Drosophila kelch is an oligomeric ring canal actin organizer

A Novel Kelch-Like-1 Is Involved in Antioxidant Response by Regulating Antioxidant Enzyme System in Penaeus vannamei

Heavy metals are typical cumulative pollutants that can enter and poison the human body through the food chain. However, the molecular mechanism of heavy metal-induced oxidative stress is unclear. In this study, we characterize PvKelch-like-1 from P. vannamei and explore its antioxidant roles in immune regulation of crustaceans. PvKelch-like-1 full length contains 2107 nucleotides, consists of a 5′ untranslated region (UTR) of 79 bp, a 3′ UTR of 180 bp, and a ORF of 1848 encoded 615 amino acids, which contain a BTB, BACK and Kelch motif, putative molecular mass and isoelectric point were 69 KDa and 6.54. PvKelch-like-1 mRNA was ubiquitously expressed in all detected tissue of P. vannamei, and mRNA expression levels were significantly up-regulated from 6 to 24 h after cadmium stress and reached the highest level (3.2-fold) at 12 h in the hepatopancreas. Subcellular localization analysis revealed that PvKelch-like-1 was localized in the nucleus. Silencing PvKelch-like-1 significantly increased reactive oxygen species (ROS) (1.61-fold) production and DNA damage (1.32-fold) in the shrimp hemolymph, and significantly decreased total hemocyte counts (THC) (0.64-fold) at 6 h in hemolymph. Additionally, the antioxidant genes PvCAT (0.43-fold), PvMnSOD (0.72-fold), PvGST (0.31-fold) and PvGPx (0.59-fold) at 6 h were decreased significantly in PvKelch-like-1 silenced shrimp after cadmium stress. Overexpression of PvKelch-like-1 has the opposite results in enzyme activity. The SOD (2.44-fold) and CAT (2.19-fold) activities were significantly increased after overexpressing PvKelch-like-1. These results suggest that PvKelch-like-1 plays a vital role in shrimp innate immune defense by positively regulating the expression of antioxidant enzyme genes to respond to cadmium stress.

Genetic Risk of Trigger Finger: Results of a Genomewide Association Study

BACKGROUND

Trigger finger, or stenosing tenosynovitis, is one of the most common conditions affecting the hand, yet its pathophysiology remains poorly understood, and genetic association studies of trigger finger are lacking. The purpose of this study was to identify single-nucleotide polymorphisms associated with trigger finger through a genomewide approach.

METHODS

The authors performed a case-control genomewide association study in the Partners HealthCare Biobank. Single-nucleotide polymorphism- and gene-based association analyses were carried out after quality control, imputation, and filtering.

RESULTS

Among 942 trigger finger cases and 24,472 controls, the authors tested 7,846,471 single-nucleotide polymorphisms for association with trigger finger. In the single-nucleotide polymorphism-based analysis, a single locus on chromosome 13 corresponding to KLHL1 met the genomewide significance threshold (lead single-nucleotide polymorphism rs59988404; OR, 1.74; 95 percent CI, 1.47 to 2.07; p = 1.99 × 10). After mapping, gene-based analysis demonstrated a significant association with POLE2 (p = 7.53 × 10) on chromosome 14. Among trigger finger cases, rs59988404 genotype was significantly associated with the total number of trigger finger procedures performed (p = 0.026).

CONCLUSIONS

In the first reported genomewide association study of trigger finger, the authors report significant associations of KLHL1 and POLE2 with risk of trigger finger. The authors' results may help to elucidate the pathophysiology of trigger finger and facilitate an individualized, precision-medicine treatment approach.

CLINICAL QUESTION/LEVEL OF EVIDENCE

Risk, III.

Simultaneous exposure to vinylcyclohexene and methylmercury in Drosophila melanogaster: biochemical and molecular analyses

Background

Exposure to vinylcyclohexene (VCH) and methylmercury (MeHg⁺) can induce oxidative stress and gene modulation. Several studies have been evaluating the effects of VCH and MeHg⁺, but little is known about interactive effects between them. This work aimed to assess the exposure and co-exposure effects of MeHg⁺ and VCH on oxidative stress and gene modulation in Drosophila melanogaster.

Methods

Reactive species production, glutathione S-transferase (GST) and acetylcholinesterase (AChE) activities were evaluated after exposure and co-exposure to VCH (1 mM) and MeHg⁺ (0.2 mM) for one or three days in the head and body (thorax and abdomen) of flies. The expression of genes related to redox state and inflammatory response was evaluated after exposure and co-exposure to VCH and MeHg⁺ for three days.

Results

Survival decreased only in flies co-exposed to VCH and MeHg⁺ for three days. All treatments increased total reactive species production after one day of exposure. However, no significant changes were observed in the head after three days of exposure. One day of exposure to VCH caused an increase in the head GST activity, whereas MeHg⁺ induced an increase after three days of exposure. Regarding the body, all treatments increased GST activity after one day of exposure, but only the flies exposed to MeHg⁺ presented an increase in GST activity after three days of exposure. Treatments did not alter AChE activity in the head. As for gene expression, there was a significant increase in the Relish transcription factor gene in the flies’ body, but Nrf2, Keap1, Jafrac1, TrxR1, and NF-κβ were not altered.

Conclusion

The results suggest that exposure to VCH and MeHg⁺ induce oxidative stress and activation of an inflammatory response in fruit flies.

Proximity labeling reveals novel interactomes in live Drosophila tissue

Gametogenesis is dependent on intercellular communication facilitated by stable intercellular bridges connecting developing germ cells. During Drosophila oogenesis, intercellular bridges (referred to as ring canals; RCs) have a dynamic actin cytoskeleton that drives their expansion to a diameter of 10 μm. Although multiple proteins have been identified as components of RCs, we lack a basic understanding of how RC proteins interact together to form and regulate the RC cytoskeleton. Thus, here, we optimized a procedure for proximity-dependent biotinylation in live tissue using the APEX enzyme to interrogate the RC interactome. APEX was fused to four different RC components (RC-APEX baits) and 55 unique high-confidence prey were identified. The RC-APEX baits produced almost entirely distinct interactomes that included both known RC proteins and uncharacterized proteins. A proximity ligation assay was used to validate close-proximity interactions between the RC-APEX baits and their respective prey. Furthermore, an RNA interference screen revealed functional roles for several high-confidence prey genes in RC biology. These findings highlight the utility of enzyme-catalyzed proximity labeling for protein interactome analysis in live tissue and expand our understanding of RC biology.

Molecular basis of cullin-3 (Cul3) ubiquitin ligase subversion by vaccinia virus protein A55

BTB-Kelch proteins are substrate-specific adaptors for cullin-3 (Cul3) RING-box-based E3 ubiquitin ligases, mediating protein ubiquitylation for subsequent proteasomal degradation. Vaccinia virus encodes three BTB-Kelch proteins: A55, C2, and F3. Viruses lacking A55 or C2 have altered cytopathic effects in cultured cells and altered pathology in vivo Previous studies have shown that the ectromelia virus orthologue of A55 interacts with Cul3 in cells. We report that the N-terminal BTB-BACK (BB) domain of A55 binds directly to the Cul3 N-terminal domain (Cul3-NTD), forming a 2:2 complex in solution. We solved the structure of an A55BB/Cul3-NTD complex from anisotropic crystals diffracting to 2.3/3.7 Å resolution in the best/worst direction, revealing that the overall interaction and binding interface closely resemble the structures of cellular BTB/Cul3-NTD complexes, despite low sequence identity between A55 and cellular BTB domains. Surprisingly, despite this structural similarity, the affinity of Cul3-NTD for A55BB was stronger than for cellular BTB proteins. Glutamate substitution of the A55 residue Ile-48, adjacent to the canonical φX(D/E) Cul3-binding motif, reduced affinity of A55BB for Cul3-NTD by at least 2 orders of magnitude. Moreover, Ile-48 and the φX(D/E) motif are conserved in A55 orthologues from other poxviruses, but not in the vaccinia virus proteins C2 or F3. The high-affinity interaction between A55BB and Cul3-NTD suggests that, in addition to directing the Cul3-RING E3 ligase complex to degrade cellular/viral target proteins that are normally unaffected, A55 may also sequester Cul3 from cellular adaptor proteins, thereby protecting substrates of these cellular adaptors from ubiquitylation and degradation.

Targeted substrate degradation by Kelch controls the actin cytoskeleton during ring canal expansion

During Drosophila oogenesis, specialized actin-based structures called ring canals form and expand to accommodate growth of the oocyte. Previous work demonstrated that Kelch and Cullin 3 function together in a Cullin 3-RING ubiquitin ligase complex (CRL3^Kelch) to organize the ring canal cytoskeleton, presumably by targeting a substrate for proteolysis. Here, we use tandem affinity purification followed by mass spectrometry to identify HtsRC as the CRL3^Kelch ring canal substrate. CRISPR-mediated mutagenesis of HtsRC revealed its requirement in the recruitment of the ring canal F-actin cytoskeleton. We present genetic evidence consistent with HtsRC being the CRL3^Kelch substrate, as well as biochemical evidence indicating that HtsRC is ubiquitylated and degraded by the proteasome. Finally, we identify a short sequence motif in HtsRC that is necessary for Kelch binding. These findings uncover an unusual mechanism during development wherein a specialized cytoskeletal structure is regulated and remodeled by the ubiquitin-proteasome system.

Subcellular Specialization and Organelle Behavior in Germ Cells

Gametes, eggs and sperm, are the highly specialized cell types on which the development of new life solely depends. Although all cells share essential organelles, such as the ER (endoplasmic reticulum), Golgi, mitochondria, and centrosomes, germ cells display unique regulation and behavior of organelles during gametogenesis. These germ cell-specific functions of organelles serve critical roles in successful gamete production. In this chapter, I will review the behaviors and roles of organelles during germ cell differentiation.

Stay Connected: A Germ Cell Strategy

Germ cells develop as a cyst of interconnected sibling cells in a broad range of organisms in both sexes. A well-established function of intercellular connectivity is to transport cytoplasmic materials from 'nurse' cells to oocytes, a critical process for developing functional oocytes in ovaries of many species. However, there are situations where connectivity exists without a nursing mechanism, and the biological meaning of such connectivity remains obscure. In this review, we summarize current knowledge on the formation of intercellular connectivity, and discuss its meaning by visiting multiple examples of germ cell connectivity observed in evolutionarily distant species.

Genome-wide identification and expression analysis of the BTB domain-containing protein gene family in tomato

BTB (broad-complex, tramtrack, and bric-a-brac) family proteins are characterized by the presence of a protein-protein interaction BTB domain. BTB proteins have diverse functions, including transcriptional regulation, protein degradation, chromatin remodeling, and cytoskeletal regulation. However, little is known about this gene family in tomato (Solanum lycopersicum), the most important model plant for crop species. In this study, 38 BTB genes were identified based on tomato whole-genome sequence. Phylogenetic analysis of BTB proteins in tomato revealed that SlBTB proteins could be divided into at least 4 subfamilies. The SlBTB proteins contains 1-3 BTB domains, and several other types of functional domains, including KCTD (Potassium channel tetramerization domain-containing), the MATH (meprin and TRAF homology), ANK (Ankyrin repeats), NPR1 (nonexpressor of pathogenesis-related proteins1), NPH3 (Nonphototropic Hypocotyl 3), TAZ zinc finger, C-terminal Kelch, Skp1 and Arm (Armadillo/beta-catenin-like repeat) domains are also found in some tomato BTB proteins. Moreover, their expression patterns in tissues/stages, in response to different abiotic stress treatments and hormones were also investigated. This study provides the first comprehensive analysis of BTB gene family in the tomato genome. The data will undoubtedly be useful for better understanding the potential functions of BTB genes, and their possible roles in mediating hormone cross-talk and abiotic stress in tomato as well as in some other relative species.

Ectodermal-Neural Cortex 1 Isoforms Have Contrasting Effects on MC3T3-E1 Osteoblast Mineralization and Gene Expression

The importance of Wnt pathway signaling in development of bone has been well established. Here we investigated the role of a known Wnt target, ENC1 (ectodermal-neural cortex 1; NRP/B), in osteoblast differentiation. Enc1 expression was detected in mouse osteoblasts, chondrocytes, and osteocytes by in situ hybridization, and osteoblastic expression was verified in differentiating primary cultures and MC3T3-E1 pre-osteoblast cells, with 57 kDa and 67 kDa ENC1 protein isoforms detected throughout differentiation. Induced knockdown of both ENC1 isoforms reduced alkaline phosphatase staining and virtually abolished MC3T3-E1 mineralization. At culture confluence, Alpl (alkaline phosphatase liver/bone/kidney) expression was markedly reduced compared with control cells, and there was significant and coordinated alteration of other genes involved in cellular phosphate biochemistry. In contrast, with 67 kDa-selective knockdown mineralized nodule formation was enhanced and there was a two-fold increase in Alpl expression at confluence. There was enhanced expression of Wnt/β-catenin target genes with knockdown of both isoforms at this time-point and a five-fold increase in Frzb (Frizzled related protein) with 67 kDa-selective knockdown at mineralization, indicating possible ENC1 interactions with Wnt signaling in osteoblasts. These results are the first to demonstrate a role for ENC1 in the control of osteoblast differentiation. Additionally, the contrasting mineralization phenotypes and transcriptional patterns seen with coordinate knockdown of both ENC1 isoforms vs selective knockdown of 67 kDa ENC1 suggest opposing roles for the isoforms in regulation of osteoblastic differentiation, through effects on Alpl expression and phosphate cellular biochemistry. This study is the first to report differential roles for the ENC1 isoforms in any cell lineage. J. Cell. Biochem. 118: 2141-2150, 2017. © 2016 Wiley Periodicals, Inc.

Cul3-KLHL20 ubiquitin ligase: physiological functions, stress responses, and disease implications

Cullin-RING ubiquitin ligases are the largest Ubiquitin ligase family in eukaryotes and are multi-protein complexes. In these complexes, the Cullin protein serves as a scaffold to connect two functional modules of the ligases, the catalytic subunit and substrate-binding subunit. KLHL20 is a substrate-binding subunit of Cullin3 (Cul3) ubiquitin ligase. Recent studies have identified a number of substrates of KLHL20-based ubiquitin ligase. Through ubiquitination of these substrates, KLHL20 elicits diverse cellular functions, some of which are associated with human diseases. Furthermore, the functions, subcellular localizations, and expression of KLHL20 are regulated by several physiological and stressed signals, which allow KLHL20 to preferentially act on certain substrates to response to these signals. Here, we provide a summary of the functions and regulations of KLHL20 in several physiological processes and stress responses and its disease implications.

Actin Cytoskeletal Organization in Drosophila Germline Ring Canals Depends on Kelch Function in a Cullin-RING E3 Ligase

The Drosophila Kelch protein is required to organize the ovarian ring canal cytoskeleton. Kelch binds and cross-links F-actin in vitro, and it also functions with Cullin 3 (Cul3) as a component of a ubiquitin E3 ligase. How these two activities contribute to cytoskeletal remodeling in vivo is not known. We used targeted mutagenesis to investigate the mechanism of Kelch function. We tested a model in which Cul3-dependent degradation of Kelch is required for its function, but we found no evidence to support this hypothesis. However, we found that mutant Kelch deficient in its ability to interact with Cul3 failed to rescue the kelch cytoskeletal defects, suggesting that ubiquitin ligase activity is the principal activity required in vivo. We also determined that the proteasome is required with Kelch to promote the ordered growth of the ring canal cytoskeleton. These results indicate that Kelch organizes the cytoskeleton in vivo by targeting a protein substrate for degradation by the proteasome.

The insulator protein Suppressor of Hairy wing is required for proper ring canal development during oogenesis in Drosophila

Chromatin insulators orchestrate gene transcription during embryo development and cell differentiation by stabilizing interactions between distant genomic sites. Mutations in genes encoding insulator proteins are generally lethal, making in vivo functional analyses of insulator proteins difficult. In Drosophila, however, mutations in the gene encoding the Suppressor of Hairy wing insulator protein [Su(Hw)] are viable and female sterile, providing an opportunity to study insulator function during oocyte development. Whereas previous reports suggest that the function of Su(Hw) in oogenesis is independent of its insulator activity, many aspects of the role of Su(Hw) in Drosophila oogenesis remain unexplored. Here we show that mutations in su(Hw) result in smaller ring canal lumens and smaller outer ring diameters, which likely obstruct molecular and vesicle passage from nurse cells to the oocyte. Fluorescence microscopy reveals that lack of Su(Hw) leads to excess accumulation of Kelch (Kel) and Filament-actin (F-actin) proteins in the ring canal structures of developing egg chambers. Furthermore, we found that misexpression of the Src oncogene at 64B (Src64B) may cause ring canal development defects as microarray analysis and real-time RT-PCR revealed there is a three fold decrease in Src64B expression in su(Hw) mutant ovaries. Restoration of Src64B expression in su(Hw) mutant female germ cells rescued the ring phenotype but did not restore fertility. We conclude that loss of su(Hw) affects expression of many oogenesis related genes and down-regulates Src64B, resulting in ring canal defects potentially contributing to obstruction of molecular flow and an eventual failure of egg chamber organization.

Cyst geometry in the egg chambers of Calliphora erythrocephala Mg. (Diptera: Calliphoridae) ovaries

In the germarium of polytrophic ovarioles of Calliphora erythrocephala (Mg.) fly, four mitotic divisions of cystoblasts give rise to 16-cell germ-line cysts. One cell differentiates into an oocyte, while the remaining 15 cells become nurse cells. Concomitantly actin-rich ring canals are formed at the intercellular junctions. The present study considers a mutual arrangement of the ring canals formed after the second to fourth mitoses relative to the ring canal formed after the first mitotic division in different regions of the germarium and egg chambers. During the cyst formation and its movement to the posterior end of the germarium, the ring canals are displaced relative to one another, thereby giving different branching variants of the cyst. The pattern of cell interconnections becomes stable in germarium region 2b and does not change during the cyst movement along the ovariole despite the cyst polarizes and increases in size.

Saccharomyces cerevisiae Kelch proteins and Bud14 protein form a stable 520-kDa formin regulatory complex that controls actin cable assembly and cell morphogenesis

Formins perform essential roles in actin assembly and organization in vivo, but they also require tight regulation of their activities to produce properly functioning actin structures. Saccharomyces cerevisiae Bud14 is one member of an emerging class of formin regulators that target the FH2 domain to inhibit actin polymerization, but little is known about how these regulators are themselves controlled in vivo. Kelch proteins are critical for cell polarity and morphogenesis in a wide range of organisms, but their mechanistic roles in these processes are still largely undefined. Here, we report that S. cerevisiae Kelch proteins, Kel1 and Kel2, associate with Bud14 in cell extracts to form a stable 520-kDa complex with an apparent stoichiometry of 2:2:1 Bud14/Kel1/Kel2. Using pairwise combinations of GFP- and red fluorescent protein-tagged proteins, we show that Kel1, Kel2, and Bud14 interdependently co-localize at polarity sites. By analyzing single, double, and triple mutants, we show that Kel1 and Kel2 function in the same pathway as Bud14 in regulating Bnr1-mediated actin cable formation. Loss of any component of the complex results in long, bent, and hyper-stable actin cables, accompanied by defects in secretory vesicle traffic during polarized growth and septum formation during cytokinesis. These observations directly link S. cerevisiae Kelch proteins to the control of formin activity, and together with previous observations made for S. pombe homologues tea1p and tea3p, they have broad implications for understanding Kelch function in other systems.

Unravelling the proteomic profile of rice meiocytes during early meiosis

Transfer of genetic traits from wild or related species into cultivated rice is nowadays an important aim in rice breeding. Breeders use genetic crosses to introduce desirable genes from exotic germplasms into cultivated rice varieties. However, in many hybrids there is only a low level of pairing (if existing) and recombination at early meiosis between cultivated rice and wild relative chromosomes. With the objective of getting deeper into the knowledge of the proteins involved in early meiosis, when chromosomes associate correctly in pairs and recombine, the proteome of isolated rice meiocytes has been characterized by nLC-MS/MS at every stage of early meiosis (prophase I). Up to 1316 different proteins have been identified in rice isolated meiocytes in early meiosis, being 422 exclusively identified in early prophase I (leptotene, zygotene, or pachytene). The classification of proteins in functional groups showed that 167 were related to chromatin structure and remodeling, nucleic acid binding, cell-cycle regulation, and cytoskeleton. Moreover, the putative roles of 16 proteins which have not been previously associated to meiosis or were not identified in rice before, are also discussed namely: seven proteins involved in chromosome structure and remodeling, five regulatory proteins [such as SKP1 (OSK), a putative CDK2 like effector], a protein with RNA recognition motifs, a neddylation-related protein, and two microtubule-related proteins. Revealing the proteins involved in early meiotic processes could provide a valuable tool kit to manipulate chromosome associations during meiosis in rice breeding programs. The data have been deposited to the ProteomeXchange with the PXD001058 identifier.

The novel BTB-kelch protein, KBTBD8, is located in the Golgi apparatus and translocates to the spindle apparatus during mitosis

Proteins of the BTB-kelch family are known to be involved in multiple biological processes such as migration, cytoskeleton arrangement, regulation of cell morphology, protein ubiquitination and gene expression. KBTBD8 is a new member of this family. The gene was found in a comparative transcriptome analysis of pluripotent stem cells and was therefore suggested to play a role in the regulation of pluripotency. Comparative analysis of the gene and protein sequences revealed a high conservation throughout evolution especially in the characteristic domains of BTB, BACK and kelch. We identified the Golgi apparatus as the subcellular localization of the KBTBD8 protein in non-dividing cells and could show that KBTBD8 co-localizes with α-tubulin on the spindle apparatus of mitotic cells suggesting a role in cell proliferation. In conclusion, KBTBD8 is a new member of the BTB-kelch superfamily that is located in the Golgi apparatus and translocates to the spindle apparatus during mitosis.

Orbit/CLASP is required for germline cyst formation through its developmental control of fusomes and ring canals in Drosophila males

Orbit, a Drosophila ortholog of microtubule plus-end enriched protein CLASP, plays an important role in many developmental processes involved in microtubule dynamics. Previous studies have shown that Orbit is required for asymmetric stem cell division and cystocyte divisions in germline cysts and for the development of microtubule networks that interconnect oocyte and nurse cells during oogenesis. Here, we examined the cellular localization of Orbit and its role in cyst formation during spermatogenesis. In male germline stem cells, distinct localization of Orbit was first observed on the spectrosome, which is a spherical precursor of the germline-specific cytoskeleton known as the fusome. In dividing stem cells and spermatogonia, Orbit was localized around centrosomes and on kinetochores and spindle microtubules. After cytokinesis, Orbit remained localized on ring canals, which are cytoplasmic bridges between the cells. Thereafter, it was found along fusomes, extending through the ring canal toward all spermatogonia in a cyst. Fusome localization of Orbit was not affected by microtubule depolymerization. Instead, our fluorescence resonance energy transfer experiments suggested that Orbit is closely associated with F-actin, which is abundantly found in fusomes. Surprisingly, F-actin depolymerization influenced neither fusome organization nor Orbit localization on the germline-specific cytoskeleton. We revealed that two conserved regions of Orbit are required for fusome localization. Using orbit hypomorphic mutants, we showed that the protein is required for ring canal formation and for fusome elongation mediated by the interaction of newly generated fusome plugs with the pre-existing fusome. The orbit mutation also disrupted ring canal clustering, which is essential for folding of the spermatogonia after cytokinesis. Orbit accumulates around centrosomes at the onset of spermatogonial mitosis and is required for the capture of one of the duplicated centrosomes onto the fusome. Moreover, Orbit is involved in the proper orientation of spindles towards fusomes during synchronous mitosis of spermatogonial cysts.

Selective proteasomal degradation of the B'β subunit of protein phosphatase 2A by the E3 ubiquitin ligase adaptor Kelch-like 15

Protein phosphatase 2A (PP2A), a ubiquitous and pleiotropic regulator of intracellular signaling, is composed of a core dimer (AC) bound to a variable (B) regulatory subunit. PP2A is an enzyme family of dozens of heterotrimers with different subcellular locations and cellular substrates dictated by the B subunit. B'β is a brain-specific PP2A regulatory subunit that mediates dephosphorylation of Ca(2+)/calmodulin-dependent protein kinase II and tyrosine hydroxylase. Unbiased proteomic screens for B'β interactors identified Cullin3 (Cul3), a scaffolding component of E3 ubiquitin ligase complexes, and the previously uncharacterized Kelch-like 15 (KLHL15). KLHL15 is one of ∼40 Kelch-like proteins, many of which have been identified as adaptors for the recruitment of substrates to Cul3-based E3 ubiquitin ligases. Here, we report that KLHL15-Cul3 specifically targets B'β to promote turnover of the PP2A subunit by ubiquitylation and proteasomal degradation. Comparison of KLHL15 and B'β tissue expression profiles suggests that the E3 ligase adaptor contributes to selective expression of the PP2A/B'β holoenzyme in the brain. We mapped KLHL15 residues critical for homodimerization as well as interaction with Cul3 and B'β. Explaining PP2A subunit selectivity, the divergent N terminus of B'β was found necessary and sufficient for KLHL15-mediated degradation, with Tyr-52 having an obligatory role. Although KLHL15 can interact with the PP2A/B'β heterotrimer, it only degrades B'β, thus promoting exchange with other regulatory subunits. E3 ligase adaptor-mediated control of PP2A holoenzyme composition thereby adds another layer of regulation to cellular dephosphorylation events.

Platelet microRNAs: From platelet biology to possible disease biomarkers and therapeutic targets

Although anucleated, platelets contain megakaryocyte-derived messenger ribonucleic acid (mRNA) which can be translated to produce protein molecules. Recently, platelets have been found to contain small (∼23 base pair) non-coding microRNAs (miRNAs) derived from hairpin-like precursors. MiRNAs can specifically silence their mRNA targets regulating mRNA translation. Platelet miRNAs are reported to bind to important platelet target mRNAs involved in platelet reactivity including P2Y12 ADP receptor, GPIIb receptor, and cyclic AMP-dependent protein kinase A. They also regulate important functions such as platelet shape change, granules secretion, and platelet activation. Platelet miRNAs were also proposed as biomarkers of arteriosclerosis, although their role in vascular inflammation needs to be elucidated. Further, the possibility of using miRNAs as therapeutic tools has emerged. Using synthetic oligo-nucleotides that antagonize miRNAs binding to their mRNAs-targets or synthetic miRNAs mimics that enhance endogenous miRNAs function potentially will ultimately lead to the manipulation of platelet miRNAs expression and function with significant effects on specific protein levels and overall platelet reactivity.

The conserved scavenger receptor cysteine-rich superfamily in therapy and diagnosis

The scavenger receptor cysteine-rich (SRCR) superfamily of soluble or membrane-bound protein receptors is characterized by the presence of one or several repeats of an ancient and highly conserved protein module, the SRCR domain. This superfamily (SRCR-SF) has been in constant and progressive expansion, now up to more than 30 members. The study of these members is attracting growing interest, which parallels that in innate immunity. No unifying function has been described to date for the SRCR domains, this being the result of the limited knowledge still available on the physiology of most members of the SRCR-SF, but also of the sequence versatility of the SRCR domains. Indeed, involvement of SRCR-SF members in quite different functions, such as pathogen recognition, modulation of the immune response, epithelial homeostasis, stem cell biology, and tumor development, have all been described. This has brought to us new information, unveiling the possibility that targeting or supplementing SRCR-SF proteins could result in diagnostic and/or therapeutic benefit for a number of physiologic and pathologic states. Recent research has provided structural and functional insight into these proteins, facilitating the development of means to modulate the activity of SRCR-SF members. Indeed, some of these approaches are already in use, paving the way for a more comprehensive use of SRCR-SF members in the clinic. The present review will illustrate some available evidence on the potential of well known and new members of the SRCR-SF in this regard.

Germ cell intercellular bridges

Stable intercellular bridges are a conserved feature of gametogenesis in multicellular animals observed more than 100 years ago, but their function was unknown. Many of the components necessary for this structure have been identified through the study of cytokinesis in Drosophila; however, mammalian intercellular bridges have distinct properties from those of insects. Mammalian germ cell intercellular bridges are composed of general cytokinesis components with additional germ cell-specific factors including TEX14. TEX14 is an inactive kinase essential for the maintenance of stable intercellular bridges in gametes of both sexes but whose loss specifically impairs male meiosis. TEX14 acts to impede the terminal steps of abscission by competing for essential component CEP55, blocking its interaction in nongerm cells with ALIX and TSG101. Additionally, TEX14-interacting protein RBM44, whose localization in stabile intercellular bridges is limited to pachytene and secondary spermatocytes, may participate in processes such as RNA transport but is nonessential to the maintenance of intercellular bridge stability.

The cytoprotective role of the Keap1-Nrf2 pathway

An elaborate network of highly inducible proteins protects aerobic cells against the cumulative damaging effects of reactive oxygen intermediates and toxic electrophiles, which are the major causes of neoplastic and chronic degenerative diseases. These cytoprotective proteins share common transcriptional regulation, through the Keap1-Nrf2 pathway, which can be activated by various exogenous and endogenous small molecules (inducers). Inducers chemically react with critical cysteine residues of the sensor protein Keap1, leading to stabilisation and nuclear translocation of transcription factor Nrf2, and ultimately to coordinate enhanced expression of genes coding for cytoprotective proteins. In addition, inducers inhibit pro-inflammatory responses, and there is a linear correlation spanning more than six orders of magnitude of concentrations between inducer and anti-inflammatory activity. Genetic deletion of transcription factor Nrf2 renders cells and animals much more sensitive to the damaging effects of electrophiles, oxidants and inflammatory agents in comparison with their wild-type counterparts. Conversely, activation of the Keap1-Nrf2 pathway allows survival and adaptation under various conditions of stress and has protective effects in many animal models. Cross-talks with other signalling pathways broadens the role of the Keap1-Nrf2 pathway in determining the fate of the cell, impacting fundamental biological processes such as proliferation, apoptosis, angiogenesis and metastasis.

Interaction of orthopoxviruses with the cellular ubiquitin-ligase system

Protein modification by ubiquitin or ubiquitin-like polypeptides is important for the fate and functions of the majority of proteins in the eukaryotic cell and can be involved in regulation of various biological processes, including protein metabolism (degradation), protein transport to several cellular compartments, rearrangement of cytoskeleton, and transcription of cytoprotective genes. The accumulated experimental data suggest that the ankyrin-F-box-like and BTB-kelch-like proteins of orthopoxviruses, represented by the largest viral multigene families, interact with the cellular Cullin-1- and Cullin-3-containing ubiquitin-protein ligases, respectively. In addition, orthopoxviruses code for their own RING-domain-containing ubiquitin ligase. In this review, this author discusses the differences between variola (smallpox), monkeypox, cowpox, vaccinia, and ectromelia (mousepox) viruses in the organization of ankyrin-F-box and BTB-kelch protein families and their likely functions.

Kelch-like homologue 9 mutation is associated with an early onset autosomal dominant distal myopathy

Distal myopathies are a heterogeneous group of disorders characterized by progressive weakness and muscular atrophy, beginning in distal limb muscles and affecting proximal limb muscles at a later stage. We studied a large German kindred with 10 affected members. Weakness and atrophy of the anterior tibial muscles started between the ages of 8 and 16 years, followed by atrophy of intrinsic hand muscles. Progression was slow, and patients retained the ability to walk until the seventh decade. Serum creatinine kinase levels were increased in the range of 150–1400 U/l. Muscle biopsies showed myopathic changes, whereas immunohistochemistry showed normal expression of marker proteins for muscular dystrophies. Patients had reduced sensation with stocking-glove distribution in the distal limbs in later life. Nerve conduction studies revealed no evidence of neuropathy. Genome-wide linkage analysis in this family revealed a new locus for distal myopathy at 9p21.2-p22.3 (multipoint logarithm of the odds ratio = 4.21). By positional cloning we found a heterozygous mutation L95F in the Kelch-like homologue 9 gene, encoding a bric-a-brac Kelch protein. Molecular modelling indicated that the mutation may interfere with the interaction of the bric-a-brac domain with Cullin 3. Coimmunoprecipitation experiments confirmed that the mutation reduces association with Cullin 3 in the Kelch-like homologue 9-Cullin 3–E3 ubiquitin ligase complex, which is involved in ubiquitin-dependent protein degradation. We identified a unique form of early onset autosomal dominant distal myopathy which is associated with a Kelch-like homologue 9 mutation and interferes with normal skeletal muscle through a novel pathogenetic mechanism.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 4: intercellular bridges, mitochondria, nuclear envelope, apoptosis, ubiquitination, membrane/voltage-gated channels, methylation/acetylation, and transcription factors

As germ cells divide and differentiate from spermatogonia to spermatozoa, they share a number of structural and functional features that are common to all generations of germ cells and these features are discussed herein. Germ cells are linked to one another by large intercellular bridges which serve to move molecules and even large organelles from the cytoplasm of one cell to another. Mitochondria take on different shapes and features and topographical arrangements to accommodate their specific needs during spermatogenesis. The nuclear envelope and pore complex also undergo extensive modifications concomitant with the development of germ cell generations. Apoptosis is an event that is normally triggered by germ cells and involves many proteins. It occurs to limit the germ cell pool and acts as a quality control mechanism. The ubiquitin pathway comprises enzymes that ubiquitinate as well as deubiquitinate target proteins and this pathway is present and functional in germ cells. Germ cells express many proteins involved in water balance and pH control as well as voltage-gated ion channel movement. In the nucleus, proteins undergo epigenetic modifications which include methylation, acetylation, and phosphorylation, with each of these modifications signaling changes in chromatin structure. Germ cells contain specialized transcription complexes that coordinate the differentiation program of spermatogenesis, and there are many male germ cell-specific differences in the components of this machinery. All of the above features of germ cells will be discussed along with the specific proteins/genes and abnormalities to fertility related to each topic.

Subcellular localization of Mayven following expression of wild type and mutant EGFP tagged cDNAs

BACKGROUND

Process formation by glial cells is crucial to their function. Mayven, an actin binding, multi-domain polypeptide, and member of the BTB-BACK-Kelch family have been shown to be important in oligodendrocyte process extension. To assess the role of Mayven in neural cell process extension we have tracked the subcellular distribution of exogenous Mayven following expression of a rat Mayven -EGFP cDNA in a variety of neural cell backgrounds and specifically in OEC tranfectants following drug treatment to disrupt the integrity of the cytoskeleton. A comparison was made between the subcellular localization following transient transfection of OECs with full-length Mayven cDNA and a series of mutant domain constructs.

RESULTS

The subcellular location of Mayven in OEC transfectants showed a characteristic distribution with intense foci of staining towards the process tips corresponding to regions of accumulated Mayven overlapping in part with lammelipodial actin and was absent from the filipodia and the outer membrane. This signature pattern was also observed in Schwann cells, Oli-Neu cells, astrocytes and the neuroblastoma cell line B104 transfectants and resembled the exogenous and endogenous Mayven distribution in oligodendrocytes. This contrasted with the localization pattern in non-neural cells. There was a re-localization of Mayven in OEC transfectants following drug treatment to challenge the integrity of the actin cytoskeleton while breakdown of the microtubular component had no discernible impact on the accumulation of Mayven in the process tips. Deletion of the first three amino acids of the SH3 motif of the putative Fyn Kinase binding domain at the amino terminus significantly compromised this signature pattern as did the removal of the last Kelch repeat unit of six unit Kelch domain comprising the carboxyl terminus. In addition, there was a reduction in process length in mutant transfectants. Co-expression studies with a haemagglutinin (HA) tagged wild type Mayven cDNA and EGFP tagged mutant cDNAs suggested a homomeric interaction mediated by the BTB/POZ domain.

CONCLUSIONS

Exogenous Mayven is transported to the lamellipodia in neural transfectants associating with the actin cytoskeletal network. In addition to the importance of the internal BTB/POZ domain, this subcellular distribution pattern is dependent on the presence of an intact amino and carboxyl terminus.

Drosophila Kelch functions with Cullin-3 to organize the ring canal actin cytoskeleton

In addition to cross-linking F-actin, Drosophila Kelch is a component of a cullin-RING ubiquitin ligase complex required for morphogenesis of ring canals during oogenesis.

Drosophila melanogaster Kelch (KEL) is the founding member of a diverse protein family defined by a repeated sequence motif known as the KEL repeat (KREP). Several KREP proteins, including Drosophila KEL, bind filamentous actin (F-actin) and contribute to its organization. Recently, a subset of KREP proteins has been shown to function as substrate adaptor proteins for cullin-RING (really interesting new gene) ubiquitin E3 ligases. In this study, we demonstrate that association of Drosophila KEL with Cullin-3, likely in a cullin-RING ligase, is essential for the growth of Drosophila female germline ring canals. These results suggest a role for protein ubiquitylation in the remodeling of a complex F-actin cytoskeletal structure.

A Kelch repeat protein, Cokel1p, associates with microtubules and is involved in appressorium development in Colletotrichum orbiculare

Kelch repeat proteins are conserved in diverse organisms and some are known to mediate fundamental cellular functions. We isolated the gene CoKEL1, encoding a novel kelch repeat protein, from Colletotrichum orbiculare. Analysis of a cokel1 mutant indicated that CoKEL1 is involved in proper appressorium development and cell wall synthesis. Appressoria produced by cokel1 disruption mutants showed irregular shape and impairment of turgor generation and the mutant appressoria rarely penetrated to form infection hyphae in host epidermal cells. Accordingly, cokel1 mutants had reduced pathogenicity on host leaves compared with the wild type. Furthermore, the cokel1 mutant was more sensitive to cell-wall-degrading enzymes and showed altered labeling with the cell wall stain Calcofluor white. Cokel1p was localized on cortical and spindle microtubules in vegetative hyphae. These results suggest that Cokel1p is a microtubule-associated protein involved in infection-related morphogenesis and pathogenicity. This is the first report that a kelch repeat protein is required for the pathogenicity of a fungal plant pathogen.

COP9 limits dendritic branching via Cullin3-dependent degradation of the actin-crosslinking BTB-domain protein Kelch

Components of the COP9 signalosome (CSN), a key member of the conserved 26S proteasome degradation pathway, have been detected to be altered in patients of several debilitating syndromes. These findings suggest that CSN acts in neural circuits, but the exact function of CSN in brain remains unidentified. Previously, using Drosophila peripheral nervous system (PNS) as a model system, we determined that CSN is a critical regulator of dendritic morphogenesis. We found that defects in CSN led to the strikingly contrast phenotype of either reducing or stimulating dendritic branching. In particular, we have reported that CSN stimulates dendritic branching via Cullin1-mediated proteolysis. Here we describe that CSN inhibits dendritic arborization in PNS neurons acting via control of Cullin3 function: loss of Cullin3 causes excessive dendritic branching. We also identified a downstream target for Cullin3-dependent degradation in neurons – the actin-crosslinking BTB-domain protein Kelch. Inappropriate accumulation of Kelch, either due to the impaired Cullin3-dependent turnover, or ectopic expression of Kelch, leads to uncontrolled dendritic branching. These findings indicate that the CSN pathway modulates neuronal network in a multilayer manner, providing the foundation for new insight into the CSN role in human mental retardation disorders and neurodegenerative disease.

Printor, a novel torsinA-interacting protein implicated in dystonia pathogenesis

Early onset generalized dystonia (DYT1) is an autosomal dominant neurological disorder caused by deletion of a single glutamate residue (torsinA DeltaE) in the C-terminal region of the AAA(+) (ATPases associated with a variety of cellular activities) protein torsinA. The pathogenic mechanism by which torsinA DeltaE mutation leads to dystonia remains unknown. Here we report the identification and characterization of a 628-amino acid novel protein, printor, that interacts with torsinA. Printor co-distributes with torsinA in multiple brain regions and co-localizes with torsinA in the endoplasmic reticulum. Interestingly, printor selectively binds to the ATP-free form but not to the ATP-bound form of torsinA, supporting a role for printor as a cofactor rather than a substrate of torsinA. The interaction of printor with torsinA is completely abolished by the dystonia-associated torsinA DeltaE mutation. Our findings suggest that printor is a new component of the DYT1 pathogenic pathway and provide a potential molecular target for therapeutic intervention in dystonia.

SCA8 mRNA expression suggests an antisense regulation of KLHL1 and correlates to SCA8 pathology

An increasing number of inherited neurodegenerative diseases are known to be caused by the expansion of unstable trinucleotide repeat tracts. Spinocerebellar ataxia type 8 (SCA8) has been identified as being partly caused by a CTG expansion in an untranslated, endogenous antisense RNA that overlaps the Kelch-like 1 (KLHL1) gene. Clinically, SCA8 patients show similar features to those with the other SCAs, including limb and truncal ataxia, ataxic dysarthria and horizontal nystagmus, all of which are signs of dysfunction of the cerebellar system. However, allele sizes within the SCA8 proposed pathogenic range have been reported in patients with ataxia of unknown etiology, in individuals from pedigrees with other SCA or Friedreich's ataxia, and in patients with Alzheimer's disease, schizophrenia or parkinsonism. These observations suggest that mutation of the SCA8 locus might affect neurons other than the cerebellum. Antisense transcripts are known to regulate complementary sense transcripts and are involved in several biologic functions, such as development, adaptive response, and viral infection. In order to test whether SCA8 affects the KLHL1 expression by antisense RNA in brain cells, we examined the expression pattern of KLHL1 and SCA8 in human tissues and in mouse brain regions. SCA8 expression was colocalized with KLHL1 transcript in many brain regions whose functions are correlated to the clinical symptoms of SCA8 patients. These findings lead to the hypothesis of a possible relevance that SCA8 transcript downregulates KLHL1 expression through an antisense mechanism, which then leads to SCA8 neuropathogenesis.

Comparative genome analysis of filamentous fungi reveals gene family expansions associated with fungal pathogenesis

Fungi and oomycetes are the causal agents of many of the most serious diseases of plants. Here we report a detailed comparative analysis of the genome sequences of thirty-six species of fungi and oomycetes, including seven plant pathogenic species, that aims to explore the common genetic features associated with plant disease-causing species. The predicted translational products of each genome have been clustered into groups of potential orthologues using Markov Chain Clustering and the data integrated into the e-Fungi object-oriented data warehouse (http://www.e-fungi.org.uk/). Analysis of the species distribution of members of these clusters has identified proteins that are specific to filamentous fungal species and a group of proteins found only in plant pathogens. By comparing the gene inventories of filamentous, ascomycetous phytopathogenic and free-living species of fungi, we have identified a set of gene families that appear to have expanded during the evolution of phytopathogens and may therefore serve important roles in plant disease. We have also characterised the predicted set of secreted proteins encoded by each genome and identified a set of protein families which are significantly over-represented in the secretomes of plant pathogenic fungi, including putative effector proteins that might perturb host cell biology during plant infection. The results demonstrate the potential of comparative genome analysis for exploring the evolution of eukaryotic microbial pathogenesis.

Ectromelia virus BTB/kelch proteins, EVM150 and EVM167, interact with cullin-3-based ubiquitin ligases

Cellular proteins containing BTB and kelch domains have been shown to function as adapters for the recruitment of substrates to cullin-3-based ubiquitin ligases. Poxviruses are the only family of viruses known to encode multiple BTB/kelch proteins, suggesting that poxviruses may modulate the ubiquitin pathway through interaction with cullin-3. Ectromelia virus encodes four BTB/kelch proteins and one BTB-only protein. Here we demonstrate that two of the ectromelia virus-encoded BTB/kelch proteins, EVM150 and EVM167, interacted with cullin-3. Similar to cellular BTB proteins, the BTB domain of EVM150 and EVM167 was necessary and sufficient for cullin-3 interaction. During infection, EVM150 and EVM167 localized to discrete cytoplasmic regions, which co-localized with cullin-3. Furthermore, EVM150 and EVM167 co-localized and interacted with conjugated ubiquitin, as demonstrated by confocal microscopy and co-immunoprecipitation. Our findings suggest that the ectromelia virus-encoded BTB/kelch proteins, EVM150 and EVM167, interact with cullin-3 potentially functioning to recruit unidentified substrates for ubiquitination.

Subcellular localization and cytoplasmic complex status of endogenous Keap1

Keap1 acts as a sensor for oxidative/electrophilic stress, an adaptor for Cullin-3-based ubiquitin ligase, and a regulator of Nrf2 activity through the interaction with Nrf2 Neh2 domain. However, the mechanism(s) of Nrf2 migration into the nucleus in response to stress remains largely unknown due to the lack of a reliable antibody for the detection of endogenous Keap1 molecule. Here, we report the generation of a new monoclonal antibody for the detection of endogenous Keap1 molecules. Immunocytochemical analysis of mouse embryonic fibroblasts with the antibody revealed that under normal, unstressed condition, Keap1 is localized primarily in the cytoplasm with minimal amount in the nucleus and endoplasmic reticulum. This subcellular localization profile of Keap1 appears unchanged after treatment of cells with diethyl maleate, an electrophile, and/or Leptomycin B, a nuclear export inhibitor. Subcellular fractionation analysis of mouse liver cells showed similar results. No substantial change in the subcellular distribution profile could be observed in cells isolated from butylated hydroxyanisole-treated mice. Analyses of sucrose density gradient centrifugation of mouse liver cells indicated that Keap1 appears to form multiprotein complexes in the cytoplasm. These results demonstrate that endogenous Keap1 remains mostly in the cytoplasm, and electrophiles promote nuclear accumulation of Nrf2 without altering the subcellular localization of Keap1.

Sheeppox virus kelch-like gene SPPV-019 affects virus virulence

Sheeppox virus (SPPV), a member of the Capripoxvirus genus of the Poxviridae, is the etiologic agent of a significant disease of sheep in the developing world. Genomic analysis of pathogenic and vaccine capripoxviruses identified genes with potential roles in virulence and host range, including three genes with similarity to kelch-like genes of other poxviruses and eukaryotes. Here, a mutant SPPV with a deletion in the SPPV-019 kelch-like gene, DeltaKLP, was derived from the pathogenic strain SPPV-SA. DeltaKLP exhibited in vitro growth characteristics similar to those of SPPV-SA and revertant virus (RvKLP). DeltaKLP-infected cells exhibited a reduction in Ca(2+)-independent cell adhesion, suggesting that SPPV-019 may modulate cellular adhesion. When inoculated in sheep by the intranasal or intradermal routes, DeltaKLP was markedly attenuated, since all DeltaKLP-infected lambs survived infection. In contrast, SPPV-SA and RvKLP induced mortality approaching 100%. Lambs inoculated with DeltaKLP exhibited marked reduction or delay in fever response, gross lesions, viremia, and virus shedding compared to parental and revertant viruses. Together, these findings indicate that SPPV-019 is a significant SPPV virulence determinant in sheep.

Using FlyAtlas to identify better Drosophila melanogaster models of human disease

FlyAtlas, a new online resource, provides the most comprehensive view yet of expression in multiple tissues of Drosophila melanogaster. Meta-analysis of the data shows that a significant fraction of the genome is expressed with great tissue specificity in the adult, demonstrating the need for the functional genomic community to embrace a wide range of functional phenotypes. Well-known developmental genes are often reused in surprising tissues in the adult, suggesting new functions. The homologs of many human genetic disease loci show selective expression in the Drosophila tissues analogous to the affected human tissues, providing a useful filter for potential candidate genes. Additionally, the contributions of each tissue to the whole-fly array signal can be calculated, demonstrating the limitations of whole-organism approaches to functional genomics and allowing modeling of a simple tissue fractionation procedure that should improve detection of weak or tissue-specific signals.

The Kelch-like protein 1 modulates P/Q-type calcium current density

The actin-binding protein Kelch-like 1 (KLHL1) is a neuronal protein that belongs to the evolutionarily-conserved Kelch protein super-family. The mammalian KLHL1 is brain-specific, cytosolic and can form multimers and bind actin filaments. KLHL1's function is likely that of an actin-organizing protein, possibly modulating neurite outgrowth, the dynamic morphology of dendritic spine heads; or anchoring proteins essential for post-synaptic function, like ion channels. Targeted deletion of the KLHL1 gene in Purkinje neurons results in dendritic deficits in these neurons, abnormal gait, and progressive loss of motor coordination in mice [He Y, Zu T, Benzow KA, Orr HT, Clark HB, Koob MD (2006) Targeted deletion of a single SCA8 ataxia locus allele in mice causes abnormal gait, progressive loss of motor coordination, and Purkinje cell dendritic deficits. J Neurosci 26:9975-9982]. Here we tested the hypothesis that KLHL1 may interact and modulate voltage-gated calcium channels by assessing the interaction of the principal subunit of P/Q-type channels, alpha(1A), with KLHL1. Experiments in human embryonic kidney line HEK 293 (HEK) cells and cerebellar primary cultures revealed co-incidence of alpha(1A) and KLHL1 immunoreactivity when testing both the endogenous or epitope-tagged versions of the proteins. Similarly, co-immunoprecipitation experiments in HEK cells and brain tissue exposed the presence of KLHL1 in protein samples immunoprecipitated with FLAG-tagged or alpha(1A) antibodies. Functional studies of KLHL1 on P/Q-type current properties probed with whole-cell patch clamp revealed a significant increase in mean current density in the presence of KLHL1 (80% increase; from -13.2+/-2.0 pA/pF to -23.7+/-4.2 pA/pF, P<0.02), as well as a shift in steady state activation V(50) of -5.5 mV (from 12.8+/-1.8 mV to 7.3+/-1.0 mV, P<0.02). Our data are consistent with a modulatory effect of KLHL1 on the P/Q-type calcium channel function and suggest a possible novel role for KLHL1 in cellular excitability.

The Cullin3 ubiquitin ligase functions as a Nedd8-bound heterodimer

Cullins are members of a family of scaffold proteins that assemble multisubunit ubiquitin ligase complexes to confer substrate specificity for the ubiquitination pathway. Cullin3 (Cul3) forms a catalytically inactive BTB-Cul3-Rbx1 (BCR) ubiquitin ligase, which becomes functional upon covalent attachment of the ubiquitin homologue neural-precursor-cell-expressed and developmentally down regulated 8 (Nedd8) near the C terminus of Cul3. Current models suggest that Nedd8 activates cullin complexes by providing a recognition site for a ubiquitin-conjugating enzyme. Based on the following evidence, we propose that Nedd8 activates the BCR ubiquitin ligase by mediating the dimerization of Cul3. First, Cul3 is found as a neddylated heterodimer bound to a BTB domain-containing protein in vivo. Second, the formation of a Cul3 heterodimer is mediated by a Nedd8 molecule, which covalently attaches itself to one Cul3 molecule and binds to the winged-helix B domain at the C terminus of the second Cul3 molecule. Third, complementation experiments revealed that coexpression of two distinct nonfunctional Cul3 mutants can rescue the ubiquitin ligase function of the BCR complex. Likewise, a substrate of the BCR complex binds heterodimeric Cul3, suggesting that the Cul3 complex is active as a dimer. These findings not only provide insight into the architecture of the active BCR complex but also suggest assembly as a regulatory mechanism for activation of all cullin-based ubiquitin ligases.

Born to bind: the BTB protein-protein interaction domain

The BTB domain is a protein-protein interaction motif that is found throughout eukaryotes. It determines a unique tri-dimensional fold with a large interaction surface. The exposed residues are highly variable and can permit dimerization and oligomerization, as well as interaction with a number of other proteins. BTB-containing proteins are numerous and control cellular processes that range from actin dynamics to cell-cycle regulation. Here, we review findings in the field of transcriptional regulation to illustrate how the high variability of the BTB has allowed related transcription factors to evolve different functional abilities. We then report how recent work has showed that, in spite of their high sequence divergence and apparently unrelated functions, many BTB-containing proteins have at least one shared role: the recruitment of degradation targets to E3 ubiquitin ligase complexes. Taken together, these findings illustrate diverse and convergent functions of a versatile protein-protein interaction domain.

Targeted deletion of a single Sca8 ataxia locus allele in mice causes abnormal gait, progressive loss of motor coordination, and Purkinje cell dendritic deficits

Spinocerebellar ataxia type 8 (SCA8) patients typically have a slowly progressive, adult-onset ataxia. SCA8 is dominantly inherited and is caused by large CTG repeat expansions in the untranslated antisense RNA of the Kelch-like 1 gene (KLHL1), but the molecular mechanism through which this expansion leads to disease is still unknown. To more fully characterize the underlying molecular mechanisms involved in SCA8, we developed a mouse model in which Klhl1 is deleted in either all tissues or is deleted specifically in Purkinje cells only. We found that mice that are either homozygous or heterozygous for the Klhl1 deletion have significant gait abnormalities at an early age and develop a significant loss of motor coordination by 24 weeks of age. This loss progresses more rapidly in homozygous knock-outs. Mice with Klhl1 specifically deleted in only Purkinje cells had a loss of motor coordination that was almost identical to the total-tissue deletion mice. Finally, we found significant Purkinje cell dendritic deficits, as measured by the thickness of the molecular layer, in all mice in which Klhl1 was deleted (both total and Purkinje cell-specific deletions) and an intermediate reduction in molecular layer thickness in mice with reduced levels of Klhl1 expression (heterozygous deletions). The results from this mouse model show that even a partial loss of Klhl1 function leads to degeneration of Purkinje cell function and indicates that loss of KLHL1 activity is likely to play a significant part in the underlying pathophysiology of SCA8.

Non-invasive genetic diagnosis of male infertility using spermatozoal RNA: KLHL10 mutations in oligozoospermic patients impair homodimerization

Infertility affects an estimated 7% of men worldwide, nearly a quarter of whom are diagnosed as idiopathic. The genetic etiologies of idiopathic male infertility are unknown, partly due to lack of simple diagnostic techniques. Moreover, the transmission risk of such genetic defects to offspring born from assisted reproductive techniques is increasingly becoming a concern for physicians and infertile couples. We explored the feasibility of obtaining full-length mRNAs from transcriptionally inert human spermatozoa in semen as a non-invasive diagnostic tool for identifying germline mutations in candidate infertility-associated genes. The efficacy of reverse-transcription PCR on spermatozoal RNA from infertile patients with wide-ranging sperm concentrations varied between 91 and 99% for multiple haploid germ cell-expressed genes. Using this methodology, we identified seven oligozoospermic patients with missense and splicing mutations in the germ cell-specific gene, KLHL10. Three of 270 (1.1%) severely oligozoospermic patients (<10(6) sperm/ml) harbor KLHL10 alterations that were absent in 394 controls and exhibited significant association (P=0.02). Two KLHL10 missense mutations (A313T and Q216P) resulted in impaired homodimerization with the wild-type protein in yeast interaction assays, suggesting a functional deficiency. This study demonstrates the utility of this approach for analysis of haploid germ cell-expressed genes regulating post-meiotic events including sperm maturation, motility and fertilization. The development of non-invasive techniques to analyze genetic defects of human spermatogenesis, previously possible only with invasive testis biopsies, provides important diagnostic and therapeutic implications for reproductive medicine.

Differential subcellular localization and activity of kelch repeat proteins KLHDC1 and KLHDC2

We have previously identified and characterized human KLHDC2/HCLP-1, a kelch repeat protein that interacts with and inhibits transcription factor LZIP. In this study, we identified and characterized a paralog of KLHDC2 called KLHDC1. KLHDC1 and KLHDC2 share about 50% identity at the level of amino acid sequence and both gene loci localize to human chromosome 14q21.3. This cluster of KLHDC1 and KLHDC2 genes is highly conserved in vertebrates ranging from pufferfish to human. Both genes are expressed highly in skeletal muscle, but weakly in various other tissues. While KLHDC2 was predominantly found in the nucleus, KLHDC1 is a cytoplasmic protein. Neither KLHDC1 nor KLHDC2 binds to actin. In addition, KLHDC1 was unable to inhibit LZIP/CREB3-mediated transcriptional activation. Thus, KLHDC1 and KLHDC2 have differential localization and activity in cultured mammalian cells.

Overexpression of Nd1, a novel Kelch family protein, in the heart of transgenic mice protects against doxorubicin-induced cardiomyopathy

Doxorubicin is one of the most effective drugs available for cancer chemotherapy. However, the clinical use of doxorubicin has been greatly limited because of severe side effects on cardiomyocytes. Since Nd1-L, a novel actin-binding protein, is expressed most abundantly in the heart of adult mice, we examined a role of Nd1-L in doxorubicin-induced cardiomyopathy. When doxorubicin (5 mg/kg x 4 times) was injected into adult mice at a 3-day-interval, approximately 50% of injected mice died within 4 weeks of the first injection. Nd1-L mRNA expression in the heart decreased within 3 weeks after the first injection and many cardiomyocytes of injected mice died by apoptosis. Overexpression of Nd1-L in the heart of transgenic mice protected the cardiomyocytes from apoptosis and improved survival rate after doxorubicin injection. Furthermore, activation of Erk1/2 was observed in cultured cells overexpressing Nd1-L. Thus, Nd1-L plays a critical role in protecting the heart from doxorubicin-induced cardiomyopathy.

Detection of Autoantibodies to the BTB-kelch Protein KLHL7 in Cancer Sera

The aim of the study was to search for novel targets of autoantibodies in patients with paraneoplastic neurological syndromes (PNS). PNS are mediated by immune reactions against autoantigen(s) shared by the cancer cells and the nervous system. By serological screening of a rat cerebellum cDNA expression library using anti-Hu-positive sera from three patients with paraneoplastic encephalomyelitis (PEM), we identified an open reading frame encoding an isoform of the BTB-kelch protein KLHL7. Immunohistochemical studies demonstrated that the KLHL7 protein is expressed in the nuclei of neurones, but not in other tissues including various cancers. However, the KLHL7 protein was detected in the nuclei of cancer cell lines. Antibodies to KLHL7 were detected by an immunoprecipitation assay in sera from 12 of 254 (4.7%) patients with various cancers and 2 of 170 blood donors (1.2%). None of 50 sera from patients with multiple sclerosis were positive for KLHL7 antibodies. Sixteen patients with classical PNS and anti-Hu or anti-Yo antibodies were also negative for KLHL7 antibodies. Seven cancer patients with KLHL7 antibodies had various signs of neurological disease that could be related to cancer, whereas the remaining five seropositive cancer patients had no clinical signs of possible PNS. The present results indicate that KLHL7 antibodies are associated with various cancers, and in some patients also with neurological disease. Whether KLHL7 antibodies can be used as paraneoplastic markers for PNS remains to be determined.

Identification and isolation of a BTB-POZ-containing gene expressed in oocytes and early embryos of the zebrafish Danio rerio

In this report, we describe the cloning of a cDNA from the zebrafish Danio rerio encoding a protein containing a BTB-POZ domain closely resembling the BTBD1 and BTBD2 proteins previously identified in mammals. However, unlike other BTB-POZ-containing genes, expression of this gene in adults is most abundant in oocytes, where the RNA can be detected at all stages of oogenesis examined. The presence of the RNA persists through early cleavage, but is decreased significantly by gastrulation. Although the function of this gene has yet to be determined, its resemblance to the BTB-POZ family of genes coupled with its expression pattern suggests that it may have an important function in oogenesis and (or) early zebrafish development.

Vaccinia virus kelch protein A55 is a 64 kDa intracellular factor that affects virus-induced cytopathic effect and the outcome of infection in a murine intradermal model

The vaccinia virus (VACV) protein A55 is a BTB/kelch protein with a broad-complex, tramtrack and bric-a-brac (BTB) domain in the N-terminal region and five kelch repeats in the C-terminal half. The BTB/kelch subgroup of the kelch superfamily of proteins has been associated with a wide variety of functions including regulation of the cytoskeleton. VACV contains three genes predicted to encode BTB/kelch proteins: A55R, F3L and C2L. The A55R gene product has been identified as an intracellular protein of 64 kDa that is expressed late in infection. A VACV strain lacking 93.6 % of the A55R open reading frame (vΔA55) was constructed and found to have an unaltered growth rate in vivo but a different plaque morphology and cytopathic effect, as well as reduced development of VACV-induced Ca2+-independent cell/extracellular matrix adhesion. In a murine intradermal model of VACV infection, a virus lacking the A55R gene induced larger lesions than wild-type and revertant control viruses.