Loss of Num1-mediated cortical dynein anchoring negatively impacts respiratory growth.

Num1 is a multifunctional protein that both tethers mitochondria to the plasma membrane and anchors dynein to the cell cortex during nuclear inheritance. Previous work has examined the impact loss of Num1-based mitochondrial tethering has on dynein function in Saccharomyces cerevisiae; here, we elucidate its impact on mitochondrial function. We find that like mitochondria, Num1 is regulated by changes in metabolic state, with the protein levels and cortical distribution of Num1 differing between fermentative and respiratory growth conditions. In cells lacking Num1, we observe a reproducible respiratory growth defect, suggesting a role for Num1 in not only maintaining mitochondrial morphology, but also function. A structure-function approach revealed that, unexpectedly, Num1-mediated cortical dynein anchoring is important for normal growth under respiratory conditions. The severe respiratory growth defect in Δnum1 cells is not specifically due to the canonical functions of dynein in nuclear migration but is dependent on the presence of dynein, as deletion of DYN1 in Δnum1 cells partially rescues respiratory growth. We hypothesize that misregulated dynein present in cells that lack Num1 negatively impacts mitochondrial function resulting in defects in respiratory growth.

Effect of nonsteroidal anti-inflammatory drugs (aspirin and naproxen) on inflammation-associated proteomic profiles in mouse plasma and prostate during TMPRSS2-ERG (fusion)-driven prostate carcinogenesis.

Recent preclinical studies have shown that the intake of nonsteroidal anti-inflammatory drugs (NSAIDs) aspirin and naproxen could be an effective intervention strategy against TMPRSS2-ERG fusion-driven prostate tumorigenesis. Herein, as a follow-up mechanistic study, employing TMPRSS2-ERG (fusion) positive tumors and plasma from TMPRSS2-ERG. Ptenflox/flox mice, we profiled the stage specific proteomic changes (focused on inflammatory circulating and prostate tissue/tumor-specific cytokines, chemokines, and growth factors/growth signaling-associated molecules) that contribute to prostate cancer (PCa) growth and progression in the TMPRSS2-ERG fusion-driven mouse model of tumorigenesis. In addition, the association of the protective effects of NSAIDs (aspirin 1400 ppm and naproxen 400 ppm) with the modulation of these specific molecular pathways was determined. A sandwich Elisa based membrane array-proteome profiler identifying 111 distinct signaling molecules was employed. Overall, the plasma and prostate tissue sample analyses identified 54 significant and differentially expressed cytokines, chemokines, and growth factors/growth signaling-associated molecules between PCa afflicted mice (TMPRSS2-ERG. Ptenflox/flox, age-matched noncancerous controls, NSAIDs-supplemented and no-drug controls). Bioinformatic analysis of the array outcomes indicated that the protective effect of NSAIDs was associated with reduced expression of (a) tumor promoting inflammatory molecules (M-CSF, IL-33, CCL22, CCL12, CX3CL1, CHI3L1, and CD93), (b) growth factors- growth signaling-associated molecules (Chemerin, FGF acidic, Flt-3 ligand, IGFBP-5, and PEDF), and (c) tumor microenvironment/stromal remodeling proteins MMP2 and MMP9. Overall, our findings corroborate the pathological findings that protective effects of NSAIDs in TMPSS2-ERG fusion-driven prostate tumorigenesis are associated with antiproliferative and anti-inflammatory effects and possible modulation of the immune cell enriched microenvironment.

Evidence that the catalytic mechanism of heme a synthase involves the formation of a carbocation stabilized by a conserved glutamate.

In eukaryotes and many aerobic prokaryotes, the final step of aerobic respiration is catalyzed by an aa3-type cytochrome c oxidase, which requires a modified heme cofactor, heme a. The conversion of heme b, the prototypical cellular heme, to heme o and ultimately to heme a requires two modifications, the latter of which is conversion of a methyl group to an aldehyde, catalyzed by heme a synthase (HAS). The N- and C-terminal halves of HAS share homology, and each half contains a heme-binding site. Previous reports indicate that the C-terminal site is occupied by a heme b cofactor. The N-terminal site may function as the substrate (heme o) binding site, although this has not been confirmed experimentally. Here, we assess the role of conserved residues from the N- and C-terminal heme-binding sites in HAS from prokaryotic (Shewanella oneidensis) and eukaryotic (Saccharomyces cerevisiae) species - SoHAS/CtaA and ScHAS/Cox15, respectively. A glutamate within the N-terminal site is found to be critical for activity in both types of HAS, consistent with the hypothesis that a carbocation forms transiently during catalysis. In contrast, the residue occupying the analogous C-terminal position is dispensable for enzyme activity. In SoHAS, the C-terminal heme ligands are critical for stability, while in ScHAS, substitutions in either heme-binding site have little effect on global structure. In both species, in vivo accumulation of heme o requires the presence of an inactive HAS variant, highlighting a potential regulatory role for HAS in heme o biosynthesis.

Work-related experiences of prostate cancer survivors in Australia: a qualitative study.

BACKGROUND: Prostate cancer (PCa) is the most diagnosed cancer in Australian men, and the number of survivors is growing with advances in diagnosis and treatment. Work participation following PCa diagnosis and treatment becomes a significant aspect of quality of life and survivorship. Using a qualitative phenomenological approach, we explored the work-related experiences of PCa survivors in Australia. METHODS: Semi-structured telephone interviews were conducted with 16 men (6 salaried employees, 10 self-employed; 8 diagnosed ≥ 5 years) purposively sampled from a community setting. Interviews were inductively analysed. RESULTS: Five main themes emerged: motivations to work; treatment decisions and work; the effects of PCa and its treatment on ability to participate in work; being an employee versus being self-employed; and personal agency. PCa and its treatment side-effects were detrimental to men's work capacity and ability, and could persist over an extended period. Most men expressed a strong desire to retain work or return to work. Discussions with healthcare professionals about work-related consequences were largely missing when treatment decisions were made. Self-employed men faced greater challenges than their salaried counterparts due to high financial burden and limited social and business support. Family, workplace and wider community support, and self-care, enhanced men's work participation experiences. CONCLUSIONS: PCa and its treatment substantially and persistently impacted men's working lives, and their experiences were diverse and multifaceted. Self-employed and long-term PCa survivors face greater challenges and are at high risk of poor work outcomes. A systematic approach and involvement of stakeholders at all levels is required to support ongoing work participation.

Characterization of stage-specific tumor progression in TMPRSS2-ERG (fusion)-driven and non-fusion-driven prostate cancer in GEM models.

In the present study, we performed a comparative stage-specific pathological and molecular marker evaluation of TMPRSS2-ERG fusion and PTEN loss-driven (TMPRSS2-ERG. Ptenflox/flox ) versus non-fusion-driven prostate tumorigenesis (Hi-Myc) in mice. Anterior, ventral, and dorsolateral prostates were collected from mice at different ages (or time points post-Cre induction). Results indicated that growth and progression of prostatic intraepithelial lesions to adenocarcinoma stages occurred in both mice models albeit at different rates. In the TMPRSS2-ERG. Ptenflox/flox mice, the initiation of tumorigenesis was slow, but subsequent progression through different stages became increasingly faster. Adenocarcinoma stage was reached early on; however, no high-grade undifferentiated tumors were observed. Conversely, in the Hi-Myc+/- mice, tumorigenesis initiation was rapid; however, progression through different stages was relatively slower and it took a while to reach the more aggressive phenotype stage. Nevertheless, at the advanced stages in the Hi-Myc+/- mice, high-grade undifferentiated tumors were observed compared to the later stage tumors observed in the fusion-driven TMPRSS2-ERG. Ptenflox/flox mice. These results were corroborated by the stage specific-pattern in the molecular expression of proliferation markers (PCNA and c-Myc); androgen receptor (AR); fusion-resultant overexpression of ERG; Prostein (SLC45-A3); and angiogenesis marker (CD-31). Importantly, there was a significant increase in immune cell infiltrations, which increased with the stage of tumorigenesis, in the TMPRSS2-ERG fusion-positive tumors relative to fusion negative tumors. Together, these findings are both novel and highly significant in establishing a working preclinical model for evaluating the efficacy of interventions during different stages of tumorigenesis in TMPRSS2-ERG fusion-driven PCa.

A revised model of TRAIL-R2 DISC assembly explains how FLIP(L) can inhibit or promote apoptosis.

The long FLIP splice form FLIP(L) can act as both an inhibitor and promoter of caspase-8 at death-inducing signalling complexes (DISCs) formed by death receptors such as TRAIL-R2 and related intracellular complexes such as the ripoptosome. Herein, we describe a revised DISC assembly model that explains how FLIP(L) can have these opposite effects by defining the stoichiometry (with respect to caspase-8) at which it converts from being anti- to pro-apoptotic at the DISC. We also show that in the complete absence of FLIP(L), procaspase-8 activation at the TRAIL-R2 DISC has significantly slower kinetics, although ultimately the extent of apoptosis is significantly greater. This revised model of DISC assembly also explains why FLIP's recruitment to the TRAIL-R2 DISC is impaired in the absence of caspase-8 despite showing that it can interact with the DISC adaptor protein FADD and why the short FLIP splice form FLIP(S) is the more potent inhibitor of DISC-mediated apoptosis.

Exploring the role of general practitioners in addressing financial toxicity in cancer patients.

PURPOSE: Financial toxicity (FT) describes financial distress or hardship as an outcome of cancer and its treatment. Minimising the impact of FT requires early assessment and intervention. General practice plays a significant role in the support of a person with cancer and may have an important role in the management of FT. The purpose of this study was to understand perspectives of general practitioners (GP) on addressing FT in the primary care setting, which may then help inform strategies to further support collaborative efforts to address FT. METHODS: A qualitative interpretive approach was utilised for this study. GPs were recruited through a GP conference and other professional networks using purposive, snowballing sampling techniques. Data collection continued until sufficient rich data had been obtained. Interviews were recorded and transcribed verbatim. The data were analysed using inductive analysis techniques. RESULTS: Twenty (n = 20) GPs participated in semi-structured in-depth telephone interviews. GPs identified that their role positions them well to provide some FT support, but there are limitations. Perceptions and philosophies about cancer management were drivers of referrals and financial conversations. Priorities for care of FT by GPs included improved cost information provision and accessible support. CONCLUSION: GPs can play an important role in helping to address FT associated with cancer and its treatments if supported with the right information.

Human proteins that interact with RNA/DNA hybrids.

RNA/DNA hybrids form when RNA hybridizes with its template DNA generating a three-stranded structure known as the R-loop. Knowledge of how they form and resolve, as well as their functional roles, is limited. Here, by pull-down assays followed by mass spectrometry, we identified 803 proteins that bind to RNA/DNA hybrids. Because these proteins were identified using in vitro assays, we confirmed that they bind to R-loops in vivo. They include proteins that are involved in a variety of functions, including most steps of RNA processing. The proteins are enriched for K homology (KH) and helicase domains. Among them, more than 300 proteins preferred binding to hybrids than double-stranded DNA. These proteins serve as starting points for mechanistic studies to elucidate what RNA/DNA hybrids regulate and how they are regulated.

Palliative care providers' use of digital health and perspectives on technological innovation: a national study.

BACKGROUND: While the need for digital health capability and technological innovation in palliative care services is growing rapidly, relatively little is known about the current uptake and views of individual palliative care practitioners. This study aims to explore palliative care practitioners' current use of and perspectives on digital health innovation in palliative care. METHODS: A descriptive cross-sectional survey with a web-based questionnaire was used. Participants were multidisciplinary palliative care practitioners in Australia. RESULTS: Surveys were returned by 170 medical, nursing, and allied health practitioners working in palliative care. Most respondents reported using a variety of digital health technology associated with clinical information systems, mobile devices, SMS text messaging, teleconferencing, and Wi-Fi. These technologies were used for the purpose of communicating with other health professionals, accessing web-based or mobile health palliative care resources, collecting or managing patient data, and providing information or education. However, few reported electronic access to patients' advance care planning documentation or could update these data. Respondents were moderately confident in their ability to use digital health, held positive beliefs that palliative care could be enhanced through digital health, and were generally supportive of ongoing innovation through digitally-enable models of care. Palliative care providers would most like to see digital health innovations in the areas of client health records, telehealth, and personal health tracking. CONCLUSION: This is the first national study of digital health in Australian palliative care providers. It contributes new knowledge in this important area of palliative care practice to guide policy and education, whilst informing future directions for research.

The AAA ATPase Afg1 preserves mitochondrial fidelity and cellular health by maintaining mitochondrial matrix proteostasis.

Mitochondrial functions are critical for cellular physiology; therefore, several conserved mechanisms are in place to maintain the functional integrity of mitochondria. However, many of the molecular details and components involved in ensuring mitochondrial fidelity remain obscure. Here, we identify a novel role for the conserved mitochondrial AAA ATPase Afg1 in mediating mitochondrial protein homeostasis during aging and in response to various cellular challenges. Saccharomyces cerevisiae cells lacking functional Afg1 are hypersensitive to oxidative insults, unable to tolerate protein misfolding in the matrix compartment and exhibit progressive mitochondrial failure as they age. Loss of the Afg1 ortholog LACE-1 in Caenorhabditis elegans is associated with reduced lifespan, impeded oxidative stress tolerance, impaired mitochondrial proteostasis in the motor neuron circuitry and altered behavioral plasticity. Our results indicate that Afg1 is a novel protein quality control factor, which plays an important evolutionarily conserved role in mitochondrial surveillance, and cellular and organismal health.

Palliative care in the context of immune and targeted therapies: A qualitative study of bereaved carers' experiences in metastatic melanoma.

BACKGROUND: Immune and targeted therapies continue to transform treatment outcomes for those with metastatic melanoma. However, the role of palliative care within this treatment paradigm is not well understood. AIM: To explore bereaved carers' experiences of immune and targeted therapy treatment options towards end of life for patients with metastatic melanoma. DESIGN: An interpretive, qualitative study using a social constructivist framework was utilised. Interviews were recorded, transcribed and analysed using grounded theory methods. SETTING/PARTICIPANTS: Participants (n = 20) were bereaved carers of patients who had received some form of immune and/or targeted therapy at one of three Australian metropolitan melanoma treatment centres. RESULTS: Carers struggled to reconcile the positive discourse around the success of immune and targeted therapies in achieving long-term disease control, and the underlying uncertainty in predicting individual responses to therapy. Expectations that immune and targeted therapies necessarily provide longer-term survival were evident. Difficulty in prognostication due to clinical uncertainty and a desire to maintain hope resulted in lack of preparedness for treatment failure and end of life. CONCLUSION: Immune and targeted therapies have resulted in increased prognostic challenges. There is a need to engage, educate and support patients and carers to prepare and plan amid these challenges. Educational initiatives must focus on improving communication between patients, carers and clinicians; the differences between palliative and end-of-life care; and increased competency of clinicians in having goals-of-care discussions. Clinicians must recognise and communicate the benefit of collaborative palliative care to meet patient and family needs holistically and comprehensively.

Factors influencing variation in investigations after a negative CT brain scan in suspected subarachnoid haemorrhage: a qualitative study.

INTRODUCTION: Variation in the approach to the patient with a possible subarachnoid haemorrhage (SAH) has been previously documented. The purpose of this study was to identify factors that influence emergency physicians' decisions about diagnostic testing after a normal CT brain scan for ED patients with a headache suspicious of a SAH. METHODS: We conducted an interview-based qualitative study informed by social constructionist theory. Fifteen emergency physicians from six EDs across Queensland, Australia, underwent individual face-to-face or telephone interviews. Content analysis was performed whereby transcripts were examined and coded independently by two co-investigators, who then jointly agreed on the influencing factors. RESULTS: Six categories of influencing factors were identified. Patient interaction was at the forefront of the identified factors. This shared decision-making process incorporated 'what the patient wants' but may be biased by how the clinician communicates the benefits and harms of the diagnostic options to the patient. Patient risk profile, practice evidence and guidelines were also important. Other influencing factors included experiential factors of the clinician, consultation with colleagues and external influences where practice location and work processes impose constraints on test ordering external to the preferences of the clinician or patient. The six categories were organised within a conceptual framework comprising four components: the context, the evidence, the experience and the decision. CONCLUSIONS: When clinicians are faced with a diagnostic challenge, such as the workup of a patient with suspected SAH, there are a number of influencing factors that can result in a variation in approach. These need to be considered in approaches to improve the appropriateness and consistency of medical care.

The Assembly Factor Pet117 Couples Heme a Synthase Activity to Cytochrome Oxidase Assembly.

Heme a is an essential metalloporphyrin cofactor of the mitochondrial respiratory enzyme cytochrome c oxidase (CcO). Its synthesis from heme b requires several enzymes, including the evolutionarily conserved heme a synthase (Cox15). Oligomerization of Cox15 appears to be important for the process of heme a biosynthesis and transfer to maturing CcO. However, the details of this process remain elusive, and the roles of any additional CcO assembly factors that may be involved remain unclear. Here we report the systematic analysis of one such uncharacterized assembly factor, Pet117, and demonstrate in Saccharomyces cerevisiae that this evolutionarily conserved protein is necessary for Cox15 oligomerization and function. Pet117 is shown to reside in the mitochondrial matrix, where it is associated with the inner membrane. Pet117 functions at the later maturation stages of the core CcO subunit Cox1 that precede Cox1 hemylation. Pet117 also physically interacts with Cox15 and specifically mediates the stability of Cox15 oligomeric complexes. This Cox15-Pet117 interaction observed by co-immunoprecipitation persists in the absence of heme a synthase activity, is dependent upon Cox1 synthesis and early maturation steps, and is further dependent upon the presence of the matrix-exposed, unstructured linker region of Cox15 needed for Cox15 oligomerization, suggesting that this region mediates the interaction or that the interaction is lost when Cox15 is unable to oligomerize. Based on these findings, it was concluded that Pet117 mediates coupling of heme a synthesis to the CcO assembly process in eukaryotes.

Analysis of Oligomerization Properties of Heme a Synthase Provides Insights into Its Function in Eukaryotes.

Heme a is an essential cofactor for function of cytochrome c oxidase in the mitochondrial electron transport chain. Several evolutionarily conserved enzymes have been implicated in the biosynthesis of heme a, including the heme a synthase Cox15. However, the structure of Cox15 is unknown, its enzymatic mechanism and the role of active site residues remain debated, and recent discoveries suggest additional chaperone-like roles for this enzyme. Here, we investigated Cox15 in the model eukaryote Saccharomyces cerevisiae via several approaches to examine its oligomeric states and determine the effects of active site and human pathogenic mutations. Our results indicate that Cox15 exhibits homotypic interactions, forming highly stable complexes dependent upon hydrophobic interactions. This multimerization is evolutionarily conserved and independent of heme levels and heme a synthase catalytic activity. Four conserved histidine residues are demonstrated to be critical for eukaryotic heme a synthase activity and cannot be substituted with other heme-ligating amino acids. The 20-residue linker region connecting the two conserved domains of Cox15 is also important; removal of this linker impairs both Cox15 multimerization and enzymatic activity. Mutations of COX15 causing single amino acid conversions associated with fatal infantile hypertrophic cardiomyopathy and the neurological disorder Leigh syndrome result in impaired stability (S344P) or catalytic function (R217W), and the latter mutation affects oligomeric properties of the enzyme. Structural modeling of Cox15 suggests these two mutations affect protein folding and heme binding, respectively. We conclude that Cox15 multimerization is important for heme a biosynthesis and/or transfer to maturing cytochrome c oxidase.

Small Molecule Inhibition of the Ubiquitin-specific Protease USP2 Accelerates cyclin D1 Degradation and Leads to Cell Cycle Arrest in Colorectal Cancer and Mantle Cell Lymphoma Models.

Deubiquitinases are important components of the protein degradation regulatory network. We report the discovery of ML364, a small molecule inhibitor of the deubiquitinase USP2 and its use to interrogate the biology of USP2 and its putative substrate cyclin D1. ML364 has an IC50 of 1.1 µm in a biochemical assay using an internally quenched fluorescent di-ubiquitin substrate. Direct binding of ML364 to USP2 was demonstrated using microscale thermophoresis. ML364 induced an increase in cellular cyclin D1 degradation and caused cell cycle arrest as shown in Western blottings and flow cytometry assays utilizing both Mino and HCT116 cancer cell lines. ML364, and not the inactive analog 2, was antiproliferative in cancer cell lines. Consistent with the role of cyclin D1 in DNA damage response, ML364 also caused a decrease in homologous recombination-mediated DNA repair. These effects by a small molecule inhibitor support a key role for USP2 as a regulator of cell cycle, DNA repair, and tumor cell growth.

The eukaryotic enzyme Bds1 is an alkyl but not an aryl sulfohydrolase.

The eukaryotic enzyme Bds1 in Saccharomyces cerevisiae is a metallo-ß-lactamase-related enzyme evolutionarily originating from bacterial horizontal gene transfer that serves an unknown biological role. Previously, Bds1 was reported to be an alkyl and aryl sulfatase. However, we demonstrate here that Bds1 acts on primary alkyl sulfates (of 6-12 carbon atoms) but not the aryl sulfates p-nitrophenyl sulfate and p-nitrocatechol sulfate. The apparent catalytic rate constant for hydrolysis of the substrate 1-hexyl sulfate by Bds1 is over 100 times lower than that of the reaction catalyzed by its bacterial homolog SdsA1. We show that Bds1 shares a catalytic mechanism with SdsA1 in which the carbon atom of the sulfate ester is the subject of nucleophilic attack, rather than the sulfur atom, resulting in C-O bond lysis. In contrast to SdsA1 and another bacterial homolog with selectivity for secondary alkyl sulfates named Pisa1, Bds1 does not show any substantial activity towards secondary alkyl sulfates. Neither Bds1 nor SdsA1 have any significant activity towards a branched primary alkyl sulfate, primary and secondary steroid sulfates, or phosphate diesters. Therefore, the enzymes homologous to SdsA1 that have been identified and characterized thus far vary in their selectivity towards primary and secondary alkyl sulfates but do not exhibit aryl sulfatase activity.

ATAD5 deficiency decreases B cell division and Igh recombination.

Mammalian ATPase family AAA domain-containing protein 5 (ATAD5) and its yeast homolog enhanced level of genomic instability 1 are responsible for unloading proliferating cell nuclear antigen from newly synthesized DNA. Prior work in HeLa and yeast cells showed that a decrease in ATAD5 protein levels resulted in accumulation of chromatin-bound proliferating cell nuclear antigen, slowed cell division, and increased genomic instability. In this study, B cells from heterozygous (Atad5(+/m)) mice were used to examine the effects of decreased cell proliferation on Ab diversity. ATAD5 haploinsufficiency did not change the frequency or spectrum of somatic hypermutation in Ab genes, indicating that DNA repair and error-prone DNA polymerase η usage were unaffected. However, immunized Atad5(+/m) mice had decreased serum IgG1 Abs, demonstrating a functional effect on class switch recombination. The mechanism of this altered immune response was then examined following ex vivo stimulation of splenic B cells, where Atad5(+/m) cells accumulated in the S phase of the cell cycle and had reduced proliferation compared with wild-type cells. These haploinsufficient cells underwent a significant decline in activation-induced deaminase expression, resulting in decreased switch region DNA double-strand breaks and interchromosomal translocations in the Igh locus. Class switch recombination to several isotypes was also reduced in Atad5(+/m) cells, although the types of end-joining pathways were not affected. These results describe a defect in DNA replication that affects Igh recombination via reduced cell division.

The positioning of palliative care in acute care: A multiperspective qualitative study in the context of metastatic melanoma.

OBJECTIVE: The positioning and meaning of palliative care within the healthcare system lacks clarity which adds a level of complexity to the process of transition to palliative care. This study explores the transition to the palliative care process in the acute care context of metastatic melanoma. METHOD: A theoretical framework drawing on interpretive and critical traditions informs this research. The pragmatism of symbolic interactionism and the critical theory of Habermas brought a broad orientation to the research. Integration of the theoretical framework and grounded-theory methods facilitated data generation and analysis of 29 interviews with patients, family carers, and healthcare professionals. RESULTS: The key analytical findings depict a scope of palliative care that was uncertain for users of the system and for those working within the system. Becoming "palliative" is not a defined event; nor is there unanimity around referral to a palliative care service. As such, ambiguity and tension contribute to the difficulties involved in negotiating the transition to palliative care. SIGNIFICANCE OF RESULTS: Our findings point to uncertainty around the scopes of practice in the transition to palliative care. The challenge in the transition process lies in achieving greater coherency of care within an increasingly specialized healthcare system. The findings may not only inform those within a metastatic melanoma context but may contribute more broadly to palliative practices within the acute care setting.

Modulation of the respiratory supercomplexes in yeast: enhanced formation of cytochrome oxidase increases the stability and abundance of respiratory supercomplexes.

Yeast cells deficient in the Rieske iron-sulfur subunit (Rip1) of ubiquinol-cytochrome c reductase (bc1) accumulate a late core assembly intermediate, which weakly associates with cytochrome oxidase (CcO) in a respiratory supercomplex. Expression of the N-terminal half of Rip1, which lacks the C-terminal FeS-containing globular domain (designated N-Rip1), results in a marked stabilization of trimeric and tetrameric bc1-CcO supercomplexes. Another bc1 mutant (qcr9Δ) stalled at the same assembly intermediate is likewise converted to stable supercomplex species by the expression of N-Rip1, but not by expression of intact Rip1. The N-Rip1-induced stabilization of bc1-CcO supercomplexes is independent of the Bcs1 translocase, which mediates Rip1 translocation during bc1 biogenesis. N-Rip1 induces the stabilization of bc1-CcO supercomplexes through an enhanced formation of CcO. The association of N-Rip1 with the late core bc1 assembly intermediate appears to confer stabilization of a CcO assembly intermediate. This induced stabilization of CcO is dependent on the Rcf1 supercomplex stabilization factor and only partially dependent on the presence of cardiolipin. N-Rip1 exerts a related induction of CcO stabilization in WT yeast, resulting in enhanced respiration. Additionally, the impact of CcO stabilization on supercomplexes was observed by means other than expression of N-Rip1 (via overexpression of CcO subunits Cox4 and Cox5a), demonstrating that this is a general phenomenon. This study presents the first evidence showing that supercomplexes can be stabilized by the stimulated formation of CcO.

Complex formation between S100B protein and the p90 ribosomal S6 kinase (RSK) in malignant melanoma is calcium-dependent and inhibits extracellular signal-regulated kinase (ERK)-mediated phosphorylation of RSK.

S100B is a prognostic marker for malignant melanoma. Increasing S100B levels are predictive of advancing disease stage, increased recurrence, and low overall survival in malignant melanoma patients. Using S100B overexpression and shRNA(S100B) knockdown studies in melanoma cell lines, elevated S100B was found to enhance cell viability and modulate MAPK signaling by binding directly to the p90 ribosomal S6 kinase (RSK). S100B-RSK complex formation was shown to be Ca(2+)-dependent and to block ERK-dependent phosphorylation of RSK, at Thr-573, in its C-terminal kinase domain. Additionally, the overexpression of S100B sequesters RSK into the cytosol and prevents it from acting on nuclear targets. Thus, elevated S100B contributes to abnormal ERK/RSK signaling and increased cell survival in malignant melanoma.