Molecular cloning of cDNA for the import precursor of human coupling factor 6 of H(+)-ATP synthase in mitochondria

Overexpressing microRNA-203 alleviates myocardial infarction via interacting with long non-coding RNA MIAT and mitochondrial coupling factor 6

Myocardial infarction (MI) is one of the leading causes of high mortality worldwide. Long non-coding RNA myocardial infarction associated transcript (MIAT) and mitochondrial coupling factor 6 (CF6) aggravate MI. This study aimed to elucidate whether miR-203 interacted with MIAT and CF6 in MI. Results revealed that MIAT and CF6 expressions were upregulated and that miR-203 was downregulated in mouse myocardial tissues after MI, as well as in hypoxic mouse cardiomyocytes. The overexpression of MIAT in mouse cardiomyocytes raised CF6 expression, whereas the knockdown of MIAT had the opposite effect. Mechanistically, the luciferase reporter and RNA pull-down assays corroborated the binding between miR-203 and CF6 3'UTR and between miR-203 and MIAT. The simultaneous overexpression of miR-203 and MIAT restored the reduction of CF6 caused by miR-203 overexpression alone, and the overexpression of miR-203 diminished the percentage of infarct area and the apoptosis of cardiomyocytes in vivo. Our findings corroborate that overexpressing miR-203 alleviates MI via interacting with MIAT and CF6.

Nutritional regulation of coupling factor 6, a novel vasoactive and proatherogenic peptide

High sodium, high glucose, and obesity are important risk factors for age-related diseases such as cardiovascular disease (CVDs), stroke, and cancer. Coupling factor 6 (CF6) is released from vascular endothelial cells and functions as a circulating peptide that inhibits prostacyclin and nitric oxide generation by intracellular acidosis. High glucose elevates CF6 by activation of protein kinase C and p38 mitogen-activated protein kinase, whereas CF6 causes type 2 diabetes mellitus, resulting in a high glucose vicious cycle. Low glucose increases inhibitory factor peptide 1, an endogenous inhibitor of CF6. High salt intake increases CF6 through nuclear factor κB signaling, whereas CF6 induces salt-sensitive hypertension and salt-induced congestive heart failure. Oral administration of vitamin C cancels salt-induced increase in CF6, and estrogen replacement leads to the delayed onset of CF6-induced salt-sensitive hypertension and the rescue from cardiac systolic dysfunction. Because CF6 contributes to the onset of CVDs, nutritional regulation of CF6 will shed light on the understanding of preventive strategy and mechanisms for CVDs and a target for therapy.

Persistent STAT5 activation in myeloid neoplasms recruits p53 into gene regulation

STAT (Signal Transducer and Activator of Transcription) transcription factors are constitutively activated in most hematopoietic cancers. We previously identified a target gene, LPP/miR-28 (LIM domain containing preferred translocation partner in lipoma), induced by constitutive activation of STAT5, but not by transient cytokine-activated STAT5. miR-28 exerts negative effects on thrombopoietin receptor signaling and platelet formation. Here, we demonstrate that, in transformed hematopoietic cells, STAT5 and p53 must be synergistically bound to chromatin for induction of LPP/miR-28 transcription. Genome-wide association studies show that both STAT5 and p53 are co-localized on the chromatin at 463 genomic positions in proximal promoters. Chromatin binding of p53 is dependent on persistent STAT5 activation at these proximal promoters. The transcriptional activity of selected promoters bound by STAT5 and p53 was significantly changed upon STAT5 or p53 inhibition. Abnormal expression of several STAT5-p53 target genes (LEP, ATP5J, GTF2A2, VEGFC, NPY1R and NPY5R) is frequently detected in platelets of myeloproliferative neoplasm (MPN) patients, but not in platelets from healthy controls. In conclusion, persistently active STAT5 can recruit normal p53, like in the case of MPN cells, but also p53 mutants, such as p53 M133K in human erythroleukemia cells, leading to pathologic gene expression that differs from canonical STAT5 or p53 transcriptional programs.

Coupling factor 6 as a novel vasoactive and proatherogenic peptide in vascular endothelial cells

Coupling factor 6 (CF6) is composed of 76 amino acids and is present in the peripheral stalk of mitochondrial ATP synthase. The generation of CF6 is positively regulated by tumor necrosis factor alpha and shear stress via nuclear factor kappaB, and by high glucose via protein kinase C and p38 mitogen-activated protein kinase. CF6 is released outside of the cells from vascular endothelial cells, and binds to the beta-subunit of the plasma membrane-bound ATP synthase in vascular endothelial cells and leads to intracellular acidosis. CF6 produces vasoconstriction, and the biological active site resides at the C-terminal portion. CF6 suppresses prostacyclin generation via inhibition of cytosolic phospholipase A(2). CF6 also suppresses nitric oxide synthase activity via an increase in asymmetric dimethylarginine and a decrease in platelet/endothelial cell adhesion molecule-1. CF6 induces the gene and protein expression of proatherogenic molecules such as endothelin 2, urokinase type plasminogen activator receptor, estrogen receptor beta, a soluble short form of vascular endothelial growth factor receptor-1, and lectin-like oxidized low-density lipoprotein receptor-1. The plasma level of CF6 is elevated in patients with essential hypertension, diabetes mellitus, end-stage renal disease, acute myocardial infarction, and coronary heart disease. It is likely that CF6 contributes to the pathogenesis of cardiovascular diseases, but further intensive investigation is needed.

High glucose promotes the release and expression of novel vasoactive peptide, coupling factor 6, in human umbilical vein endothelial cells

As a novel vasoactive peptide, plasma coupling factor 6 (CF6) was shown to be elevated in patients with diabetes mellitus, yet the mechanism involved is unknown. We studied CF6 protein release and its potential mechanism in human umbilical vein endothelial cells (HUVECs) incubated with high glucose levels. High glucose level enhanced CF6 expression and peptide secretion in HUVECs in a time- and concentration-dependent manner, which was independent of increased osmolarity. PKC or p38 MAPK inhibition significantly suppressed high glucose-mediated CF6 release in HUVECs, and the inhibition rate was -45% and -30%, respectively. Also, high glucose-induced CF6 production was antagonized by insulin treatment. Hence, high glucose increases the expression and secretion of CF6 in endothelial cells and appears to be mediated by PKC and p38 MAPK activity.

Plasma Level of Mitochondrial Coupling Factor 6 Increases in Patients With Coronary Heart Disease

BACKGROUND

The aim of the present study was to investigate alterations in the plasma level of coupling factor 6 (CF6), a novel endogenous inhibitor of prostacyclin, in patients with coronary heart disease.

METHODS AND RESULTS

In total, 35 patients with coronary heart disease and 20 age-matched healthy subjects were examined. Plasma levels of CF6 and 6-keto-prostaglandin (PG)F(1a) (a stable metabolite of prostacyclin) were measured using radioimmunoassay. The plasma level of CF6 was significantly increased in patients (254.1+/-29.8 pg/ml vs 219.4 +/-36.7 pg/ml in controls, p<0.0001), whereas that of 6-keto-PGF(1a) was significantly decreased (23.4 +/-2.3 pg/ml vs 26.1+/-4.5 pg/ml in controls, p=0.001). Moreover, after percutaneous transluminal coronary angioplasty (PTCA) and stent therapy, the level of CF6 was further increased by 30% to 330.4+/-26.0 pg/ml, and that of 6-keto-PGF (1a) was decreased by 42% to 13.5+/-2.0 pg/ml, compared with baseline (all p<0.01). Univariate analysis showed a significant result that the plasma level of CF6 was inversely correlated with that of 6-keto-PGF(1a) in the patients. The plasma ratio of CF6 to 6-keto-PGF(1a) was 8.4 in the control group and that in patients with coronary heart disease was increased to 24.4 after the therapy from 10.9 before therapy.

CONCLUSIONS

The results suggest that an increased CF6 level may be responsible in part for the decreased prostacyclin level observed in patients with coronary heart disease, in particular after PTCA and stent therapy. As a potential risk factor for coronary heart disease, CF6 might have important clinical significance.

Plasma concentration of coupling factor 6 and cardiovascular events in patients with end-stage renal disease

BACKGROUND

Plasma asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase (NOS), is an independent predictor of overall mortality and cardiovascular outcome in hemodialysis patients. However, not only ADMA but also traditional risk factors account for only part of the high cardiovascular morbidity and mortality in these patients. We investigated cross-sectionally the association between coupling factor 6 (CF6), an endogenous inhibitor of prostacyclin synthesis, and cardiovascular events in 95 hemodialysis patients.

METHODS

Plasma CF6 level was measured by radioimmunoassay, whereas plasma ADMA level by high-performance liquid chromatography (HPLC).

RESULTS

Plasma levels of CF6 and ADMA were threefold higher in hemodialysis patients than in control individuals, and there was a positive correlation between these two compounds (r=0.25, P < 0.05). Plasma CF6 level was positively correlated with serum creatinine level (r=0.36, P < 0.01) and was reduced after dialysis (P < 0.05). Plasma CF6 and ADMA levels were both higher in hemodialysis patients complicating ischemic heart disease (myocardial infarction and/or angina) than in those free of cardiovascular events. In a multiple regression model, plasma CF6 level (r=0.24, P=0.023) and ADMA level (r=0.26, P=0.023) were independently related to the occurrence of ischemic heart disease in hemodialysis patients.

CONCLUSION

CF6 is a novel risk factor for ischemic heart disease in end-stage renal disease (ESRD). Synergism of this peptide and ADMA might contribute to its occurrence presumably by inhibition of prostacyclin and nitric oxide production. A prospective study is needed to evaluate this issue more precisely.

Plasma Mitochondrial Coupling Factor 6 in Patients with Acute Myocardial Infarction

Previous studies have shown that mitochondrial coupling factor 6 (CF6) is an endogenous peptide that inhibits prostacyclin (PGI2) synthesis in vascular endothelial cells. In this study, we measured the plasma CF6 level of patients with acute myocardial infarction (AMI) to observe dynamic changes of CF6. All patients showed elevated plasma CF6 levels upon admission for treatment of AMI. Their CF6 levels peaked approximately 72 h after the onset of AMI and remained high for 7 days. At 7 days, their CF6 levels decreased to the level seen upon admission, but not to within a normal range. Hyperlipidemic patients had significantly greater CF6 levels at 24 h after onset of AMI than patients with a normal lipid profile. On admission, the plasma CF6 level in patients with a cardiac function of Killip class > or =II was higher than that in patients with a Killip class I cardiac function. At 3 days after the onset of AMI, the plasma CF6 levels of patients with a creatinine kinase (CK) peak value > or =1,500 units/l were significantly higher than those of patients with a CK peak value <1,500 units/l (p =0.05). At 7 days after the onset of AMI, the plasma CF6 levels of patients who received no reperfusion were significantly higher than those of patients who received a successful reperfusion. The plasma CF6 levels of AMI patients at admission, at 24 h, and at 3 days after onset of symptoms correlated positively with the cardiac function by Killip classification, respectively. At 24 h after onset of AMI, the plasma CF6 levels correlated positively with plasma total cholesterol levels and low-density lipoprotein levels. At 3 days, the plasma level of CF6 correlated positively with the plasma CK peak value and correlated negatively with left ventricular ejection fraction. These results suggest that the plasma CF6 level was elevated in patients with AMI.

Circulating coupling factor 6 in human hypertension

OBJECTIVE

Coupling factor 6 is an endogenous inhibitor of prostacyclin synthesis and might function as an endogenous vasoconstrictor in the fashion of a circulating hormone in rats. We investigated the role of coupling factor 6 in human hypertension.

METHODS AND RESULTS

The patients with essential hypertension (EH) (n = 30) received a series of normal salt diet (12 g salt/day) for 3 days, low salt diet (2 g salt/day) for 7 days, and high salt diet (20-23 g salt/day) for 7 days. Normotensive control subjects (n = 27) received normal and low salt diets. The plasma level of coupling factor 6, measured by radioimmunoassay, during normal salt diet was higher in patients with EH than in normotensive subjects (17.6 +/- 1.7 versus 12.8 +/- 0.5 ng/ml, P < 0.01). Whereas the plasma level of coupling factor 6 was unchanged after salt restriction in normotensive subjects, it was decreased after salt restriction (from 12 g/day to 2 g/day) and was increased after salt loading (from 2 g/day to 20-23 g/day) in patients with EH. This increase in plasma level of coupling factor 6 was abolished by oral administration of ascorbic acid, but the level of blood pressure was unaffected. The percentage changes in plasma coupling factor 6 level after salt restriction and loading were positively correlated with those in mean blood pressure (r = 0.57, P < 0.01), and negatively correlated with those in plasma nitric oxide level (r = -0.51, P < 0.05).

CONCLUSION

These indicate that circulating coupling factor 6 is elevated in human hypertension and modulated by salt intake presumably via reactive oxygen species.

Mitochondrial coupling factor 6 is present on the surface of human vascular endothelial cells and is released by shear stress

BACKGROUND

We showed that mitochondrial coupling factor 6 (CF6), an endogenous inhibitor of prostacyclin synthesis, is present in the systemic circulation as a pressor substance in rats. We investigated the possibility of vascular endothelial cells as a source of circulating CF6.

METHODS AND RESULTS

We used 2 cultured endothelial cell lines, human umbilical vein endothelial cells (HUVECs) and ECV 304 cells (transformed HUVECs), for this study. Immunofluorescence microscopy of both ECV 304 and HUVECs confirmed the surface-associated immunoreactivity of anti-CF6 antibody on the plasma membrane. The concentration of CF6 in the medium increased gradually with time in both ECV 304 and HUVECs in static conditions. Exposure of ECV 304 and HUVECs to a fluid shear stress enhanced the release of CF6: In ECV 304, the concentration of CF6 in the medium (ng. well(-1). 6 hours(-1)) was 2.1+/-0.8 at baseline, 4.3+/-0.8 after shear at 15 dynes/cm(2), and 57.7+/-8.4 after shear at 25 dynes/cm(2). CF6 contents in the cell homogenate and mitochondria were both significantly increased after exposure of ECV 304 to 6-hour shear at 15 dynes/cm(2), whereas they were unchanged after shear stress at 25 dynes/cm(2). The ratio of CF6 to GAPDH mRNA was enhanced significantly, by 1.8+/-0.2-fold, after 6-hour shear stress at 25 dynes/cm(2). Flow cytometry analysis revealed that the surface-associated CF6 was significantly increased in a 3-hour static condition after the previous exposure of the cells to shear stress for 3 hours.

CONCLUSIONS

Vascular endothelial cells are a source of CF6, and shear stress regulates the release of the surface-associated CF6.

Mitochondrial coupling factor 6 as a potent endogenous vasoconstrictor

We demonstrated recently that coupling factor 6, an essential component of the energy-transducing stalk of mitochondrial ATP synthase, suppresses the synthesis of prostacyclin in vascular endothelial cells. Here, we tested the hypothesis that coupling factor 6 is present on the cell surface and is involved in the regulation of systemic circulation. This peptide is present on the surface of CRL-2222 vascular endothelial cells and is released by these cells into the medium. In vivo, the peptide circulates in the vascular system of the rat, and its gene expression and plasma concentration are higher in spontaneously hypertensive rats (SHRs) than in normotensive controls. Elevation of blood pressure with norepinephrine did not affect the plasma concentration of coupling factor 6. Intravenous injection of recombinant peptide increased blood pressure, apparently by suppressing prostacyclin synthesis, whereas a specific Ab to coupling factor 6 decreased systemic blood pressure concomitantly with an increase in plasma prostacyclin. Interestingly, the antibody's hypotensive effect could be abolished by treating with the cyclooxygenase inhibitor indomethacin. These findings indicate that mitochondrial coupling factor 6 functions as a potent endogenous vasoconstrictor in the fashion of a circulating hormone and may suggest a new mechanism for hypertension.

A novel inhibitory effect on prostacyclin synthesis of coupling factor 6 extracted from the heart of spontaneously hypertensive rats

The possible presence of an unknown prostacyclin synthesis inhibitory substance has been reported in some strains of rats. We purified the inhibitory substance from the heart of spontaneously hypertensive rats by collecting active fractions after gel-filtration column chromatography and two steps of reverse-phase high performance liquid chromatography. The amino acid composition and automated gas-phase sequencing of the full-length substance and fragments cleaved by AspN indicated that the prostacyclin-inhibitory peptide was identical to coupling factor 6. Recombinant rat coupling factor 6, which was synthesized using a cleavable fusion protein strategy, attenuated base-line and bradykinin (10(-6) M)-induced prostacyclin synthesis and [3H]arachidonic acid (AA) release in human umbilical vein endothelial cells in a dose-dependent manner (10(-9)-10(-7) M). Exogenous AA- and prostaglandin H2-induced prostacyclin synthesis were unchanged even after treatment with 10(-7) M recombinant coupling factor 6. Base-line and bradykinin-induced [3H]AA release were suppressed by arachidonyltrifluoromethyl ketone, a relatively specific inhibitor of cytosolic phospholipase A2 at 40 microM, and simultaneous administration of coupling factor 6 showed no further effect. Neither oleyloxyethyl phosphorylcholine at 1 microM nor bromoenol lactone at 1 microM affected AA release. Preincubation (1 min) with 10(-7) M recombinant coupling factor 6 had no influence on adenosine diphosphate- and collagen-induced platelet aggregations. We conclude that coupling factor 6 possesses a novel function of prostacyclin synthesis inhibition in endothelial cells via suppression of Ca2+-dependent cytosolic phospholipase A2, although it is unclear whether coupling factor 6 functions in normal conditions or only in pathophysiological states.

The role of the stalk in the coupling mechanism of F1F0-ATPases

The extrinsic and intrinsic membrane sectors of F1F0-ATPases are linked by a slender stalk 40-50 A in length. The stalk transmits the energy produced by oxidative or photosynthetic phosphorylation from the intrinsic sector, F0, to the catalytic sites in the extrinsic F1 sector. How this is achieved is unknown, but long-range conformational changes linked to transmembrane proton transport may be involved. In bacterial and chloroplast F1F0-ATPases, the stalk is probably a composite of subunits delta and epsilon, part of the gamma-subunit, and the extrinsic membrane domains of 2 subunits (identical or non-identical according to the species) that are bound to the membrane by their N-terminal regions. The stalk in the bovine mitochondrial enzyme appears to be more complex, and the gamma, delta, epsilon, OSCP, F6, b and d subunits all contribute to it. A bovine stalk complex has been assembled in vitro from bacterially expressed OSCP, F6, b and d, both in the presence and in the absence of F1-ATPase. One molecule of each of these subunits is present in the assembled complex, as there is also in each native F1F0-ATPase assembly. Providing that suitable crystals can be obtained, the stalk complex and the F1.stalk complex may permit the high resolution structure of bovine F1-ATPase to be extended into the stalk domain.

Molecular cloning and sequence of two cDNAs for human subunit c of H(+)-ATP synthase in mitochondria

Two cDNAs encoding different signal peptides (61 and 66 amino acid residues) and the same mature protein have been cloned from a human cDNA library with a rat subunit c cDNA. The amino acid sequence of the mature human subunit c of mitochondrial H(+)-ATP synthase was completely identical with those of the mature bovine, sheep and rat subunit c.

Molecular cloning and sequence of cDNAs for the import precursors of oligomycin sensitivity conferring protein, ATPase inhibitor protein, and subunit c of H(+)-ATP synthase in rat mitochondria

Four cDNAs for the import precursors of oligomycin sensitivity conferring protein (OSCP), ATPase inhibitor protein (IF1) and subunit cs (encoded by P1 and P2 genes) of rat mitochondrial H(+)-ATP synthase have been cloned from a rat cDNA library. The import precursors and the mature polypeptides of rat OSCP, IF1, subunit c (P1) and subunit c (P2) consisted of 23/190, 25/82, 61/75 and 66/75 amino acids, respectively.