Donatella Degl'Innocenti

PP60V-SRC PHOSPHORYLATES AND ACTIVATES LOW MOLECULAR WEIGHT PHOSPHOTYROSINE-PROTEIN PHOSPHATASE

Low M phosphotyrosine-protein phosphatase belongs to the non-receptor cytosolic phosphotyrosine-protein phosphatase subfamily. It has been demonstrated that this enzyme dephosphorylates receptor tyrosine kinases, namely the epidermal growth factor receptor in vitro and the platelet-derived growth factor receptor in vivo. Low M phosphotyrosine-protein phosphatase is constitutively tyrosine-phosphorylated in NIH/3T3 cells transformed by pp60. The same tyrosine kinase, previously immunoprecipitated, phosphorylates this enzyme in vitro as well. Phosphorylation is enhanced using phosphatase inhibitors and phenylarsine oxide-inactivated phosphatase, consistently with the existence of an auto-dephosphorylation process. Intermolecular dephosphorylation is demonstrated adding the active enzyme in a solution containing the inactivated and previously phosphorylated one. This tyrosine phosphorylation correlates with an increase in catalytic activity. Our results provide evidence of a physiological mechanism of low M phosphotyrosine-protein phosphatase activity regulation.

Inhibition of cellular response to platelet-derived growth factor by low M r phosphotyrosine protein phosphatase overexpression

The role of low M r phosphotyrosine protein phosphatase (PTPase) in the control of cell proliferation was studied. A synthetic gene coding for PTPase was transfected and expressed in NIH/3T3 fibroblasts. The effects of the enzyme were particularly evident when cells were stimulated by platelet‐derived growth factor (PDGF). The mitogenic response to PDGF was decreased and the inhibition reached 90%. This effect was more pronounced with respect to fetal calf serum stimulation. Hormone‐dependent autophosphorylation of the PDGF receptor was significantly reduced. These results demonstrate that low M r PTPase, a cytosolic enzyme, not only affects cellular response to PDGF but also reduces the membrane receptor autophosphorylation.

Expression and turnover of acylphosphatase (muscular isoenzyme) in L6 myoblasts during myogenesis

Acylphosphatase (muscular isoenzyme) levels have been measured in L6J1 myoblasts either proliferating or differentiating into myotubes. Results indicated that the increase in enzyme levels during differentiation is very similar to that of creatine kinase, a specific muscular enzyme. The half-lives of acylphosphatase in myoblasts and myotubes were also determined; t1/2 values of 3 h 30 min (myoblasts), and 2 h 18 min (myotubes) were found. These results indicate that acylphosphatase could be considered a short-lived muscle-specific protein and that its increase in myotubes must be accompanied by an activation of its breakdown.

Angiotensin II upregulates renin-angiotensin system in human isolated T lymphocytes

This study was aimed at investigating the effects of Angiotensin (Ang) II stimulation on T lymphocytes mRNA expression of angiotensinogen (AGTN), angiotensin-converting enzyme (ACE) and AT1-receptor (R) and on ACE activity and Ang II content. The effects of Ang II stimulus were studied in lipopolysaccharide (LPS)-stimulated or not stimulated lymphocytes. mRNA expression for interferon-gamma (INF-gamma) was also studied to investigate whether a link between lymphocyte RAS and immunological function might occur. mRNAs for AGTN, ACE and AT1-R were obtained from peripheral blood of 18 healthy subjects and were quantified by real time quantitative transcriptase-polymerase chain reaction (PCR). ACE activity was assayed in cell pellets and supernatants by measuring the hippuric acid formation by high performance liquid chromatography (HPLC) and Ang II cell content was measured by radioimmunoassay (RIA) after HPLC separation. All determination were performed under baseline conditions and after the addition of 10(e- 13) M Ang II to LPS-stimulated or unstimulated lymphocytes. Ang II caused a significant upregulation of T subset lymphocytes gene expression of ACE and AT1-R and of INF gamma, and a marked increase in ACE activity and cell Ang II concentration. AGTN gene was never expressed. All these effects were further enhanced in T lymphocytes presitmulated by LPS and completely inhibited by Irbesartan. Our findings strongly support the evidence of a positive Ang II driven autocrine loop that upregulates cell RAS of isolated lymphocytes and activates the immuno response. The immuno-potentiating effect of Ang II, specifically shown in T subset, can be deleterious when local RAS are disregulated as in cardiovascular atherosclerotic disease.

Alteration of acylphosphatase levels in familial Alzheimer's disease fibroblasts with presenilin gene mutations

Acylphosphatase (AcPase), an enzyme that modulates the activity of Ca(2+)-ATPase by hydrolysing its phosphorylated moiety, has been found to be significantly higher in cultured skin fibroblasts from donors affected by early onset familial Alzheimers disease (EOFAD) with PS-1 and PS-2 gene mutations. Of the two known isoenzymes of acylphosphatase, only the erythrocyte one accounts for the total increase in activity. No relevant alteration was observed in phosphotyrosine phosphatase activity (PTPase), in Ca(2+)-ATPase and Na+, K(+)-ATPase activities of the same cells as compared to age-matched controls. This finding could suggest a possible explanation for the calcium-dependent biochemical alterations previously described in Alzheimers disease fibroblasts.

Intravitreal Infliximab Clearance in a Rabbit Model: Different Sampling Methods and Assay Techniques

PURPOSE To investigate the clearance of intravitreal infliximab with the use of different sampling techniques and immunoassay methods in rabbits. METHODS Infliximab (1.6 mg) was intravitreally injected into both eyes of 47 rabbits. Two approaches were used to collect the vitreous: the classic method and a microsampling technique. Whereas the classic method consists of collection of the whole vitreous after enucleation, the microsampling technique consisted of the aspiration of small (10-15 microL) samples with a 200-microL syringe. Samples were taken from 30 minutes to 40 days using both methods and were then compared. Infliximab concentration was estimated with competitive ELISA, dot blot analysis, and Western blot analysis. RESULTS The vitreous half-life of infliximab was estimated to be 6.5 +/- 0.6 days. The data indicated monoexponential decay reaching its conclusion after approximately 40 days. This decay was preceded by 4-day-long diffusion in the vitreous. Microsampling proved to be effective in the vitreous collection, giving statistically comparable signals (+/- 4%, P = 0.68) with respect to the classic procedure. ELISA proved to be the best analytical technique--especially if coupled with microsamplings--because of its lower detection limit, precision, and reduced amount of sample needed. No differences were observed between half-life values obtained by ELISA and dot blot analysis (P = 0.081) and Western blot analysis (P = 0.614). CONCLUSIONS The findings of this study added to the knowledge of infliximab clearance in the vitreous and confirmed the validity of a microsampling technique that was compared with the classic one. ELISA was found to be the best analytical technique when using microsampling.

Three-dimensional structural characterization of a novel Drosophila melanogaster acylphosphatase.

Analysis of the Drosophila melanogaster EST database led to the discovery and cloning of a novel acylphosphatase. The CG18505 gene coding for a new enzyme (AcPDro2) is clearly distinct from the previously described CG16870Acyp gene, which also codes for a D. melanogaster acylphosphatase (AcPDro). The putative catalytic residues, together with residues held to stabilize the acylphosphatase fold, are conserved in the two encoded proteins. Crystals of AcPDro2, which belong to the trigonal space group P3(1)21, with unit-cell parameters a = b = 45.8, c = 98.6 angstroms, gamma = 120 degrees, allowed the solution of the protein structure by molecular replacement and its refinement to 1.5 angstroms resolution. The AcPDro2 active-site structure is discussed.

Acylphosphatase is involved in differentiation of K562 cells.

The level of both isoforms of acylphosphatase was evaluated in the human erythroleukemia K562 cell line during differentiation. K562 cells were treated with PMA, which induces megakaryocytic differentiation, and with aphidicolin or hemin, which stimulate erythrocytic differentiation. While the MT isoform showed an average 10-fold increase independently of the differentiating agent used, only hemin treatment caused a similar increase of the CT isoform, suggesting a different role of the two isoforms in the cell. Treatment with either hemin or aphidicolin of K562 cells overexpressing the two acylphosphatase isoforms suggested the possibility that acylphosphatases play a role in the onset of differentiation.

Polyglutamine repeats are associated to specific sequence biases that are conserved among eukaryotes.

Nine human neurodegenerative diseases, including Huntingtons disease and several spinocerebellar ataxia, are associated to the aggregation of proteins comprising an extended tract of consecutive glutamine residues (polyQs) once it exceeds a certain length threshold. This event is believed to be the consequence of the expansion of polyCAG codons during the replication process. This is in apparent contradiction with the fact that many polyQs-containing proteins remain soluble and are encoded by invariant genes in a number of eukaryotes. The latter suggests that polyQs expansion and/or aggregation might be counter-selected through a genetic and/or protein context. To identify this context, we designed a software that scrutinize entire proteomes in search for imperfect polyQs. The nature of residues flanking the polyQs and that of residues other than Gln within polyQs (insertions) were assessed. We discovered strong amino acid residue biases robustly associated to polyQs in the 15 eukaryotic proteomes we examined, with an over-representation of Pro, Leu and His and an under-representation of Asp, Cys and Gly amino acid residues. These biases are conserved amongst unrelated proteins and are independent of specific functional classes. Our findings suggest that specific residues have been co-selected with polyQs during evolution. We discuss the possible selective pressures responsible of the observed biases.

GSH system in relation to redox state in dystrophic skin fibroblasts.

Glutathione and GSH-related enzymes were determined in human Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) skin fibroblasts in order to relate muscular dystrophy to the redox state of the cell. The analysis of GSH, GSSG and total GSH levels in normal and dystrophic-cultured fibroblasts shows no differences in normal growth condition. However, the specific activity of two GSH-related enzymes, glutathione S-transferases (GST) and gamma-glutamylcysteine synthetase (gamma-GCS), shows significant variations between normal and both types of dystrophic skin fibroblasts. These results suggest that even in normal growth condition some components of GSH metabolism may be altered. A condition of sublethal oxidation obtained by H(2)O(2) treatment was able to show a difference in the cellular response of GSH system components between normal and dystrophic cells. While in DMD cells there is a decrease of roughly 55% in GSH and of 30% in total GSH concentration, no changes are measured in normal and BMD cells. The remarkable increase in glutathione peroxidase (GPx) activity and decrease in GSH-reductase (GR) activity measured in DMD cells can in part explain these changes. These results indicate a different capacity of DMD cells to support oxidative stress with respect to BMD and normal cells, and suggest a possible role of the GSH-antioxidant system in dystrophic pathology.