Interaction between acylphosphatase and SERCA in SH-SY5Y cells

Ca²⁺ transport by sarco/endoplasmic reticulum, tightly coupled with the enzymatic activity of Ca²⁺-dependent ATPase, controls the cell cycle through the regulation of genes operating in the critical G₁ to S checkpoint. Experimental studies demonstrated that acylphosphatase actively hydrolyses the phosphorylated intermediate of sarco/endoplasmic reticulum calcium ATPase (SERCA) and therefore enhances the activity of Ca²⁺ pump. In this study we found that SH-SY5Y neuroblastoma cell division was blocked by entry into a quiescent G₀-like state by thapsigargin, a high specific SERCA inhibitor, highlighting the regulatory role of SERCA in cell cycle progression. Addition of physiological amounts of acylphosphatase to SY5Y membranes resulted in a significant increase in the rate of ATP hydrolysis of SERCA. In synchronized cells a concomitant variation of the level of acylphosphatase isoenzymes opposite to that of intracellular free calcium during the G₁ and S phases occurs. Particularly, during G₁ phase progression the isoenzymes content declined steadily and hit the lowest level after 6 h from G₀ to G₁ transition with a concomitant significant increase of calcium levels. No changes in free calcium and acylphosphatase levels upon thapsigargin inhibition were observed. Moreover, a specific binding between acylphosphatase and SERCA was demonstrated. No significant change in SERCA-2 expression was found. These findings suggest that the hydrolytic activity of acylphosphatase increase the turnover of the phosphoenzyme intermediate with the consequences of an enhanced efficiency of calcium transport across endoplasmic reticulum and a subsequent decrease in cytoplasmic calcium levels. A hypothesis about the modulation of SERCA activity by acylphosphatase during cell cycle in SY5Y cells in discussed.     

Twenty years of artificial directional selection have shaped the genome of the Italian Large White pig breed

In this study, we investigated at the genome‐wide level if 20 years of artificial directional selection based on boar genetic evaluation obtained with a classical BLUP animal model shaped the genome of the Italian Large White pig breed. The most influential boars of this breed (n = 192), born from 1992 (the beginning of the selection program of this breed) to 2012, with an estimated breeding value reliability of >0.85, were genotyped with the Illumina Porcine SNP60 BeadChip. After grouping the boars in eight classes according to their year of birth, filtered single nucleotide polymorphisms (SNPs) were used to evaluate the effects of time on genotype frequency changes using multinomial logistic regression models. Of these markers, 493 had a P_Bonferroni < 0.10. However, there was an increasing number of SNPs with a decreasing level of allele frequency changes over time, representing a continuous profile across the genome. The largest proportion of the 493 SNPs was on porcine chromosome (SSC) 7, SSC2, SSC8 and SSC18 for a total of 204 haploblocks. Functional annotations of genomic regions, including the 493 shifted SNPs, reported a few Gene Ontology terms that might underly the biological processes that contributed to increase performances of the pigs over the 20 years of the selection program. The obtained results indicated that the genome of the Italian Large White pigs was shaped by a directional selection program derived by the application of methodologies assuming the infinitesimal model that captured a continuous trend of allele frequency changes in the boar population.     

Effect of pH on the interaction of botulinum neurotoxins A, B and E with liposomes.

The interaction of botulinum neurotoxin serotypes A, B and E with membranes of different lipid compositions was examined by photolabelling with two photoreactive phosphatidylcholine analogues that monitor the polar region and the hydrophobic core of the lipid bilayer. At neutral pH the neurotoxins interacted both with the polar head groups and with fatty acid chains of phospholipids. At acidic pHs the neurotoxins underwent structural changes characterized by a more extensive interaction with lipids. Both the heavy and light chain subunits of the neurotoxins were involved in the process. The change in the nature and extent of toxin-lipid interaction occurred in the pH range 4-6 and was not influenced by the presence of polysialogangliosides. The present data are in agreement with the idea that botulinum neurotoxins enter into nerve cells from a low pH intracellular compartment.     

Effect of acylphosphates on Ca2+ uptake by sarcoplasmic reticulum vesicles

The data presented in this paper concern a kinetic study of the calcium uptake by sarcoplasmic reticulum vesicles and of the hydrolysis of the substrates which support the process. The results show that substrates which are different from ATP, acetylphosphate, and carbamylphosphate are able to support calcium transport. The technique used to follow the process allows us to detect continuously the changes in the concentration of the calcium present in the external medium. In our experimental conditions the calcium uptake supported by all the high energy substrates tested proceeds for several seconds at a constant rate, presumably corresponding to the “steady state” of the process; furthermore the calcium transport is clearly Ca²⁺ and Mg²⁺ dependent: the lowering of the Ca⁺ concentration in the medium from 10^?4 to 10^?5m causes a remarkable reduction of the V of the calcium transport and an apparent increase of the affinity of the sarcoplasmic reticulum vesicles for the acylphosphates; in the absence of Mg²⁺, none of the substrates is able to support the calcium uptake which increases in the presence of rising amounts of Mg²⁺ in the reaction medium. Furthermore, both the calcium transport and the substrate hydrolysis appear to follow the Michaelis-Menten kinetics in the presence of acylphosphates but not in the presence of ATP. The hydrolytic activity of sarcoplasmic reticulum vesicles on ATP and acylphosphates reveals a clear Mg²⁺ dependence; furthermore, in the absence of free Ca²⁺ and in the presence of 5 mm Mg²⁺, the high energy substrates tested reveal a different susceptibility to the hydrolitic attack by sarcoplasmic reticulum vesicles.     

Porcine liver low Mr phosphotyrosine protein phosphatase: The amino acid sequence

Porcine low M_r phosphotyrosine protein phosphatase has been purified and the complete amino acid sequence has been determined. Both enzymic and chemical cleavages are used to obtain protein fragments. FAB mass spectrometry and enzymic subdigestion followed by Edman degradation have been used to determine the structure of the NH₂-terminal acylated tryptic peptide. The enzyme consists of 157 amino acid residues, is acetylated at the NH₂-terminus, and has arginine as COOH-terminal residue. It shows kinetic parameters very similar to other known low Mr PTPases. This PTPase is strongly inhibited by pyridoxal 5-phosphate (K=21M) like the low Mr PTPases from bovine liver, rat liver (AcP2 isoenzyme), and human erythrocyte (Bslow isoenzyme). The comparison of the 40–73 sequence with the corresponding sequence of other low Mr PTPases from different sources demonstrates that this isoform is highly homologous to the isoforms mentioned above, and shows a lower homology degree with respect to rat AcP1 and human Bfast isoforms. A classification of low M_r PTPase isoforms based on the type-specific sequence and on the sensitivity to pyridoxal 5-phosphate inhibition has been proposed.Abbreviations used PTPase phosphotyrosine protein phosphatase - TFA trifluoroacetic acid - SDS sodium dodecylsulfate - T tryptic peptides - SP endoproteinase Glu-C peptides - FAB fast atom bombardment - Ac acetyl - HPLC high-performance liquid chromatography - OPA o-phtaldialdehyde - PMSF phenylmethylsulfonyl fluoride - CD45 leukocyte common-antigen PTPase - LAR leukocyte-antigen-related PTPase - PTP IB human placental PTPase     

Comparative biochemistry of the ubiquinol-cytochrome c oxidoreductase (EC 1.10.2.2) isolated from different heart mitochondria

The ubiquinol-cytochrome c oxidoreductase (bc1 complex, EC 1.10.2.2) has been isolated from the heart mitochondria of beef, chicken, turkey, duck and tuna with an identical procedure. The polypeptide composition of the different complexes, compared using SDS-polyacrylamide gel electrophoresis, shows that the three subunits carrying the prosthetic groups of the enzyme are highly conserved in all species. Also the large subunits I and II (core proteins) and band VI appear to be conserved in structure, while subunits VII and VIIa show a most remarkable structural variation in the various complexes. The steady-state ubiquinol-cytochrome c reductase analysis of the active enzymes indicates that all the bc1 complexes follow essentially a ping-pong mechanism, with the cytochrome c substrate displaying a partial competitive inhibition vs the ubiquinol substrate. The cytochrome c specificity of the reductase activity clearly is different in the various bc1 complexes, whereas the quinol specificity appears to be identical in all the enzymes.     

TiME for TMEM106B

TMEM106B variants are genetically associated with frontotemporal lobar degeneration with TDP‐43 pathology (FTLD‐TDP), and are considered a major risk factor for this disease. As TMEM106B may be involved in other pathologies such as Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS), uncovering its cellular functions has become a priority. In this issue of The EMBO Journal, Schwenk et al ( 2014 ) combine loss‐of‐function experiments, live imaging and proteomics to unveil the physiological roles played by TMEM106B and its binding partner MAP6 in lysosomal function and transport.     

Molecular mechanisms of endocrine resistance and their implication in the therapy of breast cancer

The use of endocrine agents is a safe and effective treatment in the management of hormone-sensitive breast cancer. Unfortunately, sooner or later, tumor cells develop resistance to endocrine manipulation making useless this approach. During the last decade, new molecules and intracellular signaling pathways involved in endocrine resistance have been identified. Several studies have documented that estrogen receptor signaling may maintain a pivotal role in the tumor growth despite the failure of a previous hormonal treatment. In this review we will discuss the general principles for optimizing the choice of endocrine therapy based on an understanding of the molecular mechanisms responsible for resistance to the different anti-hormonal agents.     

Levels of complement C3 and C4 components in Amerindians living in an area with high prevalence of tuberculosis

The levels of complement C3 and C4 components were determined in non-indigenous (creoles) and indigenous (Warao) populations, the latter with an extremely high tuberculosis (TB) rate. Serum samples from 209 adults were studied and classified in 4 groups taking into account tuberculin skin tests (TST): (1) the group of Warao patients (58 positive for the TST, WP TST+ and 9 negative for the TST, WP TST-), (2) the group of creole patients (34 positive for the TST, CP TST+ and 9 negative for the TST, CP TST-), (3) the group of healthy Warao controls (38 positive and 14 negative for TST, WC TST+ and WC TST-, respectively), (4) the creole controls (26 positive and 21 negative for the TST, CC TST+ and CC TST-, respectively). With respect to the results concerning the measurement of both complement C3 and C4 components with the exception of the WC TST and the CC groups, the WP TST+ and WP TST- as well as WC TST+ groups showed a significant frequency of individuals with decreased levels of complement C3 component (20.6, 33.3, and 26.3%, respectively) and also C4 component (12.0, 11.1, and 13.3%, respectively) in comparison to both creole patients (CP TST+, 8.82% and CP TST-, 0% and CP TST+, 5.88% and CP TST-, 0%) for C3 and C4, respectively. The study of these parameters carried out in 15 Warao subjects with active infection, before and after anti-TB chemotherapy,statisticallyconfirmedthat the effective chemotherapy did not restore normal levels of the complement C3 and C4 components among Warao patients. Aditional tests for hepatitis B or hepatitis C infection, and the profile of the hepatic proteins were not associated to the deficiency in production of the complement components.In conclusion, the results show that within the Warao population, a high percentage of subjects exhibit decreased levels of both complement C3 and C4 components independent of latent or active infection and the status of TST.