Nuclear bodies (NBs) are ultrastructurally defined granules predominantly found in dividing cells. Here we show that PML, a protein involved in the t(15;17) translocation of acute promyelocytic leukaemia (APL), is specifically bound to a NB. PML and several NB‐associated proteins, found as auto‐antigens in primary biliary cirrhosis (PBC), are co‐localized and co‐regulated. The APL‐derived PML‐RAR alpha fusion protein is shown to be predominantly localized in the cytoplasm, whereas a fraction is nuclear and delocalizes the NB antigens to multiple smaller nuclear clusters devoid of ultrastructural organization. RA administration (which in APL patients induces blast differentiation and consequently complete remissions) causes the re‐aggregation of PML and PBC auto‐antigens onto the NB, while PML‐RAR alpha remains mainly cytoplasmic. Thus, PML‐RAR alpha expression leads to a RA‐reversible alteration of a nuclear domain. These results shed a new light on the pathogenesis of APL and provide a molecular link between NBs and oncogenesis.

We report the isolation of 10 differentially expressed cDNAs in the process of apoptosis induced by the p53 tumor suppressor. As a global analytical method, we performed a differential display of mRNA between mouse Ml myeloid leukemia cells and derived clone LTR6 cells, which contain a stably transfected temperature-sensitive mutant of p53. At 32°C wild-type p53 function is activated in LTR6 cells, resulting in programmed cell death.

Developmentally regulated genes in Drosophila, which are conserved through evolution, are potential candidates for key functions in biological processes such as cell cycle, programmed cell death, and cancer. We report cloning and characterization of the human homologue of the Drosophila seven in absentia gene (HUMSIAH), which codes for a 282 amino acids putative zinc finger protein. HUMSIAH is localized on human chromosome 16ql2-ql3. This gene is activated during the physiological program of cell death in the intestinal epithelium. Moreover, human cancer-derived cells selected for suppression of their tumorigenic phenotype exhibit constitutively elevated levels of HUMSIAH mRNA. A similar pattern of expression is also displayed by the p2lwan. These results suggest that mammalian seven in absentia gene, which is a target for activation by p53, may play a role in apoptosis and tumor suppression.

BCMA is a human gene expressed preferentially in mature B lymphocytes as a 1.2 kb mRNA, which encodes a 184 amino acid peptide (BCMAp). The study of BCMA mRNA expression, using human malignant B cell lines characteristic of different stages of B lymphocyte differentiation, demonstrated that the BCMA mRNA is absent in the pro-B lymphocyte stage. It is expressed faintly at the pre-B cell stage and its expression increases with B lymphocyte maturation. Polyclonal antibodies were used to show, by cellular fractionation and immunoprecipitation, that BCMAp is a non-glycosylated integral membrane protein. Furthermore, BCMAp inserts, in vitro, into canine microsomes, as a type I integral membrane protein. Cell surface labeling showed that BCMAp is not expressed in the plasma membrane of mature B lymphocytes. Immunofluorescence studies revealed that BCMAp lies in a cap-like structure near the nucleus, that was identified as the Golgi apparatus by co-localization of BCMAp with CTR433, a marker of the medial cisternae of the Golgi apparatus. Confocal scanning laser microscopy of U266 plasma cells labeled with markers of various Golgi apparatus subcompartments strongly suggests that BCMAp is located in the cis part of the Golgi apparatus. Thus, BCMAp is the first Golgi resident protein with a tissue specificity and whose expression is linked to the stage of differentiation of B lymphocytes. The location of BCMAp in the Golgi apparatus and its high expression in plasmocytes (secreting large amounts of Ig) suggest that BCMAp is implicated in the intracellular traffic of Ig.

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Percutaneous 4-OHT gel has a local impact on tumor proliferation. It could be tested in future prospective trials of chemoprevention or ductal carcinoma in situ adjuvant hormonotherapy.

SIAH-1, the human homologue of the drosophila seven in absentia gene, is a p53-p21 Waf-1 inducible gene. We report that stable transfection with SIAH-1 of the epithelial breast cancer cell line MCF-7 blocks its growth process. The transfectants show a redistribution of SIAH-1 protein within the nucleus, more speci®cally to the nuclear matrix, associated to dramatic changes in cell morphology and defective mitosis. Multinucleated giant cells (2 ± 12 nuclei in more than 50% cells) were a most striking observation associated with tubulin spindle disorganization and defective cytokinesis. There were also present at high frequency abortive mitotic ®gures, DNA bridges and persistance of intercellular bridges and midbodies, along with an increased expression of p21 Waf-1 . These results indicate that the mechanism of growth arrest induced by SIAH-1 in MCF-7 cells involves disorganization of the mitotic program, mainly during nuclei separation and cytokinesis.

Interphasic nuclear organization has a key function in genome biology. We demonstrate that p21 WAF-1 , by inf luencing gene expression and inducing chromosomal repositioning in tumor suppression, plays a major role as a nuclear organizer. Transfection of U937 tumor cells with p21 WAF-1 resulted in expression of the HUMSIAH (human seven in absentia homologue), Rb, and Rbr-2 genes and strong suppression of the malignant phenotype. p21 WAF-1 drastically modified the compartmentalization of the nuclear genome. DNase I genome exposure and f luorescence in situ hybridization show, respectively, a displacement of the sensitive sites to the periphery of the nucleus and repositioning of chromosomes 13, 16, 17, and 21. These findings, addressing nuclear architecture modulations, provide potentially significant perspectives for the understanding of tumor suppression.