ICBP90, inverted CCAAT box-binding protein of 90 kDa, has been reported as a regulator of topoisomerase IIa expression. We present evidence here that ICBP90 binds to methyl-CpG when at least one symmetrically methylated-CpG dinucleotides is presented as its recognition sequence. A SET and RING finger-associated (SRA) domain accounts for the high binding affinity of ICBP90 for methyl-CpG dinucleotides. This protein constitutes a complex with HDAC1 also via its SRA domain, and bound to methylated promoter regions of various tumor suppressor genes, including p16INK4A and p14 ARF , in cancer cells. It has been reported that expression of ICBP90 was upregulated by E2F-1, and we confirmed that the upregulation was caused by binding of E2F-1 to the intron1 of ICBP90, which contains two E2F-1-binding motifs. Our data also revealed accumulation of ICBP90 in breast-cancer cells, where it might suppress expression of tumor suppressor genes through deacetylation of histones after recruitment of HDAC1. The data reported here suggest that ICBP90 is involved in cell proliferation by way of methylation-mediated regulation of certain genes.

We previously reported that upregulation of SMYD3, a histone H3 lysine-4-specific methyltransferase, plays a key role in the proliferation of colorectal carcinoma (CRC) and hepatocellular carcinoma (HCC). In the present study, we reveal that SMYD3 expression is also elevated in the great majority of breast cancer tissues. Similarly to CRC and HCC, silencing of SMYD3 by small interfering RNA to this gene resulted in the inhibited growth of breast cancer cells, suggesting that increased SMYD3 expression is also essential for the proliferation of breast cancer cells. Moreover, we show here that SMYD3 could promote breast carcinogenesis by directly regulating expression of the proto-oncogene WNT10B. These data imply that augmented SMYD3 expression plays a crucial role in breast carcinogenesis, and that inhibition of SMYD3 should be a novel therapeutic strategy for treatment of breast cancer. (Cancer Sci 2006; 97: 113-118) R ecent molecular studies have disclosed that breast carcinogenesis involves not only genetic alterations in oncogenes and tumor suppressor genes, but also epigenetic dysregulation of a number of genes associated with growth, survival, cell motility and differentiation.(1-3) For example, several oncogenes have been described as being amplified in breast cancer, including HER2, EGFR, MYC, CCND1, Although expression profile analysis using cDNA microarray or DNA chip technology has facilitated the identification of genes with altered expression in cancer, the mechanisms of deregulated expression need to be further investigated. A multistep model of mammary carcinogenesis has been proposed; transformation of normal cells leads to atypical ductal hyperplasia, ductal carcinoma in situ (DCIS), and eventually invasive ductal carcinoma (IDC). However, precise molecular mechanisms underlying breast cancer remain unresolved.Chromatin is composed of genomic DNA and nuclear proteins including histones, and serves as the template for processing genetic information. The dynamic DNA-protein structure of chromatin is influenced by epigenetic modifications on both the DNA and nucleosomal histones. Under the euchromatin state where chromatin forms a relaxed state, the underlying DNA is accesible to transcription factors. In contrast, DNA in the heterochromatin state, where chromatin forms a condensed state, is transcriptionally restricted and thus untranscribed. Recent advances have shown that covalent histone modifications play critical roles in chromatin structure.One of the best-characterized modifications is acetylation, which is controlled by both histone acetyltransferases and deacetylases. Additionally, histone methylation has emerged as another modification that significantly impacts chromatin structure. We reported previously that SMYD3 shows histone H3-K4-specific methyltransferase activity, leading to transcriptional activation of downstream genes including Nkx2.8, and that elevated SMYD3 expression is involved in the growth of human colorectal carcinoma (CRC) and hepatocellular carcinoma (HCC) cells. (14)...

Breast cancer is one of the most common cancers among women. To discover molecular targets that are applicable for development of novel breast cancer therapy, we previously did genome-wide expression profile analysis of 81 breast cancers and found dozens of genes that were highly and commonly up-regulated in breast cancer cells. Among them, we here focused on one gene that encodes PDZ-binding kinase/T-LAK cell-originated protein kinase (PBK/TOPK), including a kinase domain. Northern blot analyses using mRNAs of normal human organs, breast cancer tissues, and cancer cell lines indicated this molecule to be a novel cancer/testis antigen. Reduction of PBK/TOPK expression by small interfering RNA resulted in significant suppression of cell growth probably due to dysfunction in the cytokinetic process. Immunocytochemical analysis with anti-PBK/TOPK antibody implicated a critical role of PBK/TOPK in an early step of mitosis. PBK/ TOPK could phosphorylate histone H3 at Ser 10 in vitro and in vivo, and mediated its growth-promoting effect through histone H3 modification. Because PBK/TOPK is the cancer/ testis antigen and its kinase function is likely to be related to its oncogenic activity, we suggest PBK/TOPK to be a promising molecular target for breast cancer therapy. (Cancer Res 2006; 66(18): 9186-95)

The structure of O-glycosylated proteins is altered in breast cancer cells, but the mechanisms of such an aberrant modification have been largely unknown. We here report critical roles of a novel druggable target, polypeptide N-acetylgalactosaminyltransferase 6 (GALNT6), which is upregulated in a great majority of breast cancers and encodes a glycosyltransferase responsible for initiating mucin-type O-glycosylation. Knockdown of GALNT6 by small interfering RNA significantly enhanced cell adhesion function and suppressed the growth of breast cancer cells. Western blot and immunostaining analyses indicated that wild-type GALNT6 protein could glycosylate and stabilize an oncoprotein mucin 1 (MUC1), which was upregulated with GALNT6 in breast cancer specimens. Furthermore, knockdown of GALNT6 or MUC1 led to similar morphologic changes of cancer cells accompanied by the increase of cell adhesion molecules β-catenin and E-cadherin. Our findings implied that overexpression of GALNT6 might contribute to mammary carcinogenesis through aberrant glycosylation and stabilization of MUC1 and that screening of GALNT6 inhibitors would be valuable for the development of novel therapeutic modalities against breast cancer. Cancer Res; 70(7); 2759-69. ©2010 AACR.

Breast cancer is generated through a multistep genetic and epigenetic process including activations of oncogenes and inactivations of tumor suppressor genes. Here, we report a critical role of ubiquitin-conjugating enzyme E2T (UBE2T), an E2 ubiquitin-conjugating enzyme, in mammary carcinogenesis. Immunocytochemical staining and in vitro binding assay revealed that UBE2T interacted and colocalized with the BRCA1/BRCA1-associated RING domain protein (BARD1) complex. Knocking down of UBE2T expression with small interfering RNA drastically suppressed the growth of breast cancer cells. Interestingly, in vivo ubiquitination assay indicated BRCA1 to be polyubiquitinated by incubation with wild-type UBE2T protein, but not with C86A-UBE2T protein, an E2 activity-dead mutant, in which the 86th residue of cysteine was replaced with alanine. Furthermore, knocking down of UBE2T protein induced upregulation of BRCA1 protein in breast cancer cells, whereas its overexpression caused the decrease of the BRCA1 protein. Our data imply a critical role of UBE2T in development and/or progression of breast cancer through the interaction with and the regulation of the BRCA1/BARD1 complex. [Cancer Res 2009;69(22):8752-60]

To elucidate the molecular mechanisms of mammary carcinogenesis and discover novel therapeutic targets for breast cancer, we previously carried out genome-wide expression profile analysis of

To elucidate molecular mechanisms of mammary carcinogenesis and discover novel therapeutic targets for breast cancer, we previously carried out a genome-wide expression profile analysis of 81 breast cancer cases by means of a combination of cDNA microarray and laser microbeam microdissection. Among the upregulated genes, we focused on the functional significance of protein regulator of cytokinesis 1 (PRC1) in the development of breast cancer. Western blot analysis using breast cancer cell lines revealed a significant increase in endogenous PRC1 levels in G 2 /M phase. Treatment of breast cancer cells with small interfering RNA against PRC1 effectively suppressed its expression and inhibited the growth of breast cancer cell lines T47D and HBC5. Furthermore, we found an interaction between PRC1 and kinesin family member 2C/mitotic centromereassociated kinesin (KIF2C/MCAK) by coimmunoprecipitation and immunoblotting using COS-7 cells, in which these molecules were introduced exogenously. These findings suggest the involvement of a PRC1-KIF2C/MCAK complex in breast tumorigenesis, and this complex should be a promising target for the development of novel treatments for breast cancer. (Cancer Sci 2007; 98: 174-181)

Introduction Cancer therapies directed at specific molecular targets in signaling pathways of cancer cells, such as tamoxifen, aromatase inhibitors and trastuzumab, have proven useful for treatment of advanced breast cancers. However, increased risk of endometrial cancer with long-term tamoxifen administration and of bone fracture due to osteoporosis in postmenopausal women undergoing aromatase inhibitor therapy are recognized side effects. These side effects as well as drug resistance make it necessary to search for novel molecular targets for drugs on the basis of well-characterized mechanisms of action.