The budding yeast Ipl1/Aurora protein kinase regulates mitotic spindle disassembly

Ipl1p is the budding yeast member of the Aurora family of protein kinases, critical regulators of genomic stability that are required for chromosome segregation, the spindle checkpoint, and cytokinesis. Using time-lapse microscopy, we found that Ipl1p also has a function in mitotic spindle disassembly that is separable from its previously identified roles. Ipl1-GFP localizes to kinetochores from G1 to metaphase, transfers to the spindle after metaphase, and accumulates at the spindle midzone late in anaphase. Ipl1p kinase activity increases at anaphase, and ipl1 mutants can stabilize fragile spindles. As the spindle disassembles, Ipl1p follows the plus ends of the depolymerizing spindle microtubules. Many Ipl1p substrates colocalize with Ipl1p to the spindle midzone, identifying additional proteins that may regulate spindle disassembly. We propose that Ipl1p regulates both the kinetochore and interpolar microtubule plus ends to regulate its various mitotic functions.     

Proprotein convertase cleavage liberates a fibrillogenic fragment of a resident glycoprotein to initiate melanosome biogenesis

Lysosome-related organelles are cell type-specific intracellular compartments with distinct morphologies and functions. The molecular mechanisms governing the formation of their unique structural features are not known. Melanosomes and their precursors are lysosome-related organelles that are characterized morphologically by intralumenal fibrous striations upon which melanins are polymerized. The integral membrane protein Pmel17 is a component of the fibrils and can nucleate their formation in the absence of other pigment cell-specific proteins. Here, we show that formation of intralumenal fibrils requires cleavage of Pmel17 by a furin-like proprotein convertase (PC). As in the generation of amyloid, proper cleavage of Pmel17 liberates a lumenal domain fragment that becomes incorporated into the fibrils; longer Pmel17 fragments generated in the absence of PC activity are unable to form organized fibrils. Our results demonstrate that PC-dependent cleavage regulates melanosome biogenesis by controlling the fibrillogenic activity of a resident protein. Like the pathologic process of amyloidogenesis, the formation of other tissue-specific organelle structures may be similarly dependent on proteolytic activation of physiological fibrillogenic substrates.     

Prevalence and typing of HPV DNA in atypical squamous cells in pregnant women

OBJECTIVE: To determine the prevalence and typing of HPV DNA in pregnant women with a diagnosis of atypical squamous cells (ASC) and to assess whether pregnancy-related changes contribute to the diagnosis of ASC. STUDY DESIGN: HPV testing was performed on residual specimens from the ThinPrep Pap test (Cytyc Corp., Boxborough, Massachusetts, U.S.A.) in pregnant women diagnosed as ASC (study group, n = 105), low and high grade squamous intraepithelial lesion (LSIL and HSIL) (positive control, n = 33) and negative for epithelial cell abnormality (negative control, n = 20). All cases were reviewed by 2 cytopathologists to obtain consensus diagnoses using the Bethesda System 2001 criteria. The study group cases were further subcategorized into ASC of undetermined significance (ASCUS, n = 99) and ASC cannot exclude HSIL (ASC-H, n = 6). HPV testing was also performed on an ASC control group consisting of 68 consecutive ASC cases in nonpregnant women, matched by age. RESULTS: Mean patient age was 23.7 years for the study group and 25.6 years for the ASC control group. HPV DNA was detected in 88.6% of cases in the study group, including 87.9% of ASC-US and 100% of ASC-H cases. Of the HPV positive cases, 79.6%, 4.3%, 5.4% and 10.8% had high-risk, mixed high- and low-risk, low-risk and unknown HPV types, respectively. The most frequent HPV types detected were: types 52 (31.2%), 16 (15.1%), 39 (11.8%), 53 (10.8%), and 18 and 58 (9.7% each). Multiple viral types were detected in 43.0% of cases. The prevalence of HPV DNA in the positive and negative controls in pregnant women was 100% and 55%, respectively. HPV DNA was detected in 83.8% of the ASC control group. CONCLUSION: Regardless of pregnancy-related changes, the prevalence of HPV DNA in pregnant women (88.6%) was similar to that found in ASC in nonpregnant women of the same reproductive-age group (83.8%), and the high-risk types accounted for the vast majority of cases (83.9%). These findings demonstrate that pregnancy-related changes do not contribute to the diagnosis of ASC in this subset of women. Furthermore, the high HPV DNA prevalence in reproductive-age women (< 40 years) suggests that HPV testing may have limited utility in effective management of these patients.     

Insertion mutagenesis of Escherichiacoli GroEL

To gain insights into the in vivo folding and assembly of bacterial chaperonins, groEL was subjected to insertion mutagenesis using transposon ISlacZ/in. Four GroEL-LacZ fusions and the corresponding insertion mutants were obtained after residues 34, 90, 291, and 367. Apical domain insertion mutants GroEL291 and GroEL367 were degraded into monomeric 30- and 40-kDa fragments, respectively. Only the latter was fully soluble, suggesting that proper isomerization of an essentially complete apical domain is required for efficient protomer folding. Truncated variants were inactive as minichaperones as they failed to restore the growth of groEL140 cells at 43 degrees C whether or not GroES was co-expressed. A 31-residue insertion in equatorial helix D led to complete degradation of GroEL90. By contrast, extraneous amino acids were tolerated at equatorial position 34, indicating that this region is highly flexible. Nevertheless, GroEL34 did not fold as efficiently as authentic GroEL and reached only a heptameric conformation.     

Angiotensin II and its receptors in human endocardial endothelial cells: role in modulating intracellular calcium

The aims of the present study are to investigate the presence and distribution of angiotensin II (Ang II), as well as AT1 and AT2 receptors, in endocardial endothelial cells (EECs) and to determine if the effect of Ang II on intracellular calcium in these cells is mediated via the AT1 or the AT2 receptor. Immunofluorescence and 3D confocal microscopy techniques were used on 20-week-old fetal human EECs. Our results showed that Ang II and its receptors, the AT1 and the AT2 types, are present and exhibit a different distribution in human EECs. Ang II labelling is found throughout the cell with a fluorescence signal higher in the cytosol when compared with the nucleus. Like Ang II, the AT1 receptor fluorescence signal is also homogeneously distributed in human EECs but with a preferential labelling at the level of the nucleus, while the AT2 receptor labelling is solely present in the nucleus. Using fluo-3 and 3D confocal microscopy technique, superfusion of human EECs with increasing concentration of Ang II induced a dose-dependent sustained increase in free cytosolic and nuclear Ca2+ levels. This effect of Ang II on human EEC's intracellular Ca2+ ([Ca2+]) was completely prevented by losartan, an AT1 receptor antagonist. Our results suggest that Ang II, as well as AT1 and AT2 receptors, is present but differentially distributed in EECs of 20-week-old fetal human hearts, and that the AT1 receptor mediates the effects of Ang II on [Ca2+]i in these cells.     

Cytochrome oxidase assembly does not require catalytically active cytochrome C

Cytochrome c oxidase (COX), the terminal enzyme of the mitochondrial respiratory chain, catalyzes the transfer of electrons from reduced cytochrome c to molecular oxygen. COX assembly requires the coming together of nuclear- and mitochondrial-encoded subunits and the assistance of a large number of nuclear gene products acting at different stages of maturation of the enzyme. In Saccharomyces cerevisiae, expression of cytochrome c, encoded by CYC1 and CYC7, is required not only for electron transfer but also for COX assembly through a still unknown mechanism. We have attempted to distinguish between a functional and structural requirement of cytochrome c in COX assembly. A cyc1/cyc7 double null mutant strain was transformed with the cyc1-166 mutant gene (Schweingruber, M. E., Stewart, J. W., and Sherman, F. (1979) J. Biol. Chem. 254, 4132-4143) that expresses stable but catalytically inactive iso-1-cytochrome c. The COX content of the cyc1/cyc7 double mutant strain harboring non-functional iso-1-cytochrome c has been characterized spectrally, functionally, and immunochemically. The results of these studies demonstrate that cytochrome c plays a structural rather than functional role in assembly of cytochrome c oxidase. In addition to its requirement for COX assembly, cytochrome c also affects turnover of the enzyme. Mutants containing wild type apocytochrome c in mitochondria lack COX, suggesting that only the folded and mature protein is able to promote COX assembly.     

Vaccination with a Melan-A peptide selects an oligoclonal T cell population with increased functional avidity and tumor reactivity

Both the underlying molecular mechanisms and the kinetics of TCR repertoire selection following vaccination against tumor Ags in humans have remained largely unexplored. To gain insight into these questions, we performed a functional and structural longitudinal analysis of the TCR of circulating CD8(+) T cells specific for the HLA-A2-restricted immunodominant epitope from the melanocyte differentiation Ag Melan-A in a melanoma patient who developed a vigorous and sustained Ag-specific T cell response following vaccination with the corresponding synthetic peptide. We observed an increase in functional avidity of Ag recognition and in tumor reactivity in the postimmune Melan-A-specific populations as compared with the preimmune blood sample. Improved Ag recognition correlated with an increase in the t(1/2) of peptide/MHC interaction with the TCR as assessed by kinetic analysis of A2/Melan-A peptide multimer staining decay. Ex vivo analysis of the clonal composition of Melan-A-specific CD8(+) T cells at different time points during vaccination revealed that the response was the result of asynchronous expansion of several distinct T cell clones. Some of these T cell clones were also identified at a metastatic tumor site. Collectively, these data show that tumor peptide-driven immune stimulation leads to the selection of high-avidity T cell clones of increased tumor reactivity that independently evolve within oligoclonal populations.     

NMR studies of the aggregation of glucagon-like peptide-1: formation of a symmetric helical dimer

Nuclear magnetic resonance (NMR) spectroscopy reveals that higher-order aggregates of glucagon-like peptide-1-(7-36)-amide (GLP-1) in pure water at pH 2.5 are disrupted by 35% 2,2,2-trifluoroethanol (TFE), and form a stable and highly symmetric helical self-aggregate. NMR spectra show that the helical structure is identical to that formed by monomeric GLP-1 under the same experimental conditions [Chang et al., Magn. Reson. Chem. 37 (2001) 477-483; Protein Data Bank at RCSB code: 1D0R], while amide proton exchange rates reveal a dramatic increase of the stability of the helices of the self-aggregate. Pulsed-field gradient NMR diffusion experiments show that the TFE-induced helical self-aggregate is a dimer. The experimental data and model calculations indicate that the dimer is a parallel coiled coil, with a few hydrophobic residues on the surface that may cause aggregation in pure water. The results suggest that the coiled coil dimer is an intermediate state towards the formation of higher aggregates, e.g. fibrils.     

Ribozyme inhibition of alphavirus replication

A model system to examine the expression and antiviral activity of trans-acting ribozymes in mammalian cells has been developed and evaluated. Hairpin ribozymes were engineered to cleave a specific site, identified by a combinatorial activity-based selection method, within genomic and subgenomic RNA species of Sindbis virus. Transiently transfected cells expressed moderate levels of ribozyme (approximately 50,000 molecules/cell) with predominant nuclear localization and a short half-life (23 min). Stable cell lines expressed ribozymes at modest levels (approximately 2,000 molecules/cell). Ribozyme-mediated RNA cleavage activity was detected in cell extracts. Clonal cell lines were challenged with recombinant Sindbis virus, and viral replication was examined using plaque formation and green fluorescent protein assays. Significant inhibition of viral replication was observed in cells expressing the active antiviral ribozyme, and lower levels of inhibition in control cells expressing inactive or irrelevant ribozymes. These findings are consistent with a model in which inhibition of viral replication occurs via ribozyme cleavage of viral RNAs, suggesting that ribozymes may represent useful antiviral agents.