Subcellular localization of microsomal triglyceride transfer protein

Microsomal triglyceride transfer protein (MTP) is essential for the assembly of apolipoprotein B-containing lipoproteins. Within the endoplasmic reticulum, it transfers lipid from the membrane to the forming lipoprotein. Recent evidence suggests that it may also function within the Golgi apparatus. To address this hypothesis, we developed a polyclonal antibody to MTP and used it in a series of studies on mouse liver and McArdle-RH7777 (McA) cells. Western blot analysis demonstrated the presence of MTP within mouse hepatic-Golgi apparatus-rich fractions. In addition, in vitro lipid transfer assays demonstrated the presence of triglyceride transfer activity within the Golgi fractions. Immunohistochemical studies with mouse liver demonstrated the presence of MTP within all hepatocytes, but not in nonparenchymal cells. The subcellular location of MTP in McA cells was investigated using confocal microscopy. MTP colocalized with the trans-Golgi network (TGN) 38 and Golgi SNARE (soluble N-ethylmalemide-sensitive factor attachment protein receptor) of 28 kDa (GS28), markers for the trans- and cis-Golgi apparatus, respectively. Morphometric analyses indicated that approximately 17% of the MTP signal colocalized with the TGN38, while 33% of the trans-Golgi marker colocalized with the MTP. Approximately 17% of the MTP signal colocalized with the GS28, whereas 53% of the cis-Golgi marker colocalized with the MTP. The results provide unequivocal evidence for the location of MTP within the Golgi apparatus, and further highlight the importance of this organelle in the assembly of lipoproteins.     

Characterization of Novel CSF Tau and ptau Biomarkers for Alzheimer’s Disease

Cerebral spinal fluid (CSF) Aβ42, tau and p181tau are widely accepted biomarkers of Alzheimer’s disease (AD). Numerous studies show that CSF tau and p181tau levels are elevated in mild-to-moderate AD compared to age-matched controls. In addition, these increases might predict preclinical AD in cognitively normal elderly. Despite their importance as biomarkers, the molecular nature of CSF tau and ptau is not known. In the current study, reverse-phase high performance liquid chromatography was used to enrich and concentrate tau prior to western-blot analysis. Multiple N-terminal and mid-domain fragments of tau were detected in pooled CSF with apparent sizes ranging from <20 kDa to ~40 kDa. The pattern of tau fragments in AD and control samples were similar. In contrast, full-length tau and C-terminal-containing fragments were not detected. To quantify levels, five tau ELISAs and three ptau ELISAs were developed to detect different overlapping regions of the protein. The discriminatory potential of each assay was determined using 20 AD and 20 age-matched control CSF samples. Of the tau ELISAs, the two assays specific for tau containing N-terminal sequences, amino acids 9-198 (numbering based on tau 441) and 9-163, exhibited the most significant differences between AD and control samples. In contrast, CSF tau was not detected with an ELISA specific for a more C-terminal region (amino acids 159-335). Significant discrimination was also observed with ptau assays measuring amino acids 159-p181 and 159-p231. Interestingly, the discriminatory potential of p181 was reduced when measured in the context of tau species containing amino acids 9-p181. Taken together, these results demonstrate that tau in CSF occurs as a series of fragments and that discrimination of AD from control is dependent on the subset of tau species measured. These assays provide novel tools to investigate CSF tau and ptau as biomarkers for other neurodegenerative diseases.     

Inhibition of the dopamine D1 receptor signaling by PSD-95

Dopamine D1 receptors play an important role in movement, reward, and learning and are implicated in a number of neurological and psychiatric disorders. These receptors are concentrated in dendritic spines of neurons, including the spine head and the postsynaptic density. D1 within spines is thought to modulate the local channels and receptors to control the excitability and synaptic properties of spines. The molecular mechanisms mediating D1 trafficking, anchorage, and function in spines remain elusive. Here we show that the synaptic scaffolding protein PSD-95 thought to play a role in stabilizing glutamate receptors in the postsynaptic density, interacts with D1 and regulates its trafficking and function. Interestingly, the D1-PSD-95 interaction does not require the well characterized domains of PSD-95 but is mediated by the carboxyl-terminal tail of D1 and the NH(2) terminus of PSD-95, a region that is recognized only recently to participate in protein-protein interaction. Co-expression of PSD-95 with D1 in mammalian cells inhibits the D1-mediated cAMP accumulation without altering the total expression level or the agonist binding properties of the receptor. The diminished D1 signaling is mediated by reduced D1 expression at the cell surface as a consequence of an enhanced constitutive, dynamin-dependent endocytosis. In addition, genetically engineered mice lacking PSD-95 show a heightened behavioral response to either a D1 agonist or the psychostimulant amphetamine. These studies demonstrate a role for a glutamatergic scaffold in dopamine receptor signaling and trafficking and identify a new potential target for the modulation of abnormal dopaminergic function.     

Hyperkalemic periodic paralysis M1592V mutation modifies activation in human skeletal muscle Na+ channel

Mutations in thehuman skeletal muscle Na⁺ channelunderlie the autosomal dominant disease hyperkalemic periodic paralysis (HPP). Muscle fibers from affected individuals exhibit sustained Na⁺ currents thought to depolarizethe sarcolemma and thus inactivate normalNa⁺ channels. We expressed humanwild-type or M₁₅₉₂V mutant-subunits with the ₁-subunitin Xenopus laevis oocytes and recordedNa⁺ currents using two-electrodeand cut-open oocyte voltage-clamp techniques. The most prominentfunctional difference betweenM₁₅₉₂V mutant and wild-typechannels is a 5- to 10-mV shift in the hyperpolarized direction of thesteady-state activation curve. The shift in the activation curve forthe mutant results in a larger overlap with the inactivation curve thanthat observed for wild-type channels. Accordingly, the current throughM₁₅₉₂V channels displays a larger noninactivating component than does that through wild-type channels atmembrane potentials near 40 mV. The functional properties of theM₁₅₉₂V mutant resemble those ofthe previously characterized HPPT₇₀₄M mutant. Both clinicallysimilar phenotypes arise from mutations located at a distance from theputative voltage sensor of the channel.

     

Development of a capture/enrichment sandwich ELISA for the rapid detection of enteropathogenic and enterohaemorrhagic Escherichia coli O26 strains

AIMS: To improve the sensitivity of a monoclonal antibody (MAb 2F3) based enteropathogenic Escherichia coli (EPEC)/enterohaemorrhagic E. coli (EHEC) serogroup O26-specific sandwich ELISA (sELISA), using a capture/enrichment format of the assay. METHODS AND RESULTS: The sELISA utilized an EPEC/EHEC O26-specific MAb 2F3 as the capture reagent and an E. coli serogroup O26 lipopolysaccharide-specific polyclonal antibody in the development stage. Wells containing faeces test samples from bovine enteritis cases and agar colony sweep cultures from human diarrhoea cases, after a 2-h capture stage, were washed and enrichment of the captured cells was encouraged by addition of tryptone soya broth. After overnight incubation, the contents of each well were transferred to sterile wells and the sELISA completed. Any sELISA positive samples were then subcultured onto blood agar to recover and further characterize the positive cultures. The assay had a sensitivity of 10(3) CFU ml(-1). ELISA positive samples consisted of 21 (4.8%) of the 442 bovine and 19 (3.7%) of the 519 human samples tested, and ELISA positive EPEC/EHEC O26 strains were isolated from 11 and three of these samples respectively. CONCLUSION: The capture/enrichment method improved the sensitivity of a MAb-based sELISA for the detection of EPEC/EHEC O26 strains, and also contributed to an improved isolation rate of the organism from field samples. SIGNIFICANCE AND IMPACT OF THE STUDY: The application of a specific MAb in a capture/enrichment format of the sELISA, provides a prospectively suitable screening method for the detection of pathogenic bacteria from mixed culture samples.     

New spatially explicit method for detecting extracellular protease activity in biofilms

A novel method of detecting extracellular protease activity at biofilm-substratum interfaces was developed. This method utilizes fluorescent molecules bound to cellulose substrata with a lectin. Extracellular proteases degrade the lectin and release the fluorochrome into solution. This new technique and a standard dissolved-substrate assay detected similar responses of biofilm extracellular protease activity to experimental manipulation of N supply. Combination of this technique with confocal scanning laser microscopy allowed direct visualization of microspatial patterns of bacterial distribution and extracellular protease activity at the biofilm-substratum interface.     

CD8 T cell-mediated killing of Cryptococcus neoformans requires granulysin and is dependent on CD4 T cells and IL-15

Granulysin is located in the acidic granules of cytotoxic T cells. Although the purified protein has antimicrobial activity against a broad spectrum of microbial pathogens, direct evidence for granulysin-mediated cytotoxicity has heretofore been lacking. Studies were performed to examine the regulation and activity of granulysin expressed by CD8 T cells using Cryptococcus neoformans, which is one of the most common opportunistic pathogens of AIDS patients. IL-15-activated CD8 T cells acquired anticryptococcal activity, which correlated with the up-regulation of granulysin. When granules containing granulysin were depleted using SrCl(2,) or when the gene was silenced using 21-nt small interfering RNA duplexes, the antifungal effect of CD8 T cells was abrogated. Concanamycin A and EGTA did not affect the antifungal effect, suggesting that the activity of granulysin was perforin independent. Following stimulation by the C. neoformans mitogen, CD8 T cells expressed granulysin and acquired antifungal activity. This activity required CD4 T cells and was dependent upon accessory cells. Furthermore, IL-15 was both necessary and sufficient for granulysin up-regulation in CD8 T cells. These observations are most consistent with a mechanism whereby C. neoformans mitogen is presented to CD4 T cells, which in turn activate accessory cells. The resultant IL-15 activates CD8 T cells to express granulysin, which is responsible for antifungal activity.     

Molecular characterization of a ring X chromosome in a male with short stature

We report the molecular characterization of a ring X chromosome that was transmitted from a mother to a male who has short stature and minor dysmorphic features. This represents only the second reported ring X chromosome in a male. The ring is derived from breakage within the Xp pseudoautosomal region (PAR) and just proximal to the Xq PAR. The total amount of deleted material is 700-900 kb DNA and includes six known transcribed genes. Interestingly, SHOX, a gene implicated in short stature, is not deleted from the ring chromosome. Possible pathogenetic explanations for the patient's clinical features include insufficient dosage of deleted genes, a position effect on SHOX expression, and cell death during development because of ring chromosome nondisjunction. The findings are also relevant to observations made of "complete" ring chromosomes.