Early but not late conformational changes of tau in association with ubiquitination of neurofibrillary pathology in Alzheimer's disease brains.

In Alzheimer's disease, tau protein undergoes post-translational modifications including hyperphosphorylation and truncation, which promotes two major conformational changes associated with progressive N-terminal folding. Along with the development of the disease, tau ubiquitination was previously shown to emerge in the early and intermediate stages of the disease, which is closely associated with early tau truncation at aspartic acid 421, but not with a subsequently truncated tau molecule at glutamic acid 391. In the same group of cases, using multiple immunolabeling and confocal microscopy, a possible relationship between the ubiquitin-targeting of tau and the progression of conformational changes adopted by the N-terminus of this molecule was further studied. A comparable number of neurofibrillary tangles was found displaying ubiquitin, an early conformation recognized by the Alz-50 antibody, and a phosphorylation. However, a more reduced number of neurofibrillary tangles were immunoreactive to Tau-66 antibody, a late tau conformational change marker. When double-labeling profiles of neurofibrillary tangles were assessed, ubiquitination was clearly demonstrated in tau molecules undergoing early N-terminal folding, but was barely observed in late conformational changes of the N-terminus adopted by tau. The same pattern of colocalization was visualized in neuritic pathology. Overall, these results indicate that a more intact conformation of the N-terminus of tau may facilitate tau ubiquitination, but this modification may not occur in a late truncated and more compressed folding of the N-terminus of the tau molecule.

Fragmentation of the Golgi Apparatus in Neuroblastoma Cells Is Associated with Tau-Induced Ring-Shaped Microtubule Bundles.

Abnormal fibrillary aggregation of tau protein is a pathological condition observed in Alzheimer's disease and other tauopathies; however, the presence and pathological significance of early non-fibrillary aggregates of tau remain under investigation. In cell and animal models expressing normal or modified tau, toxic effects altering the structure and function of several membranous organelles have also been reported in the absence of fibrillary structures; however, how these abnormalities are produced is an issue yet to be addressed. In order to obtain more insights into the mechanisms by which tau may disturb intracellular membranous elements, we transiently overexpressed human full-length tau and several truncated tau variants in cultured neuroblastoma cells. After 48 h of transfection, either full-length or truncated tau forms produced significant fragmentation of the Golgi apparatus (GA) with no changes in cell viability. Noteworthy is that in the majority of cells exhibiting dispersion of the GA, a ring-shaped array of cortical or perinuclear microtubule (Mt) bundles was also generated under the expression of either variant of tau. In contrast, Taxol treatment of non-transfected cells increased the amount of Mt bundles but not sufficiently to produce fragmentation of the GA. Tau-induced ring-shaped Mt bundles appeared to be well-organized and stable structures because they were resistant to Nocodazole post-treatment and displayed a high level of tubulin acetylation. These results further indicate that a mechanical force generated by tau-induced Mt-bundling may be responsible for Golgi fragmentation and that the repeated domain region of tau may be the main promoter of this effect.

HPV16-E6 Oncoprotein Activates TGF-ß and Wnt/ß-Catenin Pathways in the Epithelium-Mesenchymal Transition of Cataracts in a Transgenic Mouse Model.

OBJECTIVE: This work aimed to determine if cataractous changes associated with EMT occurring in the K14E6 mice lenses are associated with TGF-ß and Wnt/ß-catenin signaling activation. MATERIALS AND METHODS: Cataracts of K14E6 mice were analysed histologically; and components of TGF-ß and Wnt/ß-catenin signaling were evaluated by Western blot, RT-qPCR, in situ RT-PCR, IHC, or IF technics. Metalloproteinases involved in EMT were also assayed using zymography. The endogenous stabilisation of Smad7 protein was also assessed using an HDAC inhibitor. RESULTS: The K14E6 mice, which displayed binocular cataracts in 100% of the animals, exhibited loss of tissue organisation, cortical liquefaction, and an increase in the number of hyperproliferative-nucleated cells with mesenchymal-like characteristics in the lenses. Changes in lenses' cell morphology were due to actin filaments reorganisation, activation of TGF-ß and Wnt/ß-catenin pathways, and the accumulation of MTA1 protein. Finally, the stabilisation of Smad7 protein diminishes cell proliferation, as well as MTA1 protein levels. CONCLUSION: The HPV16-E6 oncoprotein induces EMT in transgenic mice cataracts. The molecular mechanism may involve TGF-ß and Wnt/ß-catenin pathways, suggesting that the K14E6 transgenic mouse could be a useful model for the study or treatment of EMT-induced cataracts.

The PDZ-Binding Motif of HPV16-E6 Oncoprotein Modulates the Keratinization and Stemness Transcriptional Profile In Vivo.

OBJECTIVE: The aim of this work was to compare the early gene expression profiles in the skin of HPV16-E6 transgenic mice regulated by the E6 PDZ-binding motif. MATERIALS AND METHODS: The global transcriptional profiles in dorsal skin biopsies from K14E6 and K14E6Δ146-151 transgenic mice were compared using microarrays. Relevant genes obtained from the most differentially expressed processes were further examined by RT-qPCR, in situ RT-PCR, Western blot, or immunofluorescence. RESULTS: The transcriptomic landscape of K14E6 versus K14E6Δ146-151 shows that the most affected expression profiles were those related to keratinocyte differentiation, stem cell maintenance, and keratinization. Additionally, downregulation of epidermal stemness markers such as K15 and CD34, as well as the upregulation of cytokeratin 6b, appeared to be dependent on the E6 PDZ-binding motif. Finally, wound healing, a physiological process linked to stemness, is impaired in the K14E6 mice compared to K14E6Δ146-151. CONCLUSION: The E6 PDZ-binding motif appears to affect stemness and keratinization during early stages of skin carcinogenesis. As E6 plays a significant role in HPV-induced skin carcinogenesis, the K14E6 versus K14E6Δ146-151 transcriptional profile provides a source of valuable data to uncover novel E6 functions in the skin.

Expression of Tau Produces Aberrant Plasma Membrane Blebbing in Glial Cells Through RhoA-ROCK-Dependent F-Actin Remodeling.

Abnormal aggregation of Tau in glial cells has been reported in Alzheimer's disease (AD) and other tauopathies; however, the pathological significance of these aggregates remains unsolved to date. In this study, we evaluated whether full-length Tau (Tau441) and its aspartic acid421-truncated Tau variant (Tau421) produce alterations in the normal organization of the cytoskeleton and plasma membrane (PM) when transiently expressed in cultured C6-glial cells. Forty-eight hours post-transfection, abnormal microtubule bundling was observed in the majority of the cells, which expressed either Tau441 or Tau421. Moreover, both variants of Tau produced extensive PM blebbing associated with cortical redistribution of filamentous actin (F-Actin). These effects were reverted when Tau-expressing cells were incubated with drugs that depolymerize F-Actin. In addition, when glial cells showing Tau-induced PM blebbing were incubated with inhibitors of the Rho-associated protein kinase (ROCK) signaling pathway, both formation of abnormal PM blebs and F-Actin remodeling were avoided. All of these effects were initiated upstream by abnormal Tau-induced microtubule bundling, which may release the microtubule-bound guanine nucleotide exchange factor-H1 (GEF-H1) into the cytoplasm in order to activate its major effector RhoA-GTPase. These results may represent a new mechanism of Tau toxicity in which Tau-induced microtubule bundling produces activation of the Rho-GTPase-ROCK pathway that in turn mediates the remodeling of cortical Actin and PM blebbing. In AD and other tauopathies, these Tau-induced abnormalities may occur and contribute to the impairment of glial activity.

Entamoeba histolytica and E. dispar Calreticulin: inhibition of classical complement pathway and differences in the level of expression in amoebic liver abscess.

The role of calreticulin (CRT) in host-parasite interactions has recently become an important area of research. Information about the functions of calreticulin and its relevance to the physiology of Entamoeba parasites is limited. The present work demonstrates that CRT of both pathogenic E. histolytica and nonpathogenic E. dispar species specifically interacted with human C1q inhibiting the activation of the classical complement pathway. Using recombinant EhCRT protein, we demonstrate that CRT interaction site and human C1q is located at the N-terminal region of EhCRT. The immunofluorescence and confocal microscopy experiments show that CRT and human C1q colocalize in the cytoplasmic vesicles and near to the surface membrane of previously permeabilized trophozoites or are incubated with normal human serum which is known to destroy trophozoites. In the presence of peripheral mononuclear blood cells, the distribution of EhCRT and C1q is clearly over the surface membrane of trophozoites. Nevertheless, the level of expression of CRT in situ in lesions of amoebic liver abscess (ALA) in the hamster model is different in both Entamoeba species; this molecule is expressed in higher levels in E. histolytica than in E. dispar. This result suggests that EhCRT may modulate some functions during the early moments of the host-parasite relationship.

Gene expression profile regulated by the HPV16 E7 oncoprotein and estradiol in cervical tissue.

The HPV16 E7 oncoprotein and 17ß-estradiol are important factors for the induction of premalignant lesions and cervical cancer. The study of these factors is crucial for a better understanding of cervical tumorigenesis. Here, we assessed the global gene expression profiles induced by the HPV16 E7 oncoprotein and/or 17ß-estradiol in cervical tissue of FvB and K14E7 transgenic mice. We found that the most dramatic changes in gene expression occurred in K14E7 and FvB groups treated with 17ß-estradiol. A large number of differentially expressed genes involved in the immune response were observed in 17ß-estradiol treated groups. The E7 oncoprotein mainly affected the expression of genes involved in cellular metabolism. Our microarray data also identified differentially expressed genes that have not previously been reported in cervical cancer. The identification of genes regulated by E7 and 17ß-estradiol, provides the basis for further studies on their role in cervical carcinogenesis.

Disruption of MDCK cell tight junctions by the free-living amoeba Naegleria fowleri.

Naegleria fowleri is the aetiological agent of primary amoebic meningoencephalitis. This parasite invades its host by penetrating the olfactory mucosa. However, the mechanism of epithelium penetration is not well understood. In the present study, we evaluated the effect of N. fowleri trophozoites and the non-pathogenic Naegleria gruberi on Madin-Darby canine kidney (MDCK) tight junction proteins, including claudin-1, occludin and ZO-1, as well as on the actin cytoskeleton. Trophozoites from each of the free-living amoeba species were co-cultured with MDCK cells in a 1 : 1 ratio for 1, 3, 6 or 10 h. Light microscopy revealed that N. fowleri caused morphological changes as early as 3 h post-infection in an epithelial MDCK monolayer. Confocal microscopy analysis revealed that after 10 h of co-culture, N. fowleri trophozoites induced epithelial cell damage, which was characterized by changes in the actin apical ring and disruption of the ZO-1 and claudin-1 proteins but not occludin. Western blot assays revealed gradual degradation of ZO-1 and claudin-1 as early as 3 h post-infection. Likewise, there was a drop in transepithelial electrical resistance that resulted in increased epithelial permeability and facilitated the invasion of N. fowleri trophozoites by a paracellular route. In contrast, N. gruberi did not induce alterations in MDCK cells even at 10 h post-infection. Based on these results, we suggest that N. fowleri trophozoites disrupt epithelial monolayers, which could enable their penetration of the olfactory epithelium and subsequent invasion of the central nervous system.

Human caliciviruses detected in Mexican children admitted to hospital during 1998-2000, with severe acute gastroenteritis not due to other enteropathogens.

Few studies exist regarding the frequency of human caliciviruses as single etiologic agents in sporadic cases, or in outbreaks occurring in children hospitalized for acute gastroenteritis. In this study, a total of 1,129 children of <5 years of age and hospitalized due to acute diarrhea were enrolled from three main hospitals in Mexico City during a period of 3 years (March 1998 to December 2000). After analyzing all fecal samples for several enteropathogens, 396 stools that remained negative were further screened for human caliciviruses by RT-PCR using a primer set specific to norovirus and sapovirus. Human caliciviruses were detected in 5.6% (22/396) of the children. The minimum incidence rate for 1999 were 5.3% (7/132) for 1999 and 7.8% (13/167) for 2000, since only fecal specimens that tested negative to other enteric pathogens were examined. Positive samples were further characterized using specific GI and GII primers and sequencing. Norovirus GII was detected in 19/22 samples, most of them were GII/4, while sapovirus GI/2 was detected in one sample. Associations between the presence of human calicivirus and clinical and epidemiological data revealed that diarrhea occurred with a seasonal pattern, and that children hospitalized due to human calicivirus disease scored an average of 13 +/- 3.2 (SD) points on the Vesikari scale, which corresponded to severe episodes. These results highlight that human caliciviruses, by themselves, are enteropathogens of acute severe diarrhea among young Mexican children requiring hospitalization and that their detection is important in order to reduce the diagnosis gap.

A carboxymethyl-cellulose plaque assay for feline calicivirus.

The standardization of a plaque assay for feline calicivirus in Crandell Reese feline kidney cells using carboxymethyl-cellulose as an overlay medium is described in this report. This methodology gives comparable counts as compared to the standard assay, and prevents monolayer roll over and peel off, as well as easy medium removal. Cell fixation and staining is performed in a considerably reduced period of time, compared to agarose-based methods.

Construction of an internal RT-PCR standard control for the detection of human caliciviruses in stool.

RT-PCR is the most sensitive assay for the detection of human caliciviruses (HuCV) in stool and environmental samples. However, false negative results are commonly obtained due to the presence of RT-PCR inhibitors. In order to exclude such false negative results, an internal control (IC) was developed for the assay by cloning a 319 nt sequence of the Norwalk virus (NV) polymerase containing a 156 nt cDNA insert. The RT-PCR assay was carried out using RNA derived from the constructed plasmid and a primer set previously described for calicivirus detection, resulting in a 475 nt product. Distinct bands of the internal control and the viral specific RT-PCR products (319 nt) were obtained when the internal control was added to the samples. Similar results were also obtained when both the control RNA and viral RNA were seeded into stool samples from asymptomatic volunteers, or when the internal control was included into positive samples. Since the primer set used in the assays can detect a wide range of strains in both norovirus and sapovirus genera, this internal control should have a broad application for the diagnosis of human caliciviruses diagnosis in both clinical and environmental samples.

La, PTB, and PAB proteins bind to the 3(') untranslated region of Norwalk virus genomic RNA.

Noroviruses are human enteric caliciviruses for which no cell culture is available. Consequently, the mechanisms and factors involved in their replication have been difficult to study. In an attempt to analyze the cis- and trans-acting factors that could have a role in NV replication, the 3(')-untranslated region of the genome was studied. Use of Zuker's mfold-2 software predicted that NV 3(')UTR contains a stem-loop structure of 47 nts. Proteins from HeLa cell extracts, such as La and PTB, form stable complexes with this region. The addition of a poly(A) tail (24 nts) to the 3(')UTR permits the specific binding of the poly(A) binding protein (PABP) present in HeLa cell extracts, as well as the recombinant PABP. Since La, PTB, and PABP are important trans-acting factors required for viral translation and replication, these RNA-protein interactions may play a role in NV replication or translation.