Anna Gréen

Characterization of sequence variations in human histone H1.2 and H1.4 subtypes

In humans, eight types of histone H1 exist (H1.1–H1.5, H1°, H1t and H1oo), all consisting of a highly conserved globular domain and less conserved N‐ and C‐terminal tails. Although the precise functions of these isoforms are not yet understood, and H1 subtypes have been found to be dispensable for mammalian development, it is now clear that specific functions may be assigned to certain individual H1 subtypes. Moreover, microsequence variations within the isoforms, such as polymorphisms or mutations, may have biological significance because of the high degree of sequence conservation of these proteins. This study used a hydrophilic interaction liquid chromatographic method to detect sequence variants within the subtypes. Two deviations from wild‐type H1 sequences were found. In K562 erythroleukemic cells, alanine at position 17 in H1.2 was replaced by valine, and, in Raji B lymphoblastoid cells, lysine at position 173 in H1.4 was replaced by arginine. We confirmed these findings by DNA sequencing of the corresponding gene segments. In K562 cells, a homozygous GCC→GTC shift was found at codon 18, giving rise to H1.2 Ala17Val because the initial methionine is removed in H1 histones. Raji cells showed a heterozygous AAA→AGA codon change at position 174 in H1.4, corresponding to the Lys173Arg substitution. The allele frequency of these sequence variants in a normal Swedish population was found to be 6.8% for the H1.2 GCC→GTC shift, indicating that this is a relatively frequent polymorphism. The AAA→AGA codon change in H1.4 was detected only in Raji cells and was not present in a normal population or in six other cell lines derived from individuals suffering from Burkitts lymphoma. The significance of these sequence variants is unclear, but increasing evidence indicates that minor sequence variations in linker histones may change their binding characteristics, influence chromatin remodeling, and specifically affect important cellular functions.

Translocation of histone H1 subtypes between chromatin and cytoplasm during mitosis in normal human fibroblasts.

Histone H1 is an important constituent of chromatin, which undergoes major structural rearrangements during mitosis. However, the role of H1, multiple H1 subtypes, and H1 phosphorylation is still unclear. In normal human fibroblasts, phosphorylated H1 was found located in nuclei during prophase and in both cytoplasm and condensed chromosomes during metaphase, anaphase, and telophase as detected by immunocytochemistry. Moreover, we detected remarkable differences in the distribution of the histone H1 subtypes H1.2, H1.3, and H1.5 during mitosis. H1.2 was found in chromatin during prophase and almost solely in the cytoplasm of metaphase and early anaphase cells. In late anaphase, it appeared in both chromatin and cytoplasm and again in chromatin during telophase. H1.5 distribution pattern resembled that of H1.2, but H1.5 was partitioned between chromatin and cytoplasm during metaphase and early anaphase. H1.3 was detected in chromatin in all cell cycle phases. We propose therefore, that H1 subtype translocation during mitosis is controlled by phosphorylation, in combination with H1 subtype inherent affinity. We conclude that H1 subtypes, or theirphosphorylated forms, may leave chromatin in a regulated way to give access for chromatin condensing factors or transcriptional regulators during mitosis.

Hammarby Sjöstad–an interdisciplinary case study of the integration of photovoltaics in a new ecologically sustainable residential area in Stockholm

The integration of photovoltaic (PV) systems in apartment buildings in a new residential area, Hammarby Sjostad in Stockholm, has been studied using an interdisciplinary approach including e.g. interviews with actors and modelling of PV systems in PVSYST. Four of the ten construction companies represented in the area will install PV systems. The yearly electricity production from these systems has been estimated to be 63 MWh or equal to an electricity demand of 38 (out of 2300) households in the area. Interviews reveal that obstacles for the integration of PV in buildings are e.g. perceived expense and a lack of knowledge. The choice of PV technology is based more on economy, aesthetic appearance, and a wish to demonstrate environmental concern, than on optimal system performance. By integrating renewable energy technologies in the buildings, the construction companies will lay a ground for an ecologically sustainable living, but how these opportunities are utilised by future residents, managers, and caretakers of the buildings will be of decisive importance for the final outcome.

Assessment of HaloPlex Amplification for Sequence Capture and Massively Parallel Sequencing of Arrhythmogenic Right Ventricular Cardiomyopathy–Associated Genes

The genetic basis of arrhythmogenic right ventricular cardiomyopathy (ARVC) is complex. Mutations in genes encoding components of the cardiac desmosomes have been implicated as being causally related to ARVC. Next-generation sequencing allows parallel sequencing and duplication/deletion analysis of many genes simultaneously, which is appropriate for screening of mutations in disorders with heterogeneous genetic backgrounds. We designed and validated a next-generation sequencing test panel for ARVC using HaloPlex. We used SureDesign to prepare a HaloPlex enrichment system for sequencing of DES, DSC2, DSG2, DSP, JUP, PKP2, RYR2, TGFB3, TMEM43, and TTN from patients with ARVC using a MiSeq instrument. Performance characteristics were determined by comparison with Sanger, as the gold standard, and TruSeq Custom Amplicon sequencing of DSC2, DSG2, DSP, JUP, and PKP2. All the samples were successfully sequenced after HaloPlex capture, with >99% of targeted nucleotides covered by >20×. The sequences were of high quality, although one problematic area due to a presumptive context-specific sequencing error-causing motif located in exon 1 of the DSP gene was detected. The mutations found by Sanger sequencing were also found using the HaloPlex technique. Depending on the bioinformatics pipeline, sensitivity varied from 99.3% to 100%, and specificity varied from 99.9% to 100%. Three variant positions found by Sanger and HaloPlex sequencing were missed by TruSeq Custom Amplicon owing to loss of coverage.

Histone H1 interphase phosphorylation becomes largely established in G1 or early S phase and differs in G1 between T-lymphoblastoid cells and normal T cells

BackgroundHistone H1 is an important constituent of chromatin, and is involved in regulation of its structure. During the cell cycle, chromatin becomes locally decondensed in S phase, highly condensed during metaphase, and again decondensed before re-entry into G1. This has been connected to increasing phosphorylation of H1 histones through the cell cycle. However, many of these experiments have been performed using cell-synchronization techniques and cell cycle-arresting drugs. In this study, we investigated the H1 subtype composition and phosphorylation pattern in the cell cycle of normal human activated T cells and Jurkat T-lymphoblastoid cells by capillary electrophoresis after sorting of exponentially growing cells into G1, S and G2/M populations.ResultsWe found that the relative amount of H1.5 protein increased significantly after T-cell activation. Serine phosphorylation of H1 subtypes occurred to a large extent in late G1 or early S phase in both activated T cells and Jurkat cells. Furthermore, our data confirm that the H1 molecules newly synthesized during S phase achieve a similar phosphorylation pattern to the previous ones. Jurkat cells had more extended H1.5 phosphorylation in G1 compared with T cells, a difference that can be explained by faster cell growth and/or the presence of enhanced H1 kinase activity in G1 in Jurkat cells.ConclusionOur data are consistent with a model in which a major part of interphase H1 phosphorylation takes place in G1 or early S phase. This implies that H1 serine phosphorylation may be coupled to changes in chromatin structure necessary for DNA replication. In addition, the increased H1 phosphorylation of malignant cells in G1 may be affecting the G1/S transition control and enabling facilitated S-phase entry as a result of relaxed chromatin condensation. Furthermore, increased H1.5 expression may be coupled to the proliferative capacity of growth-stimulated T cells.

The pan-ErbB tyrosine kinase inhibitor canertinib induces caspase-mediated cell death in human T-cell leukemia (Jurkat) cells.

Canertinib is a novel ErbB-receptor inhibitor currently in clinical development for the treatment of solid tumors overexpressing ErbB-receptors. We have recently demonstrated that canertinib displays anti-proliferative and pro-apoptotic effects in human myeloid leukemia cells devoid of ErbB-receptors. The mechanism mediating these effects are however unknown. In this study, we show that canertinib is able to act as a multi-kinase inhibitor by inhibition of several intracellular kinases involved in T-cell signaling such as Akt, Erk1/2 and Zap-70, and reduced Lck protein expression in the human T-cell leukemia cell line Jurkat. Treatment with canertinib at a concentration of 2 μM caused accumulation of Jurkat cells in the G(1) cell cycle phase and increased doses induced apoptosis in a time-dependent manner. Apoptotic signs of treated cells were detected by Annexin V staining and cleavage of PARP, caspase-3, -8, -9, -10 and Bid. A subset of the pro-apoptotic signals mediated by canertinib could be significantly reduced by specific caspase inhibitors. Taken together, these results demonstrate the dual ability of canertinib to downregulate important signaling pathways and to activate caspase-mediated intrinsic apoptosis pathway in human T-cell leukemia cells.

Histone H1 dephosphorylation is not a general feature in early apoptosis.

Histone H1 is a family of nucleosomal proteins that exist in a number of subtypes. These subtypes can be modified after translation in various ways, above all by phosphorylation. Increasing levels of H1 phosphorylation has been correlated with cell cycle progression, while both phosphorylation and dephosphorylation of histone H1 have been linked to the apoptotic process. Such conflicting results may depend on which various apoptosis-inducing agents cause apoptosis via different apoptotic pathways and often interfere with cell proliferation. Therefore, we investigated the relation between apoptosis and H1 phosphorylation in Jurkat cells after apoptosis induction via both the extrinsic and intrinsic pathways and by taking cell cycle effects into account. After apoptosis induction by anti-Fas, no significant dephosphorylation, as measured by capillary electrophoresis, or cell cycle-specific effects were detected. In contrast, H1 subtypes were rapidly dephosphorylated when apoptosis was induced by camptothecin. We conclude that histone H1 dephosphorylation is not connected to apoptosis in general but may be coupled to apoptosis by the intrinsic pathway or to concomitant growth inhibitory signaling.

Could Dissimilar Phenotypic Effects of ACTB Missense Mutations Reflect the Actin Conformational Change? Two Novel Mutations and Literature Review

The beta-actin gene encodes 1 of 6 different actin proteins. De novo heterozygous missense mutations in ACTB have been identified in patients with Baraitser-Winter syndrome (BRWS) and also in patients with developmental disorders other than BRWS, such as deafness, dystonia, and neutrophil dysfunction. We describe 2 different novel de novo missense ACTB mutations, c.208C>G (p.Pro70Ala) and c.511C>T (p.Leu171Phe), found by trio exome sequencing analysis of 2 unrelated patients: an 8-year-old boy with a suspected BRWS and a 4-year-old girl with unclear developmental disorder. The mutated residue in the first case is situated in the actin H-loop, which is involved in actin polymerization. The mutated residue in the second case (p.Leu171Phe) is found at the actin barbed end in the W-loop, important for binding to profilin and other actin-binding molecules. While the boy presented with a typical BRWS facial appearance, the girl showed facial features not recognizable as a BRWS gestalt as well as ventricular arrhythmia, cleft palate, thrombocytopenia, and gray matter heterotopia. We reviewed previously published ACTB missense mutations and ascertained that a number of them do not cause typical BRWS. By comparing clinical and molecular data, we speculate that the phenotypic differences found in ACTB missense mutation carriers might supposedly be dependent on the conformational change of ACTB.

Homozygous missense MYBPC3 Pro873His mutation associated with increased risk for heart failure development in hypertrophic cardiomyopathy: MYBPC3 Pro873His mutation

Hypertrophic cardiomyopathy (HCM) is a primary autosomal‐dominant disorder of the myocardium with variable expressivity and penetrance. Occasionally, homozygous sarcomere genetic variants emerge while genotyping HCM patients. In these cases, a more severe HCM phenotype is generally seen. Here, we report a case of HCM that was diagnosed clinically at 39 years of age. Initial symptoms were shortness of breath during exertion. Successively, he developed a wide array of severe clinical manifestations, which progressed to an ominous end‐stage heart failure that resulted in heart transplantation. Genotype analysis revealed a missense MYBPC3 variant NM_000256.3:c.2618C>A,p.(Pro873His) that presented in the homozygous form. Conflicting interpretations of pathogenicity have been reported for the Pro873His MYBPC3 variant described here. Our patient, presenting with two copies of the variant and devoid of a normal allele, progressed to end‐stage heart failure, which supports the notion of a deleterious effect of this variant in the homozygous form.