Identification in the rat brain of a set of nuclear proteins interacting with H1° mRNA

Establishment and Preliminary Characterization of Three Astrocytic Cells Lines Obtained from Primary Rat Astrocytes by Sub-Cloning

Gliomas are complex and heterogeneous tumors that originate from the glial cells of the brain. The malignant cells undergo deep modifications of their metabolism, and acquire the capacity to invade the brain parenchyma and to induce epigenetic modifications in the other brain cell types. In spite of the efforts made to define the pathology at the molecular level, and to set novel approaches to reach the infiltrating cells, gliomas are still fatal. In order to gain a better knowledge of the cellular events that accompany astrocyte transformation, we developed three increasingly transformed astrocyte cell lines, starting from primary rat cortical astrocytes, and analyzed them at the cytogenetic and epigenetic level. In parallel, we also studied the expression of the differentiation-related H1.0 linker histone variant to evaluate its possible modification in relation with transformation. We found that the most modified astrocytes (A-FC6) have epigenetic and chromosomal alterations typical of cancer, and that the other two clones (A-GS1 and A-VV5) have intermediate properties. Surprisingly, the differentiation-specific somatic histone H1.0 steadily increases from the normal astrocytes to the most transformed ones. As a whole, our results suggest that these three cell lines, together with the starting primary cells, constitute a potential model for studying glioma development.

Pleiotropic roles of cold shock proteins with special emphasis on unexplored cold shock protein member of Plasmodium falciparum

The cold shock domain (CSD) forms the hallmark of the cold shock protein family that provides the characteristic feature of binding with nucleic acids. While much of the information is available on bacterial, plants and human cold shock proteins, their existence and functions in the malaria parasite remains undefined. In the present review, the available information on functions of well-characterized cold shock protein members in different organisms has been collected and an attempt was made to identify the presence and role of cold shock proteins in malaria parasite. A single Plasmodium falciparum cold shock protein (PfCoSP) was found in P. falciparum which is reported to be essential for parasite survival. Essentiality of PfCoSP underscores its importance in malaria parasite life cycle. In silico tools were used to predict the features of PfCoSP and to identify its homologues in bacteria, plants, humans, and other Plasmodium species. Modelled structures of PfCoSP and its homologues in Plasmodium species were compared with human cold shock protein 'YBOX-1' (Y-box binding protein 1) that provide important insights into their functioning. PfCoSP model was subjected to docking with B-form DNA and RNA to reveal a number of residues crucial for their interaction. Transcriptome analysis and motifs identified in PfCoSP implicate its role in controlling gene expression at gametocyte, ookinete and asexual blood stages of malaria parasite. Overall, this review emphasizes the functional diversity of the cold shock protein family by discussing their known roles in gene expression regulation, cold acclimation, developmental processes like flowering transition, and flower and seed development, and probable function in gametocytogenesis in case of malaria parasite. This enables readers to view the cold shock protein family comprehensively.

Cold shock proteins: from cellular mechanisms to pathophysiology and disease

Cold shock proteins are multifunctional RNA/DNA binding proteins, characterized by the presence of one or more cold shock domains. In humans, the best characterized members of this family are denoted Y-box binding proteins, such as Y-box binding protein-1 (YB-1). Biological activities range from the regulation of transcription, splicing and translation, to the orchestration of exosomal RNA content. Indeed, the secretion of YB-1 from cells via exosomes has opened the door to further potent activities. Evidence links a skewed cold shock protein expression pattern with cancer and inflammatory diseases. In this review the evidence for a causative involvement of cold shock proteins in disease development and progression is summarized. Furthermore, the potential application of cold shock proteins for diagnostics and as targets for therapy is elucidated.

Extracellular vesicles shed by melanoma cells contain a modified form of H1.0 linker histone and H1.0 mRNA-binding proteins

Extracellular vesicles (EVs) are now recognized as a fundamental way for cell-to-cell horizontal transfer of properties, in both physiological and pathological conditions. Most of EV-mediated cross-talk among cells depend on the exchange of proteins, and nucleic acids, among which mRNAs, and non-coding RNAs such as different species of miRNAs. Cancer cells, in particular, use EVs to discard molecules which could be dangerous to them (for example differentiation-inducing proteins such as histone H1.0, or antitumor drugs), to transfer molecules which, after entering the surrounding cells, are able to transform their phenotype, and even to secrete factors, which allow escaping from immune surveillance. Herein we report that melanoma cells not only secrete EVs which contain a modified form of H1.0 histone, but also transport the corresponding mRNA. Given the already known role in tumorigenesis of some RNA binding proteins (RBPs), we also searched for proteins of this class in EVs. This study revealed the presence in A375 melanoma cells of at least three RBPs, with apparent MW of about 65, 45 and 38 kDa, which are able to bind H1.0 mRNA. Moreover, we purified one of these proteins, which by MALDI-TOF mass spectrometry was identified as the already known transcription factor MYEF2.

Nuclear and nucleolar activity of linker histone variant H1.0

Histone H1.0 belongs to the class of linker histones (H1), although it is substantially distinct from other histone H1 family members. The differences can be observed in the chromosomal location and organization of the histone H1.0 encoding gene, as well as in the length and composition of its amino acid chain. Whereas somatic (H1.1-H1.5) histone H1 variants are synthesized in the cell cycle S-phase, histone H1.0 is synthesized throughout the cell cycle. By replacing somatic H1 variants during cell maturation, histone H1.0 is gradually deposited in low dividing cells and achieves the highest level of expression in the terminally differentiated cells. Compared to other differentiation-specific H1 histone (H5) characteristic for unique tissue and organisms, the distribution of histone H1.0 remains non-specific. Classic investigations emphasize that histone H1.0 is engaged in the organization of nuclear chromatin accounting for formation and maintenance of its nucleosomal and higher-order structure, and thus influences gene expression. However, the recent data confirmed histone H1.0 peculiar localization in the nucleolus and unexpectedly revealed its potential for regulation of nucleolar, RNA-dependent, activity via interaction with other proteins. According to such findings, histone H1.0 participates in the formation of gene-coded information through its control at both transcriptional and translational levels. In order to reappraise the biological significance of histone H1.0, both aspects of its activity are presented in this review.

Regulation of mRNA transport, localization and translation in the nervous system of mammals (Review)

Post-transcriptional control of mRNA trafficking and metabolism plays a critical role in the actualization and fine tuning of the genetic program of cells, both in development and in differentiated tissues. Cis-acting signals, responsible for post-transcriptional regulation, reside in the RNA message itself, usually in untranslated regions, 5′ or 3′ to the coding sequence, and are recognized by trans-acting factors: RNA-binding proteins (RBPs) and/or non-coding RNAs (ncRNAs). ncRNAs bind short mRNA sequences usually present in the 3′-untranslated (3′-UTR) region of their target messages. RBPs recognize specific nucleotide sequences and/or secondary/tertiary structures. Most RBPs assemble on mRNA at the moment of transcription and shepherd it to its destination, somehow determining its final fate. Regulation of mRNA localization and metabolism has a particularly important role in the nervous system where local translation of pre-localized mRNAs has been implicated in developing axon and dendrite pathfinding, and in synapse formation. Moreover, activity-dependent mRNA trafficking and local translation may underlie long-lasting changes in synaptic efficacy, responsible for learning and memory. This review focuses on the role of RBPs in neuronal development and plasticity, as well as possible connections between ncRNAs and RBPs.

Oligodendroglioma cells synthesize the differentiation-specific linker histone H1˚ and release it into the extracellular environment through shed vesicles

Chromatin remodelling can be involved in some of the epigenetic modifications found in tumor cells. One of the mechanisms at the basis of chromatin dynamics is likely to be synthesis and incorporation of replacement histone variants, such as the H1° linker histone. Regulation of the expression of this protein can thus be critical in tumorigenesis. In developing brain, H1° expression is mainly regulated at the post-transcriptional level and RNA-binding proteins (RBPs) are involved. In the past, attention mainly focused on the whole brain or isolated neurons and little information is available on H1° expression in other brain cells. Even less is known relating to tumor glial cells. In this study we report that, like in maturing brain and isolated neurons, H1° synthesis sharply increases in differentiating astrocytes growing in a serum-free medium, while the corresponding mRNA decreases. Unexpectedly, in tumor glial cells both H1° RNA and protein are highly expressed, in spite of the fact that H1° is considered a differentiation-specific histone variant. Persistence of H1° mRNA in oligodendroglioma cells is accompanied by high levels of H1° RNA-binding activities which seem to be present, at least in part, also in actively proliferating, but not in differentiating, astrocytes. Finally, we report that oligodendroglioma cells, but not astrocytes, release H1° protein into the culture medium by shedding extracellular vesicles. These findings suggest that deregulation of H1° histone expression can be linked to tumorigenesis.