Co-Translational Membrane Targeting and Holo-Translocon Docking of Ribosomes Translating the SRP Receptor.

Many integral membrane proteins are produced by translocon-associated ribosomes. The assembly of ribosomes translating membrane proteins on the translocons is mediated by a conserved system, composed of the signal recognition particle and its receptor (FtsY in Escherichia coli). FtsY is a peripheral membrane protein, and its role late during membrane protein targeting involves interactions with the translocon. However, earlier stages in the pathway have remained obscure, namely, how FtsY targets the membrane in vivo and where it initially docks. Our previous studies have demonstrated co-translational membrane-targeting of FtsY translation intermediates and identified a nascent FtsY targeting-peptide. Here, in a set of in vivo experiments, we utilized tightly stalled FtsY translation intermediates, pull-down assays and site-directed cross-linking, which revealed FtsY-nascent chain-associated proteins in the cytosol and on the membrane. Our results demonstrate interactions between the FtsY-translating ribosomes and cytosolic chaperones, which are followed by directly docking on the translocon. In support of this conclusion, we show that translocon over-expression increases dramatically the amount of membrane associated FtsY-translating ribosomes. The co-translational contacts of the FtsY nascent chains with the translocon differ from its post-translational contacts, suggesting a major structural maturation process. The identified interactions led us to propose a model for how FtsY may target the membrane co-translationally. On top of our past observations, the current results may add another tier to the hypothesis that FtsY acts stoichiometrically in targeting ribosomes to the membrane in a constitutive manner.

CD44 Splice Variants as Potential Players in Alzheimer's Disease Pathology.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by cognitive deficits, deposition of amyloid-ß (Aß) plaques, intracellular neurofibrillary tangles, and neuronal cell death. Neuroinflammation is commonly believed to participate in AD pathogenesis. CD44 is an inflammation-related gene encoding a widely-distributed family of alternatively spliced cell surface glycoproteins that have been implicated in inflammation, metastases, and inflammation-linked neuronal injuries. Here we investigated the expression patterns of CD44S (which does not contain any alternative exon) and CD44 splice variants in postmortem hippocampal samples from AD patients and matched non-AD controls. The expression of CD44S and CD44 splice variants CD44V3, CD44V6, and CD44V10 was significantly higher in AD patients compared to non-AD controls. Immunohistochemistry of human hippocampal sections revealed that CD44S differentially localized to neuritic plaques and astrocytes, whereas CD44V3, CD44V6, and CD44V10 expression was mostly neuronal. Consistent with these findings, we found that the expression of CD44V6 and CD44V10 was induced by Aß peptide in neuroblastoma cells and primary neurons. Furthermore, in loss of function studies we found that both CD44V10-specific siRNA and CD44V10 antibody protected neuronal cells from Aß-induced toxicity, suggesting a causal relationship between CD44V10 and neuronal cell death. These data indicate that certain CD44 splice variants contribute to AD pathology and that CD44V10 inhibition may serve as a new neuroprotective treatment strategy for this disease.

Neu-164 and Neu-107, two novel antioxidant and anti-myeloperoxidase compounds, inhibit acute cigarette smoke-induced lung inflammation.

Cigarette smoke is a profound proinflammatory stimulus that causes acute lung inflammation and chronic lung disease, including chronic obstructive pulmonary disease (COPD, emphysema, and chronic bronchitis), via a variety of mechanisms, including oxidative stress. Cigarette smoke contains high levels of free radicals, whereas inflammatory cells, including macrophages and neutrophils, express enzymes, including NADPH oxidase, nitric oxide synthase, and myeloperoxidase, that generate reactive oxygen species in situ and contribute to inflammation and tissue damage. Neu-164 and Neu-107 are small-molecule inhibitors of myeloperoxidase, as well as potent antioxidants. We hypothesized that Neu-164 and Neu-107 would inhibit acute cigarette smoke-induced inflammation. Adult C57BL/6J mice were exposed to mainstream cigarette smoke for 3 days to induce acute inflammation and were treated daily by inhalation with Neu-164, Neu-107, or dexamethasone as a control. Inflammatory cells and cytokines were assessed by bronchoalveolar lavage and histology. mRNA levels of endogenous antioxidant genes heme oxygenase-1 and glutamate-cysteine ligase modifier subunit were determined by qPCR. Cigarette smoke exposure induced acute lung inflammation with accumulation of neutrophils and upregulation of proinflammatory cytokines, including IL-6, macrophage inflammatory protein-2, and keratinocyte-derived cytokine. Both Neu-164 and Neu-107 significantly reduced the accumulation of inflammatory cells and the expression of inflammatory cytokines as effectively as dexamethasone. Upregulation of endogenous antioxidant genes was dampened. Neu-164 and Neu-107 inhibit acute cigarette smoke-induced inflammation by scavenging reactive oxygen species in cigarette smoke and by inhibiting further oxidative stress caused by inflammatory cells. These compounds may have promise in preventing or treating lung disease associated with chronic smoke exposure, including COPD.

Widespread occurrence of antisense transcription in the human genome.

An increasing number of eukaryotic genes are being found to have naturally occurring antisense transcripts. Here we study the extent of antisense transcription in the human genome by analyzing the public databases of expressed sequences using a set of computational tools designed to identify sense-antisense transcriptional units on opposite DNA strands of the same genomic locus. The resulting data set of 2,667 sense-antisense pairs was evaluated by microarrays containing strand-specific oligonucleotide probes derived from the region of overlap. Verification of specific cases by northern blot analysis with strand-specific riboprobes proved transcription from both DNA strands. We conclude that > or =60% of this data set, or approximately 1,600 predicted sense-antisense transcriptional units, are transcribed from both DNA strands. This indicates that the occurrence of antisense transcription, usually regarded as infrequent, is a very common phenomenon in the human genome. Therefore, antisense modulation of gene expression in human cells may be a common regulatory mechanism.