The calcium-dependent interaction between S100B and the mitochondrial AAA ATPase ATAD3A and the role of this complex in the cytoplasmic processing of ATAD3A

ATAD3 is a limiting factor in mitochondrial biogenesis and adipogenesis of white adipocyte-like 3T3-L1 cells

ATAD3 is a vital ATPase of the inner mitochondrial membrane of pluri-cellular eukaryotes, with largely unknown functions but early required for organism development as necessary for mitochondrial biogenesis. ATAD3 knock-down in C. elegans inhibits at first the development of adipocyte-like intestinal tissue so we used mouse adipocyte model 3T3-L1 cells to analyze ATAD3 functions during adipogenesis and lipogenesis in a mammalian model. ATAD3 function was studied by stable and transient modulation of ATAD3 expression in adipogenesis- induced 3T3-L1 cells using Knock-Down and overexpression strategies, exploring different steps of adipocyte differentiation and lipogenesis. We show that (i) an increase in ATAD3 is preceding differentiation-induced mitochondrial biogenesis; (ii) downregulation of ATAD3 inhibits adipogenesis, lipogenesis, and impedes overexpression of many mitochondrial proteins; (iii) ATAD3 re-expression rescues the phenotype of ATAD3 KD, and (iv) differentiation and lipogenesis are accelerated by ATAD3 overexpression, but inhibited by expression of a dominant-negative mutant. We further show that the ATAD3 KD phenotype is not due to altered insulin signal but involves a limitation of mitochondrial biogenesis linked to Drp1. These results demonstrate that ATAD3 is limiting for in vitro mitochondrial biogenesis and adipogenesis/lipogenesis and therefore that ATAD3 mutation/over- or under-expression could be involved in adipogenic and lipogenic pathologies.

Advancements in unravelling the fundamental function of the ATAD3 protein in multicellular organisms

ATPase family AAA domain containing protein 3, commonly known as ATAD3 is a versatile mitochondrial protein that is involved in a large number of pathways. ATAD3 is a transmembrane protein that spans both the inner mitochondrial membrane and outer mitochondrial membrane. It, therefore, functions as a connecting link between the mitochondrial lumen and endoplasmic reticulum facilitating their cross-talk. ATAD3 contains an N-terminal domain which is amphipathic in nature and is inserted into the membranous space of the mitochondria, while the C-terminal domain is present towards the lumen of the mitochondria and contains the ATPase domain. ATAD3 is known to be involved in mitochondrial biogenesis, cholesterol transport, hormone synthesis, apoptosis and several other pathways. It has also been implicated to be involved in cancer and many neurological disorders making it an interesting target for extensive studies. This review aims to provide an updated comprehensive account of the role of ATAD3 in the mitochondria especially in lipid transport, mitochondrial-endoplasmic reticulum interactions, cancer and inhibition of mitophagy.

Knockdown of hCINAP sensitizes colorectal cancer cells to ionizing radiation

Colorectal cancer (CRC) poses a significant challenge in terms of treatment due to the prevalence of radiotherapy resistance. However, the underlying mechanisms responsible for radio-resistance in CRC have not been thoroughly explored. This study aimed to shed light on the role of human coilin interacting nuclear ATPase protein (hCINAP) in radiation-resistant HT-29 and SW480 CRC cells (HT-29-IR and SW480-IR) and investigate its potential implications. Firstly, radiation-resistant CRC cell lines were established by subjecting HT-29 and SW480 cells to sequential radiation exposure. Subsequent analysis revealed a notable increase in hCINAP expression in radiation-resistant CRC cells. To elucidate the functional role of hCINAP in radio-resistance, knockdown experiments were conducted. Remarkably, knockdown of hCINAP resulted in an elevation of reactive oxygen species (ROS) generation upon radiation treatment and subsequent activation of apoptosis mediated by mitochondria. These observations indicate that hCINAP depletion enhances the radiosensitivity of CRC cells. Conversely, when hCINAP was overexpressed, it was found to enhance the radio-resistance of CRC cells. This suggests that elevated hCINAP expression contributes to the development of radio-resistance. Further investigation revealed an interaction between hCINAP and ATPase family AAA domain containing 3A (ATAD3A). Importantly, ATAD3A was identified as an essential factor in hCINAP-mediated radio-resistance. These findings establish the involvement of hCINAP and its interaction with ATAD3A in the regulation of radio-resistance in CRC cells. Overall, the results of this study demonstrate that upregulating hCINAP expression may improve the survival of radiation-exposed CRC cells. Understanding the intricate molecular mechanisms underlying hCINAP function holds promise for potential strategies in targeted radiation therapy for CRC. These findings emphasize the importance of further research to gain a comprehensive understanding of hCINAP's precise molecular mechanisms and explore its potential as a therapeutic target in overcoming radio-resistance in CRC. By unraveling the complexities of hCINAP and its interactions, novel therapeutic approaches may be developed to enhance the efficacy of radiation therapy and improve outcomes for CRC patients.

The value of ATAD3A as a potential biomarker for bladder cancer

BACKGROUND

Bladder cancer (BCa) is a highly malignant tumor, and if left untreated, it can develop severe hematuria and tumor metastasis, thereby endangering the patient's life. The purpose of this paper was to detect the expression of ATAD3A in BCa and research the relationship between ATAD3A and pathological features of bladder cancer and the prognosis of patients.

METHODS

First, the expression of ATAD3A in BCa and normal bladder tissues was analyzed based on the UALCAN and Oncomine public databases. Second, 491 cases of surgically resected bladder cancer specimens and 110 cases of normal adjacent tissues were immunohistochemically stained. The expression of ATAD3A was quantified, and the value and prognosis of ATAD3A as a biomarker of BCa were evaluated.

RESULTS

The expression of ATAD3A in bladder cancer tissues was higher than that in normal bladder mucosa. High expression of ATAD3A was correlated with patient age, tumor size, number of tumors, distant metastasis, lymph node metastasis, lymphovascular invasion, and TNM stage (p < 0.05). Overexpression of ATAD3A is closely related to cancer patient survival. The mean survival time of bladder cancer patients with high ATAD3A expression was shorter than those with low ATAD3A levels. According to the relative comparing result, the high ATAD3A expression herald reduced overall survival in BCa patients.

CONCLUSIONS

The abnormal overexpression of ATAD3A may be related to the initiation and progress of bladder cancer. The upregulation of ATAD3A can be used as an effective indicator to diagnose bladder cancer and predict tumor progression. Furthermore, the combination of information from public databases and the results of clinical sample analysis can help us better understand the mechanism of action of molecular oncogenes in bladder cancer.

Molecular Pathways Implicated in Radioresistance of Glioblastoma Multiforme: What Is the Role of Extracellular Vesicles?

Glioblastoma multiforme (GBM) is a primary brain tumor that is very aggressive, resistant to treatment, and characterized by a high degree of anaplasia and proliferation. Routine treatment includes ablative surgery, chemotherapy, and radiotherapy. However, GMB rapidly relapses and develops radioresistance. Here, we briefly review the mechanisms underpinning radioresistance and discuss research to stop it and install anti-tumor defenses. Factors that participate in radioresistance are varied and include stem cells, tumor heterogeneity, tumor microenvironment, hypoxia, metabolic reprogramming, the chaperone system, non-coding RNAs, DNA repair, and extracellular vesicles (EVs). We direct our attention toward EVs because they are emerging as promising candidates as diagnostic and prognostication tools and as the basis for developing nanodevices for delivering anti-cancer agents directly into the tumor mass. EVs are relatively easy to obtain and manipulate to endow them with the desired anti-cancer properties and to administer them using minimally invasive procedures. Thus, isolating EVs from a GBM patient, supplying them with the necessary anti-cancer agent and the capability of recognizing a specified tissue-cell target, and reinjecting them into the original donor appears, at this time, as a reachable objective of personalized medicine.

Targeting ATAD3A-PINK1-mitophagy axis overcomes chemoimmunotherapy resistance by redirecting PD-L1 to mitochondria

Only a small proportion of patients with triple-negative breast cancer benefit from immune checkpoint inhibitor (ICI) targeting PD-1/PD-L1 signaling in combination with chemotherapy. Here, we discovered that therapeutic response to ICI plus paclitaxel was associated with subcellular redistribution of PD-L1. In our immunotherapy cohort of ICI in combination with nab-paclitaxel, tumor samples from responders showed significant distribution of PD-L1 at mitochondria, while non-responders showed increased accumulation of PD-L1 on tumor cell membrane instead of mitochondria. Our results also revealed that the distribution pattern of PD-L1 was regulated by an ATAD3A-PINK1 axis. Mechanistically, PINK1 recruited PD-L1 to mitochondria for degradation via a mitophagy pathway. Importantly, paclitaxel increased ATAD3A expression to disrupt proteostasis of PD-L1 by restraining PINK1-dependent mitophagy. Clinically, patients with tumors exhibiting high expression of ATAD3A detected before the treatment with ICI in combination with paclitaxel had markedly shorter progression-free survival compared with those with ATAD3A-low tumors. Preclinical results further demonstrated that targeting ATAD3A reset a favorable antitumor immune microenvironment and increased the efficacy of combination therapy of ICI plus paclitaxel. In summary, our results indicate that ATAD3A serves not only as a resistant factor for the combination therapy of ICI plus paclitaxel through preventing PD-L1 mitochondrial distribution, but also as a promising target for increasing the therapeutic responses to chemoimmunotherapy.

ATAD3A mediates activation of RAS-independent mitochondrial ERK1/2 signaling, favoring head and neck cancer development

BACKGROUND

Targeting mitochondrial oncoproteins presents a new concept in the development of effective cancer therapeutics. ATAD3A is a nuclear-encoded mitochondrial enzyme contributing to mitochondrial dynamics, cholesterol metabolism, and signal transduction. However, its impact and underlying regulatory mechanisms in cancers remain ill-defined.

METHODS

We used head and neck squamous cell carcinoma (HNSCC) as a research platform and achieved gene depletion by lentiviral shRNA and CRISPR/Cas9. Molecular alterations were examined by RNA-sequencing, phospho-kinase profiling, Western blotting, RT-qPCR, immunohistochemistry, and immunoprecipitation. Cancer cell growth was assessed by MTT, colony formation, soft agar, and 3D cultures. The therapeutic efficacy in tumor development was evaluated in orthotopic tongue tumor NSG mice.

RESULTS

ATAD3A is highly expressed in HNSCC tissues and cell lines. Loss of ATAD3A expression suppresses HNSCC cell growth and elicits tumor regression in orthotopic tumor-bearing mice, whereas gain of ATAD3A expression produces the opposite effects. From a mechanistic perspective, the tumor suppression induced by the overexpression of the Walker A dead mutant of ATAD3A (K358) produces a potent dominant-negative effect due to defective ATP-binding. Moreover, ATAD3A binds to ERK1/2 in the mitochondria of HNSCC cells in the presence of VDAC1, and this interaction is essential for the activation of mitochondrial ERK1/2 signaling. Most importantly, the ATAD3A-ERK1/2 signaling axis drives HNSCC development in a RAS-independent fashion and, thus, tumor suppression is more effectively achieved when ATAD3A knockout is combined with RAS inhibitor treatment.

CONCLUSIONS

These findings highlight the novel function of ATAD3A in regulating mitochondrial ERK1/2 activation that favors HNSCC development. Combined targeting of ATAD3A and RAS signaling may potentiate anticancer activity for HNSCC therapeutics.

Systematic review and cumulative meta-analysis of the diagnostic accuracy of glial fibrillary acidic protein vs. S100 calcium binding protein B as blood biomarkers in observational studies of patients with mild or moderate acute traumatic brain injury

Traumatic brain injuries (TBIs) and sports-related concussions (SRCs) are the leading causes of hospitalization and death in subjects <45 years old in the USA and Europe. Some biomarkers (BMs) have been used to reduce unnecessary cranial computed tomography (CCT). In recent years, the astroglial S100 calcium-binding B protein (S100B) has prevented approximately 30% of unnecessary CCTs. Glial fibrillary acidic protein (GFAP) has also been studied in direct comparison with S100B. The aim of our cumulative meta-analysis (cMA) is to compare - in the context of hospital emergency departments or SRC conditions - the differences in diagnostic accuracy (DA), sensitivity (Se) and specificity (Sp) of GFAP and S100B. The main cMA inclusion criterion was the assessment of both BMs in the included subjects since 2010, with blood samples drawn 1-30 h from the suspected TBI or SRC. The risk-of-bias (RoB) score was determined, and both the publication bias (with the Begg, Egger and Duval trim-and-fill tests) and sensitivity (with the box-and-whiskers plot) were analyzed for outliers. Seven studies with 899 subjects and nine observations (samples) were included. The diagnostic odds ratios (dORs) with their prediction intervals (PIs), Se and Sp (analyzed with a hierarchical model to respect the binomial data structure) were assessed, and a random-effects MA and a cMA of the difference in the BMs dOR natural logarithms (logOR(G-S)) between the BMs were performed. The cMA of dOR(G-S) was significant (5.78 (CI 2-16.6)) probably preventing approximately 50% of unnecessary CCTs. Further work is needed to standardize and harmonize GFAP laboratory methods.

Emerging Links between Control of Mitochondrial Protein ATAD3A and Cancer

Spanning from the mitochondria's outer surface to the inner membrane, the nuclear-encoded protein ATAD3A maintains vital roles in regulating mitochondrial dynamics, homeostasis, metabolism, and interactions with the endoplasmic reticulum. Recently, elevated levels of ATAD3A have been reported in several types of cancer and to be tightly correlated with cancer development and progression, including increased cancer cell potential of proliferation, metastasis, and resistance to chemotherapy and radiotherapy. In the current review, we reveal ATAD3A as the link between mitochondrial functions and cancer biology and the accumulating evidence presenting ATAD3A as an attractive target for the development of novel cancer therapy to inhibit aberrant cancer metabolism and progression.

The S100B Protein and Partners in Adipocyte Response to Cold Stress and Adaptive Thermogenesis: Facts, Hypotheses, and Perspectives

In mammals, adipose tissue is an active secretory tissue that responds to mild hypothermia and as such is a genuine model to study molecular and cellular adaptive responses to cold-stress. A recent study identified a mammal-specific protein of the endoplasmic reticulum that is strongly induced in the inguinal subcutaneous white adipocyte upon exposure to cold, calsyntenin 3β (CLSTN3β). CLSTN3β regulates sympathetic innervation of thermogenic adipocytes and contributes to adaptive non-shivering thermogenesis. The calcium- and zinc-binding S100B is a downstream effector in the CLSTN3β pathways. We review, here, the literature on the transcriptional regulation of the S100b gene in adipocyte cells. We also rationalize the interactions of the S100B protein with its recognized or hypothesized intracellular (p53, ATAD3A, CYP2E1, AHNAK) and extracellular (Receptor for Advanced Glycation End products (RAGE), RPTPσ) target proteins in the context of adipocyte differentiation and adaptive thermogenesis. We highlight a chaperon-associated function for the intracellular S100B and point to functional synergies between the different intracellular S100B target proteins. A model of non-classical S100B secretion involving AHNAK/S100A10/annexin2-dependent exocytosis by the mean of exosomes is also proposed. Implications for related areas of research are noted and suggestions for future research are offered.

The Zn2+ and Ca2+ -binding S100B and S100A1 proteins: beyond the myths

The S100 genes encode a conserved group of 21 vertebrate-specific EF-hand calcium-binding proteins. Since their discovery in 1965, S100 proteins have remained enigmatic in terms of their cellular functions. In this review, we summarize the calcium- and zinc-binding properties of the dimeric S100B and S100A1 proteins and highlight data that shed new light on the extracellular and intracellular regulation and functions of S100B. We point out that S100B and S100A1 homodimers are not functionally interchangeable and that in a S100A1/S100B heterodimer, S100A1 acts as a negative regulator for the ability of S100B to bind Zn²⁺ . The Ca²⁺ and Zn²⁺ -dependent interactions of S100B with a wide array of proteins form the basis of its activities and have led to the derivation of some initial rules for S100B recognition of protein targets. However, recent findings have strongly suggested that these rules need to be revisited. Here, we describe a new consensus S100B binding motif present in intracellular and extracellular vertebrate-specific proteins and propose a new model for stable interactions of S100B dimers with full-length target proteins. A chaperone-associated function for intracellular S100B in adaptive cellular stress responses is also discussed. This review may help guide future studies on the functions of S100 proteins in general.

Ketogenic diet attenuates cerebellar atrophy progression in a subject with a biallelic variant at the ATAD3A locus

The ATPase AAA-domain protein 3 (ATAD3) is a ubiquitously expressed mitochondrial protein involved in mitochondrial dynamics, DNA-nucleoid structural organization, cholesterol transport and steroidogenesis. Mutations within the ancestral ATAD3A gene are strongly associated with neurological abnormalities due to alterations in the mitochondrial function and homeostasis. Here, we report the case of a subject diagnosed with developmental delay associated with ataxia and progressive atrophy of both cerebellar hemispheres and cerebellar vermis, despite exhibiting a normal biochemical profile. By whole exome sequencing, we identified two biallelic single nucleotide variants within the coding region of ATAD3A in the affected subject. Both variants were previously reported as monoallelic variants with uncertain clinical significance. Importantly, the variant ATAD3A c.251T>C leads to an amino acid change of a highly conserved residue across species and in silico analysis revealed structural alteration in the ATAD3A protein. Ketogenic diet was administered to the subject as a novel therapeutic approach. Notably, the treatment correlated with a reduction in cerebellum atrophy progression and the gradual enhancement of the subject’s physical skills, vitality and personal interactions. Thus, we report the first subject with a homozygous status for the ATAD3A c.251T>C (p.Thr84Met) variant. We propose that this mutation led to an alteration of the mitochondrial function, causing the neurological symptoms observed in the subject. The symptoms were partially alleviated following ketogenic diet, improving the subject’s quality of life.

Glial Fibrillary Acidic Protein (GFAP) Outperforms S100 Calcium-Binding Protein B (S100B) and Ubiquitin C-Terminal Hydrolase L1 (UCH-L1) as Predictor for Positive Computed Tomography of the Head in Trauma Subjects

OBJECTIVE

Traumatic brain injuries (TBIs) are largely underdiagnosed and may have persistent refractory consequences. Current assessments for acute TBI are limited to physical examination and imaging. Biomarkers such as glial fibrillary acidic protein (GFAP), ubiquitin C-terminal hydrolase L1 (UCH-L1), and S100 calcium-binding protein B (S100B) have shown predictive value as indicators of TBI and potential screening tools.

METHODS

In total, 37 controls and 118 unique trauma subjects who received a clinically ordered head computed tomography (CT) in the emergency department of a level 1 trauma center were evaluated. Blood samples collected at 0-8 hours (initial) and 12-32 hours (delayed) postinjury were analyzed for GFAP, UCH-L1, and S100B concentrations. These were then compared in CT-negative and CT-positive subjects.

RESULTS

Median GFAP, UCH-L1, and S100B concentrations were greater in CT-positive subjects at both timepoints compared with CT-negative subjects. In addition, median UCH-L1 and S100B concentrations were lower at the delayed timepoint, whereas median GFAP concentrations were increased. As predictors of a positive CT of the head, GFAP outperformed UCH-L1 and S100B at both timepoints (initial: 0.89 sensitivity, 0.62 specificity; delayed: 0.94 sensitivity, 0.67 specificity). GFAP alone also outperformed all possible combinations of biomarkers.

CONCLUSIONS

GFAP, UCH-L1, and S100B demonstrated utility for rapid prediction of a CT-positive TBI within 0-8 hours of injury. GFAP exhibited the greatest predictive power at 12-32 hours. Furthermore, these results suggest that GFAP alone has greater utility for predicting a positive CT of the head than UCH-L1, S100B, or any combination of the 3.

De novo Blood Biomarkers in Autism: Autoantibodies against Neuronal and Glial Proteins

Autism spectrum disorders (ASDs) are the most common neurodevelopmental disorders with unidentified etiology. The behavioral manifestations of ASD may be a consequence of genetic and/or environmental pathology in neurodevelopmental processes. In this limited study, we assayed autoantibodies to a panel of vital neuronal and glial proteins in the sera of 40 subjects (10 children with ASD and their mothers along with 10 healthy controls, age-matched children and their mothers). Serum samples were screened using Western Blot analysis to measure immunoglobulin (IgG) reactivity against a panel of 9 neuronal proteins commonly associated with neuronal degeneration: neurofilament triplet proteins (NFP), tubulin, microtubule-associated proteins (tau), microtubule-associated protein-2 (MAP-2), myelin basic protein (MBP), myelin-associated glycoprotein (MAG), α-synuclein (SNCA) and astrocytes proteins such as glial fibrillary acidic protein (GFAP) and S100B protein. Our data show that the levels of circulating IgG class autoantibodies against the nine proteins were significantly elevated in ASD children. Mothers of ASD children exhibited increased levels of autoantibodies against all panel of tested proteins except for S100B and tubulin compared to age-matched healthy control children and their mothers. Control children and their mothers showed low and insignificant levels of autoantibodies to neuronal and glial proteins. These results strongly support the importance of anti-neuronal and glial protein autoantibodies biomarker in screening for ASD children and further confirm the importance of the involvement of the maternal immune system as an index that should be considered in fetal in utero environmental exposures. More studies are needed using larger cohort to verify these results and understand the importance of the presence of such autoantibodies in children with autism and their mothers, both as biomarkers and their role in the mechanism of action of autism and perhaps in its treatment.

Cellular and molecular mechanisms of sarcopenia: the S100B perspective

Primary sarcopenia is a condition of reduced skeletal muscle mass and strength, reduced agility, and increased fatigability and risk of bone fractures characteristic of aged, otherwise healthy people. The pathogenesis of primary sarcopenia is not completely understood. Herein, we review the essentials of the cellular and molecular mechanisms of skeletal mass maintenance; the alterations of myofiber metabolism and deranged properties of muscle satellite cells (the adult stem cells of skeletal muscles) that underpin the pathophysiology of primary sarcopenia; the role of the Ca²⁺ -sensor protein, S100B, as an intracellular factor and an extracellular signal regulating cell functions; and the functional role of S100B in muscle tissue. Lastly, building on recent results pointing to S100B as to a molecular determinant of myoblast-brown adipocyte transition, we propose S100B as a transducer of the deleterious effects of accumulation of reactive oxygen species in myoblasts and, potentially, myofibers concurring to the pathophysiology of sarcopenia.

ATAD3 proteins: brokers of a mitochondria-endoplasmic reticulum connection in mammalian cells

In yeast, a sequence of physical and genetic interactions termed the endoplasmic reticulum (ER)-mitochondria organizing network (ERMIONE) controls mitochondria-ER interactions and mitochondrial biogenesis. Several functions that characterize ERMIONE complexes are conserved in mammalian cells, suggesting that a similar tethering complex must exist in metazoans. Recent studies have identified a new family of nuclear-encoded ATPases associated with diverse cellular activities (AAA+-ATPase) mitochondrial membrane proteins specific to multicellular eukaryotes, called the ATPase family AAA domain-containing protein 3 (ATAD3) proteins (ATAD3A and ATAD3B). These proteins are crucial for normal mitochondrial-ER interactions and lie at the heart of processes underlying mitochondrial biogenesis. ATAD3A orthologues have been studied in flies, worms, and mammals, highlighting the widespread importance of this gene during embryonic development and in adulthood. ATAD3A is a downstream effector of target of rapamycin (TOR) signalling in Drosophila and exhibits typical features of proteins from the ERMIONE-like complex in metazoans. In humans, mutations in the ATAD3A gene represent a new link between altered mitochondrial-ER interaction and recognizable neurological syndromes. The primate-specific ATAD3B protein is a biomarker of pluripotent embryonic stem cells. Through negative regulation of ATAD3A function, ATAD3B supports mitochondrial stemness properties.

Baculovirus LEF-11 Hijack Host ATPase ATAD3A to Promote Virus Multiplication in Bombyx mori cells

Research on molecular mechanisms that viruses use to regulate the host apparatus is important in virus infection control and antiviral therapy exploration. Our previous research showed that the Bombyx mori nucleopolyhedrovirus (BmNPV) LEF-11 localized to dense regions of the cell nucleus and is required for viral DNA replication. Herein, we examined the mechanism of LEF-11 on BmNPV multiplication and demonstrated that baculovirus LEF-11 interacts with Bombyx mori ATAD3A and HSPD1 (HSP60) protein. Furthermore, we showed that LEF-11 has the ability to induce and up-regulate the expression of ATAD3A and HSPD1, phenomena that were both reversed upon knockdown of lef-11. Our findings showed that ATAD3A and HSPD1 were necessary and contributed to BmNPV multiplication in Bombyx mori cells. Moreover, ATAD3A was found to directly interact with HSPD1. Interestingly, ATAD3A was required for the expression of HSPD1, while the knockdown of HSPD1 had no obvious effect on the expression level of ATAD3A. Taken together, the data presented in the current study demonstrated that baculovirus LEF-11 hijacks the host ATPase family members, ATAD3A and HSPD1, efficiently promote the multiplication of the virus. This study furthers our understanding of how baculovirus modulates energy metabolism of the host and provides a new insight into the molecular mechanisms of antiviral research.

Time-dependent uptake and trafficking of vesicles capturing extracellular S100B in cultured rat astrocytes

Astrocytes, the most heterogeneous glial cells in the central nervous system, contribute to brain homeostasis, by regulating a myriad of functions, including the clearance of extracellular debris. When cells are damaged, cytoplasmic proteins may exit into the extracellular space. One such protein is S100B, which may exert toxic effects on neighboring cells unless it is removed from the extracellular space, but the mechanisms of this clearance are poorly understood. By using time-lapse confocal microscopy and fluorescently labeled S100B (S100B-Alexa⁴⁸⁸ ) and fluorescent dextran (Dextran⁵⁴⁶ ), a fluid phase uptake marker, we examined the uptake of fluorescently labeled S100B-Alexa⁴⁸⁸ from extracellular space and monitored trafficking of vesicles that internalized S100B-Alexa⁴⁸⁸ . Initially, S100B-Alexa⁴⁸⁸ and Dextran⁵⁴⁶ internalized with distinct rates into different endocytotic vesicles; S100B-Alexa⁴⁸⁸ internalized into smaller vesicles than Dextran⁵⁴⁶ . At a later stage, S100B-Alexa⁴⁸⁸ -positive vesicles substantially co-localized with Dextran⁵⁴⁶ -positive endolysosomes and with acidic LysoTracker-positive vesicles. Cell treatment with anti-receptor for advanced glycation end products (RAGE) antibody, which binds to RAGE, a 'scavenger receptor', partially inhibited uptake of S100B-Alexa⁴⁸⁸ , but not of Dextran⁵⁴⁶ . The dynamin inhibitor dynole 34-2 inhibited internalization of both fluorescent probes. Directional mobility of S100B-Alexa⁴⁸⁸ -positive vesicles increased over time and was inhibited by ATP stimulation, an agent that increases cytosolic free calcium concentration ([Ca²⁺ ]_i ). We conclude that astrocytes exhibit RAGE- and dynamin-dependent vesicular mechanism to efficiently remove S100B from the extracellular space. If a similar process occurs in vivo, astroglia may mitigate the toxic effects of extracellular S100B by this process under pathophysiologic conditions. This study reveals the vesicular clearance mechanism of extracellular S100B in astrocytes. Initially, fluorescent S100B internalizes into smaller endocytotic vesicles than dextran molecules. At a later stage, both probes co-localize within endolysosomes. S100B internalization is both dynamin- and RAGE-dependent, whereas dextran internalization is dependent on dynamin. Vesicle internalization likely mitigates the toxic effects of extracellular S100B and other waste products.

Caenorhabditis elegans ATAD-3 modulates mitochondrial iron and heme homeostasis

ATAD3 (ATPase family AAA domain-containing protein 3) is a mitochondrial protein, which is essential for cell viability and organismal development. ATAD3 has been implicated in several important cellular processes such as apoptosis regulation, respiratory chain function and steroid hormone biosynthesis. Moreover, altered expression of ATAD3 has been associated with several types of cancer. However, the exact mechanisms underlying ATAD3 effects on cellular metabolism remain largely unclear. Here, we demonstrate that Caenorhabditis elegans ATAD-3 is involved in mitochondrial iron and heme homeostasis. Knockdown of atad-3 caused mitochondrial iron- and heme accumulation. This was paralleled by changes in the expression levels of several iron- and heme-regulatory genes as well as an increased heme uptake. In conclusion, our data indicate a regulatory role of C. elegans ATAD-3 in mitochondrial iron and heme metabolism.

High expression of CDC6 is associated with accelerated cell proliferation and poor prognosis of epithelial ovarian cancer

Cell division cycle 6 (CDC6) is an essential regulator of DNA replication and plays important roles in the activation and maintenance of the checkpoint mechanisms in the cell cycle. CDC6 has been associated with the oncogenic activities in human cancers, but the biological function and clinical significance of CDC6 in EOC remain unclear. The aim of the present study is to examine the effect of CDC6 on epithelial ovarian cancer (EOC) cells proliferation. We found that CDC6 protein level was up-regulated in EOC tissues compared with the normal ovary tissues. CDC6 expression correlated significantly with FIGO stage (p<0.001), differentiation grade (p=0.002), ascites (p<0.001), malignant tumor cells in ascites (p=0.004), and lymph node status (p<0.001). In vitro, after the release of ovarian cancer cell line (HO8910) from serum starvation, the expression of CDC6, cyclinD1, and PCNA was up-regulated, whereas p16 expression was down-regulated. Furthermore, down-regulation of CDC6 in HO8910 cells decreased cell proliferation and colony formation. HO8910 cells transfected with sh CDC6#1 underwent G1 phase cell cycle arrest. Collectively, this study provides a novel regulatory signaling pathway of CDC6-regulated EOC growth and a new potential therapeutic target for EOC patients.

Molecular signatures that correlate with induction of lens regeneration in newts: lessons from proteomic analysis

Background

Amphibians have the remarkable ability to regenerate missing body parts. After complete removal of the eye lens, the dorsal but not the ventral iris will transdifferentiate to regenerate an exact replica of the lost lens. We used reverse-phase nano-liquid chromatography followed by mass spectrometry to detect protein concentrations in dorsal and ventral iris 0, 4, and 8 days post-lentectomy. We performed gene expression comparisons between regeneration and intact timepoints as well as between dorsal and ventral iris.

Results

Our analysis revealed gene expression patterns associated with the ability of the dorsal iris for transdifferentiation and lens regeneration. Proteins regulating gene expression and various metabolic processes were enriched in regeneration timepoints. Proteins involved in extracellular matrix, gene expression, and DNA-associated functions like DNA repair formed a regeneration-related protein network and were all up-regulated in the dorsal iris. In addition, we investigated protein concentrations in cultured dorsal (transdifferentiation-competent) and ventral (transdifferentiation-incompetent) iris pigmented epithelial (IPE) cells. Our comparative analysis revealed that the ability of dorsal IPE cells to keep memory of their tissue of origin and transdifferentiation is associated with the expression of proteins that specify the dorso-ventral axis of the eye as well as with proteins found highly expressed in regeneration timepoints, especially 8 days post-lentectomy.

Conclusions

The study deepens our understanding in the mechanism of regeneration by providing protein networks and pathways that participate in the process.

Electronic supplementary material

The online version of this article (doi:10.1186/s40246-014-0022-y) contains supplementary material, which is available to authorized users.

Mitochondrial protein ATPase family, AAA domain containing 3A correlates with radioresistance in glioblastoma

BACKGROUND

ATPase-family, AAA domain containing 3A (ATAD3A) is located on human chromosome 1p36.33, and high endogenous expression may associate with radio- and chemosensitivity. This study was conducted to investigate the significance of ATAD3A in glioblastoma multiforme (GBM).

METHODS

Clinical significance of ATAD3A expression was assessed by immunohistochemistry in 67 GBM specimens, and prognostic value was assessed in 32 GBM patients statistically. To investigate in vitro phenotypic effects of ATAD3A, cell viability was measured using a clonogenic survival assay under either knockdown or ectopic expression of ATAD3A in GBM cell lines. The effects of ATAD3A knockdown on targeted DNA repair-associated proteins in T98G cells were evaluated using immunofluorescence and Western blotting.

RESULTS

Clinically, high expression of ATAD3A was independent of O(6)-DNA methylguanine-methyltransferase methylation status and correlated with worse prognosis. In vitro, high ATAD3A-expressing T98G cells were more resistant to radiation-induced cell death compared with control and low endogenous ATAD3A U87MG cells. After silencing ATAD3A, T98G cells became more sensitive to radiation. On the other hand, enforced ATAD3A expression in U87MG cells exhibited increased radioresistance. ATAD3A may coordinate with aldo-keto reductase genes and participate in bioactivation or detoxication of temozolomide. Surprisingly, deficient DNA repair after irradiation was observed in T98G/ATAD3A knockdown as a result of decreased nuclear ataxia telangiectasia mutated kinase and histones H2AX and H3, which was also evidenced by the sustained elevation of poly (ADP-ribose) polymerase prior to and after radiation treatment.

CONCLUSION

Our data suggest that high expression of ATAD3A is an independent biomarker for radioresistance in GBM. ATAD3A could be a potential target for therapy.

Metabolism and function of mitochondrial cardiolipin

Since it has been recognized that mitochondria are crucial not only for energy metabolism but also for other cellular functions, there has been a growing interest in cardiolipin, the specific phospholipid of mitochondrial membranes. Indeed, cardiolipin is a universal component of mitochondria in all eukaryotes. It has a unique dimeric structure comprised of two phosphatidic acid residues linked by a glycerol bridge, which gives rise to unique physicochemical properties. Cardiolipin plays an important role in the structural organization and the function of mitochondrial membranes. In this article, we review the literature on cardiolipin biology, focusing on the most important discoveries of the past decade. Specifically, we describe the formation, the migration, and the degradation of cardiolipin and we discuss how cardiolipin affects mitochondrial function. We also give an overview of the various phenotypes of cardiolipin deficiency in different organisms.

Mitochondrial cardiolipin/phospholipid trafficking: the role of membrane contact site complexes and lipid transfer proteins

Historically, cellular trafficking of lipids has received much less attention than protein trafficking, mostly because its biological importance was underestimated, involved sorting and translocation mechanisms were not known, and analytical tools were limiting. This has changed during the last decade, and we discuss here some progress made in respect to mitochondria and the trafficking of phospholipids, in particular cardiolipin. Different membrane contact site or junction complexes and putative lipid transfer proteins for intra- and intermembrane lipid translocation have been described, involving mitochondrial inner and outer membrane, and the adjacent membranes of the endoplasmic reticulum. An image emerges how cardiolipin precursors, remodeling intermediates, mature cardiolipin and its oxidation products could migrate between membranes, and how this trafficking is involved in cardiolipin biosynthesis and cell signaling events. Particular emphasis in this review is given to mitochondrial nucleoside diphosphate kinase D and mitochondrial creatine kinases, which emerge to have roles in both, membrane junction formation and lipid transfer.

Functions of S100 proteins

The S100 protein family consists of 24 members functionally distributed into three main subgroups: those that only exert intracellular regulatory effects, those with intracellular and extracellular functions and those which mainly exert extracellular regulatory effects. S100 proteins are only expressed in vertebrates and show cell-specific expression patterns. In some instances, a particular S100 protein can be induced in pathological circumstances in a cell type that does not express it in normal physiological conditions. Within cells, S100 proteins are involved in aspects of regulation of proliferation, differentiation, apoptosis, Ca2+ homeostasis, energy metabolism, inflammation and migration/invasion through interactions with a variety of target proteins including enzymes, cytoskeletal subunits, receptors, transcription factors and nucleic acids. Some S100 proteins are secreted or released and regulate cell functions in an autocrine and paracrine manner via activation of surface receptors (e.g. the receptor for advanced glycation end-products and toll-like receptor 4), G-protein-coupled receptors, scavenger receptors, or heparan sulfate proteoglycans and N-glycans. Extracellular S100A4 and S100B also interact with epidermal growth factor and basic fibroblast growth factor, respectively, thereby enhancing the activity of the corresponding receptors. Thus, extracellular S100 proteins exert regulatory activities on monocytes/macrophages/microglia, neutrophils, lymphocytes, mast cells, articular chondrocytes, endothelial and vascular smooth muscle cells, neurons, astrocytes, Schwann cells, epithelial cells, myoblasts and cardiomyocytes, thereby participating in innate and adaptive immune responses, cell migration and chemotaxis, tissue development and repair, and leukocyte and tumor cell invasion.

Atad3 function is essential for early post-implantation development in the mouse

The mitochondrial AAA+-ATPase ATAD3 is implicated in the regulation of mitochondrial and ER dynamics and was shown to be necessary for larval development in Caenorhabditis elegans. In order to elucidate the relevance of ATAD3 for mammalian development, the phenotype of an Atad3 deficient mouse line was analyzed. Atad3 deficient embryos die around embryonic day E7.5 due to growth retardation and a defective development of the trophoblast lineage immediately after implantation into the uterus. This indicates an essential function of Atad3 for the progression of the first steps of post-implantation development at a time point when mitochondrial biogenesis and ATP production by oxidative phosphorylation are required. Therefore, murine Atad3 plays an important role in the biogenesis of mitochondria in trophoblast stem cells and in differentiating trophoblasts. At the biochemical level, we report here that ATAD3 is present in five native mitochondrial protein complexes of different sizes, indicating complex roles of the protein in mitochondrial architecture and function.

An efficient expression and purification strategy for the production of S100 proteins in Escherichia coli

S100 proteins belong to a family of small, acidic, EF-hand Ca ( 2+) -binding proteins and have been found to exert both intracellular and extracellular functions in regulation of Ca ( 2+) homeostasis, cytoskeletal dynamics, cell cycle, motility and differentiation. As a result, they have been widely investigated for their association with diseases, such as, neurological diseases, cardiomyopathy, neoplasias and inflammatory diseases. To facilitate further studies of S100 proteins, we reported a simple and efficient method for the expression and purification of human S100A4 and S100A11 proteins in Escherichia coli. Since S100 proteins share many common physical and chemical characteristics, we expect that this approach can be extended to the production of most S100 proteins.

ATAD3, a vital membrane bound mitochondrial ATPase involved in tumor progression

ATAD3 (ATPase family AAA Domain-containing protein 3) is a mitochondrial membrane bound ATPase whose function has not yet been discovered but its role is essential for embryonic development. The ATAD3 gene has existed since the pluri-cellular organisms with specialized tissues and has remained unique until vertebrates. In primates and human, two other genes have appeared (called ATAD3B and ATAD3C versus ATAD3A the ancestral gene). ATAD3 knock-down in different non-transformed cell lines is associated with drastic changes in the mitochondrial network, inhibition of proliferation and modification of the functional interactions between mitochondria and endoplasmic reticulum. However, the analysis of the cellular properties of ATAD3A and ATAD3B in different human cancer cell lines shows on the contrary that they can present anti-proliferative and chemoresistant properties. ATAD3 may therefore be implicated in an unknown but essential and growth-linked mitochondrial function existing since pluri-cellular organization and involved in tumorigenesis.

ATAD3B is a human embryonic stem cell specific mitochondrial protein, re-expressed in cancer cells, that functions as dominant negative for the ubiquitous ATAD3A

Here we report on the identification of a human pluripotent embryonic stem cell (hESC) specific mitochondrial protein that is re-expressed in cancer cells, ATAD3B. ATAD3B belongs to the AAA+ ATPase ATAD3 protein family of mitochondrial proteins specific to multicellular eukaryotes. Using loss- and gain-of-function approaches, we show that ATAD3B associates with the ubiquitous ATAD3A species, negatively regulates the interaction of ATAD3A with matrix nucleoid complexes and contributes to a mitochondria fragmentation phenotype. We conclude that ATAD3B is a negative regulator of ATAD3A and may function as an adaptor of mitochondrial homeostasis and metabolism in hESCs and cancer cells.

S100 calcium binding proteins and ion channels

S100 Ca(2+)-binding proteins have been associated with a multitude of intracellular Ca(2+)-dependent functions including regulation of the cell cycle, cell differentiation, cell motility and apoptosis, modulation of membrane-cytoskeletal interactions, transduction of intracellular Ca(2+) signals, and in mediating learning and memory. S100 proteins are fine tuned to read the intracellular free Ca(2+) concentration and affect protein phosphorylation, which makes them candidates to modulate certain ion channels and neuronal electrical behavior. Certain S100s are secreted from cells and are found in extracellular fluids where they exert unique extracellular functions. In addition to their neurotrophic activity, some S100 proteins modulate neuronal electrical discharge activity and appear to act directly on ion channels. The first reports regarding these effects suggested S100-mediated alterations in Ca(2+) fluxes, K(+) currents, and neuronal discharge activity. Recent reports revealed direct and indirect interactions with Ca(2+), K(+), Cl(-), and ligand activated channels. This review focuses on studies of the physical and functional interactions of S100 proteins and ion channels.

MICS-1 interacts with mitochondrial ATAD-3 and modulates lifespan in C. elegans

Caenorhabditis elegans open reading frame T21C9.1 encodes an uncharacterized protein, which is here named MICS-1 (mitochondrial scaffolding protein-1). It is predicted to be the homolog of human outer mitochondrial membrane protein 25 (OMP25 or synaptojanin-2-binding protein), which is a PDZ domain containing protein with a putative role in cellular stress response pathways. Here, we provide evidence that MICS-1 is an interacting partner of mitochondrial protein ATAD-3 (homologue of human ATAD3), which is essential for C. elegans development. We demonstrate that mics-1(RNAi) animals or mics-1 mutants display enhanced longevity with an increased mean lifespan of up to 54% compared to control animals. Of note, also atad-3(RNAi) promoted longevity, although to a lesser extend (29% compared to controls). In addition, thermal stress of mics-1 mutants induced low reactive oxygen species (ROS) production, whereas atad-3(RNAi) animals were highly sensitive to this assay, displaying drastically increased ROS levels. Further studies revealed that MICS-1 and ATAD-3 associated longevity was partially dependent on the presence of DAF-16. However, for both conditions, we also found a DAF-16 independent extension of lifespan. Finally, we observed an additional lifespan extension in mics-1 mutants when subjected to atad-3(RNAi) whereas heat induced ROS production was even aggravated under this condition. This suggests (partially) independent effects of MICS-1 and ATAD-3 on lifespan and ROS production in vivo.