KOMPEITO, an Atypical Arabidopsis Rhomboid-Related Gene, Is Required for Callose Accumulation and Pollen Wall Development

Fertilization is a key event for sexually reproducing plants. Pollen-stigma adhesion, which is the first step in male-female interaction during fertilization, requires proper pollen wall patterning. Callose, which is a β-1.3-glucan, is an essential polysaccharide that is required for pollen development and pollen wall formation. Mutations in CALLOSE SYNTHASE 5 (CalS5) disrupt male meiotic callose accumulation; however, how CalS5 activity and callose synthesis are regulated is not fully understood. In this paper, we report the isolation of a kompeito-1 (kom-1) mutant defective in pollen wall patterning and pollen-stigma adhesion in Arabidopsis thaliana. Callose was not accumulated in kom-1 meiocytes or microspores, which was very similar to the cals5 mutant. The KOM gene encoded a member of a subclass of Rhomboid serine protease proteins that lacked active site residues. KOM was localized to the Golgi apparatus, and both KOM and CalS5 genes were highly expressed in meiocytes. A 220 kDa CalS5 protein was detected in wild-type (Col-0) floral buds but was dramatically reduced in kom-1. These results suggested that KOM was required for CalS5 protein accumulation, leading to the regulation of meiocyte-specific callose accumulation and pollen wall formation.

Expression and Purification of Human Mitochondrial Intramembrane Protease PARL

Rhomboid proteases are a ubiquitous superfamily of serine intramembrane peptidases that play a role in a wide variety of cellular processes. The mammalian mitochondrial rhomboid protease, Presenilin-Associated Rhomboid Like (PARL), is a critical regulator of mitochondrial homeostasis through the cleavage of its substrates, which have roles in mitochondrial quality control and apoptosis. However, neither structural nor functional information for this important protease is available, because the expression of eukaryotic membrane proteins to sufficient levels in an active form often represents a major bottleneck for in vitro studies. Here we present an optimized protocol for expression and purification of the human PARL protease using the eukaryotic expression host Pichia pastoris. The PARL gene construct was generated in tandem with green fluorescent protein (GFP), which allowed for the selection of high expressing clones and monitoring during the large-scale expression and purification steps. We discuss the production protocol with precise details for each step. The protocol yields 1 mg of pure PARL per liter of yeast culture.

Accuracy of rib palpation for dry needling of deep periscapular musculature, measured with ultrasound

INTRODUCTION

Dry needling of the periscapular musculature is a procedure commonly performed by physical therapists. Needling of the deep musculature may be challenging, and use of a thoracic rib as a "backstop" is often applied to prevent inadvertent puncture of the pleura. The aim of this study was to: 1) To examine the accuracy rate of experienced physical therapists in identifying a mid-scapular thoracic rib using palpation, 2) to understand patient characteristics that affect the accuracy rate, and 3) to examine if therapist confidence levels were associated with palpatory accuracy.

METHODS

Two experienced physical therapists attempted to palpate a thoracic rib in the mid-scapular region of healthy participants (n = 101 subjects, 202 ribs), and self-reported their level of confidence in an accurate palpation. Their accuracy was verified with ultrasonography.

RESULTS

The two physical therapists were accurate on 73.3% of palpations and did not differ in accuracy (72.0% vs. 75.0%, p = 0.747). The only ultrasonographic or subject characteristic measurement that correlated with improved accuracy was a reduced muscle thickness (p = 0.032). Therapists' self-reported confidence levels did not correlate to actual accuracy (p = 0.153).

DISCUSSION

Physical therapists should be aware that palpation of a thoracic rib may not be as accurate as it may seem. The greater thickness of muscle in the area reduces the accuracy of accurate palpation.

CONCLUSION

Dry needling of the periscapular muscles should be done with caution if using a rib as a "blocking" technique.

Status update on iRhom and ADAM17: It's still complicated

Several membrane-bound proteins with a single transmembrane domain are subjected to limited proteolysis at the cell surface. This cleavage leads to the release of their biologically active ectodomains, which can trigger different signalling pathways. In many cases, this ectodomain shedding is mediated by members of the family of a disintegrins and metalloproteinases (ADAMs). ADAM17 in particular is responsible for the cleavage of several proinflammatory mediators, growth factors, receptors and adhesion molecules. Due to its direct involvement in the release of these signalling molecules, ADAM17 can be positively and negatively involved in various physiological processes as well as in inflammatory, fibrotic and malignant pathologies. This central role of ADAM17 in a variety of processes requires strict multi-level regulation, including phosphorylation, various conformational changes and endogenous inhibitors. Recent research has shown that an early, crucial control mechanism is interaction with certain adapter proteins identified as iRhom1 and iRhom2, which are pseudoproteases of the rhomboid superfamily. Thus, iRhoms have also a decisive influence on physiological and pathophysiological signalling processes regulated by ADAM17. Their characteristic gene expression profiles, the specific consequences of gene knockouts and finally the occurrence of disease-associated mutations suggest that iRhom1 and iRhom2 undergo different gene regulation in order to fulfil their function in different cell types and are therefore only partially redundant. Therefore, there is not only interest in ADAM17, but also in iRhoms as therapeutic targets. However, to exploit the therapeutic potential, the regulation of ADAM17 activity and in particular its interaction with iRhoms must be well understood.

Quantitative Multiplex Substrate Profiling of Peptidases by Mass Spectrometry

Proteolysis is an integral component of life and has been implicated in many disease processes. To improve our understanding of peptidase function, it is imperative to develop tools to uncover substrate specificity and cleavage efficiency. Here, we combine the quantitative power of tandem mass tags (TMTs) with an established peptide cleavage assay to yield quantitative Multiplex Substrate Profiling by Mass Spectrometry (qMSP-MS). This assay was validated with papain, a well-characterized cysteine peptidase, to generate cleavage efficiency values for hydrolysis of 275 unique peptide bonds in parallel. To demonstrate the breath of this assay, we show that qMSP-MS can uncover the substrate specificity of minimally characterized intramembrane rhomboid peptidases, as well as define hundreds of proteolytic activities in complex biological samples, including secretions from lung cancer cell lines. Importantly, our qMSP-MS library uses synthetic peptides whose termini are unmodified, allowing us to characterize not only endo- but also exo-peptidase activity. Each cleaved peptide sequence can be ranked by turnover rate, and the amino acid sequence of the best substrates can be used for designing fluorescent reporter substrates. Discovery of peptide substrates that are selectively cleaved by peptidases which are active at the site of disease highlights the potential for qMSP-MS to guide the development of peptidase-activating drugs for cancer and infectious disease.

Effects of pulling direction on upper trapezius and rhomboid muscle activity

[Purpose] This study examined the activation of the rhomboid muscle according to the angle of the arm. [Subjects and Methods] The current study was conducted on 15 healthy males. The participants performed the pulling exercise in 5 conditions. The surface electromyography system was used to measure the muscle activities of the rhomboid and upper trapezius. [Results] The activity of the upper trapezius in condition 5 was significantly increased compared to that in condition 4. The activity of the rhomboid in condition 4 was significantly increased compared to that in conditions 1 and 5. [Conclusion] This study showed that performing a pulling exercise with the arms raised above the head (shoulder flexion at 120°) is more effective for reducing upper trapezius tension, while also selectively strengthening the rhomboid muscle.

Rhomboid proteases in human disease: Mechanisms and future prospects

Rhomboids are intramembrane serine proteases that cleave the transmembrane helices of substrate proteins, typically releasing luminal/extracellular domains from the membrane. They are conserved in all branches of life and there is a growing recognition of their association with a wide range of human diseases. Human rhomboids, for example, have been implicated in cancer, metabolic disease and neurodegeneration, while rhomboids in apicomplexan parasites appear to contribute to their invasion of host cells. Recent advances in our knowledge of the structure and the enzyme function of rhomboids, and increasing efforts to identify specific inhibitors, are beginning to provide important insight into the prospect of rhomboids becoming future therapeutic targets. This article is part of a Special Issue entitled: Proteolysis as a Regulatory Event in Pathophysiology edited by Stefan Rose-John.

A New Method to Determine the Transmembrane Conformation of Substrates in Intramembrane Proteolysis by Deep-UV Resonance Raman Spectroscopy

We present a new method based on deep-UV resonance Raman spectroscopy to determine the backbone conformation of intramembrane protease substrates. The classical amide vibrational modes reporting on the conformation of just the transmembrane region of the substrate can be resolved from solvent exchangeable regions outside the detergent micelle by partial deuteration of the solvent. In the presence of isotopically triple-labeled intramembrane protease, these amide modes can be accurately measured to monitor the transmembrane conformation of the substrate during intramembrane proteolysis.

A novel technique for full thickness medial canthal reconstruction; playing with broken lines

Purpose

To introduce a new modification of transposition flap technique for reconstruction of the medial canthal region.

Methods

This prospective study included 58 patients with the full thickness involvement of both upper and lower lid in the medial canthal area. Reconstruction of posterior lamella was performed by utilizing periosteal flaps and tarsoconjunctival grafts, and anterior lamellar reconstruction was performed using transposition of multiple full-thickness skin flaps, a modified form of rhomboid flap technique. Post-surgical outcomes, advantages, and drawbacks of this technique are discussed.

Results

Between 2010 and 2014, 58 patients with basal cell carcinoma (BCC), proven by histopathologic study, underwent medial canthal reconstruction. The mean age was 72.8 ± 8.3 years. In 30 patients, the lacrimal apparatus was excised, and periosteal flaps or tarsoconjunctival grafts were prepared to reconstruct the posterior lamella. Anterior lamellar reconstruction was performed in all patients, and the mean number of transposition flaps was 3.63 in addition to the blepharoplasty flap. Patients were followed for 24 months. None of the patients developed flap necrosis or other intraoperative and postoperative complications, with acceptable aesthetic and functional outcomes.

Conclusion

Full-thickness reconstruction of the medial canthal area by utilizing periosteal flaps and modified transposition flap technique all in one session can be considered an alternative method in medial canthal reconstruction, with acceptable functional and aesthetic outcomes.

Safety and efficacy of the keystone and rhomboid flaps for immediate reconstruction after wide local excision of non-head and neck melanomas

Background

After wide local excision of cutaneous melanoma, large defects not amenable to simple primary closure are often covered with skin grafts. We report our experience using the rhomboid and keystone flaps to immediately close large axial and extremity wounds after potentially curative surgery for non-head and neck melanomas.

Methods

Between January 2011 and September 2016, demographic, operative, pathologic, and outcome data were prospectively collected on 60 patients who underwent wide local excision of melanoma followed by immediate flap reconstruction. Flaps were of either rhomboid or keystone type. Chi-square analysis was used to compare relationships between factors.

Results

All procedures were done by the senior author and as outpatient surgery. No patient required a surgical drain unless they were undergoing concomitant radical regional node dissection. Flap separation (arbitrarily defined as a >5-mm dehiscence of the suture line) occurred in 16/61 patients (26 %). No patient had flap loss. The risk of flap morbidity was significantly higher if the primary tumor was on the distal extremity—10 of 24 patients (42 %), all with keystone flaps—than if it was on the trunk or the proximal extremity (6/37 patients, 16 %), p = 0.04. There were no margins positive for either invasive or in situ melanoma in the entire cohort.

Conclusions

Simple transposition flaps can successfully cover large defects after melanoma excision without the need for skin grafting. Keystone flaps in the distal extremity are more prone to separation, but this is minor and does not result in flap loss. There is minimal risk of a positive margin requiring flap takedown and a second re-excision.

Cryptosporidium parvum rhomboid1 has an activity in microneme protein CpGP900 cleavage

Background

Apicomplexan parasites actively release transmembrane (TM) adhesive proteins involved in host cell attachment and invasion. Rhomboids, a family of intramembrane serine proteases, cleave these secreted adhesive proteins within their TM domains as an essential step in completing the invasion process. In Cryptosporidium parvum, the activity of rhomboids in cleaving microneme proteins (MICs) has not been reported. In the present study, the interaction between C. parvum rhomboids (CpROM1 and CpROM4) and C. parvum microneme proteins (CpGP900 and CpTRAP-C1) was investigated using yeast two-hybrid assay and co-immunoprecipitation assays.

Results

Our study demonstrated that CpROM1 protein could interact with CpGP900 protein in co-transformed AH109 yeasts. Analysis of these proteins in co-transfected mammalian cells showed that the cleavage product of the CpGP900 protein was detected in the co-transfected cells. As control, CpGP900 only was transfected into cells and no cleavage was observed. The results suggested that CpGP900 protein was the substrate of CpROM1. Moreover, CpROM1 and CpROM4 could not cleave CpTRAP-C1 protein, which is the substrate of T. gondii rhomboid 2.

Conclusions

Our results showed that CpROM1 is an active protease that is involved in microneme protein CpGP900 cleavage, which lay the foundation for further research on the mechanisms of C. parvum invasion.

PARL: The mitochondrial rhomboid protease

The rhomboid family comprises evolutionary conserved intramembrane proteases involved in a wide spectrum of biologically relevant activities. A mitochondrion-localized rhomboid, called PARL in mammals, and conserved in yeast and Drosophila as RBD1/PCP1 and rho-7, respectively, plays an indispensable role in cell homeostasis as illustrated by the severe phenotypes caused by its genetic ablation in the various investigated species. Although several substrates of PARL have been proposed to explain these phenotypes, there remains a lot of controversy in this important area of research. We review here the putative functions and substrates of PARL and its orthologues in different species, highlighting areas of uncertainty, and discuss its potential involvement in some prevalent diseases such as type II diabetes and Parkinson's disease.

Developmental roles of Rhomboid proteases

Rhomboid proteins have emerged as one of the most tantalizing and diverse families of proteases. Gene duplication events and structural alterations have sculpted the varied roles of this protein family, maintaining a conserved structural core throughout the bacterial, plant and animal kingdoms. Unresolved questions pop up at many junctions. This review will focus on a distinct class of Rhomboid proteins that plays an essential role in development. It will outline the diverse mechanisms by which these proteins are regulated, and the implications on the biological processes they control. While most of the review will deal with Rhomboids in Drosophila, a system that has been studied in the greatest detail, it will also explore parallels and differences in the function of Rhomboids in the flour beetle T. casteneum and the worm C. elegans.

Efficacy of a potential DNA vaccine encoding Cryptosporidium baileyi rhomboid protein against homologous challenge in chickens

The parasite Cryptosporidium baileyi can infect the larynx, trachea, bursa and cloaca of poultry, causing high mortality during severe infection and leading to substantial economic losses of the poultry industry. The rhomboid protein is very important in Cryptosporidium infection. In this study, a nucleic acid based vaccine candidate pEGFP-CbROM was constructed. After orally challenging with C. baileyi oocysts, the corresponding immune responses induced were analyzed and the immunoprotective effect evaluated in chickens. Obtained results revealed that this nucleic acid based vaccine could induce antibody responses and peripheral blood T lymphocytes proliferation significantly (P<0.05), while the peripheral blood B lymphocyte proliferation increased significantly (P<0.05) only at a high dose of 100μg of pEGFP-CbROM, compared with the PBS control group. After C. baileyi infection, the duration of oocysts shedding was shortened by 2days in the 100μg pEGFP-CbROM group, and the rate of reduction could reach to around 71.3%. While no significant difference in body weight gain was observed among the immunized groups (P>0.05), the differences between the immunized and the non-immunized groups were found to be significant (P<0.05). Our data provides a useful basis for further work in cryptosporidiosis prevention and treatment.

ESCRT-0 complex modulates Rbf-mutant cell survival by regulating Rhomboid endosomal trafficking and EGFR signaling

The Rb tumor suppressor is conserved in Drosophila, and its inactivation can lead to cell proliferation or death depending on the specific cellular context. Therefore, identifying genes that affect the survival of Rb-mutant cells can potentially identify novel targets for therapeutic intervention in cancer. From a genetic screen in Drosophila, we identified synthetic lethal interactions between mutations of fly Rb (rbf) and the ESCRT-0 components stam and hrs We show that inactivation of ESCRT-0 sensitizes rbf-mutant cells to undergo apoptosis through inhibition of EGFR signaling and accumulation of Hid protein. Mutation of stam inhibits EGFR signaling upstream of secreted Spi and downstream of Rhomboid expression, and causes Rhomboid protein to accumulate in the abnormal endosomes labeled with both the early and late endosomal markers Rab5 and Rab7. These results reveal that ESCRT-0 mutants inhibit EGFR signaling by disrupting Rhomboid endosomal trafficking in the ligand-producing cells. Because ESCRT-0 also plays crucial roles in EGFR downregulation after ligand binding, this study provides new insights into how loss of ESCRT-0 function can either increase or decrease EGFR signaling.

Groucho restricts rhomboid expression and couples EGFR activation with R8 selection during Drosophila photoreceptor differentiation

Notch and EGFR signaling pathways play important roles in photoreceptor differentiation during Drosophila eye development. Notch signaling induces Enhancer of Split (E(spl)) proteins to repress atonal (ato) expression and restrict R8 photoreceptor cell fate. The R8 precursors express rhomboid (rho), which is required for the release of active EGFR ligand to activate EGFR signaling in surrounding cells for the subsequent stepwise recruitment. However, it is not clear about the mechanisms of transcriptional regulation of rho and how the lateral inhibition of Notch signaling and rho expression are coordinated. In this study, we show that inactivation of Groucho (Gro), an evolutionally conserved transcriptional corepressor, inhibits Ato upregulation, delays R8 determination, and promotes differentiation of R2-5 type of neurons. We demonstrate that these phenotypes are caused by a combination of the loss of Notch-mediated lateral inhibition and the precocious activation of EGFR signaling due to deregulated rho expression. Blocking EGFR signaling by Pnt-RNAi in conjunction with Gro-inactivation leads to lateral inhibition defects with deregulated Ato expression and R8 differentiation. We further show that inactivation of E(spl), which are the Gro binding transcription factors, causes deregulated rho expression and extra R8 cells within and posterior to the morphogenetic furrow (MF), and that E(spl) mediates the binding of Gro to the regulatory regions of both rho and ato genes in eye disc cells. Our results suggest that Gro inhibits rho expression in undifferentiated cells and represses the expression of both ato and rho in non-R8 precursors during initiation of photoreceptor differentiation in an E(spl)-dependent manner. The latter function of Gro provides novel insights into the mechanism that coordinates R8 specification with the restriction of initial rho expression to developing R8 cells.

Inactivation of the nucleus reuniens/rhomboid causes a delay-dependent impairment of spatial working memory

Inactivation of the rodent medial prefrontal cortex (mPFC) and hippocampus or disconnection of the hippocampus from the mPFC produces deficits in spatial working memory tasks. Previous studies have shown that delay length determines the extent to which mPFC and hippocampus functionally interact, with both structures being necessary for tasks with longer delays and either structure being sufficient for tasks with shorter delays. In addition, inactivation of the nucleus reuniens (Re)/rhomboid nucleus (Rh) of the thalamus, which has bidirectional connections with the mPFC and hippocampus, also produces deficits in these tasks. However, it is unknown how delay duration relates to the function of Re/Rh. If Re/Rh are critical in modulating mPFC-hippocampus interactions, inactivation of the RE/Rh should produce a delay-dependent impairment in spatial working memory performance. To investigate this question, groups of rats were trained on one of three different spatial working memory tasks: continuous alternation (CA), delayed alternation with a five-second delay (DA5), or with a thirty-second delay (DA30). The Re/Rh were inactivated with muscimol infusions prior to testing. The results demonstrate that inactivation of RE/Rh produces a deficit only on the two DA tasks, supporting the notion that the Re/Rh is a critical orchestrator of mPFC-HC interactions.

Genetic interaction implicates iRhom2 in the regulation of EGF receptor signalling in mice

iRhoms are closely related to rhomboid intramembrane proteases but lack catalytic activity. In mammals iRhoms are known to regulate the trafficking of TACE, the protease that cleaves the membrane bound inflammatory cytokine TNF. We have mapped a spontaneously occurring mouse mutation with a loss of hair phenotype, curly bare (cub), to the Rhbdf2 locus, which encodes the iRhom2 protein. The cub deletion removes the first 268 amino acids of the iRhom2 protein but is not a loss of function. We have also identified a previously reported suppressor of cub, called Mcub (modifier of curly bare), and find it to be a loss of function allele of the amphiregulin gene (Areg). Amphiregulin is an activating ligand of the epidermal growth factor receptor (EGFR) that, like TNF, is released by TACE. Our results therefore imply a regulatory link between iRhoms and EGFR signalling in mammals. We have tested the model that the cub mutation leads to iRhom2 hyperactivity and consequently excess TACE processing of amphiregulin and elevated EGFR signalling. Our results do not support this hypothesis: we find that, compared to wild-type cells, cub mutant embryonic fibroblasts release less amphiregulin, and that the cub mutant form of iRhom2 is less able than wild type to bind to TACE and promote its maturation.

Eimeria tenella rhomboid 3 has a potential role in microneme protein cleavage

Invasion in several apicomplexan parasites, including Eimeria tenella, is accompanied by shedding of surface adhesins by intramembrane proteolysis mediated by rhomboid protease. We have previously identified E. tenella rhomboid 3 (EtROM3), but its precise role has not been elucidated. In this study, the interactions between EtROM3 and microneme (MIC) proteins were analyzed using the yeast two hybrid technique. The results showed that c-Myc-ROM3 fusion protein interacted with EtMIC4 protein in co-transformed AH109 yeasts, which was further confirmed by immunoprecipitation assay. Smaller EtMIC4 band from co-transformed cells suggested that EtROM3 was an active protease and involved in the cleavage of EtMIC4.

The roles of intramembrane proteases in protozoan parasites

Intramembrane proteolysis is widely conserved throughout different forms of life, with three major types of proteases being known for their ability to cleave peptide bonds directly within the transmembrane domains of their substrates. Although intramembrane proteases have been extensively studied in humans and model organisms, they have only more recently been investigated in protozoan parasites, where they turn out to play important and sometimes unexpected roles. Signal peptide peptidases are involved in endoplasmic reticulum (ER) quality control and signal peptide degradation from exported proteins. Recent studies suggest that repurposing inhibitors developed for blocking presenilins may be useful for inhibiting the growth of Plasmodium, and possibly other protozoan parasites, by blocking signal peptide peptidases. Rhomboid proteases, originally described in the fly, are also widespread in parasites, and are especially expanded in apicomplexans. Their study in parasites has revealed novel roles that expand our understanding of how these proteases function. Within this diverse group of parasites, rhomboid proteases contribute to processing of adhesins involved in attachment, invasion, intracellular replication, phagocytosis, and immune evasion, placing them at the vertex of host-parasite interactions. This article is part of a Special Issue entitled: Intramembrane Proteases.

Trafficking of the EGFR ligand Spitz regulates its signaling activity in polarized tissues

Epidermal growth factor receptor (EGFR) ligands undergo a complex series of processing events during their maturation to active signaling proteins. Like its mammalian homologs, the predominant Drosophila EGFR ligand Spitz is produced as a transmembrane pro-protein. In the secretory pathway, Spitz is cleaved within its transmembrane domain to release the extracellular signaling domain. This domain is modified with an N-terminal palmitate group that tethers it to the plasma membrane. We found that the pro-protein can reach the cell surface in the absence of proteolysis, but that it fails to activate the EGFR. To address why the transmembrane pro-protein is inactive, whereas membrane association through the palmitate group promotes activity, we generated a panel of chimeric constructs containing the Spitz extracellular region fused to exogenous transmembrane proteins. Although the orientation of the EGF domain and its distance from the plasma membrane varies in these chimeras, they are all active in vivo. Thus, tethering Spitz to the membrane via a transmembrane domain at either terminus does not prevent activity. Conversely, removing the N-terminal palmitate group from the C-terminally tethered pro-protein does not render it active. Furthermore, we show that the Spitz transmembrane pro-protein can activate the EGFR in a tissue culture assay, indicating that its failure to signal in vivo is not due to structural features. In polarized imaginal disc cells, unprocessed Spitz pro-protein localizes to apical puncta, whereas the active chimeric Spitz constructs are basolaterally localized. Taken together, our data support the model that localized trafficking of the pro-protein restricts its ability to activate the receptor in polarized tissues.