Improved correction of F508del-CFTR biogenesis with a folding facilitator and an inhibitor of protein ubiquitination

A growing number of diseases are linked to the misfolding of integral membrane proteins, and many of these proteins are targeted for ubiquitin-proteasome-dependent degradation. One such substrate is a mutant form of the Cystic Fibrosis Transmembrane Conductance Regulator (F508del-CFTR). Protein folding "correctors" that repair the F508del-CFTR folding defect have entered the clinic, but they are unlikely to protect the entire protein from degradation. To increase the pool of F508del-CFTR protein that is available for correction by existing treatments, we determined a structure-activity relationship to improve the efficacy and reduce the toxicity of an inhibitor of the E1 ubiquitin activating enzyme that facilitates F508del-CFTR maturation. A resulting lead compound lacked measurable toxicity and improved the ability of an FDA-approved corrector to augment F508del-CFTR folding, transport the protein to the plasma membrane, and maintain its activity. These data support a proof-of-concept that modest inhibition of substrate ubiquitination improves the activity of small molecule correctors to treat CF and potentially other protein conformational disorders.

Synthesis and evaluation of esterified Hsp70 agonists in cellular models of protein aggregation and folding

Over-expression of the Hsp70 molecular chaperone prevents protein aggregation and ameliorates neurodegenerative disease phenotypes in model systems. We identified an Hsp70 activator, MAL1-271, that reduces α-synuclein aggregation in a Parkinson's Disease model. We now report that MAL1-271 directly increases the ATPase activity of a eukaryotic Hsp70. Next, twelve MAL1-271 derivatives were synthesized and examined in a refined α-synuclein aggregation model as well as in an assay that monitors maturation of a disease-causing Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) mutant, which is also linked to Hsp70 function. Compared to the control, MAL1-271 significantly increased the number of cells lacking α-synuclein inclusions and increased the steady-state levels of the CFTR mutant. We also found that a nitrile-containing MAL1-271 analog exhibited similar effects in both assays. None of the derivatives exhibited cellular toxicity at concentrations up to 100 μm, nor were cellular stress response pathways induced. These data serve as a gateway for the continued development of a new class of Hsp70 agonists with efficacy in these and potentially other disease models.

From CFTR biology toward combinatorial pharmacotherapy: expanded classification of cystic fibrosis mutations

More than 2000 mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) have been described that confer a range of molecular cell biological and functional phenotypes. Most of these mutations lead to compromised anion conductance at the apical plasma membrane of secretory epithelia and cause cystic fibrosis (CF) with variable disease severity. Based on the molecular phenotypic complexity of CFTR mutants and their susceptibility to pharmacotherapy, it has been recognized that mutations may impose combinatorial defects in CFTR channel biology. This notion led to the conclusion that the combination of pharmacotherapies addressing single defects (e.g., transcription, translation, folding, and/or gating) may show improved clinical benefit over available low-efficacy monotherapies. Indeed, recent phase 3 clinical trials combining ivacaftor (a gating potentiator) and lumacaftor (a folding corrector) have proven efficacious in CF patients harboring the most common mutation (deletion of residue F508, ΔF508, or Phe508del). This drug combination was recently approved by the U.S. Food and Drug Administration for patients homozygous for ΔF508. Emerging studies of the structural, cell biological, and functional defects caused by rare mutations provide a new framework that reveals a mixture of deficiencies in different CFTR alleles. Establishment of a set of combinatorial categories of the previously defined basic defects in CF alleles will aid the design of even more efficacious therapeutic interventions for CF patients.

Plasmodium falciparum encodes a single cytosolic type I Hsp40 that functionally interacts with Hsp70 and is upregulated by heat shock

Heat shock protein 70 (Hsp70) and heat shock protein 40 (Hsp40) function as molecular chaperones during the folding and trafficking of proteins within most cell types. However, the Hsp70-Hsp40 chaperone partnerships within the malaria parasite, Plasmodium falciparum, have not been elucidated. Only one of the 43 P. falciparum Hsp40s is predicted to be a cytosolic, canonical Hsp40 (termed PfHsp40) capable of interacting with the major cytosolic P. falciparum-encoded Hsp70, PfHsp70. Consistent with this hypothesis, we found that PfHsp40 is upregulated under heat shock conditions in a similar pattern to PfHsp70. In addition, PfHsp70 and PfHsp40 reside mainly in the parasite cytosol, as assessed using indirect immunofluorescence microscopy. Recombinant PfHsp40 stimulated the ATP hydrolytic rates of both PfHsp70 and human Hsp70 similar to other canonical Hsp40s of yeast (Ydj1) and human (Hdj2) origin. In contrast, the Hsp40-stimulated plasmodial and human Hsp70 ATPase activities were differentially inhibited in the presence of pyrimidinone-based small molecule modulators. To further probe the chaperone properties of PfHsp40, protein aggregation suppression assays were conducted. PfHsp40 alone suppressed protein aggregation, and cooperated with PfHsp70 to suppress aggregation. Together, these data represent the first cellular and biochemical evidence for a PfHsp70-PfHsp40 partnership in the malaria parasite, and furthermore that the plasmodial and human Hsp70-Hsp40 chaperones possess unique attributes that are differentially modulated by small molecules.

Evidence for inhibition of low density lipoprotein oxidation and cholesterol accumulation by apolipoprotein H (beta2-glycoprotein I)

Low density lipoprotein (LDL) oxidation and lipid accumulation are thought to enhance the progression of atherosclerosis. Apolipoprotein H (apoH) has been implicated in the development of human atherosclerosis. However, the roles of apoH in the oxidative modification of LDL and cellular accumulation of lipid constituents remained uncharacterized. In this study, the level of plasma apoH was found to be significantly associated with the oxidative susceptibility of LDL in human subjects. Plasma levels of apoH were positively correlated with the lag time but negatively correlated with LDL oxidation rate in conjugated diene formation. By using a J774 A.1 macrophage culture system, we found that apoH could not only inhibit the formation of conjugated diene and thiobarbituric acid-reactive substances, but also reduce the electrophoretic mobility of oxidized LDL. Furthermore, apoH decreased cellular accumulation of cholesterol via a reduction in cholesterol influx and an increase in cholesterol efflux. This is the first demonstration that apoH appears to have "antioxidant"-like effects on LDL oxidation. The results also suggest that apoH can inhibit the translocation of cholesterol from extracellular pools to macrophages, suggesting that apoH may play an important role in the prevention of atherosclerosis.

Differential distribution of apolipoprotein E in young and aged spontaneously hypertensive and stroke-prone rats

OBJECTIVES

To evaluate whether the differential distribution of apolipoprotein E among lipoprotein fractions and hepatic expression of the apolipoprotein E gene are causal factors in the regulation of lipid metabolism and physiological functions in young and aged spontaneously hypertensive and stroke-prone rats.

DESIGN AND METHODS

Biochemical analyses were performed on serum and hepatic specimens from young (2-month-old) and aged (8-month-old) spontaneously hypertensive rats, stroke-prone spontaneously hypertensive rats and normotensive Wistar-Kyoto rats. Levels of apolipoprotein E among various lipoprotein fractions were determined using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Liver concentrations of apolipoprotein E mRNA were analyzed by Northern blotting and relative levels of apolipoprotein E mRNA in different strains of rats were compared. Statistical analysis was performed by measuring correlations between hepatic apolipoprotein E mRNA levels and biological parameters.

RESULTS

Levels of apolipoprotein E in high-density and low-density lipoproteins were significantly lower in hypertensive rats than in age-matched normotensive Wistar- Kyoto rats. Although there was a significant increase in high-density lipoprotein apolipoprotein E contents in all aged animals, the elevation in aged hypertensive rats was much less than that in aged normotensive rats. Levels of apolipoprotein E in the very-low-density lipoprotein fraction were diminished in young stroke-prone rats but were remarkably high in aged rats. Steady-state levels of apolipoprotein E mRNA increased with age in all strains of rats, whereas aged hypertensive rats exhibited lower apolipoprotein E mRNA levels than aged normotensive rats.

CONCLUSIONS

The distribution of apolipoprotein E among various lipoprotein fractions was dramatically altered with age, and the alteration varied among different strains of rats. The differential distribution of apolipoprotein E in young and aged spontaneously hypertensive and stroke-prone rats suggests that apolipoprotein E could be a causal factor that disturbs the homeostasis of lipids and lipoproteins and perturbs physiological functions in hypertensive rats.

Polymorphisms of the apolipoprotein B 3' variable number of tandem repeats region associated with coronary artery disease in Taiwanese

We studied the allelic frequency of the variable number of tandem repeats region 3' of the apolipoprotein B gene (apoB 3' VNTR) and its impact on coronary artery disease (CAD) in 150 patients with CAD and 153 normal controls in a Taiwan population. apoB 3' VNTR alleles were classified according to the number of repeats of a 15-bp hypervariable elements (HVE), the sequence of which was determined using the polymerase chain reaction and direct sequencing. Thirteen alleles comprising from 26 to 54 HVEs were identified. The CAD patients had greater heterozygosity (0.58 vs 0.42) and a higher frequency of long (> 36-HVE) apoB 3' VNTR alleles than the controls (18.7% vs 10.8%, p < 0.01). CAD patients with two HVE-36 alleles and no HVE-32 alleles (the two most common forms) had significantly higher concentrations of LDL-cholesterol, apolipoprotein B, and triglycerides, and significantly lower values of HDL-cholesterol and apolipoprotein AI than the control group (p < 0.01 for all comparisons). The length of the apoB 3' VNTR was not correlated with the plasma concentrations of any of the lipids. We conclude that long apoB 3' VNTR alleles occur more frequently in CAD patients, but that apoB 3'VNTR genotypic variation has little impact on the risk of dyslipidemia in Taiwanese.

Repetitive elements in the third intron of murine apolipoprotein A-I gene

Genomic DNAs containing the gene encoding apolipoprotein A-I (apoA-I) from four strains of mice and three strains of rats have been sequenced. Some peculiar repetitive sequences were found in the third intron of apoA-I of the murine species. The striking features include regular tandem repeats of C(A)4 and C(A)6 in mice and long A-tracts in rats. Not completely identical but very similar motifs were found in mice or rats belonging to the same species while repetitive elements from different species show some variation from their species-specific consensus sequences. These repetitive motifs are very similar to the sequences flanking human Alu and rodent B1 repetitive elements, although no evidence for the existence of Alu or B1 was found near the peculiar repetitive DNA sequences in apoA-I gene.

Iron and salicylate induction of cytochrome P450BM-1 in Bacillus megaterium

The effects of iron and salicylate on the expression of cytochrome P450s in Bacillus megaterium were investigated in this report. Immunoblot analysis showed that the addition of 4 mM ferric iron or 10 mM salicylate to the culture medium resulted in a significant increase in the P450BM-1 level, while the same condition had little effect on P450BM-3 expression. Substantial induction of chloramphenicol acetyltransferase (CAT) activity by iron and salicylate in B. megaterium cells bearing a P450BM-1 promoter-cat transcriptional fusion vector suggests that the induction of P450BM-1 by iron and salicylate occurs at the transcriptional level. Unexpectedly, in contrast to the bm1P1-dependent induction of P450BM-1 by pentobarbital, disruption of bm1P1 gene did not affect induction of P450BM-1 by iron and salicylate. This result suggests that the induction of P450BM-1 by iron and salicylate occurs by a bm1P1-independent mechanism. To our knowledge, this is the first example of an iron-regulated cytochrome P450 gene in prokaryotes.

Changes in plasma levels of lipids and lipoprotein composition in patients with Kawasaki disease

Studies on the response of plasma lipids and lipoproteins to Kawasaki disease are scarce so far. The purpose of this study was to investigate the changes in plasma levels of lipids and apolipoproteins as well as the composition of different lipoproteins in patients during the acute and convalescence phases of Kawasaki disease. The results showed that during the acute phase, the concentrations of plasma high density lipoprotein (HDL)-cholesterol, apolipoprotein A-I (apoA-I) and A-II (apoA-II) were significantly reduced. While the reduction of HDL-cholesterol was mainly related to the lowering of esterified and unesterified cholesterols in HDL2 during the acute stage of Kawasaki disease, most of which recovered during the subsequent convalescence phase. The plasma concentration of triglycerides was 46% higher in patients during the acute phase of Kawasaki disease than in the control subjects, which may be ascribed to the increase of triglycerides in very low density lipoprotein (VLDL), low density lipoprotein (LDL) and HDL2. The variables studied above did not appear to be independent parameters. The level of plasma apoA-I showed a stronger negative association with triglyceride concentration (r = -0.22) than apoA-II (r = -0.11) and HDL-cholesterol (r = -0.07). Furthermore, the levels of cholesterol, apoA-I and apoA-II in HDL2, but not in HDL3, were inversely correlated with the levels of triglyceride. We conclude that the temporary changes of lipid levels associated with Kawasaki disease results predominantly from alterations of lipoprotein composition.

Alterations of serum lipid levels and their biological relevances during and after pregnancy

In normal pregnancy, all women displayed a significant elevation of serum triglyceride (TG), total cholesterol (TC), low density cholesterol (LDL-C) and high density cholesterol (HDL-C) during parturition. To study the quantitative changes in serum levels of lipids and their biological relevances during and after pregnancy, blood samples were collected from 62 normally pregnant women throughout gestation and 6 to 12 weeks postpartum. Compared with 184 nonpregnant control subjects, TG, TC, LDL-C and HDL-C were significantly elevated during the second and third trimesters of pregnancy but dropped sharply after pregnancy. To further understand the effect of pregnancy on other metabolic parameters, we compared the relative levels of apolipoproteins such as apolipoprotein A-I (apoA-I) and apolipoprotein B (apoB), lipoprotein (a) (Lp(a)) and blood sugar during and after pregnancy. We found that apoB concentration progressively increased with advancing gestation, while the levels of apoA-I, Lp(a) and blood sugar were independent of gestation process. The physiological significance of hyperlipidemia during pregnancy is also discussed in this study.

Restriction fragment length polymorphisms of apolipoprotein B gene in Chinese population with coronary heart disease

Three restriction fragment length polymorphisms (RFLPs), EcoRI (R), Xbal (X), and Mspl (M) of the apolipoprotein (apo)B gene, were studied to determine their distribution frequencies and influence on the lipid profiles in 148 Chinese patients with documented coronary heart disease (CHD) and in 153 healthy subjects. The plasma concentrations of cholesterol and apoB showed no difference between the CHD patients and controls. However, CHD patients had significantly higher concentrations of low-density lipoprotein cholesterol and triglyceride and lower concentrations of high-density lipoprotein cholesterol than the controls. The frequencies of these three apoB RFLPs did not differ between the CHD patients and controls. Compared with South Asians and Caucasians, the Chinese in Taiwan showed a much lower frequency of R-, X+, and M- alleles. There was no evidence of an association between lipid profiles and RFLPs in either CHD patients or controls. The weak association of EcoRI, Xbal, and Mspl polymorphisms of the apoB gene with CHD indicates that the three RFLPs cannot be used as a predictor for the risk of CHD in the Chinese population.

Restriction fragment length polymorphisms of apolipoprotein B gene in Chinese population with coronary heart disease

Three restriction fragment length polymorphisms (RFLPs), EcoRI (R), Xbal (X), and Mspl (M) of the apolipoprotein (apo)B gene, were studied to determine their distribution frequencies and influence on the lipid profiles in 148 Chinese patients with documented coronary heart disease (CHD) and in 153 healthy subjects. The plasma concentrations of cholesterol and apoB showed no difference between the CHD patients and controls. However, CHD patients had significantly higher concentrations of low-density lipoprotein cholesterol and triglyceride and lower concentrations of high-density lipoprotein cholesterol than the controls. The frequencies of these three apoB RFLPs did not differ between the CHD patients and controls. Compared with South Asians and Caucasians, the Chinese in Taiwan showed a much lower frequency of R-, X+, and M- alleles. There was no evidence of an association between lipid profiles and RFLPs in either CHD patients or controls. The weak association of EcoRI, Xbal, and Mspl polymorphisms of the apoB gene with CHD indicates that the three RFLPs cannot be used as a predictor for the risk of CHD in the Chinese population.

A gene for cytochrome c oxidase subunit II in duck mitochondrial DNA: structural features and sequence evolution

The gene encoding cytochrome c oxidase subunit II (COXII) was amplified by polymerase chain reaction (PCR) using mitochondrial DNAs (mtDNAs) isolated from two genera of domesticated ducks, Anas platyrhnchos and Cairina muschata, and their intergeneric and intrageneric hybrids as templates. Comparison of the nucleotide sequences from the two different duck lineages shows that they have approximately 91% homology. The nucleotide substitution pattern in the duck COXII gene reveals a high transition/transversion ratio (8.8:1.0) while 93.2% of the nucleotide substitutions are silent. The duck COXII, which uses GUG as the initiation codon, contains 228 amino acid residues. Comparison of the deduced COXII amino acid sequences in duck, chicken, Xenopus laevis, mouse, bovine and human reveals five highly conserved domains. The evolutionary conservation of the primary structure of COXII implies its functional importance.

Excess energy and nitrogen balance at protein intakes above the requirement level in young men

Effects of excess energy on nitrogen balance at above the safe level of protein intake were studied in six young men. They were given test diets with a fixed protein intake of 1.2 g.kg-1.d-1 but with three successive energy (E) levels: at maintenance (1.0 E), 15% above maintenance (1.15 E) and 30% above maintenance (1.3 E), both in ascending (1.0 E, 1.15 E, 1.3 E) and descending (1.3 E, 1.15 E, 1.0 E) sequences. Duration of each dietary period was 10 d. N balance increased from 7.2 to 23.8 to 33.3 mg N.kg-1.d-1 in the ascending series and decreased from 27.8 to 17.6 to 4.8 mg N.kg-1.d-1 in the descending series. The changes in N balance per 100 kcal change in energy intake ranged between 144 and 243 mg with smaller changes at higher energy levels. Biological value and net protein utilization of the dietary protein were positively correlated with energy intake in both the ascending series and the descending series (p less than 0.001).

Identification of erythropoietin receptors in isolated membranes from Friend virus infected mice spleen cells

It has been shown that radiolabeled erythropoietin (epo) specifically binds to homogeneous epo-responsive spleen cells from mice infected with the anemic variant of the Friend virus. We now report that membranes isolated from these cells retain the ability to specifically bind epo. Spleen cells were swollen in ice-cold 10 mM Tris-Cl pH 7.4 containing 0.2 mM phenylmethyl sulfonylfluoride for 5 minutes, after which the cells were homogenized and centrifuged to remove nuclear fraction. Membranes were collected by centrifuging the supernatant at 75,000 g for 90 min. Utilizing 3H-epo labeled at the terminal sialic acids of the carbohydrate moieties or 125I-epo labeled at the tyrosine residues, it was shown that the isolated membranes contained specific epo binding sites. About 90% of the binding could be inhibited by the presence of unlabeled epo whereas no inhibition was seen with other glycoproteins and growth factors. Equilibrium could be reached in approximately 2.5 hr at 25 degrees C or 1.5 hr at 37 degrees C. Binding could be saturated at an epo concentration of about 3 nM, Scatchard analysis indicated a single class of receptors with a Kd of approximately 1.5 nM.

Effects of H2-antagonists on androgen imprinting of male hepatic functions

Many of the sex-differentiated functions of the liver of adult male rats depend upon the occurrence of neonatal androgen imprinting, a brief surge of androgen early in life. We investigated whether androgen imprinting is necessary for the development and maintenance of levels of a microsomal enzyme, estrogen-2-hydroxylase (E-20Hase), and a male-specific cytosolic estrogen binder (MEB) which are higher in adult male than in adult female rats. Cimetidine, a weakly antiandrogenic H2 blocker, was administered to pregnant and lactating rats from day 12 of gestation through weaning on day 21. Livers of male progeny, 120-150 days of age, were assayed for E-2OHase and MEB activity; a maternal dose equivalent to 2.5 times the usual human dose inhibited MEB activity in the levels of the offspring by 40% but had no effect on E-2OHase. However, a higher dose (5 times the human dose) was effective in reducing the E-2OHase activity by 50%. Rats whose mothers had received either no drug or an equivalent dose of ranitidine, another H2 blocker without antiandrogenic activity, were used as controls. The groups were not different in hepatic cytosolic androgen receptor content, body weight, or serum testosterone. In other studies, the requirement of neonatal androgen imprinting for full expression of adult levels of MEB and E-2OHase was determined. Female rats, which have low levels of E-2OHase and undetectable levels of MEB, were given androgen on day 1, on day 60 after ovariectomy, or at both times. Levels of E-2OHase equivalent to those in adult males were induced in females receiving both androgen treatments, whereas either treatment alone induced E-2OHase to the level of that in males castrated at adulthood or neonatally, which is about 50% that in normal male controls. In addition, MEB levels were induced in females to 85% of that in normal males by both androgen treatments and to 50% by administration of androgen to adult females or to adult males castrated neonatally. Administration of androgen to females during the neonatal period only did not induce MEB. We conclude that both MEB and E-2OHase require androgen imprinting for full expression in adult male rats.