Degradation of DNA topoisomerase I by a novel trypsin-like serine protease in proliferating human T lymphocytes

Activation of multiple proteolysis systems contributes to acute cadmium cytotoxicity

Cadmium exhibits both toxic and carcinogenic effects, and its cytotoxicity is linked to various cellular pathways, such as oxidative stress, ubiquitin-proteasome, and p53-mediated response pathways. The molecular mechanism(s) underlying cadmium cytotoxicity appears to be complex, but remains largely unclear. Here, we examined the effects of cadmium on the protein catabolism using two surrogate markers, DNA topoisomerases I and II alpha and its contribution to cytotoxicity. We have found that cadmium exposure induced time- and concentration-dependent decreases in the protein level of surrogate markers and therefore suggest that cadmium may be involved in proteolysis system activation. A pharmacological study further revealed the novel role(s) of these proteolytic activities and reactive oxygen species (ROS) in the cadmium-induced acute toxicity: (i) Proteasome inhibition only partially relieved the cadmium-induced proteolysis of topoisomerases; (ii) Moreover, we report for the first time that the activation of metalloproteases, serine proteases, and cysteine proteases contributes to the acute cadmium cytotoxicity; (iii) Consistent with the notion that both ROS generation and proteolysis system activation contribute to the cadmium-induced proteolysis and cytotoxicity, the scavenger N-acetylcysteine and aforementioned protease inhibition not only reduced the cadmium-induced topoisomerase degradation but also alleviated the cadmium-induced cell killing. Taken together, acute cadmium exposure may activate multiple proteolytic systems and ROS formation, subsequently leading to intracellular damage and cytotoxicity. Thus, our results provide a novel insight into potential action mechanism(s) by which cadmium exerts its cytotoxic effect and suggest potential strategies to prevent cadmium-associated acute toxicity.

Human tissue factor pathway inhibitor-2 is internalized by cells and translocated to the nucleus by the importin system

Tissue factor pathway inhibitor-2 (TFPI-2) is a serine proteinase inhibitor that induces caspase-mediated apoptosis when offered to a variety of tumor cells. In order to investigate the mechanism of TFPI-2-induced apoptosis, we initially studied the uptake and trafficking of TFPI-2 by HT-1080 cells. Exogenously offered TFPI-2 was rapidly internalized and distributed in both the cytosolic and nuclear fractions. Nuclear localization of TFPI-2 was also detected in a variety of endothelial cells constitutively expressing TFPI-2. Nuclear localization of TFPI-2 required a NLS sequence located in its Lys/Arg-rich C-terminal tail comprising residues 191-211, as a TFPI-2 construct lacking the C-terminal tail failed to localize to the nucleus. Complexes of TFPI-2 and importin-alpha were co-immunoprecipitated from cell lysates of HT-1080 cells either offered or overexpressing this protein, providing evidence that TFPI-2 was shuttled to the nucleus by the importin system. Our results provide the initial description of TFPI-2 internalization and translocation to the nucleus in a number of cells.

Subcellular transport of EKLF and switch-on of murine adult beta maj globin gene transcription

Erythroid Krüppel-like factor (EKLF) is an essential transcription factor for mammalian beta-like globin gene switching, and it specifically activates transcription of the adult beta globin gene through binding of its zinc fingers to the promoter. It has been a puzzle that in the mouse, despite its expression throughout the erythroid development, EKLF activates the adult beta(maj) globin promoter only in erythroid cells beyond the stage of embryonic day 10.5 (E10.5) but not before. We show here that expression of the mouse beta(maj) globin gene in the aorta-gonad-mesonephros region of E10.5 embryos and in the E14.5 fetal liver is accompanied by predominantly nuclear localization of EKLF. In contrast, EKLF is mainly cytoplasmic in the erythroid cells of E9.5 blood islands in which beta(maj) is silenced. Remarkably, in a cultured mouse adult erythroleukemic (MEL) cell line, the activation of the beta(maj) globin gene by dimethyl sulfoxide (DMSO) or hexamethylene-bis-acetamide (HMBA) induction is also paralleled by a shift of the subcellular location of EKLF from the cytoplasm to the nucleus. Blockage of the nuclear import of EKLF in DMSO-induced MEL cells with a nuclear export inhibitor repressed the transcription of the beta(maj) globin gene. Transient transfection experiments further indicated that the full-sequence context of EKLF was required for the regulation of its subcellular locations in MEL cells during DMSO induction. Finally, in both the E14.5 fetal liver cells and induced MEL cells, the beta-like globin locus is colocalized the PML oncogene domain nuclear body, and concentrated with EKLF, RNA polymerase II, and the splicing factor SC35. These data together provide the first evidence that developmental stage- and differentiation state-specific regulation of the nuclear transport of EKLF might be one of the steps necessary for the switch-on of the mammalian adult beta globin gene transcription.

The role of microtubule actin cross-linking factor 1 (MACF1) in the Wnt signaling pathway

MACF1 (microtubule actin cross-linking factor 1) is a multidomain protein that can associate with microfilaments and microtubules. We found that MACF1 was highly expressed in neuronal tissues and the foregut of embryonic day 8.5 (E8.5) embryos and the head fold and primitive streak of E7.5 embryos. MACF1(-/-) mice died at the gastrulation stage and displayed developmental retardation at E7.5 with defects in the formation of the primitive streak, node, and mesoderm. This phenotype was similar to Wnt-3(-/-) and LRP5/6 double-knockout embryos. In the absence of Wnt, MACF1 associated with a complex that contained Axin, beta-catenin, GSK3beta, and APC. Upon Wnt stimulation, MACF1 appeared to be involved in the translocation and subsequent binding of the Axin complex to LRP6 at the cell membrane. Reduction of MACF1 with small interfering RNA decreased the amount of beta-catenin in the nucleus, and led to an inhibition of Wnt-induced TCF/beta-catenin-dependent transcriptional activation. Similar results were obtained with a dominant-negative MACF1 construct that contained the Axin-binding region. Reduction of MACF1 in Wnt-1-expressing P19 cells resulted in decreased T (Brachyury) gene expression, a DNA-binding transcription factor that is a direct target of Wnt/beta-catenin signaling and required for mesoderm formation. These results suggest a new role of MACF1 in the Wnt signaling pathway.

Rosette-type tegumental glands associated with aesthetasc sensilla in the olfactory organ of the Caribbean spiny lobster, Panulirus argus

The lateral antennular flagellum of decapod crustaceans bears unique olfactory sensilla, namely the aesthetascs, and other sensilla types. In this study, we identify a new major tissue in the lateral flagellum of the Caribbean spiny lobster, Panulirus argus, namely "aesthetasc tegumental glands" (ATGs), based on immunostaining with antibodies against CUB serine protease (Csp), in situ hybridization with csp-specific probes, labeling with the F-actin marker phalloidin, labeling with the nuclear marker Hoechst 33258, and staining with methylene blue. Each ATG has 12-20 secretory cells arranged in a rosette. Each secretory cell has a Csp-immunoreactive basal portion and an apical portion containing granular material (metachromatic staining indicative of acid mucopolysaccharides). At the center of each secretory rosette is a phalloidin-positive common locus that gives rise to a main drainage duct projecting toward the cuticle. Scanning electron and light microscopy show that thin ducts traverse the cuticle and connect to "peg pores" proximal to the bases of the aesthetascs, with 3.4 peg pores per aesthetasc. Since the number of common loci is correlated with the number of peg pores, we conclude that each pore represents the outlet of one ATG, and that the secretions are released from them. We conclude further that ATGs and aesthetascs are functionally linked. We hypothesize that ATG secretions have antifouling and/or friction-reducing properties, and that they are spread over the surface of the aesthetascs by antennular grooming. A review of the literature suggests that ATGs are common in decapod crustacean antennules, and that rosette glands and grooming might be functionally coupled in other body areas.

The topoisomerase 1-interacting protein BTBD1 is essential for muscle cell differentiation

DNA topoisomerase I (Topo1) contributes to vital biological functions, but its regulation is not clearly understood. The BTBD1 protein was recently cloned on the basis of its interaction with the core domain of Topo1 and is expressed particularly in skeletal muscle. To determine BTBD1 functions in this tissue, the in vitro model used was the C2C12 mouse muscle cell line, which expresses BTBD1 mainly after myotube differentiation. We studied the effects of a stably overexpressed BTBD1 protein truncated of the 108 N-terminal amino-acid residues and harbouring a C-terminal FLAG tag (Delta-BTBD1). The proliferation speed of Delta-BTBD1 C2C12 cells was significantly decreased and no myogenic differentiation was observed, although these cells maintained their capacity to enter adipocyte differentiation. These alterations could be related to Topo1 deregulation. This hypothesis is further supported by the decrease in nuclear Topo1 content in Delta-BTBTD1 proliferative C2C12 cells and the switch from the main peripheral nuclear localization of Topo1 to a mainly nuclear diffuse localization in Delta-BTBTD1 C2C12 cells. Finally, this study demonstrated that BTBD1 is essential for myogenic differentiation.

An in vitro bioassay to determine individual sensitivity to glucocorticoids: induction of FKBP51 mRNA in peripheral blood mononuclear cells

Individual variation in sensitivity to glucocorticoids (GCs) poses a dilemma to the clinician. Currently available assays to determine individual sensitivity to GCs either seem imprecise, or they are based on mitogen-activated lymphocytes, although mitogens themselves may affect cellular GC sensitivity. To avoid these disadvantages, we developed an assay based on the GC-induced accumulation of the 51kDa FK506 binding protein (FKBP51) mRNA in unstimulated peripheral blood mononuclear cells (PBMC), measured using real time PCR. Of several family members tested, only FKBP51 transcript levels showed to be GC-inducible. Furthermore, our bioassay was not affected by progesterone, estradiol, and testosterone. Immunological stimulation of PBMC using tetanus toxoid did not affect bioassay results, and isolated T- and B-lymphocytes showed a similar response to GC stimulation. The intra- and inter-assay variations were 10.6 and 15.9%, respectively. Our bioassay confirms previous reports that a wide variation in GC sensitivity exists in the normal population, yet is able to clearly discriminate a patient with familial GC hyposensitivity from controls. Our bioassay may be suitable to assess altered individual GC sensitivity, and the small amount of PBMC needed for a determination makes this assay easily applicable in a pediatric setting.

Molecular interactions between poly(ADP-ribose) polymerase (PARP I) and topoisomerase I (Topo I): identification of topology of binding

The molecular interactions of poly(ADP-ribose) polymerase I (PARP I) and topoisomerase I (Topo I) have been determined by the analysis of physical binding of the two proteins and some of their polypeptide components and by the effect of PARP I on the enzymatic catalysis of Topo I. Direct association of Topo I and PARP I as well as the binding of two Topo I polypeptides to PARP I are demonstrated. The effect of PARP I on the 'global' Topo I reaction (scission and religation), and the activation of Topo I by the 36 kDa polypeptide of PARP I and catalytic modifications by poly(ADP-ribosyl)ation are also shown. The covalent binding of Topo I to circular DNA is activated by PARP I similar to the degree of activation of the 'global' Topo I reaction, whereas the religation of DNA is unaffected by PARP I. The geometry of PARP I-Topo I interaction compared to automodified PARP I was reconstructed from direct binding assays between glutathione S-transferase fusion polypeptides of Topo I and PARP I demonstrating highly selective binding, which was correlated with amino acid sequences and with the 'C clamp' model derived from X-ray crystallography.