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Chromosomal translocations are frequently associated with soft-tissue sarcomas. Fusion proteins generated by such translocations often play critical roles in tumorigenesis. Therefore, it is important to understand the function of the fusion protein to develop therapeutic interventions. The t(X;18)(p11.2;q11.2) translocation found in synovial sarcomas results in a fusion between the SYT gene on chromosome 18 and an SSX gene on the X chromosome. Although SYT-SSX fusion proteins appear to trigger synovial sarcoma development, little is known about the downstream targets of SYT-SSX. We found that the SYT-SSX fusion protein produces a dominant-negative function for SYT, which is a transcriptional coactivator. We then analyzed the gene expression profiles of SYT-SSX1-expressing HeLa cells using oligonucleotide microarrays and found that the SYT-SSX1 fusion protein directly down-regulated the expression of COM1, a regulator of cell proliferation. COM1 was found to be expressed at relatively low levels in synovial sarcoma tissues and cell lines. We then investigated the impact of conditional COM1 expression in the synovial sarcoma cell line. Increased COM1 expression resulted in induced apoptosis and in reduced cell growth and colony formation activity. Our results suggested that restoration of COM1 expression may be of therapeutic benefit in synovial sarcoma.Synovial sarcomas are aggressive tumors of adolescent and young adults that account for about 10% of all soft-tissue sarcomas. Synovial sarcomas are subdivided into biphasic and monophasic forms by their histomorphologic appearance. Biphasic synovial sarcomas contain epithelial cells arranged in glandular structures and spindle cells, whereas monophasic types are entirely composed of spindle cells. Cytogenetic analysis indicates that the chromosomal translocation t(X;18) (p11.2;q11.2) is present in the majority of these tumors, with molecular analysis of translocation breakpoints showing a disruption of the SYT (for "synovial sarcoma translocated") gene on chromosome 18q11.2 and juxtaposition to one of the SSX (for "synovial sarcoma X breakpoint") genes on Xp11.2 in a mutually exclusive fashion, with the result being a chimeric SYT-SSX protein (5, 9). The SSX gene family consists of nine contiguous members, SSX1 to SSX9, encoded on the X chromosome (12). Although the chromosomal arrangement of the SSX genes could in principle allow for heterogeneity at the breakpoint, fusions of SYT with SSX1, SSX2, and SSX4 have been reported in synovial sarcomas (6,8,9,23). The identity of the rearranged SSX gene has significant clinical impact (16).The normal SYT gene is ubiquitously expressed in a wide range of human tissues and cell lines (6). In contrast, SSX transcripts show a very restricted distribution in adult human tissues, and the expression is confined to the testis and at very low levels in the thyroid (6,11,26). SYT contains a transcriptional activating domain, rich in glycine, proline, glutamine, and tyrosine (QPGY domain). On the other hand, SSX possesses two tran...

Failure to expeditiously repair DNA at sites of double-strand breaks (DSB) ultimately is an important etiologic factor in cancer development. NBS1 plays an important role in the cellular response to DSB damage. A rare polymorphic variant of NBS1 that resulted in an isoleucine to valine substitution at amino acid position 171 (I171V) was first identified in childhood acute lymphoblastic leukemia. This polymorphic variant is located in the N-terminal region that interacts with other DNA repair factors. In earlier work, we had identified a remarkable number of structural chromosomal aberrations in a patient with pediatric aplastic anemia with a homozygous polymorphic variant of NBS1-I171V; however, it was unclear whether this variant affected DSB repair activity or chromosomal instability. In this report, we demonstrate that NBS1-I171V reduces DSB repair activity through a loss of association with the DNA repair factor MDC1. Furthermore, we found that heterozygosity in this polymorphic variant was associated with breast cancer risk. Finally, we showed that this variant exerted a dominant-negative effect on wild-type NBS1, attenuating DSB repair efficiency and elevating chromosomal instability. Our findings offer evidence that the failure of DNA repair leading to chromosomal instability has a causal impact on the risk of breast cancer development. Cancer Res; 74(14); 3707-15. Ó2014 AACR.

A proteasome degrades numerous regulatory proteins that are critical for tumor growth and is therefore recognized as a promising anticancer target. Determining proteasome activity in the tumors of mice bearing xenografts is essential for the development of novel proteasome inhibitors. We developed a system for in vivo imaging of proteasome inhibition in the tumors of living mice, using a proteasome‐sensitive fluorescent reporter, ZsProSensor‐1. This reporter consists of a green fluorescent protein, ZsGreen, fused to mouse ornithine decarboxylase, which is degraded by the proteasome without being ubiquitinated. In stably transfected cells expressing ZsProSensor‐1, the fluorescent reporter was rapidly degraded under steady‐state conditions, whereas it was stabilized in the presence of proteasome inhibitors. Subcutaneous inoculation of the transfected cells into nude mice resulted in tumor formation. When the proteasome inhibitor bortezomib was intravenously administered to mice bearing these tumors, the ZsProSensor‐1 protein accumulated in the tumors and emitted a fluorescent signal in a dose‐dependent manner. Robust fluorescence was sustained for 3 days and then gradually decreased to baseline levels within 15 days. Intravenous administration of bortezomib also showed potent antitumor activity. In contrast, oral administration of bortezomib did not result in fluorescent protein accumulation in tumors or exhibit any antitumor activity. These results indicate that in vivo imaging using the ZsProSensor‐1 fluorescent protein can be used as an indicator of antitumor activity and will be a powerful tool for the development of novel proteasome inhibitors.

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