. Modulation of castration-induced oxidative stress or Twist1/AR signaling might be a useful strategy for developing a novel therapeutics in prostate cancer, even in CRPC, which remains dependent on AR signaling by overexpressing AR.

Tip60 promotes prostate cancer cell proliferation by translocation of androgen receptor into the nucleus.

There are currently few effective therapies for castration‐resistant prostate cancer (CRPCa). CRPC which is resistant to castration is thought to result from increased activation of the androgen/androgen receptor (AR) signaling pathway, which may be augmented by AR coactivators.

Oxidative stress and androgen receptor signaling in the development and progression of castration-resistant prostate cancer.

Aberrant androgen receptor (AR) signaling plays a critical role in androgen-dependent prostate cancer (PCa), as well as in castration-resistant PCa (CRPC). Oxidative stress seems to contribute to the tumorigenesis and progression of PCa, as well as the development of CRPC, via activation of AR signaling. This notion is supported by the fact that there is an aberrant or improper regulation of the redox status in these disorders. Additionally, androgen-deprivation-induced oxidative stress seems to be involved in the pathogenesis of several disorders caused by androgen-deprivation therapy (ADT), including osteoporosis, neurodegenerative disease, and cardiovascular disease. Oxidative stress can be suppressed with antioxidants or via a reduction in reactive oxygen species production. Thus, developing new therapeutic agents that reduce oxidative stress might be useful in preventing the conversion of androgen-dependent PCa into CRPC, as well as reducing the adverse effects associated with ADT. The objective of this review is to provide an overview regarding the relationship between oxidative stress and AR signaling in the context of PCa and especially CRPC. Additionally, we discuss the potential use of antioxidant therapies in the treatment of PCa.

Clusterin Is a Critical Downstream Mediator of Stress-Induced YB-1 Transactivation in Prostate Cancer

Clusterin is a stress-activated, cytoprotective chaperone that confers broad-spectrum treatment resistance in cancer. However, the molecular mechanisms mediating CLU transcription following anticancer treatment stress remain incompletely defined. We report that Y-box binding protein-1 (YB-1) directly binds to CLU promoter regions to transcriptionally regulate clusterin expression. In response to endoplasmic reticulum stress inducers, including paclitaxel, YB-1 is translocated to the nucleus to transactivate clusterin. Furthermore, higher levels of activated YB-1 and clusterin are seen in taxane-resistant, compared with parental, prostate cancer cells. Knockdown of either YB-1 or clusterin sensitized prostate cancer cells to paclitaxel, whereas their overexpression increased resistance to taxane. Clusterin overexpression rescued cells from increased paclitaxel-induced apoptosis following YB-1 knockdown; in contrast, however, YB-1 overexpression did not rescue cells from increased paclitaxel-induced apoptosis following clusterin knockdown. Collectively, these data indicate that YB-1 transactivation of clusterin in response to stress is a critical mediator of paclitaxel resistance in prostate cancer. Mol Cancer Res; 9(12); 1755–66. ©2011 AACR.

Y-box binding protein-1 promotes castration-resistant prostate cancer growth via androgen receptor expression

The androgen receptor (AR) is well known to play a central role in the pathogenesis of prostate cancer (PCa). In several studies, AR was overexpressed in castration-resistant PCa (CRPC). However, the mechanism of AR overexpression in CRPC is not fully elucidated. Y-box binding protein-1 (YB-1) is a pleiotropic transcription factor that is upregulated in CPRC. We aimed to elucidate the role of YB-1 in castration resistance of PCa and identify therapeutic potential of targeting YB-1. Using immunohistochemistry, we found that nuclear YB-1 expression significantly correlated with the Gleason score and AR expression in PCa tissues. In PCa cells, YB-1 regulated AR expression at the transcriptional level. Furthermore, YB-1 expression and nuclear localization were upregulated in CRPC cells. Overexpression of AR, as well as YB-1, conferred castration-resistant growth in LNCaP and 22Rv1 cells. Conversely, knocking down YB-1 resulted in suppressed cell growth and induced apoptosis, which was more efficient than knocking down AR in LNCaP cells. In other types of PCa cells, such as CRPC cells, knocking down YB-1 resulted in a significant reduction of cell growth. In conclusion, these findings suggested that YB-1 induces castration resistance in androgen-dependent PCa cells via AR expression. Thus, YB-1 may be a promising therapeutic target for PCa, as well as CRPC.

Antioxidant Therapy Alleviates Oxidative Stress by Androgen Deprivation and Prevents Conversion From Androgen Dependent to Castration Resistant Prostate Cancer

PURPOSEnProstate cancer progression from androgen dependence to castration resistance results at least in part from oxidative stress induced by androgen deprivation therapy. We elucidated the state and the role of oxidative stress induced by androgen deprivation therapy and the possibility of antioxidant therapy in human prostate cancer.nnnMATERIALS AND METHODSnWe investigated 4-HNE (4-hydroxy-2-nonenal histidine adduct) staining, and Twist1, YB-1 and androgen receptor expression by immunohistochemistry in prostate cancer samples treated with or without neoadjuvant androgen deprivation therapy. Intracellular reactive oxygen species and protein expression were examined by CM-H(2)DCFDA and Western blot analysis, respectively. A cell proliferation assay and a mouse xenograft model were used to assess tumor growth.nnnRESULTSnAndrogen deprivation therapy increased oxidative stress, as shown by 4-HNE staining in human prostate cancer tissue. Twist1 and YB-1 expression was up-regulated by androgen deprivation, resulting in androgen receptor over expression. In LNCaP and 22Rv1 cells androgen deprivation increased intracellular reactive oxygen species and evoked Twist1, YB-1 and androgen receptor over expression, resulting in cell growth in a castration resistant manner. Growth was alleviated by N-acetyl-cysteine, an electrophile that supports glutathione production. N-acetyl-cysteine also decreased LNCaP and 22Rv1 tumor growth in castrated and noncastrated mice.nnnCONCLUSIONSnAndrogen deprivation therapy induced oxidative stress in in vitro and human prostate cancer. Antioxidant therapy using N-acetyl-cysteine appears to be a promising therapeutic modality for prostate cancer.