E. F. da Cruz e Silva

The Physiological Relevance of Protein Phosphatase 1 and its Interacting Proteins to Health and Disease

Protein phosphorylation is a major regulatory mechanism of signal transduction cascades in eukaryotic cells, catalysed by kinases and reversed by protein phosphatases (PPs). Sequencing of entire genomes has revealed that ~3% of all eukaryotic genes encode kinases or PPs. Surprisingly, there appear to be 2-5 times fewer PPs than kinases. Over the past two decades it has become apparent that the diversity of Ser/Thr-specific PPs (STPP) was achieved not only by the evolution of new catalytic subunits, but also by the ability of a single catalytic subunit to interact with multiple interacting proteins. PP1, a STPP, is involved in the control of important cellular mechanisms. Several isoforms of PP1 are known in mammals: PP1α, PP1β and PP1γ. The various isoforms are highly similar, except for the N- and C-termini. The current view is that since PPs possess exquisite specificities in vivo, the key control mechanism must reside in the nature of the PP1 Interacting Protein (PIP) to which they bind. An increasing number of PIPs have been identified that are responsible for regulating the catalytic activity of PPs. Indeed, the diversity of such PIPs explains the need for relatively few catalytic subunit types, and makes them attractive targets for pharmacological intervention. This review will summarize the PIPs identified using the Yeast Two Hybrid methodology and alternative techniques, for instance bioinformatic and proteomic approaches. Further, it compiles 129 PP1-PIP relevant physiological interactions that are well documented in the literature. Finally, the use of PIPs as therapeutic targets will be addressed.

Toxicity of β-amyloid in HEK293 cells expressing NR1/NR2A or NR1/NR2B N-methyl-D-aspartate receptor subunits

Neurotoxicity induced by beta-amyloid peptide (Abeta) involves glutamate toxicity, resulting from overactivation of N-methyl-D-aspartate (NMDA) receptors and elevation of intracellular calcium. However, the heterogeneity of the NMDA receptors, frequently composed of NR1 and NR2A-D subunits, has been less studied. Thus, we determined the contribution of NMDA receptor subtypes on Abeta(1-40) toxicity in HEK293 cells transiently expressing NR1/NR2A or NR1/NR2B subunits. Analysis of lactate dehydrogenase (LDH) release and trypan blue exclusion revealed an increase in Abeta(1-40) toxicity upon NR1/NR2A expression, compared to NR1/NR2B, indicating loss of plasma membrane integrity. Furthermore, Abeta(1-40) decreased intracellular ATP in cells expressing NR1/NR2A. MK-801 ((+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine maleate), a noncompetitive NMDA receptor antagonist, partially prevented the decrease in cell viability and the energy impairment. These differences were not accounted for by the activation of caspases 2, 3, 8 and 9 or calpains or by DNA fragmentation, excluding the hypothesis of apoptosis. Functional NR1/NR2A and NR1/NR2B receptor subtypes were further evidenced by single-cell calcium imaging. Stimulation of NR1/NR2A receptors with NMDA/glycine revealed an increase in intracellular calcium in cells pre-exposed to Abeta(1-40). Opposite effects were observed upon activation of NR1/NR2B receptors. These results suggest that NR1/NR2A-composed NMDA receptors mediate necrotic cell death in HEK293 cells exposed to Abeta(1-40) through changes in calcium homeostasis.

Tyr687 dependent APP endocytosis and Abeta production.

The neurotoxic Abeta peptide is derived by proteolytic processing from the Alzheimer’s amyloid precursor protein (APP), whose short cytoplasmic domain contains several phosphorylatable amino acids. The latter can be phosphorylated ‘in vitro’ and ‘in vivo,’ and in some cases phosphorylation appears to be associated with the disease condition. Using APP-GFP fusion proteins to monitor APP processing, the role of Tyr687 was addressed by mimicking its constitutive phosphorylation (Y687E) and dephosphorylation (Y687F). Contrasting effects on subcellular APP distribution were observed. Y687E-APP-GFP was targeted to the membrane but could not be detected in transferrin containing vesicular structures, and exhibited a concomitant and dramatic decrease in Abeta production. In contrast, Y687F-APP-GFP was endocytosed similarly to wild type APP, but was relatively favoured for beta-secretase cleavage. Overall, Tyr687 appears to be a critical residue determining APP targeting and processing via different pathways, including endocytosis and retrograde transport. Significantly, from a disease perspective, mimicking Tyr687 phosphorylation resulted in a hitherto undescribed inhibition of Abeta production. Our results provide novel insights into the role of direct APP phosphorylation on APP targeting, processing and Abeta production.

In Vitro performance assessment of new brushite-forming Zn- and ZnSr-substituted β-TCP bone cements

The present study investigated the in vitro performance of brushite-forming Zn- and ZnSr-substituted beta-TCP bone cements in terms of wet mechanical strength and biological response. Quantitative phase analysis and structural refinement of the powdered samples were performed by X-ray powder diffraction and Rietveld refinement technique. Initial and final setting times of the cement pastes, measured using Gilmore needles technique, showed that ZnSrCPC sets faster than ZnCPC. The measured values of the wet strength after 48 h of immersion in PBS solution at 37 degrees C showed that ZnSrCPC cements are stronger than ZnCPC cements. Human osteosarcoma-derived MG63 cell line proved the nontoxicity of the cement powders, using the resazurin metabolic assay.

Αβ Hinders Nuclear Targeting of AICD and Fe65 in Primary Neuronal Cultures

The intracellular domain of the Alzheimer’s amyloid precursor protein (AICD) has been described as an important player in the transactivation of specific genes. It results from proteolytic processing of the Alzheimer’s amyloid precursor protein (APP), as does the neurotoxic Aβ peptide. Although normally produced in cells, Aβ is typically considered to be a neurotoxic peptide, causing devastating effects. By exposing primary neuronal cultures to relatively low Aβ concentrations, this peptide was shown to affect APP processing. Our findings indicate that APP C-terminal fragments are increased with concomitant reduction in the expression levels of APP itself. AICD nuclear immunoreactivity detected under control conditions was dramatically reduced in response to Aβ exposure. Additionally, intracellular protein levels of Fe65 and GSK3 were also decreased in response to Aβ. APP nuclear signaling is altered by Aβ, affecting not only AICD production but also its nuclear translocation and complex formation with Fe65. In effect, Aβ can trigger a physiological negative feedback mechanism that modulates its own production.

Understanding fatty acid metabolism through an active learning approach

A multi‐method active learning approach (MALA) was implemented in the Medical Biochemistry teaching unit of the Biomedical Sciences degree at the University of Aveiro, using problem‐based learning as the main learning approach. In this type of learning strategy, students are involved beyond the mere exercise of being taught by listening. Less emphasis is placed on transmitting information and the focus is shifted toward developing higher order thinking (analysis, synthesis, and evaluation). However, MALA should always involve clearly identified objectives and well‐defined targets. Understanding fatty acid metabolism was one of the proposed goals of the Medical Biochemistry unit. To this end, students were challenged with a variety of learning strategies to develop skills associated with group conflict resolution, critical thinking, information access, and retrieval, as well as oral and written communication skills. Overall, students and learning facilitators were highly motivated by the diversity of learning activities, particularly due to the emphasis on correlating theoretical knowledge with human health and disease. As a quality control exercise, the students were asked to answer a questionnaire on their evaluation of the whole teaching/learning experience. Our initial analysis of the learning outcomes permits us to conclude that the approach undertaken yields results that surpass the traditional teaching methods.

POP-Gene TIMOR: first forensic DNA marker study of East-Timor people

The first population-genetics study for the world newest independent country, East Timor, is presented. In this preliminary work, part of a major ongoing study on East-Timor genetic diversity, the allele frequencies and some statistical parameters of forensic interest were determined for the 15 loci included in AmpFLSTR Identifilerk genotyping kit. A total of 107 samples, collected from East Timorese of several linguistic groups, was typed. All markers are in Hardy-Weinberg equilibrium (except for D2S1338 and D5S818, but the deviations do not reach significance after Bonferroni correction). Observed heterozigosities varied between 72% (D5S818) and 92% (D8S1179). D 2003 Elsevier B.V. All rights reserved.

Immunolocalization of PPP1C Isoforms in SH-SY5Y Cells During the Cell Cycle

Phosphoprotein phosphatase 1 (PPP1) is the most widely expressed and abundant serine/threonine protein phosphatase. PPP1 regulates a variety of cellular functions such as glycogen metabolism, mitosis and meiosis, cell-cycle arrest, apoptosis, dynamics of actin cytoskeleton, protein synthesis among others. The versatility of the PPP1 catalytic subunit (PPP1C) is achieved by associating with different regulatory subunits that target PPP1C to a particular subcellular compartment determining its substrate specificity and activity. PPP1C is expressed in mammals in three isoforms: PPP1CA, PPP1CB and PPP1CC, each encoded by distinct genes. The PPP1C gene undergoes alternative splicing to originate PPP1CC1 and PPP1CC2 variants. PPP1A and PPP1C1 are expressed virtually in all tissues but are particularly enriched in the brain. The subcellular localization of the endogenous PPP1C isoforms is not fully elucidated, but all isoforms are found in the nucleus and cytoplasm, despite some isoform-specific differences in intranuclear distribution. Furthermore, it is known that PPP1 plays a key role in mitosis where PPP1C isoforms are differentially targeted to specific subcellular structures. However, in previous studies, non-neuronal cells were used as a model system to study PPP1 distribution during the cell cycle. In the studies here described, we used the neuronal-like cell line SH-SY5Y since PPP1 is a crucial protein in several neuronal functions.

13.10 – Protein Phosphatase 1 as a Potential Mediator of Aluminum Neurotoxicity

Reversible protein phosphorylation is a ubiquitous and universal process generally regarded as the major posttranslational modification through which numerous physiological processes are regulated (Cohen 2002a; de la Fuente van Bentem et al. 2008). It is a dynamic process whereby phosphate groups are incorporated into proteins by protein kinases and removed by protein phosphatases. Thus, protein phosphorylation is a reversible process that alters the function and/or localization of target proteins and in this fashion controls various biological functions. In turn, the protein kinases and protein phosphatases, which are particularly abundant and diverse in mammalian brain, are themselves regulated by a myriad of extracellular and intracellular signals. Many of the complex functions of the mammalian central nervous system are regulated by phosphorylation/dephosphorylation of key regulatory proteins. Many extracellular messengers exert their effects in the central nervous system by modulating the intracellular concentration of specific second messengers, which in turn lead to the activation/inhibition of specific protein kinases and phosphatases. As a result, abnormal phosphorylation of key regulatory proteins has been associated with a variety of disease conditions and dysfunctional states. Defects in protein phosphorylation mechanisms operating in the mammalian central nervous system may be a common feature of many neurological and chemical-induced disease states (Gong and Iqbal 2008; Lee and Messing 2008).

Colocalization Analysis of PPP1 Isoforms and Two Novel Targeting Subunits in Breast Carcinoma

Protein phosphatase 1 (PPP1) is the PPP most ubiquitous and each isoform interact with regulatory subunits that may be responsible for their subcellular localization. We identified PPP1R15B, C1ORF71 as novel regulators and the aim of this study was their further characterization in carcinoma cells. We analysed localization of each regulator in MDA-MB-468 cells and we transfected with constructs that we made with each as a GFP-fusion protein. For PPP1 cellular localization we used specific antibodies for each isoform. We observed the cells under a fluorescent microscope and LSM and we quantified co-localization. We found a high overlap coefficient of both the novel proteins with PPP1alpha and PPP1gamma1. We propose a model in which PPP1 regulator interacts with one or two regulatory subunits that may be used as target for therapeutic strategies.