Serum S100B Level in the Management of Pediatric Minor Head Trauma: A Randomized Clinical Trial.

Importance: Minor head trauma (HT) is one of the most common causes of hospitalization in children. A diagnostic test could prevent unnecessary hospitalizations and cranial computed tomographic (CCT) scans. Objective: To evaluate the effectiveness of serum S100B values in reducing exposure to CCT scans and in-hospital observation in children with minor HT. Design, Setting, and Participants: This multicenter, unblinded, prospective, interventional randomized clinical trial used a stepped-wedge cluster design to compare S100B biomonitoring and control groups at 11 centers in France. Participants included children and adolescents 16 years or younger (hereinafter referred to as children) admitted to the emergency department with minor HT. The enrollment period was November 1, 2016, to October 31, 2021, with a follow-up period of 1 month for each patient. Data were analyzed from March 7 to May 29, 2023, based on the modified intention-to-treat and per protocol populations. Interventions: Children in the control group had CCT scans or were hospitalized according to current recommendations. In the S100B biomonitoring group, blood sampling took place within 3 hours after minor HT, and management depended on serum S100B protein levels. If the S100B level was within the reference range according to age, the children were discharged from the emergency department. Otherwise, children were treated as in the control group. Main Outcomes and Measures: Proportion of CCT scans performed (absence or presence of CCT scan for each patient) in the 48 hours following minor HT. Results: A total of 2078 children were included: 926 in the control group and 1152 in the S100B biomonitoring group (1235 [59.4%] boys; median age, 3.2 [IQR, 1.0-8.5] years). Cranial CT scans were performed in 299 children (32.3%) in the control group and 112 (9.7%) in the S100B biomonitoring group. This difference of 23% (95% CI, 19%-26%) was not statistically significant (P = .44) due to an intraclass correlation coefficient of 0.32. A statistically significant 50% reduction in hospitalizations (95% CI, 47%-53%) was observed in the S100B biomonitoring group (479 [41.6%] vs 849 [91.7%]; P < .001). Conclusions and Relevance: In this randomized clinical trial of effectiveness of the serum S100B level in the management of pediatric minor HT, S100B biomonitoring yielded a reduction in the number of CCT scans and in-hospital observation when measured in accordance with the conditions defined by a clinical decision algorithm. Trial Registration: ClinicalTrials.gov Identifier: NCT02819778.

Nrh L11R single nucleotide polymorphism, a new prediction biomarker in breast cancer, impacts endoplasmic reticulum-dependent Ca2+ traffic and response to neoadjuvant chemotherapy.

Overexpression of Bcl-2 proteins such as Bcl2L10, also referred to as Nrh, is associated with resistance to therapy and poor survival in various cancers, including breast cancer, lung cancer, and leukemia. The single nucleotide polymorphism (SNP) of BCL2L10 in its BH4 domain at position 11 (BCL2L10 Leu11Arg, rs2231292), corresponding to position 11 in the Nrh open reading frame, is reported to lower resistance towards chemotherapy, with patients showing better survival in the context of acute leukemia and colorectal cancer. Using cellular models and clinical data, we aimed to extend this knowledge to breast cancer. We report that the homozygous status of the Nrh Leu11Arg isoform (Nrh-R) is found in 9.7-11% percent of the clinical datasets studied. Furthermore, Nrh-R confers higher sensitivity towards Thapsigargin-induced cell death compared to the Nrh-L isoform, due to altered interactions with IP3R1 Ca2+ channels in the former case. Collectively, our data show that cells expressing the Nrh-R isoform are more prone to death triggered by Ca2+ stress inducers, compared to Nrh-L expressing cells. Analysis of breast cancer cohorts revealed that patients genotyped as Nrh-R/Nrh-R may have a better outcome. Overall, this study supports the notion that the rs2231292 Nrh SNP could be used as a predictive tool regarding chemoresistance, improving therapeutic decision-making processes. Moreover, it sheds new light on the contribution of the BH4 domain to the anti-apoptotic function of Nrh and identifies the IP3R1/Nrh complex as a potential therapeutic target in the context of breast cancer.

Non-linearity in lipase assays: A multicentric comparison on different analysers.

OBJECTIVES: Non-linearity in lipase assays and the ensuing gaps in results distribution have been described on Roche analysers, but have yet to be studied on other analysers. DESIGN AND METHODS: Eighteen lithium-heparinized plasma pools of lipase activities decreasing from 1700 to <4 U/L were prepared for multicentric evaluation on several analysers. Non-linearity was modelled as the difference between the polynomial regression of lipase activities depending on relative dilutions over the primary measuring range, and the linear regression of the same variables above the manufacturer's limit of linearity (MLL). Gaps in lipase distribution resulting from non-linearity were graphically evidenced through histograms. Upper limits of gaps were calculated, which are lipase activities where non-linearity biases no longer impact the diluted lipase results. RESULTS: MLLs and lipase (U/L) calculated at MLL (%biases versus MLL) were respectively: 1200 and 1124 (-6.3%) on the Architect C16000 (Abbott); 300 and 248 (-17.3%) on the Cobas c503 (Roche); 1500 and 1458 (-2.8%) on the Dimension Vista (Siemens); and 700 and 659 (-5.9%) on the Atellica CH930 (Siemens). Using Sentinel Lipase reagents on Abbott analysers, these measurements were respectively: 300 and 294 (-2.0%) on the Architect C16000, and 300 and 298 (-0.7%) on the Alinity. Setting Randox Lipase reagents on the Alinity, MLL and lipase at MLL were 953 and 776 (-18.6%), respectively. CONCLUSIONS: Considering the desirable (±14.2 %) and optimal (±7.1 %) allowable total error for lipase (EFLM/EuBIVAS), biases at manufacturer's limit of linearity were acceptable, except for Roche Cobas c503 method and Randox method on Abbott Alinity.

EGFR-dependent aerotaxis is a common trait of breast tumour cells.

BACKGROUND: Aerotaxis, the chemotactism to oxygen, is well documented in prokaryotes. We previously reported for the first time that non-tumorigenic breast epithelial cells also display unequivocal directional migration towards oxygen. This process is independent of the hypoxia-inducible factor (HIF)/prolyl hydroxylase domain (PHD) pathway but controlled by the redox regulation of epidermal growth factor receptor (EGFR), with a reactive oxygen species (ROS) gradient overlapping the oxygen gradient at low oxygen concentration. Since hypoxia is an acknowledged hallmark of cancers, we addressed the putative contribution of aerotaxis to cancer metastasis by studying the directed migration of cancer cells from an hypoxic environment towards nearby oxygen sources, modelling the in vivo migration of cancer cells towards blood capillaries. METHODS: We subjected to the aerotactic test described in our previous papers cells isolated from fresh breast tumours analysed by the Pathology Department of the Saint-Etienne University Hospital (France) over a year. The main selection criterion, aside from patient consent, was the size of the tumour, which had to be large enough to perform the aerotactic tests without compromising routine diagnostic tests. Finally, we compared the aerotactic properties of these primary cells with those of commonly available breast cancer cell lines. RESULTS: We show that cells freshly isolated from sixteen human breast tumour biopsies, representative of various histological characteristics and grades, are endowed with strong aerotactic properties similar to normal mammary epithelial cell lines. Strikingly, aerotaxis of these primary cancerous cells is also strongly dependent on both EGFR activation and ROS. In addition, we demonstrate that aerotaxis can trigger directional invasion of tumour cells within the extracellular matrix contrary to normal mammary epithelial cells. This contrasts with results obtained with breast cancer cell lines, in which aerotactic properties were either retained or impaired, and in some cases, even lost during the establishment of these cell lines. CONCLUSIONS: Altogether, our results support that aerotaxis may play an important role in breast tumour metastasis. In view of these findings, we discuss the prospects for combating metastatic spread. TRIAL REGISTRATION: IRBN1462021/CHUSTE.

Relationship Between Plasmatic Metformin Concentration and Renal Replacement Therapy: A Multicenter Cohort Study.

BACKGROUND: Metformin is the first-line treatment used for type 2 diabetes mellitus for more than 60 years. Metformin-associated lactic acidosis is the most serious adverse effect of metformin and is most widely defined as metabolic acidosis with elevated lactate levels in the presence of metformin. However, there is no consensus regarding the role of metformin in metformin-associated lactic acidosis onset. This study aimed to determine the metformin toxicity threshold (the metformin plasma concentration that predicts the occurrence of lactic acidosis) and the metformin dialysis threshold (the metformin plasma concentration strongly correlated with dialysis introduction). METHODS: This was a retrospective multicenter cohort study conducted from January 1, 2013, to December 31, 2020. All consecutive adult patients with at least one metformin-detectable blood concentration measurement were included. RESULTS: In total, 169 patients (92 men; mean age, 70 ± 11 years) were included in this study. A receiver operating characteristic analysis using Youden index showed that a metformin plasma concentration threshold of 17.9 mg/L was associated with lactic acidosis (sensitivity: 43.8%; specificity: 90.5%). Another receiver operating characteristic analysis using Youden index showed that a metformin plasma concentration threshold of 17.5 mg/L was associated with dialysis (sensitivity, 53.0%; specificity: 94.2%). CONCLUSIONS: The retrospective study design, lack of clinical data, and selection bias (patients in whom metformin was prescribed owing to pathological conditions) were major limitations, resulting in only preliminary findings. However, this study could serve as a basis for future prospective clinical studies to evaluate the use of these clinical threshold values as therapeutic guides.

Hypoxia triggers collective aerotactic migration in Dictyostelium discoideum.

Using a self-generated hypoxic assay, we show that the amoeba Dictyostelium discoideum displays a remarkable collective aerotactic behavior. When a cell colony is covered, cells quickly consume the available oxygen (O2) and form a dense ring moving outwards at constant speed and density. To decipher this collective process, we combined two technological developments: porphyrin-based O2 -sensing films and microfluidic O2 gradient generators. We showed that Dictyostelium cells exhibit aerotactic and aerokinetic response in a low range of O2 concentration indicative of a very efficient detection mechanism. Cell behaviors under self-generated or imposed O2 gradients were modeled using an in silico cellular Potts model built on experimental observations. This computational model was complemented with a parsimonious 'Go or Grow' partial differential equation (PDE) model. In both models, we found that the collective migration of a dense ring can be explained by the interplay between cell division and the modulation of aerotaxis.

The apoptosis inhibitor Bcl-xL controls breast cancer cell migration through mitochondria-dependent reactive oxygen species production.

The Bcl-xL apoptosis inhibitor plays a major role in vertebrate development. In addition to its effect on apoptosis, Bcl-xL is also involved in cell migration and mitochondrial metabolism. These effects may favour the onset and dissemination of metastasis. However, the underlying molecular mechanisms remain to be fully understood. Here we focus on the control of cell migration by Bcl-xL in the context of breast cancer cells. We show that Bcl-xL silencing led to migration defects in Hs578T and MDA-MB231 cells. These defects were rescued by re-expressing mitochondria-addressed, but not endoplasmic reticulum-addressed, Bcl-xL. The use of BH3 mimetics, such as ABT-737 and WEHI-539 confirmed that the effect of Bcl-xL on migration did not depend on interactions with BH3-containing death accelerators such as Bax or BH3-only proteins. In contrast, the use of a BH4 peptide that disrupts the Bcl-xL/VDAC1 complex supports that Bcl-xL by acting on VDAC1 permeability contributes to cell migration through the promotion of reactive oxygen species production by the electron transport chain. Collectively our data highlight the key role of Bcl-xL at the interface between cell metabolism, cell death, and cell migration, thus exposing the VDAC1/Bcl-xL interaction as a promising target for anti-tumour therapy in the context of metastatic breast cancer.

Redox regulation of EGFR steers migration of hypoxic mammary cells towards oxygen.

Aerotaxis or chemotaxis to oxygen was described in bacteria 130 years ago. In eukaryotes, the main adaptation to hypoxia currently described relies on HIF transcription factors. To investigate whether aerotaxis is conserved in higher eukaryotes, an approach based on the self-generation of hypoxia after cell confinement was developed. We show that epithelial cells from various tissues migrate with an extreme directionality towards oxygen to escape hypoxia, independently of the HIF pathway. We provide evidence that, concomitant to the oxygen gradient, a gradient of reactive oxygen species (ROS) develops under confinement and that antioxidants dampen aerotaxis. Finally, we establish that in mammary cells, EGF receptor, the activity of which is potentiated by ROS and inhibited by hypoxia, represents the molecular target that guides hypoxic cells to oxygen. Our results reveals that aerotaxis is a property of higher eukaryotic cells and proceeds from the conversion of oxygen into ROS.

Combination of a discovery LC-MS/MS analysis and a label-free quantification for the characterization of an epithelial-mesenchymal transition signature.

Disease phenotype reorganizations are the consequences of signaling pathway perturbations and protein abundance modulations. Characterizing the protein signature of a biological event allows the identification of new candidate biomarkers, new targets for treatments and selective patient therapy. The combination of discovery LC-MS/MS analyses and targeted mass spectrometry using selected reaction monitoring (SRM) mode has emerged as a powerful technology for biomarker identification and quantification owing to faster development time and multiplexing capability. The epithelial-mesenchymal transition (EMT) is a process that controls local invasion and metastasis generation by stimulating changes in adhesion and migration of cells but also in metabolic pathways. In this study, the non-transformed human breast epithelial cell line MCF10A, treated by TGFß or overexpressing mutant K-Ras(v12), two EMT inducers frequently involved in cancer progression, was used to characterize protein abundance changes during an EMT event. The LC-MS/MS analysis and label-free quantification revealed that TGFß and K-Ras(v12) induce a similar pattern of protein regulation and that besides the expected cytoskeletal changes, a strong increase in the anabolism and energy production machinery was observed. BIOLOGICAL SIGNIFICANCE: To our knowledge, this is the first proteomic analysis combining a label-free quantification with an SRM validation of proteins regulated by TGFß and K-Rasv12. This study reveals new insights in the characterization of the changes occurring during an epithelial-mesenchymal transition (EMT) event. Notably, a strong increase in the anabolism and energy production machinery was observed upon both EMT inducers.

Genetic and pharmacologic inhibition of mTORC1 promotes EMT by a TGF-ß-independent mechanism.

Epithelial-to-mesenchymal transition (EMT) is a transdifferentiation process that converts epithelial cells into highly motile mesenchymal cells. This physiologic process occurs largely during embryonic development but is aberrantly reactivated in different pathologic situations, including fibrosis and cancer. We conducted a siRNA screening targeted to the human kinome with the aim of discovering new EMT effectors. With this approach, we have identified mTOR complex 1 (mTORC1), a nutrient sensor that controls protein and lipid synthesis, as a key regulator of epithelial integrity. Using a combination of RNAi and pharmacologic approaches, we report here that inhibition of either mTOR or RPTOR triggers EMT in mammary epithelial cells. This EMT was characterized by the induction of the mesenchymal markers such as fibronectin, vimentin, and PAI-1, together with the repression of epithelial markers such as E-cadherin and ZO-3. In addition, mTORC1 blockade enhanced in vivo migratory properties of mammary cells and induced EMT independent of the TGF-ß pathway. Finally, among the transcription factors known to activate EMT, both ZEB1 and ZEB2 were upregulated following mTOR repression. Their increased expression correlated with a marked reduction in miR-200b and miR-200c mRNA levels, two microRNAs known to downregulate ZEB1 and ZEB2 expression. Taken together, our findings unravel a novel function for mTORC1 in maintaining the epithelial phenotype and further indicate that this effect is mediated through the opposite regulation of ZEB1/ZEB2 and miR-200b and miR-200c. Furthermore, these results suggest a plausible etiologic explanation for the progressive pulmonary fibrosis, a frequent adverse condition associated with the therapeutic use of mTOR inhibitors.

Bcl-wav and the mitochondrial calcium uniporter drive gastrula morphogenesis in zebrafish.

Bcl-2 proteins are acknowledged as key regulators of programmed cell death. However, increasing data suggest additional roles, including regulation of the cell cycle, metabolism and cytoskeletal dynamics. Here we report the discovery and characterization of a new Bcl-2-related multidomain apoptosis accelerator, Bcl-wav, found in fish and frogs. Genetic and molecular studies in zebrafish indicate that Bcl-wav and the recently identified mitochondrial calcium uniporter (MCU) contribute to the formation of the notochord axis by controlling blastomere convergence and extension movements during gastrulation. Furthermore, we found that Bcl-wav controls intracellular Ca(2+) trafficking by acting on the mitochondrial voltage-dependent anion channel, and possibly on MCU, with direct consequences on actin microfilament dynamics and blastomere migration guidance. Thus, from an evolutionary point of view, the original function of Bcl-2 proteins might have been to contribute in controlling the global positioning system of blastomeres during gastrulation, a critical step in metazoan development.

Amniotic fluid glial fibrillary acidic protein (AF-GFAP), a biomarker of open neural tube defects.

OBJECTIVE: Neural tube defects (NTDs) are usually identified by ultrasonography and confirmed by alpha-fetoprotein (AFP) assay and acetylcholinesterase (AchE) electrophoresis in amniotic fluid. Yet, both of these biomarkers can be found positive in other etiologies. Here, amniotic fluid glial fibrillary acidic protein (AF-GFAP), which was identified by a proteomic study, is shown to be a useful biomarker for NTD diagnosis. METHOD: Amniotic fluid glial fibrillary acidic protein was measured by an ELISA assay in 138 cases of NTDs. Seventy samples from normal pregnancies used as controls and 27 samples giving false positive or false negative results either for AchE or AFP and corresponding to fetal death (n = 8), gastroschisis (n = 8), and unexplained etiologies (n = 11) were also tested. RESULTS: Whatever the gestational age, GFAP was below 0.2 ng/mL in control samples, whereas 99.1% of open NTDs (29/29 in the anterior NTD group and 80/81 in the spina bifida group) were above this threshold. Closed NTDs were all negative (28/28). None of the other samples tested were positive, except in case of fetal death (8/8). CONCLUSIONS: Amniotic fluid glial fibrillary acidic protein is a sensitive biomarker for open NTD diagnosis with a good negative predictive value for closed NTD. Compared with AFP and AchE, our results indicate that AF-GFAP alone is more efficient than this classical association.

Data-driven modeling of SRC control on the mitochondrial pathway of apoptosis: implication for anticancer therapy optimization.

Src tyrosine kinases are deregulated in numerous cancers and may favor tumorigenesis and tumor progression. We previously described that Src activation in NIH-3T3 mouse fibroblasts promoted cell resistance to apoptosis. Indeed, Src was found to accelerate the degradation of the pro-apoptotic BH3-only protein Bik and compromised Bax activation as well as subsequent mitochondrial outer membrane permeabilization. The present study undertook a systems biomedicine approach to design optimal anticancer therapeutic strategies using Src-transformed and parental fibroblasts as a biological model. First, a mathematical model of Bik kinetics was designed and fitted to biological data. It guided further experimental investigation that showed that Bik total amount remained constant during staurosporine exposure, and suggested that Bik protein might undergo activation to induce apoptosis. Then, a mathematical model of the mitochondrial pathway of apoptosis was designed and fitted to experimental results. It showed that Src inhibitors could circumvent resistance to apoptosis in Src-transformed cells but gave no specific advantage to parental cells. In addition, it predicted that inhibitors of Bcl-2 antiapoptotic proteins such as ABT-737 should not be used in this biological system in which apoptosis resistance relied on the deficiency of an apoptosis accelerator but not on the overexpression of an apoptosis inhibitor, which was experimentally verified. Finally, we designed theoretically optimal therapeutic strategies using the data-calibrated model. All of them relied on the observed Bax overexpression in Src-transformed cells compared to parental fibroblasts. Indeed, they all involved Bax downregulation such that Bax levels would still be high enough to induce apoptosis in Src-transformed cells but not in parental ones. Efficacy of this counterintuitive therapeutic strategy was further experimentally validated. Thus, the use of Bax inhibitors might be an unexpected way to specifically target cancer cells with deregulated Src tyrosine kinase activity.

Tif1γ is essential for the terminal differentiation of mammary alveolar epithelial cells and for lactation through SMAD4 inhibition.

Transforming growth factor ß (TGFß) is widely recognised as an important factor that regulates many steps of normal mammary gland (MG) development, including branching morphogenesis, functional differentiation and involution. Tif1γ has previously been reported to temporally and spatially control TGFß signalling during early vertebrate development by exerting negative effects over SMAD4 availability. To evaluate the contribution of Tif1 γ to MG development, we developed a Cre/LoxP system to specifically invalidate the Tif1g gene in mammary epithelial cells in vivo. Tif1g-null mammary gland development appeared to be normal and no defects were observed during the lifespan of virgin mice. However, a lactation defect was observed in mammary glands of Tif1g-null mice. We demonstrate that Tif1 γ is essential for the terminal differentiation of alveolar epithelial cells at the end of pregnancy and to ensure lactation. Tif1 γ appears to play a crucial role in the crosstalk between TGFß and prolactin pathways by negatively regulating both PRL receptor expression and STAT5 phosphorylation, thereby impairing the subsequent transactivation of PRL target genes. Using HC11 cells as a model, we demonstrate that the effects of Tif1g knockdown on lactation depend on both SMAD4 and TGFß. Interestingly, we found that the Tif1γ expression pattern in mammary epithelial cells is almost symmetrically opposite to that described for TGFß. We propose that Tif1γ contributes to the repression of TGFß activity during late pregnancy and prevents lactation by inhibiting SMAD4.

Clinical performance of the carbohydrate-deficient transferrin (CDT) assay by the Sebia Capillarys2 system in case of cirrhosis. Interest of the Bio-Rad %CDT by HPLC test and Siemens N-Latex CDT kit as putative confirmatory methods.

BACKGROUND: The CDT assay used to detect chronic alcohol abuse is difficult with cirrhotic patients. This article describes the performances of several CDT assays in case of cirrhosis. The CDT-Capillarys assay by capillary zone electrophoresis was used for initial testing. Two additional methods were tested as putative confirmatory methods. METHODS: 110 patients with known hepatic status had their CDT measured by the Capillarys2 or alternative methods. Self-reported alcohol intake was used to assess the performances of CDT assays. RESULTS: Capillarys2 performance was lower in case of cirrhosis, many electropherograms displaying various abnormalities. We used the proper separation of the di- and tri-sialotransferrin peaks to select reliable profiles. This selection led to the classification of cirrhotic and non-cirrhotic patients in abusers and abstainers with similar performances. However, no interpretation was available for 54% of the cirrhotic patients and neither the BioRad %CDT by HPLC test, nor the Siemens N-Latex CDT kit was suitable as confirmatory methods for these samples. CONCLUSIONS: An attentive profile examination is required for the validation of Capillarys CDT results of cirrhotic patients. Reliability is significantly improved when samples with an improper separation are excluded. To date, no commercial test can confirm the excluded samples.

Antagonistic regulation of EMT by TIF1γ and Smad4 in mammary epithelial cells.

TGF-ß is a potent inducer of epithelial-to-mesenchymal transition (EMT), a process involved in tumour invasion. TIF1γ participates in TGF-ß signalling. To understand the role of TIF1γ in TGF-ß signalling and its requirement for EMT, we analysed the TGF-ß1 response of human mammary epithelial cell lines. A strong EMT increase was observed in TIF1γ-silenced cells after TGF-ß1 treatment, whereas Smad4 inactivation completely blocked this process. Accordingly, the functions of several TIF1γ target genes can be linked to EMT, as shown by microarray analysis. As a negative regulator of Smad4, TIF1γ could be crucial for the regulation of TGF-ß signalling. Furthermore, TIF1γ binds to and represses the plasminogen activator inhibitor 1 promoter, demonstrating a direct role of TIF1γ in TGF-ß-dependent gene expression. This study shows the molecular relationship between TIF1γ and Smad4 in TGF-ß signalling and EMT.

Active fragments from pro- and antiapoptotic BCL-2 proteins have distinct membrane behavior reflecting their functional divergence.

BACKGROUND: The BCL-2 family of proteins includes pro- and antiapoptotic members acting by controlling the permeabilization of mitochondria. Although the association of these proteins with the outer mitochondrial membrane is crucial for their function, little is known about the characteristics of this interaction. METHODOLOGY/PRINCIPAL FINDINGS: Here, we followed a reductionist approach to clarify to what extent membrane-active regions of homologous BCL-2 family proteins contribute to their functional divergence. Using isolated mitochondria as well as model lipid Langmuir monolayers coupled with Brewster Angle Microscopy, we explored systematically and comparatively the membrane activity and membrane-peptide interactions of fragments derived from the central helical hairpin of BAX, BCL-xL and BID. The results show a connection between the differing abilities of the assayed peptide fragments to contact, insert, destabilize and porate membranes and the activity of their cognate proteins in programmed cell death. CONCLUSION/SIGNIFICANCE: BCL-2 family-derived pore-forming helices thus represent structurally analogous, but functionally dissimilar membrane domains.

SLP-2 interacts with prohibitins in the mitochondrial inner membrane and contributes to their stability.

Stomatin is a member of a large family of proteins including prohibitins, HflK/C, flotillins, mechanoreceptors and plant defense proteins, that are thought to play a role in protein turnover. Using different proteomic approaches, we and others have identified SLP-2, a member of the stomatin gene family, as a component of the mitochondria. In this study, we show that SLP-2 is strongly associated with the mitochondrial inner membrane and that it interacts with prohibitins. Depleting HeLa cells of SLP-2 lead to increased proteolysis of prohibitins and of subunits of the respiratory chain complexes I and IV. Further supporting the role of SLP-2 in regulating the stability of specific mitochondrial proteins, we found that SLP-2 is up-regulated under conditions of mitochondrial stress leading to increased protein turnover. These data indicate that SLP-2 plays a role in regulating the stability of mitochondrial proteins including prohibitins and subunits of respiratory chain complexes.

The puzzling lateral flexible stalk of the ribosome.

The lateral flexible stalk of the large ribosomal subunit is made of several interacting proteins anchored to a conserved region of the 28S (26S) rRNA termed the GTPase-associated domain or thiostrepton loop. This structure is demonstrated to adopt puzzling changes of conformation following the different steps of the elongation cycle. Some of these proteins termed the P-proteins in eukaryotes and L10 and L7/L12 in bacteria, present little structural similarities between Eubacteria on one side and Archae and Eukaryotes on the other side. However, up to now, these proteins seem to present a similar macromolecular organisation and they have been involved in the same functions. Convincing evidence attests that these proteins participate in elongation factor binding to the ribosome, and it has been suggested that these proteins might be evolved in a GTP hydrolysis activating protein activity. Involvement of these proteins in the translational mechanism is discussed. Moreover, in eukaryotes, small P-proteins are also found as isolated proteins in a cytoplasmic pool that exchanges with the ribosome-associated P-proteins. Moreover, a part of the ribosomal proteins is phosphorylated (hence their P-protein names). The biological signification of these particularities is discussed.