Systematic analysis of RNA-binding proteins identifies targetable therapeutic vulnerabilities in osteosarcoma

Osteosarcoma is the most common primary malignant bone tumor with a strong tendency to metastasize, limiting the prognosis of affected patients. Genomic, epigenomic and transcriptomic analyses have demonstrated the exquisite molecular complexity of this tumor, but have not sufficiently defined the underlying mechanisms or identified promising therapeutic targets. To systematically explore RNA-protein interactions relevant to OS, we define the RNA interactomes together with the full proteome and the transcriptome of cells from five malignant bone tumors (four osteosarcomata and one malignant giant cell tumor of the bone) and from normal mesenchymal stem cells and osteoblasts. These analyses uncover both systematic changes of the RNA-binding activities of defined RNA-binding proteins common to all osteosarcomata and individual alterations that are observed in only a subset of tumors. Functional analyses reveal a particular vulnerability of these tumors to translation inhibition and a positive feedback loop involving the RBP IGF2BP3 and the transcription factor Myc which affects cellular translation and OS cell viability. Our results thus provide insight into potentially clinically relevant RNA-binding protein-dependent mechanisms of osteosarcoma.

Fates and functions of RNA-binding proteins under stress

Exposure to stress activates a well-orchestrated set of changes in gene expression programs that allow the cell to cope with and adapt to the stress, or undergo programmed cell death. RNA-protein interactions, mediating all aspects of post-transcriptional regulation of gene expression, play crucial roles in cellular stress responses. RNA-binding proteins (RBPs), which interact with sequence/structural elements in RNAs to control the steps of RNA metabolism, have therefore emerged as central regulators of post-transcriptional responses to stress. Following exposure to a variety of stresses, the dynamic alterations in the RNA-protein interactome enable cells to respond to intracellular or extracellular perturbations by causing changes in mRNA splicing, polyadenylation, stability, translation, and localization. As RBPs play a central role in determining the cellular proteome both qualitatively and quantitatively, it has become increasingly evident that their abundance, availability, and functions are also highly regulated in response to stress. Exposure to stress initiates a series of signaling cascades that converge on post-translational modifications (PTMs) of RBPs, resulting in changes in their subcellular localization, association with stress granules, extracellular export, proteasomal degradation, and RNA-binding activities. These alterations in the fate and function of RBPs directly impact their post-transcriptional regulatory roles in cells under stress. Adopting the ubiquitous RBP HuR as a prototype, three scenarios illustrating the changes in nuclear-cytoplasmic localization, RNA-binding activity, export and degradation of HuR in response to inflammation, genotoxic stress, and heat shock depict the complex and interlinked regulatory mechanisms that control the fate and functions of RBPs under stress. This article is categorized under: RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications.

An AKT1- and TRIM21-mediated Phosphodegron Controls Proteasomal Degradation of HuR Enabling Cell Survival under Heat Shock

Post-transcriptional regulation by RNA-binding proteins (RBPs) is a major mode of controlling gene expression under stress conditions. The RBP HuR regulates the translation/turnover of multiple mRNAs in stress responses. HuR is degraded in response to heat stress consequent to ubiquitination of the K182 amino acid residue. We have identified TRIM21 as the E3-ubiquitin ligase causing HuR polyubiquitination at K182 and proteasomal degradation under heat shock. The S100 and E101 residues are required for binding of TRIM21 to HuR. Heat shock-induced phosphorylation of S100 is necessary for TRIM21 interaction with HuR and subsequent degradation. We identified AKT1 as the kinase which phosphorylates S100, allowing the recognition of HuR by TRIM21. Sequential phosphorylation by AKT1 and ubiquitination by TRIM21 therefore determine a "phosphodegron" in HuR that is required for regulating the cellular level of HuR under heat shock, thereby enabling a crucial adaptive mechanism allowing cell survival in response to heat stress.

p53 and HuR combinatorially control the biphasic dynamics of microRNA-125b in response to genotoxic stress

Post-transcriptional regulation of p53, by the microRNA miR-125b and the RNA-binding protein HuR, controls p53 expression under genotoxic stress. p53 mRNA translation is repressed by miR-125b, tightly regulating its basal level of expression. The repression is relieved upon DNA damage by a decrease in miR-125b level, contributing to pulsatile expression of p53. The pulse of p53, as also of HuR, in response to UV irradiation coincides with a time-dependent biphasic change in miR-125b level. We show that the cause for the decrease in miR-125b level immediately post DNA-damage is enhanced exosomal export mediated by HuR. The subsequent increase in miR-125b level is due to p53-mediated transcriptional upregulation and enhanced processing, demonstrating miR-125b as a transcriptional and processing target of p53. p53 activates the transcription of primary miR-125b RNA from a cryptic promoter in response to UV irradiation. Together, these regulatory processes constitute reciprocal feedback loops that determine the biphasic change in miR-125b level, ultimately contributing to the fine-tuned temporal regulation of p53 expression in response to genotoxic stress.

Cooperation and competition by RNA-binding proteins in cancer

Post-transcriptional regulation of gene expression plays a major role in determining the cellular proteome in health and disease. Post-transcriptional control mechanisms are disrupted in many cancers, contributing to multiple processes of tumorigenesis. RNA-binding proteins (RBPs), the main post-transcriptional regulators, often show altered expression and activity in cancer cells. Dysregulation of RBPs contributes to many cancer phenotypes, functioning in complex regulatory networks with other cellular players such as non-coding RNAs, signaling mediators and transcription factors to alter the expression of oncogenes and tumor suppressor genes. RBPs often function combinatorially, based on their binding to target sequences/structures on shared mRNA targets, to regulate the expression of cancer-related genes. This gives rise to cooperativity and competition between RBPs in mRNA binding and resultant functional outcomes in post-transcriptional processes such as mRNA splicing, stability, export and translation. Cooperation and competition is also observed in the case of interaction of RBPs and microRNAs with mRNA targets. RNA structural change is a common mechanism mediating the cooperative/competitive interplay between RBPs and between RBPs and microRNAs. RNA modifications, leading to changes in RNA structure, add a new dimension to cooperative/competitive binding of RBPs to mRNAs, further expanding the RBP regulatory landscape. Therefore, cooperative/competitive interplay between RBPs is a major determinant of the RBP interactome and post-transcriptional regulation of gene expression in cancer cells.

Quorum Sensing by Gelsolin Regulates Programmed Cell Death 4 Expression and a Density-Dependent Phenotype in Macrophages

Quorum-sensing mechanisms that sense the density of immune cells at the site of inflammation to initiate inflammation resolution have recently been demonstrated as a major determinant of the inflammatory response. We observed a density-dependent increase in expression of the inflammatory tumor suppressor protein programmed cell death 4 (PDCD4) in mouse macrophage cells. Conditioned medium from high-density cells upregulated PDCD4 expression, revealing the presence of a secreted factor(s) acting as a macrophage quorum sensor. Secreted gelsolin (GSN) was identified as the quorum-sensing autoinducer. Alteration of GSN levels changed PDCD4 expression and the density-dependent phenotype of cells. LPS induced the expression of microRNA miR-21, which downregulated both GSN and PDCD4 expression, and reversed the high-density phenotype. The high-density phenotype was correlated with an anti-inflammatory gene expression program, which was counteracted by inflammatory stimulus. Together, our observations establish the miR-21-GSN-PDCD4 regulatory network as a crucial mediator of a macrophage quorum-sensing mechanism for the control of inflammatory responses.

RNA-binding proteins La and HuR cooperatively modulate translation repression of PDCD4 mRNA

Posttranscriptional regulation of gene expression plays a critical role in controlling the inflammatory response. An uncontrolled inflammatory response results in chronic inflammation, often leading to tumorigenesis. Programmed cell death 4 (PDCD4) is a proinflammatory tumor-suppressor gene which helps to prevent the transition from chronic inflammation to cancer. PDCD4 mRNA translation is regulated by an interplay between the oncogenic microRNA miR-21 and the RNA-binding protein (RBP) human antigen R (HuR) in response to lipopolysaccharide stimulation, but the role of other regulatory factors remains unknown. Here, we report that the RBP lupus antigen (La) interacts with the 3'-untranslated region of PDCD4 mRNA and prevents miR-21-mediated translation repression. While lipopolysaccharide causes nuclear-cytoplasmic translocation of HuR, it enhances cellular La expression. Remarkably, La and HuR were found to bind cooperatively to the PDCD4 mRNA and mitigate miR-21-mediated translation repression. The cooperative action of La and HuR reduced cell proliferation and enhanced apoptosis, reversing the pro-oncogenic function of miR-21. Together, these observations demonstrate a cooperative interplay between two RBPs, triggered differentially by the same stimulus, which exerts a synergistic effect on PDCD4 expression and thereby helps maintain a balance between inflammation and tumorigenesis.

Transcriptome-wide analysis reveals spatial correlation between N6-methyladenosine and binding sites of microRNAs and RNA-binding proteins

N6-methyladenosine (m⁶A), the most prevalent epitranscriptomic modification in eukaryotes, is enriched in 3'-untranslated regions (3'UTRs) of mRNAs. As 3'UTRs are major binding sites of RNA-binding proteins (RBPs) and microRNAs (miRNAs), m⁶A-dependent local RNA structure change may alter the accessibility of RBPs and miRNAs to their target sites and regulate mRNA function. Using a human transcriptome-wide computational analysis to investigate the relation between m⁶A, RBPs and miRNAs, we find a strong positive correlation between number of m⁶A sites, miRNAs and RBPs binding to mRNAs, suggesting m⁶A-modified mRNAs are more targeted by miRNAs and RBPs. Moreover, m⁶A sites are located proximally to miRNA target sites and binding sites of multiple RBPs. Further, miRNA target sites and RBP-binding sites located close to each other are also located proximally to m⁶A. This study indicates three-way interplay between m⁶A, microRNA and RBP binding, suggesting the influence of mRNA modifications on the miRNA and RBP interactomes.

Negative feedback regulation by HuR controls TRIM21 expression and function in response to UV radiation

The E3 ubiquitin ligase TRIM21 plays a crucial role as a negative regulator of innate immune responses. Recent evidence has also indicated the involvement of TRIM21 in the genotoxic stress response and suppressing tumorigenesis. Our previous work has demonstrated a new function of TRIM21 in inhibiting p53 protein synthesis by degrading the RNA-binding protein HuR in response to UV radiation. This suggested a pro-oncogenic role of TRIM21. In this study, we have shown that TRIM21 enhances the proliferation of MCF7 breast carcinoma cells and counteracts the decrease in cell proliferation and colony formation caused by UV-induced DNA damage. Further, this pro-oncogenic role of TRIM21 in response to DNA damage is mediated by its degradation of HuR. Conversely, we found that HuR binds to a U-rich element in the 3'UTR of TRIM21 mRNA and activates its translation, thereby constituting a negative feedback loop. We found that dihydrotanshinone-I (DHTS-I), a plant-derived product which prevents HuR binding to specific RNAs, prevented HuR-mediated upregulation of TRIM21, while increasing the HuR-mediated upregulation of p53. Together, these findings demonstrate a negative feedback regulation between TRIM21 and HuR, which may play an important role in regulating the level of p53 in the genotoxic stress response.

Post-transcriptional regulation of C-C motif chemokine ligand 2 expression by ribosomal protein L22 during LPS-mediated inflammation

Monocyte infiltration to the site of pathogenic invasion is critical for inflammatory response and host defence. However, this process demands precise regulation as uncontrolled migration of monocytes to the site delays resolution of inflammation and ultimately promotes chronic inflammation. C-C motif chemokine ligand 2 (CCL2) plays a key role in monocyte migration, and hence, its expression should be tightly regulated. Here, we report a post-transcriptional regulation of CCL2 involving the large ribosomal subunit protein L22 (RPL22) in LPS-activated, differentiated THP-1 cells. Early events following LPS treatment include transcriptional upregulation of RPL22 and its nuclear accumulation. The protein binds to the first 20 nt sequence of the 5'UTR of ccl2 mRNA. Simultaneous nuclear translocation of up-frameshift-1 protein and its interaction with RPL22 results in cytoplasmic degradation of the ccl2 mRNA at a later stage. Removal of RPL22 from cells results in increased expression of CCL2 in response to LPS causing disproportionate migration of monocytes. We propose that post-transcriptional regulation of CCL2 by RPL22 fine-tunes monocyte infiltration during a pathogenic insult and maintains homeostasis of the immune response critical to resolution of inflammation. DATABASES: Microarray data are available in NCBI GEO database (Accession No GSE126525).

A cyclometalated trinuclear Ir(iii)/Pt(ii) complex as a luminescent probe for histidine-rich proteins

A trinuclear luminescent organometallic Pt–Ir–Pt complex acts as an efficient protein staining agent due to reversible binding to histidine-rich proteins.

Integrated Regulation of HuR by Translation Repression and Protein Degradation Determines Pulsatile Expression of p53 Under DNA Damage

Expression of tumor suppressor p53 is regulated at multiple levels, disruption of which often leads to cancer. We have adopted an approach combining computational systems modeling with experimental validation to elucidate the translation regulatory network that controls p53 expression post DNA damage. The RNA-binding protein HuR activates p53 mRNA translation in response to UVC-induced DNA damage in breast carcinoma cells. p53 and HuR levels show pulsatile change post UV irradiation. The computed model fitted with the observed pulse of p53 and HuR only when hypothetical regulators of synthesis and degradation of HuR were incorporated. miR-125b, a UV-responsive microRNA, was found to represses the translation of HuR mRNA. Furthermore, UV irradiation triggered proteasomal degradation of HuR mediated by an E3-ubiquitin ligase tripartite motif-containing 21 (TRIM21). The integrated action of miR-125b and TRIM21 constitutes an intricate control system that regulates pulsatile expression of HuR and p53 and determines cell viability in response to DNA damage.

The GAIT translational control system

The interferon (IFN)‐γ‐activated inhibitor of translation (GAIT) system directs transcript‐selective translational control of functionally related genes. In myeloid cells, IFN‐γ induces formation of a multiprotein GAIT complex that binds structural GAIT elements in the 3′‐untranslated regions (UTRs) of multiple inflammation‐related mRNAs, including ceruloplasmin and VEGF‐A, and represses their translation. The human GAIT complex is a heterotetramer containing glutamyl‐prolyl tRNA synthetase (EPRS), NS1‐associated protein 1 (NSAP1), ribosomal protein L13a (L13a), and glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH). A network of IFN‐γ‐stimulated kinases regulates recruitment and assembly of GAIT complex constituents. Activation of cyclin‐dependent kinase 5 (Cdk5), mammalian target of rapamycin complex 1 (mTORC1), and S6K1 kinases induces EPRS release from its parental multiaminoacyl tRNA synthetase complex to join NSAP1 in a ‘pre‐GAIT’ complex. Subsequently, the DAPK‐ZIPK kinase axis phosphorylates L13a, inducing release from the 60S ribosomal subunit and binding to GAPDH. The subcomplexes join to form the functional GAIT complex. Each constituent has a distinct role in the GAIT system. EPRS binds the GAIT element in target mRNAs, NSAP1 negatively regulates mRNA binding, L13a binds eIF4G to block ribosome recruitment, and GAPDH shields L13a from proteasomal degradation. The GAIT system is susceptible to genetic and condition‐specific regulation. An N‐terminus EPRS truncate is a dominant‐negative inhibitor ensuring a ‘translational trickle’ of target transcripts. Also, hypoxia and oxidatively modified lipoproteins regulate GAIT activity. Mouse models exhibiting absent or genetically modified GAIT complex constituents are beginning to elucidate the physiological role of the GAIT system, particularly in the resolution of chronic inflammation. Finally, GAIT‐like systems in proto‐chordates suggests an evolutionarily conserved role of the pathway in innate immunity. WIREs RNA 2018, 9:e1441. doi: 10.1002/wrna.1441

This article is categorized under: 1

Translation > Translation Regulation

2

RNA Interactions with Proteins and Other Molecules > RNA–Protein Complexes

3

Regulatory RNAs/RNAi/Riboswitches > Riboswitches

RNA-protein UV-crosslinking Assay

RNA-protein interactions play a crucial role in every aspect of RNA metabolism, and also plays a major role in post-transcriptional gene regulation. RNA-binding proteins have been implicated in viral gene expression (Ray and Das, 2002) and microRNA-mediated gene regulation (Poria et al., 2016). Here we have described the protocol which (1) covalently links transiently interacting RNA-protein complexes by UV crosslinking, (2) removes the unprotected RNA by RNase digestion and (3) detects the RNA-protein complexes by SDS-PAGE analysis. This protocol provides a rapid and reliable means to directly assay RNA-protein interactions and their kinetics using purified proteins and also help in identifying novel RNA-protein interactions.

Polysome Analysis

Polysome analysis is a method to separate mRNAs from a cell into actively translating and non-translating fractions depending on their association with polysomes. By this protocol, cell lysates are fractionated by sucrose density gradient ultracentrifugation. Free mRNA fraction and various ribosomal fractions, such as 40S, 60S, monosomes and polysomes are collected by fractionation. Association of particular mRNAs with these fractions is detected by reverse transcription - PCR to investigate the translational state of the mRNA.

Interplay between RNA-binding protein HuR and microRNA-125b regulates p53 mRNA translation in response to genotoxic stress

Tumor suppressor protein p53 plays a crucial role in maintaining genomic integrity in response to DNA damage. Regulation of translation of p53 mRNA is a major mode of regulation of p53 expression under genotoxic stress. The AU/U-rich element-binding protein HuR has been shown to bind to p53 mRNA 3′UTR and enhance translation in response to DNA-damaging UVC radiation. On the other hand, the microRNA miR-125b is reported to repress p53 expression and stress-induced apoptosis. Here, we show that UVC radiation causes an increase in miR-125b level in a biphasic manner, as well as nuclear cytoplasmic translocation of HuR. Binding of HuR to the p53 mRNA 3′UTR, especially at a site adjacent to the miR-125b target site, causes dissociation of the p53 mRNA from the RNA-induced silencing complex (RISC) and inhibits the miR-125b-mediated translation repression of p53. HuR prevents the oncogenic effect of miR-125b by reversing the decrease in apoptosis and increase in cell proliferation caused by the overexpression of miR-125b. The antagonistic interplay between miR-125b and HuR might play an important role in fine-tuning p53 gene expression at the post-transcriptional level, and thereby regulate the cellular response to genotoxic stress.

Development of a cyclometalated iridium complex with specific intramolecular hydrogen-bonding that acts as a fluorescent marker for the endoplasmic reticulum and causes photoinduced cell death

Cyclometalated iridium complexes have important applications as phosphorescent probes for cellular imaging due to their photophysical properties. Moreover, these properties also make them potential candidates as photosensitizers for photodynamic therapy (PDT) of tumors and skin diseases. Treatment of MCF7 breast carcinoma cells with a heteroleptic phosphorescent cyclometalated iridium(III) complex C2 followed by confocal imaging indicates that the complex selectively localizes and exhibits high fluorescence in the endoplasmic reticulum. In an unprecedented approach, systematic alteration of functional groups or the metal core in C2 to synthesize a series of iridium(III) complexes (C1–C10) and an organometallic rhenium complex C11 with an imidazolyl modified phenanthroline ligand has indicated the functional groups and their interactions that are responsible for this selective localization. Remarkably, the exposure of the cells treated with C2 to irradiation at 405 nm for one hour led to membrane blebbing and cell death, demonstrating a photosensitizing property of the compound.

Origin and evolution of glutamyl-prolyl tRNA synthetase WHEP domains reveal evolutionary relationships within Holozoa

Repeated domains in proteins that have undergone duplication or loss, and sequence divergence, are especially informative about phylogenetic relationships. We have exploited divergent repeats of the highly structured, 50-amino acid WHEP domains that join the catalytic subunits of bifunctional glutamyl-prolyl tRNA synthetase (EPRS) as a sequence-informed repeat (SIR) to trace the origin and evolution of EPRS in holozoa. EPRS is the only fused tRNA synthetase, with two distinct aminoacylation activities, and a non-canonical translation regulatory function mediated by the WHEP domains in the linker. Investigating the duplications, deletions and divergence of WHEP domains, we traced the bifunctional EPRS to choanozoans and identified the fusion event leading to its origin at the divergence of ichthyosporea and emergence of filozoa nearly a billion years ago. Distribution of WHEP domains from a single species in two or more distinct clades suggested common descent, allowing the identification of linking organisms. The discrete assortment of choanoflagellate WHEP domains with choanozoan domains as well as with those in metazoans supported the phylogenetic position of choanoflagellates as the closest sister group to metazoans. Analysis of clustering and assortment of WHEP domains provided unexpected insights into phylogenetic relationships amongst holozoan taxa. Furthermore, observed gaps in the transition between WHEP domain groupings in distant taxa allowed the prediction of undiscovered or extinct evolutionary intermediates. Analysis based on SIR domains can provide a phylogenetic counterpart to palaentological approaches of discovering “missing links” in the tree of life.

Cyclometalated rhodium and iridium complexes with imidazole containing Schiff bases: Synthesis, structure and cellular imaging

Cyclometalated rhodium(III) and iridium(III) complexes (1-4) of two Schiff base ligands L1 and L2 with the general formula [M(ppy)₂(Ln)]Cl {M = Rh, Ir; ppy = 2-phenylpyridine; n = 1, 2; L = Schiff base ligand} have been synthesized. The new ligands and the complexes have been characterized with spectroscopic techniques. Electrochemistry of the complexes revealed anodic behavior, corresponding to an M(III) to M(IV) oxidation. The X-ray crystal structures of complexes 2 and 4 have also been determined to interpret the coordination behavior of the complexes. Photophysical study shows that all the complexes display fluorescence at room temperature with quantum yield of about 3 × 10^-2 to 5 × 10^-2. The electronic absorption spectra of all the complexes fit well with the computational studies. Cellular imaging studies were done with the newly synthesized complexes. To the best of our knowledge, this is the first report of organometallic complexes of rhodium(III) and iridium(III) with Schiff base ligands explored for cellular imaging. Emphasis of this work lies on the structural features, photophysical behavior, cellular uptake and imaging of the fluorescent transition metal complexes.

Abstract P2-03-11: In situ imaging of the tumor cavity during breast lumpectomy using optical coherence tomography

Re-operation rates for breast lumpectomy procedures are exceedingly high, often over 30%, depending on the institution and surgical technique. Because current standard-of-care relies on post-operative histopathology to provide a microscopic view and assessment of surgical margins, there has been great interest in developing new imaging solutions to visualize tissues intraoperatively with high-resolution, and provide real-time feedback on the margin status. While it is possible to use a variety of microscopic imaging methods in the operating suite, including frozen-section histology, touch-prep cytology, confocal or scattering-based microscopy, all these techniques are limited to visualizing margins on ex vivo resected specimens, and do not provide a means for visualizing the in situ tumor cavity for evidence of positive margins or residual disease.

Optical coherence tomography (OCT) is a high-resolution, real-time, optical biomedical imaging technology that is the optical analogue to ultrasound imaging, except images are based on backscattered near-infrared light. OCT is capable of performing optical biopsies of in situ tissue at resolutions that approach those in histopathology. With the use of an advanced computed imaging technique called ISAM (Interferometric Synthetic Aperture Microscopy), even higher imaging resolution over larger depths is possible, commensurate with the depths (1-2 mm) visualized by pathologists to determine negative, close, or positive margins. Past studies by our group and others have demonstrated the feasibility of intraoperative OCT for assessing tumor margin and lymph node status during breast cancer surgery, but to date, all studies have been performed on resected lumpectomy tissue.

In this study, we report the development of a novel handheld surgical imaging probe that enables 2-D and 3-D OCT/ISAM imaging of the in situ tumor cavity, in addition to the margins of excised specimens. To date, this handheld OCT/ISAM probe has been used in 10 breast cancer surgeries where both in situ and ex vivo imaging was performed. Four of these cases involved in situ imaging of the cavity margin after a suspicious area was visually and tactically identified, and was subsequently resected, followed by ex vivo imaging and validating post-operative histopathology. Representative cases included fibroadipose tissue, fibroadenomas, and high-grade ductal carcinoma in situ.

Distinct microstructural features identified on OCT/ISAM and confirmed with histopathology demonstrate that this technique can visualize the in situ tumor cavity, as well as the surgical margins on resected specimens, with micron-scale resolution. OCT/ISAM has the potential to determine margin status in real-time during the surgical procedure, when further surgical resection to establish clear margins and reduce re-operation rates is possible.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P2-03-11.

Abstract P1-01-23: Intraoperative optical coherence tomography for the assessment of metastatic disease in human lymph nodes

The status of lymph nodes is an important factor in staging cancer since the transport of primary cancer cells via the lymphatic system is one of the main pathways of metastasis to distant organs. During cancer surgery, lymph node status is evaluated via sentinel lymph node biopsy (SLNB), which involves the removal and analysis of the first (or sentinel) nodes along the lymphatic chain of nodes draining the primary tumor. The sentinel nodes are identified through the accumulation of a radioactive agent (technetium-99) and/or isosulfan blue dye within the nodes, frequently resulting in the resection of multiple nodes for subsequent, often time-consuming, histopathological analysis. The majority of these resected nodes are found by histological analysis to be normal, leading to unnecessary complications, including increased risk of lymphedema. Thus, a method for the in situ assessment of node status could reduce the number of normal lymph nodes that are resected. In this study we evaluated the sensitivity and specificity of three-dimensional optical coherence tomography (OCT) for the intraoperative assessment of metastatic disease in lymph nodes.

OCT is the optical analogue to ultrasound imaging, except images are based on the optical scattering properties of near-infrared light. Real-time OCT with micron-scale resolution affords optical biopsies of tissue for immediate feedback. Intraoperative OCT imaging was conducted on human lymph nodes resected from 49 subjects during breast and, head and neck cancer surgeries. Three-dimensional OCT datasets were recorded ex vivo from one or more locations per node, and marked with surgical ink for subsequent correlation to histology. These lymph nodes then underwent the standard histological processing.

A double-blinded study was performed comparing the assessment of OCT datasets to the co-registered histological findings. Three-dimensional -OCT datasets from 206 sites were independently analyzed by six observers and classified as cancerous or non-cancerous. Seventy-nine sets were identified as unsuitable for OCT analysis due to insufficient nodal tissue within the imaged field-of-view. Early training classification results from three of the six observers resulted in a sensitivity of 64.8% and a specificity of 73.3% for identifying metastatic lymph nodes intraoperatively, in real-time, compared to the gold standard of post-operative histopathology. Final study results are expected to improve with observer training and a decision tree for interpreting OCT images.

Our initial imaging studies of resected lymph nodes in human cancer subjects demonstrate the potential of OCT as a technique for real-time optical biopsy of lymph nodes for the intraoperative staging of cancer.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P1-01-23.

The HILDA complex coordinates a conditional switch in the 3'-untranslated region of the VEGFA mRNA

Cell regulatory circuits integrate diverse, and sometimes conflicting, environmental cues to generate appropriate, condition-dependent responses. Here, we elucidate the components and mechanisms driving a protein-directed RNA switch in the 3'UTR of vascular endothelial growth factor (VEGF)-A. We describe a novel HILDA (hypoxia-inducible hnRNP L-DRBP76-hnRNP A2/B1) complex that coordinates a three-element RNA switch, enabling VEGFA mRNA translation during combined hypoxia and inflammation. In addition to binding the CA-rich element (CARE), heterogeneous nuclear ribonucleoprotein (hnRNP) L regulates switch assembly and function. hnRNP L undergoes two previously unrecognized, condition-dependent posttranslational modifications: IFN-γ induces prolyl hydroxylation and von Hippel-Lindau (VHL)-mediated proteasomal degradation, whereas hypoxia stimulates hnRNP L phosphorylation at Tyr(359), inducing binding to hnRNP A2/B1, which stabilizes the protein. Also, phospho-hnRNP L recruits DRBP76 (double-stranded RNA binding protein 76) to the 3'UTR, where it binds an adjacent AU-rich stem-loop (AUSL) element, "flipping" the RNA switch by disrupting the GAIT (interferon-gamma-activated inhibitor of translation) element, preventing GAIT complex binding, and driving robust VEGFA mRNA translation. The signal-dependent, HILDA complex coordinates the function of a trio of neighboring RNA elements, thereby regulating translation of VEGFA and potentially other mRNA targets. The VEGFA RNA switch might function to ensure appropriate angiogenesis and tissue oxygenation during conflicting signals from combined inflammation and hypoxia. We propose the VEGFA RNA switch as an archetype for signal-activated, protein-directed, multi-element RNA switches that regulate posttranscriptional gene expression in complex environments.

Targeting ribosome assembly on the HCV RNA using a small RNA molecule

Translation initiation of hepatitis C Virus (HCV) RNA is the initial obligatory step of the viral life cycle, mediated through the Internal Ribosome Entry Site (IRES) present in the 5'-untranslated region (UTR). Initiation on the HCV IRES is mediated by multiple structure-specific interactions between IRES RNA and host 40S ribosomal subunit. In the present study we demonstrate that the SLIIIef domain, in isolation from other structural elements of HCV IRES, retain the ability to interact with 40S ribosome subunit. A small RNA SLRef, mimicking the SLIIIef domain was found to interact specifically with human La protein and the ribosomal protein S5 and selectively inhibit HCV RNA translation. More importantly, SLRef RNA showed significant suppression of replication in HCV monocistronic replicon and decrease of negative strand synthesis in HCV cell culture system. Finally, using Sendai virus based virosome, the targeted delivery of SLRef RNA into mice liver succeeded in selectively inhibiting HCV IRES mediated translation in vivo.

Coding region polyadenylation generates a truncated tRNA synthetase that counters translation repression

Posttranscriptional regulatory mechanisms superimpose "fine-tuning" control upon "on-off" switches characteristic of gene transcription. We have exploited computational modeling with experimental validation to resolve an anomalous relationship between mRNA expression and protein synthesis. The GAIT (gamma-interferon-activated inhibitor of translation) complex repressed VEGF-A synthesis to a low, constant rate independent of VEGF-A mRNA expression levels. Dynamic model simulations predicted an inhibitory GAIT-element-interacting factor to account for this relationship and led to the identification of a truncated form of glutamyl-prolyl tRNA synthetase (EPRS), a GAIT constituent that mediates binding to target transcripts. The truncated protein, EPRS(N1), shields GAIT-element-bearing transcripts from the inhibitory GAIT complex, thereby dictating a "translational trickle" of GAIT target proteins. EPRS(N1) mRNA is generated by polyadenylation-directed conversion of a Tyr codon in the EPRS-coding sequence to a stop codon (PAY(∗)). Genome-wide analysis revealed multiple candidate PAY(∗) targets, including the authenticated target RRM1, suggesting a general mechanism for production of C terminus-truncated regulatory proteins.

FOXC1 regulates the functions of human basal-like breast cancer cells by activating NF-κB signaling

Human basal-like breast cancer (BLBC) is an enigmatic and aggressive malignancy with a poor prognosis. There is an urgent need to identify therapeutic targets for BLBC, because current treatment modalities are limited and not effective. The forkhead box transcription factor FOXC1 has recently been identified as a critical functional biomarker for BLBC. However, how it orchestrates BLBC cells was not clear. Here we show that FOXC1 activates the transcription factor nuclear factor-κB (NF-κB) in BLBC cells by increasing p65/RelA protein stability. High NF-κB activity has been associated with estrogen receptor-negative breast cancer, particularly BLBC. The effect of FOXC1 on p65/RelA protein stability is mediated by increased expression of Pin1, a peptidyl-prolyl isomerase. FOXC1 requires NF-κB for its regulation of cell proliferation, migration and invasion. Notably, FOXC1 overexpression renders breast cancer cells more susceptible to pharmacological inhibition of NF-κB. These results suggest that BLBC cells may rely on FOXC1-driven NF-κB signaling. Interventions of this pathway may provide modalities for the treatment of BLBC.

Evolution of function of a fused metazoan tRNA synthetase

The origin and evolution of multidomain proteins are driven by diverse processes including fusion/fission, domain shuffling, and alternative splicing. The 20 aminoacyl-tRNA synthetases (AARS) constitute an ancient conserved family of multidomain proteins. The glutamyl-prolyl tRNA synthetase (EPRS) of bilaterian animals is unique among AARSs, containing two functional enzymes catalyzing ligation of glutamate and proline to their cognate transfer RNAs (tRNAs). The ERS and PRS catalytic domains in multiple bilaterian taxa are linked by variable number of helix-turn-helix domains referred to as WHEP-TRS domains. In addition to its canonical aminoacylation activities, human EPRS exhibits a noncanonical function as an inflammation-responsive regulator of translation. Recently, we have shown that the WHEP domains direct this auxiliary function of human EPRS by interacting with an mRNA stem-loop element (interferon-gamma-activated inhibitor of translation [GAIT] element). Here, we show that EPRS is present in the cnidarian Nematostella vectensis, which pushes the origin of the fused protein back to the cnidarian-bilaterian ancestor, 50-75 My before the origin of the Bilateria. Remarkably, the Nematostella EPRS mRNA is alternatively spliced to yield three isoforms with variable number and sequence of WHEP domains and with distinct RNA-binding activities. Whereas one isoform containing a single WHEP domain binds tRNA, a second binds both tRNA and GAIT element RNA. However, the third isoform contains two WHEP domains and like the human ortholog binds specifically to GAIT element RNA. These results suggest that alternative splicing of WHEP domains in the EPRS gene of the cnidarian-bilaterian ancestor gave rise to a novel molecular function of EPRS conserved during metazoan evolution.

Gamma-ray emission concurrent with the nova in the symbiotic binary V407 Cygni

Novae are thermonuclear explosions on a white dwarf surface fueled by mass accreted from a companion star. Current physical models posit that shocked expanding gas from the nova shell can produce x-ray emission, but emission at higher energies has not been widely expected. Here, we report the Fermi Large Area Telescope detection of variable gamma-ray emission (0.1 to 10 billion electron volts) from the recently detected optical nova of the symbiotic star V407 Cygni. We propose that the material of the nova shell interacts with the dense ambient medium of the red giant primary and that particles can be accelerated effectively to produce pi(0) decay gamma-rays from proton-proton interactions. Emission involving inverse Compton scattering of the red giant radiation is also considered and is not ruled out.

Detection of 16 gamma-ray pulsars through blind frequency searches using the Fermi LAT

Pulsars are rapidly rotating, highly magnetized neutron stars emitting radiation across the electromagnetic spectrum. Although there are more than 1800 known radio pulsars, until recently only seven were observed to pulse in gamma rays, and these were all discovered at other wavelengths. The Fermi Large Area Telescope (LAT) makes it possible to pinpoint neutron stars through their gamma-ray pulsations. We report the detection of 16 gamma-ray pulsars in blind frequency searches using the LAT. Most of these pulsars are coincident with previously unidentified gamma-ray sources, and many are associated with supernova remnants. Direct detection of gamma-ray pulsars enables studies of emission mechanisms, population statistics, and the energetics of pulsar wind nebulae and supernova remnants.

The GAIT system: a gatekeeper of inflammatory gene expression

Functionally related genes are coregulated by specific RNA-protein interactions that direct transcript-selective translational control. In myeloid cells, interferon (IFN)-gamma induces formation of the heterotetrameric, IFN-gamma-activated inhibitor of translation (GAIT) complex comprising glutamyl-prolyl tRNA synthetase (EPRS), NS1-associated protein 1 (NSAP1), ribosomal protein L13a and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). This complex binds defined 3' untranslated region elements within a family of inflammatory mRNAs and suppresses their translation. IFN-gamma-dependent phosphorylation, and consequent release of EPRS and L13a from the tRNA multisynthetase complex and 60S ribosomal subunit, respectively, regulates GAIT complex assembly. EPRS recognizes and binds target mRNAs, NSAP1 negatively regulates RNA binding, and L13a inhibits translation initiation by binding eukaryotic initiation factor 4G. Repression of a post-transcriptional regulon by the GAIT system might contribute to the resolution of chronic inflammation.

The Fermi Gamma-Ray Space Telescope discovers the pulsar in the young galactic supernova remnant CTA 1

Energetic young pulsars and expanding blast waves [supernova remnants (SNRs)] are the most visible remains after massive stars, ending their lives, explode in core-collapse supernovae. The Fermi Gamma-Ray Space Telescope has unveiled a radio quiet pulsar located near the center of the compact synchrotron nebula inside the supernova remnant CTA 1. The pulsar, discovered through its gamma-ray pulsations, has a period of 316.86 milliseconds and a period derivative of 3.614 x 10(-13) seconds per second. Its characteristic age of 10(4) years is comparable to that estimated for the SNR. We speculate that most unidentified Galactic gamma-ray sources associated with star-forming regions and SNRs are such young pulsars.

Polypyrimidine tract binding protein regulates IRES-mediated translation of p53 isoforms

The p53 tumor suppressor protein plays a key role in maintaining genomic integrity. Enhanced expression of p53 during genotoxic stress is due to both increased protein stability and translational upregulation. Previous reports have shown that p53 mRNA is translated from an alternative initiation codon to produce N-terminal truncated isoform (DeltaN-p53) besides full-length p53. We have demonstrated that two internal ribosome entry sites (IRESs) regulate the translation of p53 and DeltaN-p53 in a distinct cell cycle phase-dependent manner. Here, we report that polypyrimidine tract-binding protein (PTB) is a p53 IRES interacting trans-acting factor. PTB protein binds specifically to both the p53 IRESs but with differential affinity. siRNA-mediated knockdown of PTB protein results in reduction of activity of both IRESs and also the levels of both the isoforms. It is well known that DNA-damaging agents such as doxorubicin enhance the expression of p53. Our results indicate that during doxorubicin treatment, PTB protein translocates from nucleus to the cytoplasm, probably to facilitate IRES mediated p53 translation. These observations suggest that the relative cytoplasmic abundance of PTB protein, under DNA-damaging conditions, might contribute to regulating the coordinated expression of the p53 isoforms, owing to the differential affinity of PTB binding to the two p53 IRESs.

A post-transcriptional pathway represses monocyte VEGF-A expression and angiogenic activity

Monocyte-macrophage activation by interferon (IFN)-gamma is a key initiating event in inflammation. Usually, the macrophage response is self-limiting and inflammation resolves. Here, we describe a mechanism by which IFN-gamma contributes to inflammation resolution by suppressing expression of vascular endothelial growth factor-A (VEGF-A), a macrophage product that stimulates angiogenesis during chronic inflammation and tumorigenesis. VEGF-A was identified as a candidate target of the IFN-gamma-activated inhibitor of translation (GAIT) complex by bioinformatic analysis, and experimentally validated by messenger RNA-protein interaction studies. Although IFN-gamma induced persistent VEGF-A mRNA expression, translation was suppressed by delayed binding of the GAIT complex to a specific element delineated in the 3'UTR. Translational silencing resulted in decreased VEGF-A synthesis and angiogenic activity. Our results describe a unique anti-inflammatory pathway in which IFN-gamma-dependent induction of VEGF-A mRNA is translationally silenced by the same stimulus, and they suggest the GAIT system directs a post-transcriptional operon that contributes to inflammation resolution.

Macromolecular complexes as depots for releasable regulatory proteins

Multi-component, macromolecular complexes perform essential cellular functions that require spatial or temporal coordination of activities. Complexes also facilitate co-regulation of protein amounts and cellular localization of individual components. We propose a novel function of multi-component complexes as depots for regulatory proteins that, upon release, acquire new auxiliary functions. We further propose that component release is inducible and context-dependent. We describe two cases in which multi-component assemblies - the ribosome and tRNA multi-synthetase complex--function as depots. Both complexes have crucial roles in supporting protein synthesis but they also release regulatory proteins for inflammation-responsive, transcript-specific translational control. Recent evidence indicates that other macromolecular assemblies might be sources for proteins with auxiliary functions, and the depot mechanism might be widespread in nature.

The R269H mutation in presenilin-1 presenting as late-onset autosomal dominant Alzheimer's disease

Two siblings fulfilling clinical diagnostic criteria for late-onset Alzheimer's disease (AD) are reported. The family history suggested a total of nine individuals affected with AD in three generations with autosomal dominant disease transmission. Neurogenetic testing of the proband revealed a mutation, R269H, in the presenilin-1 (PS1) gene. Late-onset AD may be associated with deterministic PS1 mutations; these should be sought when the family history suggests autosomal dominant disease transmission.

Two internal ribosome entry sites mediate the translation of p53 isoforms

The p53 tumour suppressor protein has a crucial role in cell-cycle arrest and apoptosis. Previous reports show that the p53 messenger RNA is translated to produce an amino-terminal-deleted isoform (DeltaN-p53) from an internal initiation codon, which acts as a dominant-negative inhibitor of full-length p53. Here, we show that two internal ribosome entry sites (IRESs) mediate the translation of both full-length and DeltaN-p53 isoforms. The IRES directing the translation of full-length p53 is in the 5'-untranslated region of the mRNA, whereas the IRES mediating the translation of DeltaN-p53 extends into the protein-coding region. The two IRESs show distinct cell-cycle phase-dependent activity, with the IRES for full-length p53 being active at the G2-M transition and the IRES for DeltaN-p53 showing highest activity at the G1-S transition. These results indicate a novel translational control of p53 gene expression and activity.

Equality of the sexes: found in translation

Male fruit flies (and humans) have half the number of X chromosomes that females have, yet the expression of X-linked proteins in males is the same because of a sex-specific compensatory mechanism. In this issue of Cell, report that a unique two-stage translation silencing mechanism thwarts synthesis of a male-specific transcription activator in female flies, ensuring that gene dosage compensation occurs only in males.

A 25 kDa cleavage product of polypyrimidine tract binding protein (PTB) present in mouse tissues prevents PTB binding to the 5' untranslated region and inhibits translation of hepatitis A virus RNA

The 5' untranslated region (5'UTR) of the hepatitis A virus (HAV) genomic RNA contains an internal ribosome entry site (IRES) which interacts with various cellular proteins and facilitates cap-independent translation. We report the interaction of a 25kDa protein (p25), present in certain murine tissues and most abundantly in mouse kidney, with the HAV 5'UTR. This protein was found to be a cleavage product of the polypyrimidine tract-binding protein (PTB) and competed with it for binding to the HAV 5'UTR RNA. The binding site of p25 overlapped with the reported binding site of PTB. Exogenous addition of partially purified p25 to in vitro translation reactions resulted in the inhibition of HAV IRES-mediated translation, which could be rescued by the addition of purified PTB. These results suggest that p25 is a cleavage product of PTB which binds to the HAV IRES and antagonizes the translation-stimulating activity of PTB. The presence of the 25kDa cleavage product of PTB may therefore play a role in the inhibition of HAV IRES-mediated translation in mouse tissues.

Inhibition of hepatitis C virus IRES-mediated translation by small RNAs analogous to stem-loop structures of the 5'-untranslated region

Translation of the hepatitis C virus (HCV) RNA is mediated by the interaction of ribosomes and cellular proteins with an internal ribosome entry site (IRES) located within the 5'-untranslated region (5'-UTR). We have investigated whether small RNA molecules corresponding to the different stem-loop (SL) domains of the HCV IRES, when introduced in trans, can bind to the cellular proteins and antagonize their binding to the viral IRES, thereby inhibiting HCV IRES-mediated translation. We have found that a RNA molecule corresponding to SL III could efficiently inhibit HCV IRES-mediated translation in a dose-dependent manner without affecting cap-dependent translation. The SL III RNA was found to bind to most of the cellular proteins which interacted with the HCV 5'-UTR. A smaller RNA corresponding to SL e+f of domain III also strongly and selectively inhibited HCV IRES-mediated translation. This RNA molecule interacted with the ribosomal S5 protein and prevented the recruitment of the 40S ribosomal subunit. This study reveals valuable insights into the role of the SL structures of the HCV IRES in mediating ribosome entry. Finally, these results provide a basis for developing anti-HCV therapy using small RNA molecules mimicking the SL structures of the 5'-UTR to specifically block viral RNA translation.

Electrical treatment of tibial non-union: a prospective, randomised, double-blind trial

Electrical stimulation in the treatment of bony non-union has been used in different forms for many years. However, there is still a lot of uncertainty about its efficacy. We, therefore, undertook a prospective, randomised, double-blind trial to try and determine its effect. Over a period of 5 years, 34 consecutive patients with a tibial non-union met our "criteria for inclusion". Each patient had an oblique fibular osteotomy, followed by a unilateral external fixator. They were then randomly allocated one of two machines. Group 1, the active group, received electrical stimulation from an active machine. Group 2, the dummy group, had an identical machine but without any current passing through the active coils. They were then followed up for 6 months and evaluated clinically and radiologically for bony union. Unfortunately, there was by chance, an imbalance in smoking habit between the two groups. The union rate in the subgroup that smoked was 75% (6/8) in the active group as compared to 46% (6/13) in the dummy group. The active group of non-smokers had 100% (10/10) union rate, compared to 67% (2/3) in the dummy group. Overall 24 out of the 34 patients progressed to union. Out of 18, 16 (89%) in the active group showed bony union as compared to 8/16 (50%) in the dummy. There was, thus, a statistically significant positive association between tibial union and electrical stimulation (odds ratio 8, 95% CI: 1.5-41, P=0.02).

La autoantigen is required for the internal ribosome entry site-mediated translation of Coxsackievirus B3 RNA

Translation initiation in Coxsackievirus B3 (CVB3) occurs via ribosome binding to an internal ribosome entry site (IRES) located in the 5'-untranslated region (UTR) of the viral RNA. This unique mechanism of translation initiation requires various trans-acting factors from the host. We show that human La autoantigen (La) binds to the CVB3 5'-UTR and also demonstrate the dose-dependent effect of exogenously added La protein in stimulating CVB3 IRES-mediated translation. The requirement of La for CVB3 IRES mediated translation has been further demonstrated by inhibition of translation as a result of sequestering La and its restoration by exogenous addition of recombinant La protein. The abundance of La protein in various mouse tissue extracts has been probed using anti-La antibody. Pancreatic tissue, a target organ for CVB3 infection, was found to have a large abundance of La protein which was demonstrated to interact with the CVB3 5'-UTR. Furthermore, exogenous addition of pancreas extract to in vitro translation reactions resulted in a dose dependent stimulation of CVB3 IRES-mediated translation. These observations indicate the role of La in CVB3 IRES-mediated translation, and suggest its possible involvement in the efficient translation of the viral RNA in the pancreas.

Effects of hypoxia/reoxygenation on angiogenic factors and their tyrosine kinase receptors in the rat myocardium

The process of angiogenesis is initiated primarily as a consequence of hypoxic stimulation at the cellular and molecular level. Although several angiogenic growth factors have been identified, at present a detailed understanding of the interplay among inducing stimuli, growth factors, and their respective molecular targets remains to be evaluated. Here we report the effects of progressively increasing durations of moderate hypoxia on the protein expression profiles and tissue distribution patterns of the vascular endothelial growth factor system and the angiopoietin/Tie system in the adult rat myocardium. The relative temporal trends of expression of the various components of these two systems, as well as apparent relationships between Flk-1 and angiopoietin-2 and between Flt-1 and Tie-1, suggest a probable sequence of involvement during myocardial angiogenesis, as proposed in our model. Such relationships may potentially be utilized in formulating strategies for sequential gene therapy to achieve clinically relevant myocardial angiogenesis.

Hypoxia/reoxygenation promotes myocardial angiogenesis via an NF kappa B-dependent mechanism in a rat model of chronic myocardial infarction

Therapeutic angiogenesis achieved either through the use of discreet angiogenic proteins or by gene therapy is fast emerging as a highly attractive treatment modality for ischemic heart disease. Herein we examine a novel method of stimulating myocardial angiogenesis by hypoxic preconditioning at both capillary and arteriolar levels, and the potential role of NF kappa B in mediating such a response. We also investigate the functional relevance of such treatment by assessing whether the induced neovascularization can help preserve left ventricular contractile functional reserve in the setting of developing heart failure secondary to myocardial infarction. Male Sprague-Dawley rats were randomly divided into eight groups: normoxia + sham surgery (NS), normoxia + permanent left anterior descending coronary artery (LAD) occlusion (NMI), hypoxic preconditioning + sham surgery (HS), hypoxic preconditioning + permanent LAD occlusion (HMI), PDTC (NF kappa B inhibitor) + hypoxic preconditioning + LAD occlusion (PHMI), PDTC+normoxia + LAD occlusion (PNMI), PDTC + hypoxic preconditioning + sham surgery (PHS) and PDTC + normoxia + sham surgery (PNS). Rats in the preconditioned groups were subjected to systemic hypoxemic hypoxic exposure (10+/-0.4% O2) for 4 h followed by a 24-h period of normoxic reoxygenation prior to undergoing LAD occlusion. Rats in the normoxia groups were time matched with the preconditioned group and maintained under normoxic conditions for the 28-h period prior to LAD occlusion. The HMI group displayed significant increases in capillary as well as arteriolar density after 2, 4 and 7 days post-operation compared to the NMI. Prior PDTC administration prevented such increases in the PHMI group and effectively abolished the pro-angiogenic effect of hypoxic preconditioning (HP). One week after sham surgery or LAD occlusion, rats underwent a pharmacological stress test with dobutamine in progressively increasing doses which revealed significantly elevated values of dp/dt(max) at each dose point in the HMI group compared to the NMI or PHMI groups. Hypoxic preconditioning also decreases endothelial cell injury as determined by the extent of endothelial cell apoptosis using anti-VWF factor labelling and TUNEL assay. The results suggest that HP stimulates myocardial angiogenesis via redox-regulated transcription factor, NF kappa B-dependent pathway to an extent sufficient to exert significant preservation of contractile functional reserve in a rat model of myocardial infarction progressing to heart failure.

Transgene overexpression of alphaB crystallin confers simultaneous protection against cardiomyocyte apoptosis and necrosis during myocardial ischemia and reperfusion

We investigated whether enhanced expression of alphaB crystallin, a stress-inducible molecular chaperone of the small heat shock family, can protect myocardial contractile apparatus against ischemia reperfusion (I/R) injury. Transgenic mice overexpressing alphaB crystallin were generated using the 0.76 kb rat alphaB crystallin cDNA cloned into a pCAGGS plasmid driven by a human cytomegalovirus expression system. Southern analysis confirmed transgene integration and Northern and Western blotting characterized expression (3.1-fold and 6.9-fold elevations in myocardial mRNA and protein levels, respectively). Extent of functional recovery over a 3 h reperfusion period following a 20 min ischemic period in transgenic and wild-type mouse hearts was assessed using an ex vivo work-performing heart preparation. The transgenic group displayed significantly higher values of DP at R45 min (29.14+/-1.9 mm Hg vs. 17.6+/-0.7 mm Hg), R60 min (31.56+/-1.7 mm Hg vs. 17.8+/-0.8 mm Hg), and R75 min (32.5+/-2.2 mm Hg vs. 16.9+/-0.9 mm Hg), and of dLVP/dt at R45 min (1740.2+/-111.5 mm Hg.s-1 vs. 548.7+/-82.2 mm Hg.s-1) and R60 min (1199.8+/-104.6 mm Hg.s-1 vs. 466.9+/-61.1 mm Hg.s-1). The transgenic group also displayed development of less oxidative stress, decreased extent of infarction, and attenuated cardiomyocyte apoptotic cell death. Transgene overexpression of alphaB crystallin was therefore successful in diminishing the independent contributory effects of both necrosis and apoptosis on I/R-induced cell death.

Fixation of proximal humeral fractures with the Polarus nail

Thirty patients with fractures of the proximal humerus were treated by internal fixation with an intramedullary locked nail. Fourteen of these patients were more than 60 years of age; 23 patients had 2-part fractures (surgical neck fractures) and were operated on within an average of 3 days after injury. At follow-up, 20 (80%) of 25 patients showed satisfactory to excellent functional outcomes, as measured by Constant score. All but 1 fracture progressed to clinical and radiologic union. The good functional results indicate that the Polarus nail is a satisfactory mechanical device that can be used in the treatment of displaced proximal humeral fractures in both the young and the elderly with osteopenic bone.

Oxidative stress due to hypoxia/reoxygenation induces angiogenic factor VEGF in adult rat myocardium: possible role of NFkappaB

INTRODUCTION

Oxidative stress, as exerted by free radicals within biological systems, is known to exert numerous physiological and pathological effects on the cardiovascular system. Short-term exposure to environmental conditions such as low oxygen tension can cause such oxidative stress in vivo through inhalational hypoxia/reoxygenation. In this report the effects of different durations of hypoxia were investigated on myocardial protein expression of vascular endothelial growth factor (VEGF). a major angiogenic growth factor, and also explore the possible modulatory role of transcription factor NFkappaB on such expression.

METHODS

Forty eight male Sprague-Dawley rats (300 g b.w.) were randomly divided into four groups and subjected to either 1, 2 or 4 h of systemic normobaric hypoxemic hypoxia (10+/-0.4% O2) in an anesthesia chamber, or to 4 h of normoxia (ambient 20.9+/-0.4% O2) to time-match the maximal hypoxic duration. All rats were then kept under normoxic conditions. Rats were sacrificed and hearts harvested either after 2 h for later electrophoretic mobility gel shift assay for NFkappaB, or after 24 h for later Western blot analysis for VEGF.

RESULTS

Western blot analysis for VEGF revealed significantly elevated protein expression (2.4-fold compared to baseline control) in the I h group. This elevated level persisted in the 2 and 4 h groups as well. Two hours post-hypoxia gel shift assay for NFkappaB indicated significant nuclear translocation and DNA binding of this transcription factor in the 1 and 2 h groups, with moderate decrease in the 4 h group.

CONCLUSION

In vivo oxidative stress caused by systemic inhalational hypoxemic hypoxia increases cardiac VEGF protein expression and may trigger myocardial angiogenesis. The results suggest that NFkappaB modulates such an effect.

Total elbow arthroplasty as primary treatment for distal humeral fractures in elderly patients

Distal humeral fractures are difficult to treat. In the elderly population, the problems are compounded by osteoporosis and gross comminution. Open reduction and internal fixation for such fractures is sometimes difficult and may be associated with poor results. Total elbow arthroplasty has been suggested as a last-ditch effort to salvage functional use for such difficult fractures in the elderly. We followed seven patients (seven elbows) with a mean age of 81.7 years at the time of injury. Open reduction and internal fixation was considered a difficult option for these fractures. They were treated with a total elbow arthroplasty using the semi-constrained Coonrad-Morrey elbow replacement prosthesis. The duration of follow up at present is between 2 and 4 years. At the latest follow up the mean arc of flexion is 20-130 degrees. Six patients have no pain while one complains of mild pain. All elbows are stable. The Mayo elbow performance score for five elbows is excellent and two scored good. All but one patient are satisfied with the result. One patient developed superficial wound infection which resolved after antibiotic therapy. One patient has developed post-operative triceps weakness. There have been no cases of deep infection, ulnar nerve neuritis or component failure. The rarity of this procedure suggests its very narrow spectrum of indication. We feel that the short-term results do suggest an important role for semi-constrained total elbow arthroplasty in managing carefully selected comminuted distal humeral fractures in the elderly, especially those that cannot be treated by conventional open reduction and internal fixation.