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 disclose the molecular mechanism of bladder cancer, the second most common genitourinary tumor, we had previously done genome-wide expression profile analysis of 26 bladder cancers by means of cDNA microarray representing 27,648 genes. Among genes that were significantly up-regulated in the majority of bladder cancers, we here report identification of M-phase phosphoprotein 1 (MPHOSPH1) as a candidate molecule for drug development for bladder cancer. Northern blot analyses using mRNAs of normal human organs and cancer cell lines indicated this molecule to be a novel cancertestis antigen. Introduction of MPHOSPH1 into NIH3T3 cells significantly enhanced cell growth at in vitro and in vivo conditions. We subsequently found an interaction between MPHOSPH1 and protein regulator of cytokinesis 1 (PRC1), which was also up-regulated in bladder cancer cells. Immunocytochemical analysis revealed colocalization of endogenous MPHOSPH1 and PRC1 proteins in bladder cancer cells. Interestingly, knockdown of either MPHOSPH1 or PRC1 expression with specific small interfering RNAs caused a significant increase of multinuclear cells and subsequent cell death of bladder cancer cells. Our results imply that the MPHOSPH1/PRC1 complex is likely to play a crucial role in bladder carcinogenesis and that inhibition of the MPHOSPH1/PRC1 expression or their interaction should be novel therapeutic targets for bladder cancers. [Cancer Res 2007;67(7):3276-85]

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)

Breast cancer is the most common cancer among women worldwide; the breast cancer incidence and death rates for Japanese were 102.8 and 17.1 per 100 000 population, respectively, in the year 2006.(1,2) Incidence of breast cancer is increasing in most countries including the USA and Japan, and the increasing rate is much higher in countries where its incidence was previously low.(1,2) It has been known that breast cancer is a hormonedependent disease, and estrogens through an interaction with estrogen receptor (ER) drastically enhance the proliferative and metastatic activity in breast tumor cells.(3,4) However, despite the clinical benefit of interruption of the ER function with synthetic anti-estrogen drugs such as tamoxifen, the precise mechanism of an estrogen/ER signaling pathway in breast cancer progression is not well understood. Therefore, further characterization of the pathophysiologic roles of this pathway and development of novel drugs targeting this pathway should be eagerly expected to provide better management for breast cancer patients.Gene-expression profile analysis can generate a considerable amount of information for characterizing the nature of individual cancers; such information should be applied for extraction of potential molecular targets for improving clinical strategies to treat neoplastic diseases.(5,6) Through the genome-wide expression analysis of a large number of microdissected clinical cancer materials, we have identified dozens of genes that function as oncogenes in the process of development and/or progression of breast cancer, (7)(8)(9)(10)(11) bladder cancer, (12,13) synovial sarcomas, (14,15) testicular seminoma, (19,20) and identified dozens of molecules that were overexpressed in a great majority of breast cancers and were low or undetectably expressed in normal human organs.Among many over-expressed genes in breast cancers, we report in this study identification and characterization of a novel gene, brefeldin A-inhibited guanine nucleotide-exchange protein 3 (BIG3), a novel member of the BIG1/Sec7p subfamily of ADP ribosylation factor-GTP exchange factors (ARF-GEFs), to be a key molecule regulating an estrogen/estrogen receptor (ER) signaling pathway in breast cancer. We also demonstrate an interaction of BIG3 with prohibitin 2/repressor of estrogen receptor activity (PHB2/REA) protein, and that their interaction can enhance the ERα transcriptional activity. Our findings imply BIG3 to be a promising target for development of novel anti-cancer drugs for breast cancer. Materials and MethodsCell lines and clinical samples. Human breast cancer cell lines HCC1937, MCF-7, MDA-MB-231, SK-BR-3, T47D, BT-549, HCC1395, MDA-MB-157, BT-20, MDA-MB-453, ZR-75-1, BT-483, BT-474, HCC1143, HCC1500, HCC1599, and OCUB-F, as well as African green monkey SV40-transfected kidney fibroblast cell line, COS-7, were purchased from American Type Culture Collection (ATCC, Rockville, MD, USA), and cultured under their respective depositors' recommendations. All cells were cultured according to previ...