The TIM translocase in T. brucei contains Rhomboid-like proteins that are essential for mitochondrial protein import

The parasitic protozoon Trypanosoma brucei is one of the earliest branching eukaryotes that have mitochondria capable of oxidative phosphorylation. Their protein import systems are of similar complexity yet different composition than those in other eukaryotes. To elucidate the composition of the trypanosomal translocase of the inner mitochondrial membrane (TIM) we performed CoIPs of epitope-tagged TbTim17 and two other candidates in combination with SILAC-based quantitative mass spectrometry. This led to the identification of ten candidates for core TIM subunits. Eight of them were present in the previously determined inner membrane proteome and four show homology to small Tim chaperones. Three candidates, a trypanosomatid-specific 42 kDa protein (Tim42) and two putative orthologues of inactive rhomboid proteases were analyzed further. All three proteins are essential in both life cycle stages and their ablation results in a strong protein import defect in vivo and in vitro. Blue native PAGE revealed their presence in a high molecular weight complex. Unlike anticipated, trypanosomes have a highly complex TIM translocase that has extensively been redesigned. None of the three novel TIM subunits has ever been associated with mitochondrial protein import. Two of them belong to the rhomboid protease family, a member of which recently has been implicated in the ERAD translocation system. This suggests an exciting analogy between protein translocases of mitochondria and the ER.

The TIM translocase in T. brucei contains Rhomboid-like proteins that are essential for mitochondrial protein import

The parasitic protozoon Trypanosoma brucei is often considered as one of the earliest branching eukaryotes that have mitochondria capable of oxidative phosphorylation. Its protein import systems are therefore of great interest. Recently, it was shown that the outer mitochondrial membrane protein translocase is of similar complexity yet different composition than in other eukaryotes (1). In the inner membrane however, only a single orthologue of the pore forming Tim17/22/23 protein family was identified and termed TbTim17. Based on this finding it has been suggested that, instead of separate TIM22 and TIM23 complexes as in other eukaryotes, trypanosomes may have a single multifunctional translocase of the inner mitochondrial membrane (TIM) of reduced complexity. To elucidate the composition of the trypanosomal TIM complex we performed co-immunoprecipitations (CoIP) of epitope-tagged TbTim17 in combination with SILAC-based quantitative mass spectrometry. This led to the identification of 22 highly enriched TbTim17-interacting proteins. We tagged two of the top-scoring proteins for reciprocal CoIP analyses and recovered a set of ten proteins that are highly enriched in all three CoIPs. These proteins are excellent candidates for core subunits of the trypanosomal TIM complex. Eight of them were present in the previously determined inner membrane proteome and four show homology to small Tim chaperones. Three candidates, a novel trypanosomatid-specific 42 kDa protein, termed Tim42, and two putative orthologues of probably inactive rhomboid proteases were chosen for further analysis. All three proteins are essential in both life cycle stages and in a cell line that can grow in the absence of mitochondrial DNA. Additionally, their ablation by RNAi results in a strong protein import defect both in vivo and in vitro. Blue native PAGE reveals that Tim42, like TbTim17 is present in a high molecular weight complex. Moreover, ablation of either Tim42 or TbTim17 leads to a destabilization of the complex containing the other protein, suggesting a tight interaction of the two proteins. In summary our study shows that unlike anticipated trypanosomes have a highly complex TIM translocase that has extensively been redesigned. We have characterized three novel TIM subunits that have never been associated with mitochondrial protein import before. Two of them belong to the rhomboid protease family, a member of which recently has been implicated in the ERAD translocation system. Our study provides insight into mitochondrial evolution over large phylogenetic distances and suggests an exciting analogy between protein translocation systems of mitochondria and the ER.

Capillary growth, ultrastructure remodelling and exercise training in skeletal muscle of essential hypertensive patients

AIM The aim was to elucidate whether essential hypertension is associated with altered capillary morphology and density and to what extent exercise training can normalize these parameters. METHODS To investigate angiogenesis and capillary morphology in essential hypertension, muscle biopsies were obtained from m. vastus lateralis in subjects with essential hypertension (n = 10) and normotensive controls (n = 11) before and after 8 weeks of aerobic exercise training. Morphometry was performed after transmission electron microscopy, and protein levels of several angioregulatory factors were determined. RESULTS At baseline, capillary density and capillary-to-fibre ratio were not different between the two groups. However, the hypertensive subjects had 9% lower capillary area (12.7 ± 0.4 vs. 13.9 ± 0.2 μm(2)) and tended to have thicker capillary basement membranes (399 ± 16 vs. 358 ± 13 nm; P = 0.094) than controls. Protein expression of vascular endothelial growth factor (VEGF), VEGF receptor-2 and thrombospondin-1 were similar in normotensive and hypertensive subjects, but tissue inhibitor of matrix metalloproteinase was 69% lower in the hypertensive group. After training, angiogenesis was evident by 15% increased capillary-to-fibre ratio in the hypertensive subjects only. Capillary area and capillary lumen area were increased by 7 and 15% in the hypertensive patients, whereas capillary basement membrane thickness was decreased by 17% (P < 0.05). VEGF expression after training was increased in both groups, whereas VEGF receptor-2 was decreased by 25% in the hypertensive patients(P < 0.05). CONCLUSION Essential hypertension is associated with decreased lumen area and a tendency for increased basement membrane thickening in capillaries of skeletal muscle. Exercise training may improve the diffusion conditions in essential hypertension by altering capillary structure and capillary number.

A heteromeric potassium channel involved in the modulation of the plasma membrane potential is essential for the survival of African trypanosomes.

Discovery of novel drug targets may lead to improved treatment of trypanosomiasis. We characterize here 2 gene products of Trypanosoma brucei that are essential for the growth of bloodstream form (BSF) parasites, as shown by RNA interference (RNAi)-mediated down-regulation of the individual mRNAs. The primary sequences of the 2 proteins--protein encoded by gene Tb927.1.4450 (TbK1) and protein encoded by gene Tb927.9.4820 (TbK2)--indicate that both belong to the family of putative, Ca(2+)-activated potassium channels. The proteins were expressed in Xenopus laevis oocytes and their functions investigated by use of electrophysiological techniques. Only combined expression of TbK1 and TbK2 results in the formation of sizeable currents, indicating that these proteins probably assemble into a heteromeric ion channel. The current mediated by this channel shows little time and voltage dependence and displays a permeability ratio of K(+)/Na(+) of >20. The known potassium channel blocker barium inhibits this channel with a half-maximal inhibitory concentration (IC50) of 98 ± 15 μM. The membrane potential of trypanosomes was measured with a fluorescent dye. Individual RNAi-mediated down-regulation of TbK1 or TbK2 eliminates a potassium conductance in the plasma membrane of BSF. Thus, this heteromeric potassium channel is involved in the modulation of the plasma membrane potential and represents a novel drug target in T. brucei.

Functional interplay of SP family members and nuclear factor Y is essential for transcriptional activation of the human Calreticulin gene

Calreticulin (CALR) is a highly conserved, multifunctional protein involved in a variety of cellular processes including the maintenance of intracellular calcium homeostasis, proper protein folding, differentiation and immunogenic cell death. More recently, a crucial role for CALR in the pathogenesis of certain hematologic malignancies was discovered: in clinical subgroups of acute myeloid leukemia, CALR overexpression mediates a block in differentiation, while somatic mutations have been found in the majority of patients with myeloproliferative neoplasms with nonmutated Janus kinase 2 gene (JAK2) or thrombopoietin receptor gene (MPL). However, the mechanisms underlying CALR promoter activation have insufficiently been investigated so far. By dissecting the core promoter region, we could identify a functional TATA-box relevant for transcriptional activation. In addition, we characterized two evolutionary highly conserved cis-regulatory modules (CRMs) within the proximal promoter each composed of one binding site for the transcription factors SP1 and SP3 as well as for the nuclear transcription factor Y (NFY) and we verified binding of these factors to their cognate sites in vitro and in vivo.

Telomerase Inhibitor Imetelstat in Patients with Essential Thrombocythemia.

BACKGROUND Imetelstat, a 13-mer oligonucleotide that is covalently modified with lipid extensions, competitively inhibits telomerase enzymatic activity. It has been shown to inhibit megakaryocytic proliferation in vitro in cells obtained from patients with essential thrombocythemia. In this phase 2 study, we investigated whether imetelstat could elicit hematologic and molecular responses in patients with essential thrombocythemia who had not had a response to or who had had unacceptable side effects from prior therapies. METHODS A total of 18 patients in two sequential cohorts received an initial dose of 7.5 or 9.4 mg of imetelstat per kilogram of body weight intravenously once a week until attainment of a platelet count of approximately 250,000 to 300,000 per cubic millimeter. The primary end point was the best hematologic response. RESULTS Imetelstat induced hematologic responses in all 18 patients, and 16 patients (89%) had a complete hematologic response. At the time of the primary analysis, 10 patients were still receiving treatment, with a median follow-up of 17 months (range, 7 to 32 [ongoing]). Molecular responses were seen in 7 of 8 patients who were positive for the JAK2 V617F mutation (88%; 95% confidence interval, 47 to 100). CALR and MPL mutant allele burdens were also reduced by 15 to 66%. The most common adverse events during treatment were mild to moderate in severity; neutropenia of grade 3 or higher occurred in 4 of the 18 patients (22%) and anemia, headache, and syncope of grade 3 or higher each occurred in 2 patients (11%). All the patients had at least one abnormal liver-function value; all persistent elevations were grade 1 or 2 in severity. CONCLUSIONS Rapid and durable hematologic and molecular responses were observed in patients with essential thrombocythemia who received imetelstat. (Funded by Geron; ClinicalTrials.gov number, NCT01243073.).

Telomerase Is Essential for Zebrafish Heart Regeneration.

After myocardial infarction in humans, lost cardiomyocytes are replaced by an irreversible fibrotic scar. In contrast, zebrafish hearts efficiently regenerate after injury. Complete regeneration of the zebrafish heart is driven by the strong proliferation response of its cardiomyocytes to injury. Here we show that, after cardiac injury in zebrafish, telomerase becomes hyperactivated, and telomeres elongate transiently, preceding a peak of cardiomyocyte proliferation and full organ recovery. Using a telomerase-mutant zebrafish model, we found that telomerase loss drastically decreases cardiomyocyte proliferation and fibrotic tissue regression after cryoinjury and that cardiac function does not recover. The impaired cardiomyocyte proliferation response is accompanied by the absence of cardiomyocytes with long telomeres and an increased proportion of cardiomyocytes showing DNA damage and senescence characteristics. These findings demonstrate the importance of telomerase function in heart regeneration and highlight the potential of telomerase therapy as a means of stimulating cell proliferation upon myocardial infarction.

Transforming growth factor beta signaling is essential for the autonomous formation of cartilage-like tissue by expanded chondrocytes.

Cartilage is a tissue with limited self-healing potential. Hence, cartilage defects require surgical attention to prevent or postpone the development of osteoarthritis. For cell-based cartilage repair strategies, in particular autologous chondrocyte implantation, articular chondrocytes are isolated from cartilage and expanded in vitro to increase the number of cells required for therapy. During expansion, the cells lose the competence to autonomously form a cartilage-like tissue, that is in the absence of exogenously added chondrogenic growth factors, such as TGF-βs. We hypothesized that signaling elicited by autocrine and/or paracrine TGF-β is essential for the formation of cartilage-like tissue and that alterations within the TGF-β signaling pathway during expansion interfere with this process. Primary bovine articular chondrocytes were harvested and expanded in monolayer culture up to passage six and the formation of cartilage tissue was investigated in high density pellet cultures grown for three weeks. Chondrocytes expanded for up to three passages maintained the potential for autonomous cartilage-like tissue formation. After three passages, however, exogenous TGF-β1 was required to induce the formation of cartilage-like tissue. When TGF-β signaling was blocked by inhibiting the TGF-β receptor 1 kinase, the autonomous formation of cartilage-like tissue was abrogated. At the initiation of pellet culture, chondrocytes from passage three and later showed levels of transcripts coding for TGF-β receptors 1 and 2 and TGF-β2 to be three-, five- and five-fold decreased, respectively, as compared to primary chondrocytes. In conclusion, the autonomous formation of cartilage-like tissue by expanded chondrocytes is dependent on signaling induced by autocrine and/or paracrine TGF-β. We propose that a decrease in the expression of the chondrogenic growth factor TGF-β2 and of the TGF-β receptors in expanded chondrocytes accounts for a decrease in the activity of the TGF-β signaling pathway and hence for the loss of the potential for autonomous cartilage-like tissue formation.

Vital function for PRELI and essential requirement for its LEA motif

Proteins containing the late embryogenesis abundant (LEA) motif comprise an evolutionarily conserved family, long postulated to protect plant embryos from stress and death. However, the significance of LEA-containing proteins and the mechanisms behind their function remain undetermined. Here we show that PRELI, a mammalian protein that possesses tandem repeats of the LEA motif, can protect cells against staurosporine, TNF-α or UV irradiation-induced apoptosis. We found that key to PRELI-dependent mechanisms that promote cell resistance to death are the stabilization of the respiratory chain, upholding of mitochondrial membrane potential and retention of apoptogenic molecules. By in vitro and in vivo studies, we also show that the expression of mutant PRELI/LEA- proteins lacking the LEA motif, results in the complete loss of PRELI's anti-apoptotic functions. Collectively, our data uncover a new molecular player in the control of apoptosis and support the hypothesis that LEA-containing proteins are evolutionarily conserved cell protectors against stress and death. ^

Identification of essential apoptotic genes in Drosophila

Apoptosis is a normal physiological cell suicide process which is essential for tissue homeostasis and normal development of metazoans. Misregulation of apoptosis is associated with many developmental defects and human diseases. The genes involved in the regulation and execution of apoptosis are highly conserved in humans and flies. Caspases are the executioners of cell suicide. Because of the unavailability of specific fly mutants, the developmental function of many caspase genes and genetic relationship between caspases and apoptotic components were undefined in Drosophila. We isolated several mutant alleles of the initiator caspase gene dronc, the effector casase drICE, and the Mediator component Cyclin C from the GMR-hid eyFLP/FRT screens which is designed to isolate mutants of recessive cell death genes in Drosophila melanogaster. Characterization of these mutants defined that they are essential for developmental cell death in Drosophila. dronc is required for most, but not all, cell death in Drosophila. drICE is required for apoptosis in many cells and it shares redundancy with another effector caspase gene, dcp-1, in a subset of cells in Drosophila. The genetic relationship between caspases and other apoptotic components was established through mutant analysis. We found that the pro-apoptotic protein Hid induces transcription of the initiator caspase gene dronc and the GMR-induced dronc transcripts are dependent on activated effector casapses, revealing a novel regulatory mechanism to promote caspase activity in Drosophila. Cyclin C and its kinase partner Cdk8 are required for prompt transcriptional induction of dronc in cell killing contexts. In short, we define the essential pro-apoptoic function of dronc, drICE, and Cyclin C in Drosophila and reveal a novel mechanism for regulation of dronc transcription. In the long run, these studies will help us decipher the complicated regulatory mechanism of cell death in humans. ^

Ethnicity as a risk factor for diabetes incidence in a population of diagnosed hypertensives

Significant racial/ethnic differences exist in prevalence of hypertension (HTN) and non-insulin dependent diabetes mellitus (NIDDM). Hypertension is more common in diabetics than in non-diabetics, and an etiologic link between the two conditions has been proposed. Since there are few longitudinal studies of persons with both HTN and NIDDM, a retrospective cohort study was conducted to determine if ethnicity (Black, Hispanic (Mexican-American), and non-Hispanic White) was related to NIDDM incidence in a low-SES, multi-ethnic clinic population of diagnosed hypertensives. Two thousand nine hundred forty-one hypertensives free of NIDDM at baseline were followed for up to 10 years. Mean baseline age was 56 $\pm$ 12 years, M:F percent was 33:67, and Black:Hispanic:White percent was 63:17:20. There were 236 incident cases of NIDDM. In Cox proportional hazards analysis, the risk of developing NIDDM over 10 years was not related to ethnicity after controlling for significant covariates, including age, baseline blood glucose and body mass index (adjusted RR for Blacks compared to Whites =.82, 95 percent CI =.57-1.18; adjusted RR for Hispanics compared to Whites =.84, 95 percent CI =.51-1.38). This result contrasts with the increased risk of NIDDM among Blacks and Hispanics compared to Whites found in the general population. The study suggests that a diagnosis of hypertension equalizes the risk of developing NIDDM among the three ethnic groups. ^

THE RELATIONSHIP BETWEEN DEGREE OF BLOOD PRESSURE REDUCTION AND MORTALITY AMONG HYPERTENSIVES IN THE HYPERTENSION DETECTION AND FOLLOW-UP PROGRAM

The relationship between degree of diastolic blood pressure (DBP) reduction and mortality was examined among hypertensives, ages 30-69, in the Hypertension Detection and Follow-up Program (HDFP). The HDFP was a multi-center community-based trial, which followed 10,940 hypertensive participants for five years. One-year survival was required for inclusion in this investigation since the one-year annual visit was the first occasion where change in blood pressure could be measured on all participants. During the subsequent four years of follow-up on 10,052 participants, 568 deaths occurred. For levels of change in DBP and for categories of variables related to mortality, the crude mortality rate was calculated. Time-dependent life tables were also calculated so as to utilize available blood pressure data over time. In addition, the Cox life table regression model, extended to take into account both time-constant and time-dependent covariates, was used to examine the relationship change in blood pressure over time and mortality.^ The results of the time-dependent life table and time-dependent Cox life table regression analyses supported the existence of a quadratic function which modeled the relationship between DBP reduction and mortality, even after adjusting for other risk factors. The minimum mortality hazard ratio, based on a particular model, occurred at a DBP reduction of 22.6 mm Hg (standard error = 10.6) in the whole population and 8.5 mm Hg (standard error = 4.6) in the baseline DBP stratum 90-104. After this reduction, there was a small increase in the risk of death. There was not evidence of the quadratic function after fitting the same model using systolic blood pressure. Methodologic issues involved in studying a particular degree of blood pressure reduction were considered. The confidence interval around the change corresponding to the minimum hazard ratio was wide and the obtained blood pressure level should not be interpreted as a goal for treatment. Blood pressure reduction was attributed, not only to pharmacologic therapy, but also to regression to the mean, and to other unknown factors unrelated to treatment. Therefore, the surprising results of this study do not provide direct implications for treatment, but strongly suggest replication in other populations. ^

Analysis of VirB4, a membrane-associated ATPase subunit essential for T -complex transport in Agrobacterium tumefaciens

Agrobacterium tumefaciens is a plant pathogen with the unique ability to export oncogenic DNA-protein complexes (T-complexes) to susceptible plant cells and cause crown gall tumors. Delivery of the T-complexes across the bacterial membranes requires eleven VirB proteins and VirD4, which are postulated to form a transmembrane transporter. This thesis examines the subcellular localization and oligomeric structure of the 87-kDa VirB4 protein, which is one of three essential ATPases proposed to energize T-complex transport and/or assembly. Results of subcellular localization studies showed that VirB4 is tightly associated with the cytoplasmic membrane, suggesting that it is a membrane-spanning protein. The membrane topology of VirB4 was determined by using a nested deletion strategy to generate random fusions between virB4 and the periplasmically-active alkaline phosphatase, $\sp\prime phoA$. Analysis of PhoA and complementary $\beta$-galactosidase reporter fusions identified two putative periplasmically-exposed regions in VirB4. A periplasmic exposure of one of these regions was further confirmed by protease susceptibility assays using A. tumefaciens spheroplasts. To gain insight into the structure of the transporter, the topological configurations of other VirB proteins were also examined. Results from hydropathy analyses, subcellular localization, protease susceptibility, and PhoA reporter fusion studies support a model that all of the VirB proteins localize at one or both of the bacterial membranes. Immunoprecipitation and Co$\sp{2+}$ affinity chromatography studies demonstrated that native VirB4 (87-kDa) and a functional N-terminally tagged HIS-VirB4 derivative (89-kDa) interact and that the interaction is independent of other VirB proteins. A $\lambda$ cI repressor fusion assay supplied further evidence for VirB4 dimer formation. A VirB4 dimerization domain was localized to the N-terminal third of the protein, as judged by: (i) transdominance of an allele that codes for this region of VirB4; (ii) co-retention of a His-tagged N-terminal truncation derivative and native VirB4 on Co$\sp{2+}$ affinity columns; and (iii) dimer formation of the N-terminal third of VirB4 fused to the cI repressor protein. Taken together, these findings are consistent with a model that VirB4 is topologically configured as an integral cytoplasmic membrane protein with two periplasmic domains and that VirB4 assembles as homodimers via an N-terminal dimerization domain. Dimer formation is postulated to be essential for stabilization of VirB4 monomers during T-complex transporter assembly. ^

Proposal for the inclusion of misoprostol in the WHO model list of essential medicines

Gynuity