Elżbieta Heger

Human DHHC proteins: a spotlight on the hidden player of palmitoylation.

Palmitoylation is one of the most common posttranslational lipid modifications of proteins and we now know quite a lot about it. However, the state of knowledge about the enzymes that catalyze this process is clearly insufficient. This review is focused on 23 human DHHC genes and their products - protein palmitoyltransferases. Here we describe mainly the structure and function of these proteins, but also, to a lesser degree, what the substrates of the enzymes are and whether they are related to various diseases. The main aim of this review was to catalogue existing information concerning the human DHHC family of genes/proteins, making them and their functions easier to understand.

Spectrins: A structural platform for stabilization and activation of membrane channels, receptors and transporters☆

This review focuses on structure and functions of spectrin as a major component of the membrane skeleton. Recent advances on spectrin function as an interface for signal transduction mediation and a number of data concerning interaction of spectrin with membrane channels, adhesion molecules, receptors and transporters draw a picture of multifaceted protein. Here, we attempted to show the current depiction of multitask role of spectrin in cell physiology. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé.

microRNAs: fine tuning of erythropoiesis

Cell proliferation and differentiation is a complex process involving many cellular mechanisms. One of the best-studied phenomena in cell differentiation is erythrocyte development during hematopoiesis in vertebrates. In recent years, a new class of small, endogenous, non-coding RNAs called microRNAs (miRNAs) emerged as important regulators of gene expression at the post-transcriptional level. Thousands of miRNAs have been identified in various organisms, including protozoa, fungi, bacteria and viruses, proving that the regulatory miRNA pathway is conserved in evolution. There are many examples of miRNA-mediated regulation of gene expression in the processes of cell proliferation, differentiation and apoptosis, and in cancer genesis. Many of the collected data clearly show the dependence of the proteome of a cell on the qualitative and quantitative composition of endogenous miRNAs. Numerous specific miRNAs are present in the hematopoietic erythroid line. This review attempts to summarize the state of knowledge on the role of miRNAs in the regulation of different stages of erythropoiesis. Original experimental data and results obtained with bioinformatics tools were combined to elucidate the currently known regulatory network of miRNAs that guide the process of differentiation of red blood cells.

Palmitoylation of MPP1 (membrane-palmitoylated protein 1)/p55 is crucial for lateral membrane organization in erythroid cells.

Background: Lateral membrane organization is important in many essential cellular functions. Results: Lack of palmitoylation of normal or unknown anemia erythrocyte membrane proteins, specifically MPP1, leads to changes in lateral membrane organization. Conclusion: Palmitoylation of MPP1 is crucial for membrane organization and is linked to the pathogenesis of hemolytic anemia. Significance: This might be the first mechanism of biological control of membrane lateral organization. S-Acylation of proteins is a ubiquitous post-translational modification and a common signal for membrane association. The major palmitoylated protein in erythrocytes is MPP1, a member of the MAGUK family and an important component of the ternary complex that attaches the spectrin-based skeleton to the plasma membrane. Here we show that DHHC17 is the only acyltransferase present in red blood cells (RBC). Moreover, we give evidence that protein palmitoylation is essential for membrane organization and is crucial for proper RBC morphology, and that the effect is specific for MPP1. Our observations are based on the clinical cases of two related patients whose RBC had no palmitoylation activity, caused by a lack of DHHC17 in the membrane, which resulted in a strong decrease of the amount of detergent-resistant membrane (DRM) material. We confirmed that this loss of detergent-resistant membrane was due to the lack of palmitoylation by treatment of healthy RBC with 2-bromopalmitic acid (2-BrP, common palmitoylation inhibitor). Concomitantly, fluorescence lifetime imaging microscopy (FLIM) analyses of an order-sensing dye revealed a reduction of membrane order after chemical inhibition of palmitoylation in erythrocytes. These data point to a pathophysiological relationship between the loss of MPP1-directed palmitoylation activity and perturbed lateral membrane organization.

Hereditary spherocytosis: identification of several HS families with ankyrin and band 3 deficiency in a population of southwestern Poland

Red blood cells of 17 patients out of seven families diagnosed with HS from the southwest of Poland were studied. In six families a deficiency of ankyrin was detected, and in one family a band 3 (anion-exchanger protein) deficiency was detected. Patients from six families with the ankyrin deficiency had a 19–51% decrease in ankyrin 2.1, while the family with the band 3 deficiency showed a 33% decrease in this protein content. All changes were statistically significant, as analysed by the Student t test (P<0.05). Analysis of haemolysis kinetics gives a reliable indication of altered osmotic properties of the spherocytic cells.

A novel L1340P mutation in the ANK1 gene is associated with hereditary spherocytosis

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(AC)n microsatellite polymorphism and 14-nucleotide deletion in exon 42 ankyrin-1 gene in several families with hereditary spherocytosis in a population of South-Western Poland

Defects in ankyrin-1 have been implicated in approximately half of all patients with hereditary spherocytosis. However, not all polymorphisms in this gene lead to the changes in expressed protein or to the changes of the level of its expression. In this study, we report on several cases of the (AC)n microsatellite polymorphism in 3′ untranslated region of ANK1 gene found in nine families (19 patients) with hereditary spherocytosis (HS) and also in ten healthy individuals from the same territory. We also found that 14-nucleotide deletion in this region of ANK1 which was shifted by five nucleotides in relation to another 14-nucleotide deletion listed in Single Nucleotide Polymorphism National Center for Biotechnology Information (SNP NCBI) database. This deletion seems to be present only in individuals with 11/14 and 13/14 AC repeats what would be an interesting correlation between these two features. However, comparison of the data obtained for HS patients and healthy individuals indicates that both polymorphisms are not connected to the pathology of hereditary spherocytosis.

A new frameshift mutation of the β-spectrin gene associated with hereditary spherocytosis.

Dear Editor, Hereditary spherocytosis (HS) is the most frequent congenital haemolytic anaemia in Caucasians. β-spectrin defects are typically inherited in an autosomal dominant manner with the clinical presentation of HS [5, 9].We report on a newmutation in the SPTB gene (466insG) leading to a frameshift and a premature stop codon 29 codons downstream in the region encoding the C-terminal part of the dimerization domain. Most probably, instability of mutant mRNA results in spectrin deficiency and clinically moderate to serious HS. The N-terminal region of the β-spectrin subunit consists of actin-binding domain and located downstream the dimerization domain consisting of the first two spectrin repeats. During our studies on HS cases in the population of Western Poland, we found a new mutation in a family with autosomal dominant HS [2–4]. Patients with moderate symptoms of the disease were recruited: mother (C10, splenectomized) and children (C14, C9), age ranged from 27 to 67 years. Diagnostic criteria for HS were based on typical features: spherocytes on peripheral blood smears, increased osmotic fragility, splenomegaly, increased bilirubin, reticulocytosis, anaemia and symptoms of gallstone disease (Supplemental Table I). The Ethics Committee of the Medical University of Wroclaw approved the study protocol. Informed consent was obtained from all patients and healthy individuals serving as a control before entering the protocol. Molecular genetic analyses of the studied patients and the unaffected family members were performed. The nucleotide sequence of the ANK1, SPTB and SLC4A1 genes were amplified by PCR from genomic DNA. During DNA analysis of these genes, several common polymorphisms were encountered (Supplemental Table II). DNA sequencing revealed that all of the studied patients were heterozygous for novel mutation 466insG in the exon 11 of the SPTB gene (Fig. 1a, b). RBC membrane protein gel electrophoresis demonstrated deficiency of some membrane proteins: β-spectrin and ankyrin-1, thereby supporting the diagnosis of HS (data not shown). Immunoblotting of erythrocyte membrane ghosts from C14 and C10 patients with this mutation with antibody recognising an actin binding domain of βspectrin [10] could not detect a truncated protein (data not shown), suggesting that this mutant transcript might be unstable. Electronic supplementary material The online version of this article (doi:10.1007/s00277-016-2838-0) contains supplementary material, which is available to authorized users.