SSX, a family of genes clustered on the X chromosome, has been identified as a cancer–testis antigen and also forms a part of the SYT–SSX fusion gene found in synovial sarcoma, implying that it has an important role in tumorigenesis. However, knowledge of the molecular regulation of SSX is still limited. In this study, we demonstrate that SSX or its SYT fusion protein is distributed as nuclear speckles, in which it is co-localized with B cell-specific Moloney murine leukemia virus insertion site 1 (Bmi1), which is a core factor of polycomb repressor complex 1. The C-terminal residues of SSX are indispensable for the nuclear speckle distribution, while the N-terminal domain is necessary for the recruitment of Bmi1, indicating that intact SSX must be needed for interaction with Bmi1 both spatially and functionally. In addition, the N-terminus of SSX also proved to contain an intrinsic nucleolar localization signal, which mediates the nucleolar translocation of SSX in particular kinds of cell stress such as the oxidation of hydrogen peroxide or heat shock. This stress-induced translocation is reversible and accompanied by HSP 70 or p14ARF traffic, suggesting that SSX is a stress response gene. It is of note that nucleolar translocation of SSX can result in disassociation of SSX from Bmi1, with consequent down-regulation of Bmi1 activity. These novel findings regarding distinct domains of SSX and its interaction with Bmi1 may shed light on the mechanism by which synovial sarcoma develops and on the up-regulation of SSX in cancer cells.

The midbody is a structural organelle formed in late phase mitosis which is responsible for completion of cytokinesis. Although various kinds of proteins have been found to distribute or immigrate to this organelle, their functions have still not been completely worked out. In this study, we demonstrated that NAT10 (N-acetyltransferase 10, NAT10) is not only predominantly distributed in the nucleolus in interphase, but is also concentrated in the mitotic midbody during telophase. The domain in N-terminal residues 549-834 of NAT10 specifically mediated its subcellular localization. Treatment with genotoxic agents or irradiation increased concentration of NAT10 in both the nucleolus and midbody. Moreover, DNA damage induced increase of NAT10 in the midbody apparently accompanied by in situ elevation of the level of acetylated alpha-tubulin, suggesting that it plays a role in maintaining or enhancing stability of alpha-tubulin. The depletion of NAT10 induced defects in nucleolar assembly, cytokinesis and decreased acetylated alpha-tubulin, leading to G2/M cell cycle arrest or delay of mitotic exit. In addition, over-expression of NAT10 was found in a variety of soft tissue sarcomas, and correlated with tumor histological grading. These results indicate that NAT10 may play an important role in cell division through facilitating reformation of the nucleolus and midbody in the late phase of cell mitosis, and stabilization of microtubules.

In a previous study, we demonstrated that telomerase transcriptional elements-interacting factor (TEIF) could up-regulate the expression of telomerase and DNA polymerase beta, increasing resistance to genotoxic agents. Here, we further report that TEIF can be stimulated by DNA damage and we have identified a cluster of repeated polypyrimidine tracts in the promoter of TEIF, which mediate both its basal transcription and its response to genotoxic agents. These polypyrimidine tracts are arranged in three types of repeating units and in each of these units there are 14 bp length tandem sequences, which are repeated three times. These sequences are also characteristically separated by an 11 bp interval sequence. Among these units, one type (5'-CCCCCCCATCCCCG-3') has been found to be involved in the transcriptional regulation of TEIF. At the same time, PTB1 (polypyrimidine tract-binding protein 1) has been shown to repress TEIF expression through interaction with this element. Up-regulation of TEIF may be achieved by PTB1 suppression that is induced by DNA damage, or by an olignucleotide decoy, which mediates reversal of suppression. This study provides new insight into the mechanism through which TEIF is involved in DNA damage response, together with insight into the role of polypyrimidine tracts in transcription regulation.

OBJECTIVE:To confirm the nucleolar localization of telomerase-regulation associated protein-human N-acetyltransferase-like protein (hALP) and its associated functions.METHODS:Immunofluoresent staining and immunoelectron microscopy were used to detect the distribution of hALP in HeLa and Saos2 cells, and the co-localization of hALP and rDNA was analyzed by fluorescence in situ hybridization and immunofluoresence. RNAi was performed to further verify the nucleolar localization of hALP. A series of eukaryotic expression plasmids carrying various portions of hALP sequence were constructed and transiently transfected to HeLa and Saos2 cells. The expression of hALP in tumor tissues was stained by immunohistochemistry.RESULTS:hALP distributed predominantly in the nucleoli of HeLa and Saos2 cells, and colocalized with rDNA. Granular component was the precise distribution of hALP in the nucleolus under electron microscope. Nucleolar signals for hALP reduced significantly in cells transfected with hALP siRNA. The carboxy terminus of hALP including residues 549-834 was necessary for its nucleolar localization. hALP could be detected in the nucleoli of many kinds of tumor cells, including leiomyosarcoma, primitive neuroectodermal tumor, neuroblastoma, melanoma, prostatic cancer, and clear cell renal carcinoma.CONCLUSION:hALP is a nucleolar protein, and the nucleolar localization is mediated by its carboxy terminal domain, and hALP could be detected in the nucleoli of many tumor tissues, which is worthy of further investigation.

OBJECTIVE To explore the significance in the change of telomere length in mesenchymal sarcomas, through analyzing telomere length and expression of its associated proteins, including TRF1, POT1, hTERT, P53 and c-myc. METHODS The telomere length in 20 cases of osteosarcomas, 25 of chondrosarcomas, 19 of rhabdomyosarcomas, 26 of liposarcomas was measured by telomere fluorescence in situ hybridization (Telo-FISH), and the expression of TRF1, POT1, hTERT, p53 or c-myc was analyzed by immunohistochemistry, respectively. RESULTS The telomere length in osteosarcomas was significantly shorter than that of either chondrosarcomas or liposarcomas (P<0.05). Similarly, the telomere length of rhabdomyosarcoma was shorter than that of chondrosarcoma (P<0.05). Meanwhile, telomere shortening was positively correlated with down expression of telomere binding proteins TRF1 and POT1 (P<0.05), but trends were detected more frequently in positive expression of hTERT (P<0.05) and in nuclear accumulation of P53 or expression of c-myc. With advancing in histological grading, telomere length was shortened markedly in chondrosarcomas, especially in liposarcomas (P<0.05). CONCLUSION The shortening of telomere could prevail in mesenchymal sarcoma and reflect the malignant potential. Telomere attrition usually correlated with down expression of POT1, TRF1 and with increased levels of hTERT, P53 and c-myc.