Band 5, Heft 2

DNA methylation at cytosines is an important epigenetic modification that participates in gene expression regulation without changing the original DNA sequence. With the rapid progress of high-throughput sequencing techniques, whole-genome distribution of methylated cytosines and their regulatory mechanism have been revealed gradually. This has allowed the uncovering of the critical roles played by DNA methylation in the maintenance of cell pluripotency, determination of cell fate during development, and in diverse diseases. Recently, rediscovery of 5-hydroxymethylcytosine, and other types of modification on DNA, have uncovered more dynamic aspects of cell methylome regulation. The interaction of DNA methylation and other epigenetic changes remodel the chromatin structure and determine the state of gene transcription, not only permanently, but also transiently under certain stimuli. The uterus is a reproductive organ that experiences dramatic hormone stimulated changes during the estrous cycle and pregnancy, and thus provides us with a unique model for studying the dynamic regulation of epigenetic modifications. In this article, we review the current findings on the roles of genomic DNA methylation and hydroxymethylation in the regulation of gene expression, and discuss the progress of studies for these epigenetic changes in the uterus during implantation and decidualization.

Many biological roles have been assigned to proinsulin C-peptide over the years. Some appear surprisingly disparate and sometimes even contradictory, like chaperone-like actions and depository tendencies. This review summarizes recently reported biomolecular interactions of the peptide and presents how they correlate with structural and functional aspects into a partitioned molecular architecture. At the structural level, the C-peptide sequence and fold can be subdivided into three distinct parts (‘tripartite’). At the functional level, its chaperone-like abilities, self-assembly, and membrane interactions, as well as interactions with relevant proteins can be separately ascribed to these three segments. At the biological level, the assignments are compatible with the suggested roles of C-peptide in granular insulin storage, chaperone-like activities on insulin oligomers, possible depository tendencies, and proposed receptor interactions. Finally, the assignments give interesting parallels to further bioactive peptides, including glucagon and neurotensin. Provided pharmaceutical and clinical trials are successfully completed, the present interpretations should supply mechanistic explanations on C-peptide as a bioactive compound of importance in health and diabetes.

The fact that proteins are the main target of reactive species formed in the cells and extracellular fluids has led to the realization of a great deal of research devoted to revealing the molecular and biological consequences associated with the presence of intermediary protein radicals. This review article describes and comments upon the main chemical pathways involving primary proteic radicals.

This review presents a new strategy for the design of stimuli-responsive liposomes for targeted delivery – the construction of a liposome membrane (lipid bilayer) using amphiphiles able to perform a stimuli-triggered conformational flip (‘flipids’). When done simultaneously by a major or significant part of the bilayer molecules, this massive flip disrupts the liposome membrane and induces a rapid release of the liposome load specifically in response to the initial stimulus. The conformational switches incorporated into the amphiphilic molecules could potentially be controlled by various internal or external factors (pH, metal complexation, light, electric field, etc.). Using this concept, we designed a series of pH-triggerable flipids, and prepared and tested ‘fliposomes’ with extraordinary characteristics: high stability in storage and in serum combined with an instant release of their cargo in response to a weakly acidic medium.

The regulated intracellular transport of nutrient, adhesion, and growth factor receptors is crucial for maintaining cell and tissue homeostasis. Endocytosis, or endocytic membrane trafficking, involves the steps of intracellular transport that include, but are not limited to, internalization from the plasma membrane, sorting in early endosomes, transport to late endosomes/lysosomes followed by degradation, and/or recycling back to the plasma membrane through tubular recycling endosomes. In addition to regulating the localization of transmembrane receptor proteins, the endocytic pathway also controls the localization of non-receptor molecules. The non-receptor tyrosine kinase c-Src (Src) and its closely related family members Yes and Fyn represent three proteins whose localization and signaling activities are tightly regulated by endocytic trafficking. Here, we provide a brief overview of endocytosis, Src function and its biochemical regulation. We will then concentrate on recent advances in understanding how Src intracellular localization is regulated and how its subcellular localization ultimately dictates downstream functioning. As Src kinases are hyperactive in many cancers, it is essential to decipher the spatiotemporal regulation of this important family of tyrosine kinases.

The neuropilin (Nrp) family consists of multifunctional cell surface receptors with critical roles in a number of different cell and tissue types. A core aspect of Nrp function is in ligand-dependent cellular migration, where it controls the multistep process of cellular motility through integration of ligand binding and receptor signaling. At a molecular level, the role of Nrp in migration is intimately connected to the control of adhesive interactions and cytoskeletal reorganization. Here, we review the physiological role of Nrp in cellular adhesion and motility in the cardiovascular and nervous systems. We also discuss the emerging pathological role of Nrp in tumor cell migration and metastasis, providing motivation for continued efforts toward developing Nrp inhibitors.

CXCL12 and CXCL14 are evolutionarily conserved members of the CXC-type chemokine family. CXCL12 binds specifically to the G-protein-coupled receptor CXCR4 to induce the migration of primordial germ cells, hematopoietic stem cells, and inflammation-associated immune cells. In addition, CXCL12-CXCR4 signaling is often enhanced in malignant tumor cells and facilitates increased proliferation as well as metastasis. Although macrophage migration inhibitory factor and extracellular ubiquitin interact with CXCR4 as agonistic factors, CXCL12 was believed to be the sole chemokine ligand for CXCR4. However, a very recent report revealed that CXCL14 binds to CXCR4 with high affinity and efficiently inhibits CXCL12-mediated chemotaxis of hematopoietic progenitor and leukemia-derived cells. CXCL14 does not directly cross-compete with CXCL12 for the CXCR4 binding but instead inactivates CXCR4 via receptor internalization. Because both CXCL12 and CXCL14 are expressed during embryogenesis and brain development in mice, these two chemokines could function in an interactive fashion. We propose that the CXCL14 gene has been conserved from fish to man due to its role in fine-tuning the strength of CXCL12-mediated signal transduction. In addition to its biological implications, the above finding will be important for designing anti-cancer compounds targeting the CXCL12-CXCR4 signaling axis. In fact, a stabilized dimeric peptide containing the C-terminal 51–77 amino acid residues of CXCL14 has been shown to have stronger CXCL12 antagonistic activity than full-length CXCL14.

Clathrin self-assembles into a coat around vesicles filled with cargo such as nutrients, hormones, and proteins destined for degradation. Recent developments indicate clathrin is not a specialist, but is involved in different processes relevant to health and disease. Clathrin is used to strengthen centrosomes and mitotic spindles essential for chromosome segregation in cell division. In Wnt signaling, clathrin is a component of signalosomes on the plasma membrane needed to produce functional Wnt receptors. In glucose metabolism, a muscle-specific isoform, CHC22 clathrin, is key to the formation of storage compartments for GLUT4 receptor, and CHC22 dysfunction has been tied to type 2 diabetes. The activity of clathrin to self-assemble and to work with huntingtin-interacting proteins to organize actin is exploited by Listeria and enteropathic Escherichia coli in their infection pathways. Finally, there is an important connection between clathrin and human malignancies. Clathrin is argued to help transactivate tumor suppressor p53 that controls specific genes in DNA repair and apoptosis. However, this is debatable because trimeric clathrin must be made monomeric. To get insight on how the clathrin structure could be converted, the crystal structure of the trimerization domain is used in the development of the detrimerization switch hypothesis. This novel hypothesis will be relevant if connections continue to be found between CHC17 and p53 anti-cancer activity in the nucleus.