The ribosome receptor, p180, interacts with kinesin heavy chain, KIF5B

CDR2 is a dynein adaptor recruited by kinectin to regulate ER sheet organization

The endoplasmic reticulum (ER) relies on the microtubule cytoskeleton for distribution and remodelling of its extended membrane network, but how microtubule-based motors contribute to ER organization remains unclear. Using biochemical and cell-based assays, we identify cerebellar degeneration-related protein 2 (CDR2) and its paralog CDR2-like (CDR2L), onconeural antigens with poorly understood functions, as ER adaptors for cytoplasmic dynein-1 (dynein). We demonstrate that CDR2 is recruited by the integral ER membrane protein kinectin (KTN1) and that double knockout of CDR2 and CDR2L enhances KTN1-dependent ER sheet stacking, reversal of which by exogenous CDR2 requires its dynein-binding CC1 box motif. Exogenous CDR2 expression additionally promotes CC1 box-dependent clustering of ER sheets near centrosomes. CDR2 competes with the eEF1Bβ subunit of translation elongation factor 1 for binding to KTN1, and eEF1Bβ knockdown increases endogenous CDR2 levels on ER sheets, inducing their centrosome-proximal clustering. Our study describes a novel molecular pathway that implicates dynein in ER sheet organization and may be involved in the pathogenesis of paraneoplastic cerebellar degeneration.

Epithelioid inflammatory myofibroblastic sarcoma treated with Alectinib: a case report and literature review

Epithelioid inflammatory myofibroblastic sarcoma (EIMS) is an extremely rare and aggressive form of inflammatory myofibroblastic tumor. Clinically, it has a high risk of relapse and peripheral organ infiltration, and it responds poorly to conventional chemotherapy. Anaplastic lymphoma kinase (ALK) inhibitors are currently the most effective targeted therapy for EIMS. This report discusses a typical case of abdominal EIMS in a 43-year-old woman. The tumors recurred rapidly within one month after surgery. Alectinib was promptly administered upon diagnosis. However, the patient developed a severe allergic reaction to the medication. After a comprehensive assessment and symptomatic treatment, her condition stabilized, leading to a favorable prognosis. This study summarizes cases of abdominal EIMS, highlights the successful use of Alectinib for treatment, and discusses the management of medication-related complications.

Comparative transcriptome provides insights into the selection adaptation between wild and farmed foxes

The silver fox and blue fox are economically important fur species and were domesticated by humans from their wild counterparts, the arctic fox and red fox, respectively. Farmed foxes show obvious differences from their wild counterparts, including differences in physiology, body size, energy metabolism, and immunity. However, the molecular mechanisms underlying these differences are presently unclear. In this study, we built transcriptome libraries from multiple pooled tissues for each species of farmed fox, used RNA-seq to obtain a comprehensive dataset, and performed selection analysis and sequence-level analyses of orthologous genes to identify the genes that may be influenced by human domestication. More than 153.3, 248.0, 81.6, and 65.8 million clean reads were obtained and assembled into a total of 118,577, 401,520, 79,900, and 186,988 unigenes with an average length range from 521 to 667 bp for AF, BF, RF, and SF, respectively. Selective pressure analysis showed that 11 and 14 positively selected genes were identified, respectively, in the two groups (AF vs. BF and RF vs. SF). Several of these genes were associated with natural immunity (CFI and LRRFIP1), protein synthesis (GOLGA4, CEP19 and SLC35A2), and DNA damage repair (MDC1). Further functional enrichment analyses demonstrated that two positively selected genes (ACO1 and ACAD10) were involved in metabolic process (GO:0008152, p-value = .032), representing a significant enrichment. Sequence analysis of 117 orthologous genes shared by the two groups showed that the LEMD2, RRBP1, and IGBP1 genes might be affected by artificial selection in farmed foxes, with mutation sites located within sequences that are otherwise highly conserved across most mammals. Our results provide a valuable transcriptomic resource for future genetic studies and improvement in the assisted breeding of foxes and other farmed animals.

Intertwined and Finely Balanced: Endoplasmic Reticulum Morphology, Dynamics, Function, and Diseases

The endoplasmic reticulum (ER) is an organelle that is responsible for many essential subcellular processes. Interconnected narrow tubules at the periphery and thicker sheet-like regions in the perinuclear region are linked to the nuclear envelope. It is becoming apparent that the complex morphology and dynamics of the ER are linked to its function. Mutations in the proteins involved in regulating ER structure and movement are implicated in many diseases including neurodegenerative diseases such as Alzheimer’s, Parkinson’s, and amyotrophic lateral sclerosis (ALS). The ER is also hijacked by pathogens to promote their replication. Bacteria such as Legionella pneumophila and Chlamydia trachomatis, as well as the Zika virus, bind to ER morphology and dynamics-regulating proteins to exploit the functions of the ER to their advantage. This review covers our understanding of ER morphology, including the functional subdomains and membrane contact sites that the organelle forms. We also focus on ER dynamics and the current efforts to quantify ER motion and discuss the diseases related to ER morphology and dynamics.

ER - lysosome contacts at a pre-axonal region regulate axonal lysosome availability

Neuronal function relies on careful coordination of organelle organization and transport. Kinesin-1 mediates transport of the endoplasmic reticulum (ER) and lysosomes into the axon and it is increasingly recognized that contacts between the ER and lysosomes influence organelle organization. However, it is unclear how organelle organization, inter-organelle communication and transport are linked and how this contributes to local organelle availability in neurons. Here, we show that somatic ER tubules are required for proper lysosome transport into the axon. Somatic ER tubule disruption causes accumulation of enlarged and less motile lysosomes at the soma. ER tubules regulate lysosome size and axonal translocation by promoting lysosome homo-fission. ER tubule - lysosome contacts often occur at a somatic pre-axonal region, where the kinesin-1-binding ER-protein P180 binds microtubules to promote kinesin-1-powered lysosome fission and subsequent axonal translocation. We propose that ER tubule - lysosome contacts at a pre-axonal region finely orchestrate axonal lysosome availability for proper neuronal function.

Molecular basis of mRNA transport by a kinesin-1-atypical tropomyosin complex

Here, Dimitrova-Paternoga et al. present the high-resolution crystal structure of Khc–aTm1 (Drosophila kinesin-1, also called kinesin heavy chain [Khc], in complex with a putative cargo adaptor, the atypical tropomyosin [aTm1]), which mediates transport of oskar mRNA to the posterior pole of the Drosophila oocyte. They show that aTm1 binds to an evolutionarily conserved cargo binding site on Khc, demonstrate that Khc binds RNA directly, and show that aTm1 plays a stabilizing role in the interaction of Khc with RNA, which distinguishes aTm1 from classical motor adaptors.

Kinesin-1 carries cargos including proteins, RNAs, vesicles, and pathogens over long distances within cells. The mechanochemical cycle of kinesins is well described, but how they establish cargo specificity is not fully understood. Transport of oskar mRNA to the posterior pole of the Drosophila oocyte is mediated by Drosophila kinesin-1, also called kinesin heavy chain (Khc), and a putative cargo adaptor, the atypical tropomyosin, aTm1. How the proteins cooperate in mRNA transport is unknown. Here, we present the high-resolution crystal structure of a Khc–aTm1 complex. The proteins form a tripartite coiled coil comprising two in-register Khc chains and one aTm1 chain, in antiparallel orientation. We show that aTm1 binds to an evolutionarily conserved cargo binding site on Khc, and mutational analysis confirms the importance of this interaction for mRNA transport in vivo. Furthermore, we demonstrate that Khc binds RNA directly and that it does so via its alternative cargo binding domain, which forms a positively charged joint surface with aTm1, as well as through its adjacent auxiliary microtubule binding domain. Finally, we show that aTm1 plays a stabilizing role in the interaction of Khc with RNA, which distinguishes aTm1 from classical motor adaptors.

Correlation between reticulum ribosome-binding protein 1 (RRBP1) overexpression and prognosis in cervical squamous cell carcinoma

Our purpose was to evaluate the correlation between endoplasmic reticulum ribosomal binding protein 1 (RRBP1) expression in cervical squamous cell carcinoma (CSCC) and poor patient prognosis. RRBP1 is a nascent transporter that is situated on the rough endoplasmic reticulum (ER). It adjusts to the secretion of proteins in cells and alleviates ER stress, thus stimulating cell proliferation. An immunohistochemical (IHC) study was conducted to detect the expression level of RRBP1 on 96 CSCC tissue samples. Western blot and Quantitative real-time polymerase chain reaction (qRT-PCR) were performed to compare the expression levels of RRBP1 in cervical squamous cell carcinoma with healthy cervical tissues. An overexpression of RRBP1 was observed in CSCC tissues, and the expression level was associated with FIGO stage (Stage I vs. II: 52.6% vs. 74.1%, p = 0.030), and lymph node metastasis (No vs. Yes: 61.5% vs. 92.3%, p = 0.031) but not patient age and tissue differentiation. Univariate survival analysis indicated that prognosis was associated with the expression level of RRBP1 and tissue differentiation and lymph node metastasis. Analysis of the multi-factor survival Cox model proved that RRBP1 was an independent prognostic factor. In conclusion, compared with healthy cervical tissues, RRBP1 was overexpressed in CSCC tissues, illustrating that RRBP1 may be a new biomarker for the diagnosis of CSCC. The study on RRBP1 may contribute to exploring the pathogenesis of CSCC and may also guide targeted therapy for CSCC in the future.

Axonal Endoplasmic Reticulum Dynamics and Its Roles in Neurodegeneration

The physical continuity of axons over long cellular distances poses challenges for their maintenance. One organelle that faces this challenge is endoplasmic reticulum (ER); unlike other intracellular organelles, this forms a physically continuous network throughout the cell, with a single membrane and a single lumen. In axons, ER is mainly smooth, forming a tubular network with occasional sheets or cisternae and low amounts of rough ER. It has many potential roles: lipid biosynthesis, glucose homeostasis, a Ca2+ store, protein export, and contacting and regulating other organelles. This tubular network structure is determined by ER-shaping proteins, mutations in some of which are causative for neurodegenerative disorders such as hereditary spastic paraplegia (HSP). While axonal ER shares many features with the tubular ER network in other contexts, these features must be adapted to the long and narrow dimensions of axons. ER appears to be physically continuous throughout axons, over distances that are enormous on a subcellular scale. It is therefore a potential channel for long-distance or regional communication within neurons, independent of action potentials or physical transport of cargos, but involving its physiological roles such as Ca2+ or organelle homeostasis. Despite its apparent stability, axonal ER is highly dynamic, showing features like anterograde and retrograde transport, potentially reflecting continuous fusion and breakage of the network. Here we discuss the transport processes that must contribute to this dynamic behavior of ER. We also discuss the model that these processes underpin a homeostatic process that ensures both enough ER to maintain continuity of the network and repair breaks in it, but not too much ER that might disrupt local cellular physiology. Finally, we discuss how failure of ER organization in axons could lead to axon degenerative diseases, and how a requirement for ER continuity could make distal axons most susceptible to degeneration in conditions that disrupt ER continuity.

Expression of RRBP1 in epithelial ovarian cancer and its clinical significance

Hematopoietic pre-B cell leukemia transcription factor (PBX)-interacting protein (RRBP1) has been shown to participate in various aspects of malignancies. The clinical significance of RRBP1 and its involvement in the epithelial ovarian cancer have yet to be studied. The aim of the present study was to investigate the expression of RRBP1 in epithelial ovarian cancer (EOC) and its relationship with clinical characteristics and prognosis. We evaluated the mRNA and protein expression levels of RRBP1 by quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting (n=45). Immunohistochemistry and data analysis were used to examine the relationship between the expression level of RRBP1 and the clinicopathological features and prognosis of epithelial ovarian cancer. RRBP1 was highly expressed in EOC (P<0.001). The specimens were obtained from 108 patients undergoing surgery to treat epithelial ovarian cancer. RRBP1 expression was obviously related to Federation International of Gynecologie and Obstetrigue (FIGO) stage (P<0.001), histological grade (P=0.021), histological type (P=0.004), and lymph node metastasis (P=0.012) but was not related to patient age (P=0.385) or preoperative carbohydrate antigen125 (CA125) level (P=0.238). Univariate analysis showed that the prognosis of the epithelial ovarian cancer patients was related to the age of the patients, the FIGO stage, and the expression level of RRBP1 (P<0.05). Patients with higher RRBP1 expression had significantly worse overall survival (OS) (P=0.003) and disease-free survival (DFS) (P<0.001). Multivariate survival analysis proved that RRBP1 was an independent predictor of OS (P=0.003) and DFS (P<0.001). RRBP1 plays an important role in predicting the prognosis of EOC. These results show that RRBP1 is a potential target for the treatment of epithelial ovarian cancer.

The coming-of-age of nucleocytoplasmic transport in motor neuron disease and neurodegeneration

The nuclear pore is the gatekeeper of nucleocytoplasmic transport and signaling through which a vast flux of information is continuously exchanged between the nuclear and cytoplasmic compartments to maintain cellular homeostasis. A unifying and organizing principle has recently emerged that cements the notion that several forms of amyotrophic lateral sclerosis (ALS), and growing number of other neurodegenerative diseases, co-opt the dysregulation of nucleocytoplasmic transport and that this impairment is a pathogenic driver of neurodegeneration. The understanding of shared pathomechanisms that underpin neurodegenerative diseases with impairments in nucleocytoplasmic transport and how these interface with current concepts of nucleocytoplasmic transport is bound to illuminate this fundamental biological process in a yet more physiological context. Here, I summarize unresolved questions and evidence and extend basic and critical concepts and challenges of nucleocytoplasmic transport and its role in the pathogenesis of neurodegenerative diseases, such as ALS. These principles will help to appreciate the roles of nucleocytoplasmic transport in the pathogenesis of ALS and other neurodegenerative diseases, and generate a framework for new ideas of the susceptibility of motoneurons, and possibly other neurons, to degeneration by dysregulation of nucleocytoplasmic transport.

Feedback-Driven Mechanisms between Microtubules and the Endoplasmic Reticulum Instruct Neuronal Polarity

Establishment of neuronal polarity depends on local microtubule (MT) reorganization. The endoplasmic reticulum (ER) consists of cisternae and tubules and, like MTs, forms an extensive network throughout the entire cell. How the two networks interact and control neuronal development is an outstanding question. Here we show that the interplay between MTs and the ER is essential for neuronal polarity. ER tubules localize within the axon, whereas ER cisternae are retained in the somatodendritic domain. MTs are essential for axonal ER tubule stabilization, and, reciprocally, the ER is required for stabilizing and organizing axonal MTs. Recruitment of ER tubules into one minor neurite initiates axon formation, whereas ER retention in the perinuclear area or disruption of ER tubules prevent neuronal polarization. The ER-shaping protein P180, present in axonal ER tubules, controls axon specification by regulating local MT remodeling. We propose a model in which feedback-driven regulation between the ER and MTs instructs neuronal polarity.

Expression and significance of RRBP1 in esophageal carcinoma

Objective

This study was to investigate the expression and clinical significance of RRBP1 in esophageal carcinoma.

Materials and methods

RRBP1 expression was detected in 120 esophageal carcinoma and matched adjacent normal tissues, and the relationship of RRBP1 with clinicopathological characteristics and prognosis was analyzed.

Results

RRBP1 was highly expressed in esophageal carcinoma tissues compared with matched adjacent normal tissues (P<0.05). Moreover, RRBP1 expression was associated with T stage, lymph node metastasis, and TNM stage in esophageal carcinoma (P<0.05). Survival analysis revealed that RRBP1, T stage, lymph node metastasis, and TNM stage were significantly associated with patients’ prognosis.

Conclusion

RRBP1 is highly expressed in esophageal carcinoma and can serve as a potential biomarker to predict patients’ prognosis.

Comprehensive Genomic Profiling of Metastatic Squamous Cell Carcinoma of the Anal Canal

Squamous cell carcinoma of the anal canal (SCCA) is a rare gastrointestinal malignancy with an increasing annual incidence globally. The majority of cases are linked to prior infection with the human papillomavirus (HPV). For patients with metastatic SCCA, no consensus standard treatment exists. Identification of relevant targeted agents as novel therapeutic approaches for metastatic SCCA has been limited by a lack of comprehensive molecular profiling. We performed whole-exome sequencing on tumor-normal pairs from 24 patients with metastatic SCCA. Tumor tissue from 17 additional patients was analyzed using a 263-gene panel as a validation cohort. Gene expression profiling was performed on available frozen tissue to assess for differential expression patterns. Based on these findings, patient-derived xenograft (PDX) models of SCCA were generated to test targeted therapies against PI3K and EGFR. Despite a low mutation burden, mutations in PIK3CA, MLL2, and MLL3 were among the most commonly mutated genes. An association between TP53 mutations and HPV-negative SCCA tumors was observed. Gene expression analysis suggested distinct tumor subpopulations harboring PIK3CA mutations and for which HPV had integrated into the host genome. In vivo studies demonstrated improvement with anti-EGFR treatment. Gene mutation frequencies, tumor mutation burden, and gene expression patterns for metastatic SCCA appear similar to other HPV-associated malignancies.Implications: This first comprehensive genomic characterization for patients with metastatic SCCA provides further rationale for the integration of SCCA into the development of novel targeted therapies across HPV-related cancers. Mol Cancer Res; 15(11); 1542-50. ©2017 AACR.

Proteomic mapping of cytosol-facing outer mitochondrial and ER membranes in living human cells by proximity biotinylation

The cytosol-facing membranes of cellular organelles contain proteins that enable signal transduction, regulation of morphology and trafficking, protein import and export, and other specialized processes. Discovery of these proteins by traditional biochemical fractionation can be plagued with contaminants and loss of key components. Using peroxidase-mediated proximity biotinylation, we captured and identified endogenous proteins on the outer mitochondrial membrane (OMM) and endoplasmic reticulum membrane (ERM) of living human fibroblasts. The proteomes of 137 and 634 proteins, respectively, are highly specific and highlight 94 potentially novel mitochondrial or ER proteins. Dataset intersection identified protein candidates potentially localized to mitochondria-ER contact sites. We found that one candidate, the tail-anchored, PDZ-domain-containing OMM protein SYNJ2BP, dramatically increases mitochondrial contacts with rough ER when overexpressed. Immunoprecipitation-mass spectrometry identified ribosome-binding protein 1 (RRBP1) as SYNJ2BP's ERM binding partner. Our results highlight the power of proximity biotinylation to yield insights into the molecular composition and function of intracellular membranes.

ALK oncoproteins in atypical inflammatory myofibroblastic tumours: novel RRBP1-ALK fusions in epithelioid inflammatory myofibroblastic sarcoma

ALK oncogenic activation mechanisms were characterized in four conventional spindle-cell inflammatory myofibroblastic tumours (IMT) and five atypical IMT, each of which had ALK genomic perturbations. Constitutively activated ALK oncoproteins were purified by ALK immunoprecipitation and electrophoresis, and were characterized by mass spectrometry. The four conventional IMT had TPM3/4-ALK fusions (two cases) or DCTN1-ALK fusions (two cases), whereas two atypical spindle-cell IMT had TFG-ALK and TPM3-ALK fusion in one case each, and three epithelioid inflammatory myofibroblastic sarcomas had RANBP2-ALK fusions in two cases, and a novel RRBP1-ALK fusion in one case. The epithelioid inflammatory myofibroblastic sarcoma with RRBP1-ALK fusion had cytoplasmic ALK expression with perinuclear accentuation, different from the nuclear membranous ALK localization in epithelioid inflammatory myofibroblastic sarcomas with RANBP2-ALK fusions. Evaluation of three additional uncharacterized epithelioid inflammatory myofibroblastic sarcomas with ALK cytoplasmic/perinuclear- accentuation expression demonstrated RRBP1-ALK fusion in two cases. These studies show that atypical spindle-cell IMT can utilize the same ALK fusion mechanisms described previously in conventional IMT, whereas in clinically aggressive epithelioid inflammatory myofibroblastic sarcoma we identify a novel recurrent ALK oncogenic mechanism, resulting from fusion with the RRBP1 gene. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Kinectin-dependent ER transport supports the focal complex maturation required for chemotaxis in shallow gradients

Chemotaxis in shallow gradients of chemoattractants is accomplished by preferential maintenance of protrusions oriented towards the chemoattractant; however, the mechanism of preferential maintenance is not known. Here, we test the hypothesis that kinectin-dependent endoplasmic reticulum (ER) transport supports focal complex maturation to preferentially maintain correctly oriented protrusions. We knocked down kinectin expression in MDA-MB-231 cells using small interfering RNA and observed that kinectin contributes to the directional bias, but not the speed, of cell migration. Kymograph analysis revealed that the extension of protrusions oriented towards the chemoattractant was not affected by kinectin knockdown, but that their maintenance was. Immunofluorescence staining and live-cell imaging demonstrated that kinectin transports ER preferentially to protrusions oriented towards the chemoattractant. ER then promotes the maturation of focal complexes into focal adhesions to maintain these protrusions for chemotaxis. Our results show that kinectin-dependent ER distribution can be localized by chemoattractants and provide a mechanism for biased protrusion choices during chemotaxis in shallow gradients of chemoattractants.

Identification of Kinesin-1 Cargos Using Fluorescence Microscopy

Fluorescence microscopy is employed to identify Kinesin-1 cargos. Recently, the heavy chain of Kinesin-1 (KIF5B) was shown to transport the nuclear transcription factor c-MYC for proteosomal degradation in the cytoplasm. The method described here involves the study of a motorless KIF5B mutant for fluorescence microscopy. The wild-type and motorless KIF5B proteins are tagged with the fluorescent protein tdTomato. The wild-type tdTomato-KIF5B appears homogenously in the cytoplasm, while the motorless tdTomato-KIF5B mutant forms aggregates in the cytoplasm. Aggregation of the motorless KIF5B mutant induces aggregation of its cargo c-MYC in the cytoplasm. Hence, this method provides a visual means to identify the cargos of Kinesin-1. A similar strategy can be utilized to identify cargos of other motor proteins.

Endoplasmic reticulum ribosome-binding protein 1, RRBP1, promotes progression of colorectal cancer and predicts an unfavourable prognosis

BACKGROUND

Ribosome-binding protein 1 (RRBP1) has been implicated in the regulation of unfolded protein response, which is involved in almost every aspect of cancer development. We aimed to explore the significance of RRBP1 in the progression and prognosis of colorectal cancer (CRC).

METHODS

The study population consisted of 856 patients with stage I-III CRC from two hospitals. RRBP1 expression was examined by immunohistochemistry (IHC) in colorectal tissues. The correlation of RRBP1 expression and CRC occurrence was assessed in paired cancer-adjacent tissues. Factors contributing to prognosis were evaluated in a training-validation design with univariate and multivariate Cox analysis. Colorectal cancer aggressiveness caused by RRBP1 knockdown or overexpression was evaluated in CRC cells.

RESULTS

RRBP1 was aberrantly overexpressed in CRC. Compared with low-RRBP1 patients, high-RRBP1 patients had shorter disease-specific survival in the training (hazard ratio (HR), 2.423; 95% confidence interval (CI), 1.531-3.835) and validation cohorts (HR, 3.749; 95% CI, 2.166-6.448) in multivariate Cox analysis. High-RRBP1 independently predicted a shorter disease-free survival (HR, 4.821; 95% CI, 3.220-7.218) in the validation cohort. RRBP1 knockdown reduced the aggressiveness of CRC cells in vitro and inhibited the growth of CRC xenografts in vivo.

CONCLUSIONS

High RRBP1 expression facilitates CRC progression and predicts an unfavourable post-operative prognosis.

On the expansion of ribosomal proteins and RNAs in eukaryotes

While the ribosome constitution is similar in all biota, there is a considerable increase in size of both ribosomal proteins (RPs) and RNAs in eukaryotes as compared to archaea and bacteria. This is pronounced in the large (60S) ribosomal subunit (LSU). In addition to enlargement (apparently maximized already in lower eukarya), the RP changes include increases in fraction, segregation and clustering of basic residues, and decrease in hydrophobicity. The acidic fraction is lower in eukaryote as compared to prokaryote RPs. In all eukaryote groups tested, the LSU RPs have significantly higher content of basic residues and homobasic segments than the SSU RPs. The vertebrate LSU RPs have much higher sequestration of basic residues than those of bacteria, archaea and even of the lower eukarya. The basic clusters are highly aligned in the vertebrate, but less in the lower eukarya, and only within families in archaea and bacteria. Increase in the basicity of RPs, besides helping transport to the nucleus, should promote stability of the assembled ribosome as well as the association with translocons and other intracellular matrix proteins. The size and GC nucleotide bias of the expansion segments of large LSU rRNAs also culminate in the vertebrate, and should support ribosome association with the endoplasmic reticulum and other intracellular networks. However, the expansion and nucleotide bias of eukaryote LSU rRNAs do not clearly correlate with changes in ionic parameters of LSU ribosomal proteins.

Overexpression of ribosome binding protein 1 (RRBP1) in breast cancer

The molecular events that lead to malignant transformation and subsequent metastasis of breast carcinoma include alterations in the cells at genome, transcriptome and proteome levels. In this study, we used publicly available gene expression databases to identify those candidate genes which are upregulated at the mRNA level in breast cancers but have not been systematically validated at the protein level. Based on an extensive literature search, we identified ribosome binding protein 1 (RRBP1) as a candidate that is upregulated at the mRNA level in five different studies but its protein expression had not been investigated. Immunohistochemical labeling of breast cancer tissue microarrays was carried out to determine the expression of RRBP1 in a large panel of breast cancers. We found that RRBP1 was overexpressed in 84% (177/219) of breast carcinoma cases tested. The subcellular localization of RRBP1 was mainly observed to be in the cytoplasm with intense staining in the perinuclear region. Our findings suggest that RRBP1 is an interesting molecule that can be further studied for its potential to serve as a breast cancer biomarker. This study also demonstrates how the integration of biological data from available resources in conjunction with systematic evaluation approaches can be successfully applied to clinical proteomics.

Regulation of polysome assembly on the endoplasmic reticulum by a coiled-coil protein, p180

A coiled-coil microtubule-bundling protein, p180, was originally identified as one of the ribosome receptor candidates on the rough endoplasmic reticulum (ER) and is highly expressed in secretory tissues. Recently, we reported that p180 plays crucial roles in upregulating collagen biosynthesis, mainly by facilitating ribosome association on the ER. Here, we provide evidence that p180 is required to form translationally active polysome/translocon complexes on the ER. Assembly of highly-developed polysomes on the ER was severely perturbed upon loss of p180. p180 associates with polysome/translocon complexes through multiple contact sites: it was coimmunoprecipitated with the translocon complex independently of ribosomes, while it can also bind to ribosomal large subunit specifically. The responsible domain of p180 for membrane polysome assembly was identified in the C-terminal coiled-coil region. The degree of ribosome occupation of collagen and fibronectin mRNAs was regulated in response to increased traffic demands. This effect appears to be exerted in a manner specific for a specified set of mRNAs. Collectively, our data suggest that p180 is required to form translationally active polysome/translocon complexes on the ER membrane, and plays a pivotal role in highly efficient biosynthesis on the ER membrane through facilitating polysome formation in professional secretory cells.

Targeted inactivation of kinesin-1 in pancreatic β-cells in vivo leads to insulin secretory deficiency

OBJECTIVE

Suppression of Kinesin-1 by antisense oligonucleotides, or overexpression of dominant-negative acting kinesin heavy chain, has been reported to affect the sustained phase of glucose-stimulated insulin secretion in β-cells in vitro. In this study, we examined the in vivo physiological role of Kinesin-1 in β-cell development and function.

RESEARCH DESIGN AND METHODS

A Cre-LoxP strategy was used to generate conditional knockout mice in which the Kif5b gene is specifically inactivated in pancreatic β-cells. Physiological and histological analyses were carried out in Kif5b knockout mice as well as littermate controls.

RESULTS

Mice with β-cell specific deletion of Kif5b (Kif5b(fl/)⁻:RIP2-Cre) displayed significantly retarded growth as well as slight hyperglycemia in both nonfasting and 16-h fasting conditions compared with control littermates. In addition, Kif5b(fl/)⁻:RIP2-Cre mice displayed significant glucose intolerance, which was not due to insulin resistance but was related to an insulin secretory defect in response to glucose challenge. These defects of β-cell function in mutant mice were not coupled with observable changes in islet morphology, islet cell composition, or β-cell size. However, compared with controls, pancreas of Kif5b(fl/)⁻:RIP2-Cre mice exhibited both reduced islet size and increased islet number, concomitant with an increased insulin vesicle density in β-cells.

CONCLUSIONS

In addition to being essential for maintaining glucose homeostasis and regulating β-cell function, Kif5b may be involved in β-cell development by regulating β-cell proliferation and insulin vesicle synthesis.

Expansion of the trans-Golgi network following activated collagen secretion is supported by a coiled-coil microtubule-bundling protein, p180, on the ER

A coiled-coil endoplasmic reticulum (ER) protein, p180, was originally reported as a ribosome-binding receptor on the rough ER and is highly expressed in secretory tissues. Recently, we reported new functions of p180 as a microtubule-bundling protein on the ER. Here, we investigated the specific roles of p180 in the Golgi complex organization following stimulated collagen secretion. Targeted depletion of p180 by siRNA transfection caused marked reduction of TGN, while other marker levels for the cis or medial Golgi were not markedly changed. Ascorbate stimulation resulted in trans-Golgi network (TGN) expansion to the periphery in control cells that is characterized by both increased membrane amounts and extended shape. In contrast, loss of p180 resulted in retraction of the TGN regardless of ascorbate stimulation. The TGN developed to the periphery along stabilized microtubule bundles, and overexpression of MTB-1 fragment caused dominant-negative phenotypes. Once disorganized, the retracted TGN did not recover in the absence of p180 despite elevated acetylated tubulin levels. TGN46 and p180 were co-distributed in epithelial basal layer cells of human mucosal and gastrointestinal tissues. Taken together, we propose a novel function of p180-abundant ER on the TGN expansion, both of which are highly developed in various professional secretory cells.

Translocation of incoming pseudorabies virus capsids to the cell nucleus is delayed in the absence of tegument protein pUL37

After fusion of the envelope of herpesvirus particles with the host cell plasma membrane, incoming nucleocapsids are transported to nuclear pores. Inner tegument proteins pUL36, pUL37, and pUS3 remain attached to the nucleocapsid after entry and therefore might mediate interactions between the nucleocapsid and cellular microtubule-associated motor proteins during transport. To assay for the role of pUL37 in this process, we constructed a pUL37-deleted pseudorabies virus mutant, PrV-DeltaUL37/UL35GFP, which expresses a fusion protein of green fluorescent protein (GFP) and the nonessential small capsid protein pUL35, resulting in the formation of fluorescently labeled capsids. Confocal laser-scanning microscopy of rabbit kidney cells infected with PrV-DeltaUL37/UL35GFP revealed that, whereas penetration was not affected in the absence of pUL37, nuclear translocation of incoming particles was delayed by approximately 1 h compared to PrV-UL35GFP, but not abolished. In contrast, phenotypically complemented pUL37-containing virions of PrV-DeltaUL37/UL35GFP exhibited wild type-like entry kinetics. Thus, the presence of pUL37 is required for rapid nuclear translocation of incoming nucleocapsids.

Knockdown of p180 eliminates the terminal differentiation of a secretory cell line

We have previously reported that the expression in yeast of an integral membrane protein (p180) of the endoplasmic reticulum (ER), isolated for its ability to mediate ribosome binding, is capable of inducing new membrane biogenesis and an increase in secretory capacity. To demonstrate that p180 is necessary and sufficient for terminal differentiation and acquisition of a secretory phenotype in mammalian cells, we studied the differentiation of a secretory cell line where p180 levels had been significantly reduced using RNAi technology and by transiently expressing p180 in nonsecretory cells. A human monocytic (THP-1) cell line, that can acquire macrophage-like properties, failed to proliferate rough ER when p180 levels were lowered. The Golgi compartment and the secretion of apolipoprotein E (Apo E) were dramatically affected in cells expressing reduced p180 levels. On the other hand, expression of p180 in a human embryonic kidney nonsecretory cell line (HEK293) showed a significant increase in proliferation of rough ER membranes and Golgi complexes. The results obtained from knockdown and overexpression experiments demonstrate that p180 is both necessary and sufficient to induce a secretory phenotype in mammalian cells. These findings support a central role for p180 in the terminal differentiation of secretory cells and tissues.

UL36p is required for efficient transport of membrane-associated herpes simplex virus type 1 along microtubules

Microtubule-mediated anterograde transport is essential for the transport of herpes simplex virus type 1 (HSV-1) along axons, yet little is known regarding the mechanism and the machinery required for this process. Previously, we were able to reconstitute anterograde transport of HSV-1 on microtubules in an in vitro microchamber assay. Here we report that the large tegument protein UL36p is essential for this trafficking. Using a fluorescently labeled UL36 null HSV-1 strain, KDeltaUL36GFP, we found that it is possible to isolate a membrane-associated population of this virus. Although these viral particles contained normal amounts of tegument proteins VP16, vhs, and VP22, they displayed a 3-log decrease in infectivity and showed a different morphology compared to UL36p-containing virions. Membrane-associated KDeltaUL36GFP also displayed a slightly decreased binding to microtubules in our microchamber assay and a two-thirds decrease in the frequency of motility. This decrease in binding and motility was restored when UL36p was supplied in trans by a complementing cell line. These findings suggest that UL36p is necessary for HSV-1 anterograde transport.

Transport and egress of herpes simplex virus in neurons

The mechanisms of axonal transport of the alphaherpesviruses, HSV and pseudorabies virus (PrV), in neuronal axons are of fundamental interest, particularly in comparison with other viruses, and offer potential sites for antiviral intervention or development of gene therapy vectors. These herpesviruses are transported rapidly along microtubules (MTs) in the retrograde direction from the axon terminus to the dorsal root ganglion and then anterogradely in the opposite direction. Retrograde transport follows fusion and deenvelopment of the viral capsid at the axonal membrane followed by loss of most of the tegument proteins and then binding of the capsid via one or more viral proteins (VPs) to the retrograde molecular motor dynein. The HSV capsid protein pUL35 has been shown to bind to the dynein light chain Tctex1 but is likely to be accompanied by additional dynein binding of an inner tegument protein. The mechanism of anterograde transport is much more controversial with different processes being claimed for PrV and HSV: separate transport of HSV capsid/tegument and glycoproteins versus PrV transport as an enveloped virion. The controversy has not been resolved despite application, in several laboratories, of confocal microscopy (CFM), real-time fluorescence with viruses dual labelled on capsid and glycoprotein, electron microscopy in situ and immuno-electron microscopy. Different processes for each virus seem counterintuitive although they are the most divergent in the alphaherpesvirus subfamily. Current hypotheses suggest that unenveloped HSV capsids complete assembly in the axonal growth cones and varicosities, whereas with PrV unenveloped capsids are only found travelling in a retrograde direction.

Genomic implications of H(2)O (2) for cell proliferation and growth of Caco-2 cells

Evidence indicates that oxidative stress inhibits cell proliferation in several cell systems. To determine whether the proliferation of Caco-2 cells is inhibited by oxidative stress and to identify any novel key regulatory factors involved in protecting or damaging the intestine from oxidative stress, Caco-2 cells were treated with an oxidizing agent and analyzed by transcriptomic oligonucleotide microarrays. Results indicated that expression of genes involved in cell proliferation and growth, including genes involved in lipid synthesis, cell cycle progression and cell division, angiogenesis, RNA processing and translation, cAMP metabolism, cytoskeleton and cell to cell adhesion, receptor tyrosine kinases, and intracellular and extracellular signaling, were repressed. If an oxidant-induced inhibition in cell proliferation is involved in the pathogenesis of intestinal disease, information gained could help explain the mechanisms contributing to the causes and consequences of intestinal disease and could aid in the elucidation of mechanisms by which intestinal cells protect against oxidative stress.

p180 is involved in the interaction between the endoplasmic reticulum and microtubules through a novel microtubule-binding and bundling domain

p180 was originally reported as a ribosome-binding protein on the rough endoplasmic reticulum membrane, although its precise role in animal cells has not yet been elucidated. Here, we characterized a new function of human p180 as a microtubule-binding and -modulating protein. Overexpression of p180 in mammalian cells induced an elongated morphology and enhanced acetylated microtubules. Consistently, electron microscopic analysis clearly revealed microtubule bundles in p180-overexpressing cells. Targeted depletion of endogenous p180 by small interfering RNAs led to aberrant patterns of microtubules and endoplasmic reticulum in mammalian cells, suggesting a specific interaction between p180 and microtubules. In vitro sedimentation assays using recombinant polypeptides revealed that p180 bound to microtubules directly and possessed a novel microtubule-binding domain (designated MTB-1). MTB-1 consists of a predicted coiled-coil region and repeat domain, and strongly promoted bundle formation both in vitro and in vivo when expressed alone. Overexpression of p180 induced acetylated microtubules in cultured cells in an MTB-1-dependent manner. Thus, our data suggest that p180 mediates interactions between the endoplasmic reticulum and microtubules mainly through the novel microtubule-binding and -bundling domain MTB-1.

The pseudorabies virus VP1/2 tegument protein is required for intracellular capsid transport

Transport of capsids in cells is critical to alphaherpesvirus infection and pathogenesis; however, viral factors required for transport have yet to be identified. Here we provide a detailed examination of capsid dynamics during the egress phase of infection in Vero cells infected with pseudorabies virus. We demonstrate that the VP1/2 tegument protein is required for processive microtubule-based transport of capsids in the cytoplasm. A second tegument protein that binds to VP1/2, UL37, was necessary for wild-type transport but was not essential for this process. Both proteins were also required for efficient nuclear egress of capsids to the cytoplasm.

Cargo selection by specific kinesin light chain 1 isoforms

Kinesin-1 drives the movement of diverse cargoes, and it has been proposed that specific kinesin light chain (KLC) isoforms target kinesin-1 to these different structures. Here, we test this hypothesis using two in vitro motility assays, which reconstitute the movement of rough endoplasmic reticulum (RER) and vesicles present in a Golgi membrane fraction. We generated GST-tagged fusion proteins of KLC1B and KLC1D that included the tetratricopeptide repeat domain and the variable C-terminus. We find that preincubation of RER with KLC1B inhibits RER motility, whereas KLC1D does not. In contrast, Golgi fraction vesicle movement is inhibited by KLC1D but not KLC1B reagents. Both RER and vesicle movement is inhibited by preincubation with the GST-tagged C-terminal domain of ubiquitous kinesin heavy chain (uKHC), which binds to the N-terminal domain of uKHC and alters its interaction with microtubules. We propose that although the TRR domains are required for cargo binding, it is the variable C-terminal region of KLCs that are vital for targeting kinesin-1 to different cellular structures.

Review: regulation mechanisms of Kinesin-1

Kinesin-1 microtubule motors are common kinesin motors from protozoa, fungi and animals. They transport vesicular or particle cargo in a strictly regulated manner. The relatively well-studied tail inhibition mechanism is based on a conformational change that leads to an interaction of Kinesin-1's tail with the junction of neck and hinge regions. This folding causes a decrease in microtubule binding and motor activity. In fungal Kinesin-1 motors several lines of evidence suggest that a conserved tyrosine in the neck coiled-coil mediates this inhibition. In the active state, a region surrounding a conserved tryptophan in the hinge stabilises the neck coiled-coil, and prevents the tyrosine from inhibiting. Although animal and fungal Kinesin-1 motors are clearly homologous and function according to the same chemo-mechanical mechanism, they differ in their regulation. Unlike fungal Kinesin-1s, animal kinesins associate with light chains that are important for regulation and cargo interaction. Several proteins interacting with animal Kinesin-1 heavy or light chains are known, among them typical scaffolding proteins that seem to link Kinesin-1 to signalling pathways.

Targeting of herpesvirus capsid transport in axons is coupled to association with specific sets of tegument proteins

The capsids of neurotropic herpesviruses have the remarkable ability to move in specific directions within axons. By modulating bidirectional capsid transport to favor either retrograde (minus-end) or anterograde (plus-end) motion, these viruses travel to sensory ganglia or peripheral tissue at specific stages of infection. By using correlative motion analysis to simultaneously monitor the trafficking of distinct viral proteins in living neurons, we demonstrate that viral "tegument" proteins are complexed to capsids moving in axons. The removal of a subset of tegument proteins from capsids invariably preceded retrograde transport to the cell body in sensory ganglia, whereas addition of these proteins was coupled to anterograde transport of progeny capsids to the distal axon. Although capsid transport never occurred without associated tegument proteins, anterograde-specific tegument proteins were competent to travel to the distal axon independent of capsids. These findings are compatible with a model of viral bidirectional transport in which tegument proteins direct capsid traffic to specific intracellular locations during the infectious cycle.

Intracellular expression profiling by laser capture microdissection: three novel components of the neuromuscular junction

The neuromuscular junction (NMJ) is a regionally specialized area of myofibers defined, in part, by specific gene expression from underlying myonuclei. We sought to obtain a more complete picture of the mRNA transcripts and proteins playing a role in NMJ formation and maintenance using laser capture microdissection (LCM) and to define expression profiles of the nuclear domain at the NMJ. NMJs (800) were isolated from normal mouse tibialis anterior muscle by LCM, with an equal amount of adjacent non-NMJ regions isolated. Many known components of the NMJ were found significantly differentially expressed. Three differentially expressed potential novel components of the NMJ were chosen for further study, and each was validated by immunostaining with and without blocking peptides (3/3), quantitative RT-PCR (3/3), and in situ hybridization (1/3). The three genes validated were dual-specificity phosphatase-6 (DUSP6), ribosomal receptor-binding protein-1 (RRBP1), and vacuolar protein sorting-26 (VPS26). Query of each of these novel components in a 27-time point in vivo muscle regeneration series showed expression commensurate with previously known NMJ markers (nestin, alpha-ACh receptor). Understanding and discovering elements responsible for the integrity and function of NMJs is relevant to understanding neuromuscular diseases such as spinal muscular atrophy. Our LCM-based mRNA expression profiling provided us with new means of identification of specific genes potentially responsible for NMJ stability and function and new candidates for involvement in disease pathogenesis.