Role of promyelocytic leukemia (PML) sumolation in nuclear body formation, 11S proteasome recruitment, and As2O3-induced PML or PML/retinoic acid receptor alpha degradation.

Promyelocytic leukemia (PML) is the organizer of nuclear matrix domains, PML nuclear bodies (NBs), with a proposed role in apoptosis control. In acute promyelocytic leukemia, PML/retinoic acid receptor (RAR) alpha expression disrupts NBs, but therapies such as retinoic acid or arsenic trioxide (As2O3) restore them. PML is conjugated by the ubiquitin-related peptide SUMO-1, a process enhanced by As2O3 and proposed to target PML to the nuclear matrix. We demonstrate that As2O3 triggers the proteasome-dependent degradation of PML and PML/RARalpha and that this process requires a specific sumolation site in PML, K160. PML sumolation is dispensable for its As2O3-induced matrix targeting and formation of primary nuclear aggregates, but is required for the formation of secondary shell-like NBs. Interestingly, only these mature NBs harbor 11S proteasome components, which are further recruited upon As2O3 exposure. Proteasome recruitment by sumolated PML only likely accounts for the failure of PML-K160R to be degraded. Therefore, studying the basis of As2O3-induced PML/RARalpha degradation we show that PML sumolation directly or indirectly promotes its catabolism, suggesting that mature NBs could be sites of intranuclear proteolysis and opening new insights into NB alterations found in viral infections or transformation.

Heat-induced relocalization of protein kinase CK2. Implication of CK2 in the context of cellular stress.

Among various other roles described so far, protein kinase CK2 has been involved in cell cycle, proliferation, and development. Here, we show that in response to specific stresses (heat shock or UV irradiation), a pool of the cellular CK2 content relocalizes in a particular nuclear fraction, increasing the activity of the kinase there. Electron microscopic analysis shows that upon heat shock, CK2alpha and CK2beta subunits are both detected in similar speckle structures occurring in the interchromatin space but are differentially targeted inside the nucleolus. This CK2 relocalization process takes place in a time- and dose-dependent manner and is reversible upon recovery at 37 degrees C. Altogether, this work suggests CK2 be involved in the response to physiological stress in higher eukaryotic cells.

The prosome: an ubiquitous morphologically distinct RNP particle associated with repressed mRNPs and containing specific ScRNA and a characteristic set of proteins.

A novel ribonucleoprotein (RNP) particle showing a highly compact and characteristic structure in the electron microscope was found associated with globin and other repressed mRNA in the cytoplasm of duck, mouse and HeLa cells. This 19S complex is of extraordinary stability: dissociated by 0.5 M KCl or EDTA from the (still repressed) core globin mRNP, it can be purified on gradients containing 1% Sarkosyl, and resists (unfixed) caesium sulphate-dimethylsulphoxide density centrifugation. Its density of 1.31 g/cm3 indicates an RNP complex with a 15% RNA component. In mouse and duck it contains approximately 10 proteins in the 20 000-30 000 mol. wt. range, a few components of 50 000-70 000 mol. wt., and two specific small cytoplasmic RNAs (ScRNA) of 70-90 nucleotides. Both of these RNAs have identical 3'-terminal oligonucleotides. We propose the name 'prosome' for this ScRNP particle which somehow participates in negative control of mRNA translation, and we believe will prove to be ubiquitous to animal species.

Intra-lesional injection of immunostimulants in bilateral rat tumors.

Rats grafted with either two or six fragments of isogenic methylcholanthrene-induced transplantable fibrosarcomas were treated IT1 with living BCG or killed C. parvum or a mixture of both immunostimulants. Various tumor combination and therapeutic agent dosages were compared. When two fragments of the same tumor McFiFi2 (S) were grafted simultaneously, IT treatment of one of these with 2 mg of BCG induced cure of both in 50% of the animals, but IT injection of 2 X 10(9) C. parvum was completely without effect in this situation. The prognosis was however, improved when the dose of immunostimulant was increased. The best results were obtained when each individual tumor in rats with two or six simultaneous identical grafts were treated with a mixture of BCG and C. parvum. The combination of IT immunostimulant treatment and surgical excision of the treated lesion demonstrated a persistence of the curative effect on the remote untreated tumor. Double grafting with isologous non-identical tumors revealed the influence of tumor burden and of the specificity of anti-tumor action of the treatment. The distant specific regression obtained in this system implies a specific immunological mechanism mediated by effector cells and/or antibodies which can circulate, identify the target cell and destroy it. This is in accordance with morphological observations. The intimate contact between BCG and the growing structured tumor is necessary for the therapeutic phenomenon.

Occurrence of a peculiar type of adenovirus 2 penton oligomer.

Evidence was presented that in adenovirus type 2, a representative of Rosen's subgroup III, a preferential oligomer species of pentons, penton tetramers, could be detected in freshly purified penton preparations.