Epithelial cell adhesion molecules

Recognition and binding between cells are of fundamental importance for a proper function of multicellular organisms, both during embryonic development and in the adult stage. Recently several cell surface proteins that are involved in these phenomena have been discovered. In the identification of these proteins, called cell adhesion molecules (CAMs), immunological methods have played a significant role. In a different approach to studies of cell-cell binding at the molecular level, the chemical composition of intercellular junctions is being studied. Intercellular junctions are specialized cell surface domains that have been identified by electron microscopy. They are particularly well developed in epithelia. Several proteins in the junctions have now been identified and characterized. This review deals with the biochemical properties of epithelial CAMs, and those proteins that are candidates for cell-to-cell binding in the junctions. In particular, the relationships between the various CAMs and junctional proteins are discussed. The tentative biological functions of these molecules are also considered.     

Adherence molecules of pathogenic pneumococci

Adherence molecules are key players in pathogen-host interactions. These are usually surface-exposed structures that facilitate adherence to host cells, or target host serum proteins of the extracellular matrix. Our knowledge of the function of pneumococcal cell-surface structures, and the basic mechanisms underlying their interaction with host receptor molecules has dramatically increased, through molecular and structural analysis of adherence molecules. In particular, choline-binding proteins have received considerable attention because of their versatility, and their sophisticated role in the interaction with host proteins. Interestingly, subversion of host-protein functions to facilitate host invasion and immune evasion has also been attributed to intracellular or surface-exposed proteins of the pathogen. Many of these molecules do not possess the classic features of bacterial surface proteins.     

CircRNA: a rising star in plant biology

Circular RNAs (circRNAs) are covalently closed single-stranded RNA molecules, which are widespread in eukaryotic cells. As regulatory molecules, circRNAs have various functions, such as regulating gene expression, binding miRNAs or proteins, and being translated into proteins, which are important for cell proliferation and cell differentiation, individual growth and development, as well as many other biological processes. However, compared with that in animal models, studies of circRNAs in plants lags behind and, particularly, the regulatory mechanisms of biogenesis and molecular functions of plant circRNAs remain elusive. Recent studies have shown that circRNAs are wide spread in plants with tissue- or development-specific expression patterns and are responsive to a variety of environmental stresses. In this review, we summarize these advances, focusing on the regulatory mechanisms of biogenesis, molecular and biological functions of circRNAs, and the methods for investigating circRNAs. We also discuss the challenges and the prospects of plant circRNA studies.     

The small members of the JMJD protein family: Enzymatic jewels or jinxes?

Jumonji C domain-containing (JMJD) proteins are mostly epigenetic regulators that demethylate histones. However, a hitherto neglected subfamily of JMJD proteins, evolutionarily distant and characterized by their relatively small molecular weight, exerts different functions by hydroxylating proteins and RNA. Recently, unsuspected proteolytic and tyrosine kinase activities were also ascribed to some of these small JMJD proteins, further increasing their enzymatic versatility. Here, we discuss the ten human small JMJD proteins (HIF1AN, HSPBAP1, JMJD4, JMJD5, JMJD6, JMJD7, JMJD8, RIOX1, RIOX2, TYW5) and their diverse physiological functions. In particular, we focus on the roles of these small JMJD proteins in cancer and other maladies and how they are modulated in diseased cells by an altered metabolic milieu, including hypoxia, reactive oxygen species and oncometabolites. Because small JMJD proteins are enzymes, they are amenable to inhibition by small molecules and may represent novel targets in the therapy of cancer and other diseases.     

The Structural Biology of the Developing Dental Enamel Matrix

The biomineralization of the dental enamel matrix with a carbonated hydroxyapatite mineral generates one of the most remarkable examples of a vertebrate mineralized tissue. Recent advances in the molecular biology of ameloblast gene products have now revealed the primary structures of the principal proteins involved in this extracellular mineralizing system, amelogenins, tuftelins, ameloblastins, enamelins, and proteinases, but details of their secondary, tertiary, and quaternary structures, their interactions with other matrix and or cell surface proteins, and their functional role in dental enamel matrix mineralization are still largely unknown. This paper reviews our current knowledge of these molecules, the probable molecular structure of the enamel matrix, and the functional role of these extracellular matrix proteins. Recent studies on the major structural role played by the amelogenin proteins are discussed, and some new data on synthetic amelogenin matrices are reviewed.     

Transgenic study of energy homeostasis equation: implications and confounding influences.

Recently novel molecular mediators and regulatory pathways for feeding and body weight regulation have been identified in the brain and the periphery. Mice lacking or overexpressing these mediators or receptors have been produced by molecular genetic techniques, and observations on mutant mice have shed new light on the role of each element in the homeostatic loop of body weight regulation. However, the interpretation of the phenotype is under the potential influence of developmental compensation and other genetic and environmental confounds. Specific alterations of the mediators and the consequences of the altered expression patterns are reviewed here and discussed in the context of their functions as suggested from conventional pharmacological studies. Advanced gene targeting strategies in which genes can be turned on or off at desired tissues and times would undoubtedly lead to a better understanding of the highly integrated and redundant systems for energy homeostasis equation.     

Drug resistance and membrane alteration in mutants of mammalian cells.

Independent colchicine-resistant (CHR) mutants of Chinese hamster ovary cells displaying reduced permeability to colchicine have been isolated. A distinguishing feature of these membrane-altered mutants is their pleiotropic cross-resistance to a variety of unrelated compounds. Genetic characterization of the CHR lines indicate that colchicine resistance and cross-resistance to other drugs are of a dominant nature in somatic cell hybrids. Revertants of CHR have been isolated which display decreased resistance to colchicine and a corresponding decrease in resistance to other drugs. These results strongly suggest that colchicine resistance and the pleiotropic cross-resistance are the result of the same mutation(s). Biochemical studies indicate that although colchicine is transported into our cells by passive diffusion, no major alterations in the membrane lipids could be detected in mutant cells. However, there appears to be an energy-dependent process in these cells which actively maintains a permeability barrier against colchicine and other drugs. The CHR cells might be altered in this process. A new glycoprotein has been identified in mutant cell membranes which is not present in parental cells, and is greatly reduced in revertant cells. A model for colchicine-resistance is proposed which suggests that certain membrane proteins such as the new glycoprotein of CHR cells, are modulators of membrane fluidity (mmf proteins) whose molecular conformation regulates membrane permeability to a variety of compounds and that the CHR mutants are altered in their mmf proteins. The possible importance of the CHR cells as models for investigating aspects of chemotherapy related to drug resistance is discussed.     

Heat shock proteins: biological functions and clinical application as personalized vaccines for human cancer

Heat shock proteins (HSPs) are a large family of proteins with different molecular weights and different intracellular localizations. These proteins undertake crucial functions in maintaining cell homeostasis, and therefore they have been conserved during evolution. Hsp70 and Grp94/gp96, due to their peptide chaperone capacity and their ability to actively interact with professional antigen-presenting cells (APCs), are also endowed with crucial immunological functions. The immunological properties of these proteins and their implications for vaccine in human cancer will be discussed. Immunological and clinical data of phase I/II studies in melanoma and colorectal cancer patients will be reviewed.This work was presented at the first Cancer Immunology and Immunotherapy Summer School, 8–13 September 2003, Ionian Village, Bartholomeio, Peloponnese, Greece.     

Probing membrane proteins using atomic force microscopy

To gain insights into how biological molecules function, advanced technologies enabling imaging, sensing, and actuating single molecules are required. The atomic force microscope (AFM) would be one of novel potential tools for these tasks. In this study, techniques and efforts using AFM to probe biomolecules are introduced and reviewed. The state-of-art techniques for characterizing specific single receptor using the functionalized AFM tip are discussed. An example of studying the angiotensin II type 1 (AT1) receptors expressed in sensory neuronal cells by AFM with a functionalized tip is given. Perspectives for identifying and characterizing specific individual membrane proteins using AFM in living cells are provided. Given that many diseases have their roots at the molecular scale and are best understood as a malfunctioning biological nanomachines, the prospects of these unique techniques in basic biomedical research or in clinical practice are beyond our imagination.     

SARS-CoV-2 in patients with cancer: possible role of mimicry of human molecules by viral proteins and the resulting anti-cancer immunity

A few reports suggest that molecular mimicry can have a role in determining the more severe and deadly forms of COVID-19, inducing endothelial damage, disseminated intravascular coagulation, and multiorgan failure. Heat shock proteins/molecular chaperones can be involved in these molecular mimicry phenomena. However, tumor cells can display on their surface heat shock proteins/molecular chaperones that are mimicked by SARS-CoV-2 molecules (including the Spike protein), similarly to what happens in other bacterial or viral infections. Since molecular mimicry between SARS-CoV-2 and tumoral proteins can elicit an immune reaction in which antibodies or cytotoxic cells produced against the virus cross-react with the tumor cells, we want to prompt clinical studies to evaluate the impact of SARS-CoV-2 infection on prognosis and follow up of various forms of tumors. These topics, including a brief historical overview, are discussed in this paper.     

Abnormal bovine erythrocyte membrane proteins and glycoproteins during and after infection with Anaplasma marginale

The erythrocyte membrane proteins from normal and Anaplasma-infected bovine blood have been compared. Two distinct new polypeptides were present in membranes from acutely infected cells. The glycoprotein pattern was also altered: in addition to the three main bands observed in normal cells, there were four new bands present which were glycosylated. The normally found membrane glycolypeptide (250000 D) was missing. The role of these protein alterations in relation to the infectious process is discussed.     

Collagens as multidomain proteins

The number of proteins known to contain collagen-like triple helical domains is rapidly increasing. The functions of these domains are to provide molecular rods that separate spatially non-triple helical domains with varied properties and structures and to permit lateral interactions between molecules. Two-thirds of the amino acids of the triple helical domains have their side-chains at the surface of the protein. The triple helix is also a structure that is easily predictable from the primary structure. The structure of several recently discovered collagens are discussed in terms of domains and functions. The triple helical domains have sizes varying from 33 to over 1,000 amino acid residues. The longest uninterrupted triple helices are involved in the formation of the classical quarter-staggered fibrils. Other triple helical domains permit varied molecular aggregates. A very broad spectrum of non-triple helical or globular domains are interspersed by triple helices. Only those located at the extremities of the molecules are large in size, sometimes several hundred kDa, while the domains separating 2 triple helices are small (less than 50 amino acids) and provide the molecules with hinges, proteolytic cleavage sites or other specialized functions like a glycosaminoglycan attachment site. If the assembly of the 3 chains required for the triple helix formation can be controlled in vitro, collagen-like molecules offer an as yet unexploited potential for protein engineering.     

Diversity and versatility of lipid-protein interactions revealed by molecular genetic approaches

The diversity in structures and physical properties of lipids provides a wide variety of possible interactions with proteins that affect their assembly, organization, and function either at the surface of or within membranes. Because lipids have no catalytic activity, it has been challenging to define many of their precise functions in vivo in molecular terms. Those processes responsive to lipids are attuned to the native lipid environment for optimal function, but evidence that lipids with similar properties or even detergents can sometimes partially replace the natural lipid environment has led to uncertainty as to the requirement for specific lipids. The development of strains of microorganisms in which membrane lipid composition can be genetically manipulated in viable cells has provided a set of reagents to probe lipid functions. These mutants have uncovered previously unrecognized roles for lipids and provided in vivo verification for putative functions described in vitro. In this review, we summarize how these reagent strains have provided new insight into the function of lipids. The role of specific lipids in membrane protein folding and topological organization is reviewed. The evidence is summarized for the involvement of anionic lipid-enriched domains in the organization of amphitropic proteins on the membrane surface into molecular machines involved in DNA replication and cell division.     

Cell adhesion: More than just glue (Review)

The ability of cells to interact with each other and their surroundings in a co-ordinated manner depends on multiple adhesive interactions between neighbouring cells and their extracellular environment. These adhesive interactions are mediated by a family of cell surface proteins, termed cell adhesion molecules. Fortunately these adhesion molecules fall into distinct families with adhesive interactions varying in strength from strong binding involved in the maintenance of tissue architecture to more transient, less avid, dynamic interactions observed in leukocyte biology. Adhesion molecules are extremely versatile cell surface receptors which not only stick cells together but provide biochemical and physical signals that regulate a range of diverse functions, such as cell proliferation, gene expression, differentiation, apoptosis and migration. In addition, like many other cell surface molecules, they have been usurped as portals of entry for pathogens, including prions. How the mechanical and chemical messages generated from adhesion molecules are integrated with other signalling pathways (such as receptor tyrosine kinases and phosphatases) and the role that aberrant cell adhesion plays in developmental defects and disease pathology are currently very active areas of research. This review focuses on the biochemical features that define whether a cell surface molecule can act as an adhesion molecule, and discusses five specific examples of how cell adhesion molecules function as more than just 'sticky’ receptors. The discussion is confined to the signalling events mediated by members of the integrin, cadherin and immunoglobulin gene superfamilies. It is suggested that, by controlling the membrane organization of signalling receptors, by imposing spatial organization, and by regulating the local concentration of cytosolic adapter proteins, intercellular and cell-matrix adhesion is more than just glue holding cells together. Rather dynamic ‘conversations’ and the formation of multi-protein complexes between adhesion molecules, growth factor receptors and matrix macromolecules can now provide a molecular explanation for the long-observed but poorly understood requirement for a number of seemingly distinct cell surface molecules to be engaged for efficient cell function to occur.     

去泛素化酶在肿瘤上皮间质转化中的作用

肿瘤的侵袭和转移是加剧肿瘤恶化的主要原因,也是导致患者预后不良的根本原因。近年来大量研究发现,大部分肿瘤的转移都依赖于上皮间质转化(epithelial-mesenchymal transition, EMT)的发生,此外EMT也与肿瘤干性和肿瘤耐药等诸多肿瘤恶性行为密切相关,因此有效的抑制EMT的发生将可能极大的有利于肿瘤的治疗。去泛素化酶(deubiquitinating enzymes, DUBs)的主要功能之一就是通过移除底物蛋白质上泛素链,避免其通过泛素蛋白酶体途径降解,来维持细胞内蛋白质水平的动态平衡。去泛素化酶作为调节蛋白质泛素化修饰的一类重要酶类,其异常表达或酶活性的改变通常都会导致疾病的发生。众多研究发现,部分去泛素化酶在肿瘤侵袭和转移过程中表达失衡,在肿瘤转移的过程中扮演着重要的角色。EMT是指由上皮型细胞转变为间质型细胞的动态细胞生物学过程,在该过程中涉及到例如Snial1、Slug、ZEB1等EMT相关转录因子和细胞表面的例如E-钙黏着蛋白、N-钙黏着蛋白等分子标志物表达水平的变化。这些蛋白质通常具有不稳定性,易被降解等特征。EMT过程的发生,涉及到许多蛋白质稳定性的调节,而去泛素化酶作为一类维持蛋白质稳定的重要酶类,在调节这些蛋白质的稳定性方面发挥着重要的作用。EMT的发生也与TGF-β通路、Wnt通路等细胞内众多信号通路的异常活化密不可分,去泛素化酶通过介导这些信号通路的活化,从而间接的调节EMT发生发展。去泛素化酶通过调节EMT相关分子或EMT相关信号通路等多种方式直接或间接影响EMT进展,因此,通过靶向于去泛素化酶抑制肿瘤的侵袭和转移,将为肿瘤治疗提供新的治疗手段和方案,从而有效的推动肿瘤的治疗。本文主要就去泛素化酶在调节EMT相关分子以及信号通路等方面,阐述去泛素化酶在EMT过程中所发挥的重要作用及其作为肿瘤治疗靶点的可能性。     

Cell adhesion: more than just glue (review)

The ability of cells to interact with each other and their surroundings in a co-ordinated manner depends on multiple adhesive interactions between neighbouring cells and their extracellular environment. These adhesive interactions are mediated by a family of cell surface proteins, termed cell adhesion molecules. Fortunately these adhesion molecules fall into distinct families with adhesive interactions varying in strength from strong binding involved in the maintenance of tissue architecture to more transient, less avid, dynamic interactions observed in leukocyte biology. Adhesion molecules are extremely versatile cell surface receptors which not only stick cells together but provide biochemical and physical signals that regulate a range of diverse functions, such as cell proliferation, gene expression, differentiation, apoptosis and migration. In addition, like many other cell surface molecules, they have been usurped as portals of entry for pathogens, including prions. How the mechanical and chemical messages generated from adhesion molecules are integrated with other signalling pathways (such as receptor tyrosine kinases and phosphatases) and the role that aberrant cell adhesion plays in developmental defects and disease pathology are currently very active areas of research. This review focuses on the biochemical features that define whether a cell surface molecule can act as an adhesion molecule, and discusses five specific examples of how cell adhesion molecules function as more than just 'sticky' receptors. The discussion is confined to the signalling events mediated by members of the integrin, cadherin and immunoglobulin gene superfamilies. It is suggested that, by controlling the membrane organization of signalling receptors, by imposing spatial organization, and by regulating the local concentration of cytosolic adapter proteins, intercellular and cell-matrix adhesion is more than just glue holding cells together. Rather dynamic 'conversations' and the formation of multi-protein complexes between adhesion molecules, growth factor receptors and matrix macromolecules can now provide a molecular explanation for the long-observed but poorly understood requirement for a number of seemingly distinct cell surface molecules to be engaged for efficient cell function to occur.     

Senescence and the accumulation of abnormal proteins.

Mammalian cells can produce abnormal proteins in a number of different ways. These include random errors during protein synthesis, spontaneous or metabolite-induced modifications of amino acid sidechains and changes in polypeptide folding. The evidence that such alterations occur in proteins during growth and senescence is discussed. An important function controlling the accumulation of abnormal proteins is the rate at which they are hydrolysed by proteases. Modified proteins are much better protease substrates than their normal parent molecules, but in spite of this sensitivity to proteolysis they accumulate during ageing. This indicates a drop during senescence in the activity of those proteases degrading abnormal polypeptides. Ways in which abnormal proteins could inhibit cell growth and how these inhibitions may be negated during the immortalisation of diploid cells are discussed.     

Ionic channels of Paramecium: from genetics and electrophysiology to biochemistry

This paper reviews the combined genetical, electrophysiological and biochemical analysis of excitation that has been carried out in Paramecium. Paramecium cells display graded Ca++ action potentials in response to a variety of stimuli. These action potentials regulate the orientation of the ciliary beat hence the cell's swimming behaviour. A large array of mutants displaying altered behaviour have been isolated and mapped to over 20 loci. Detailed electrophysiological analyses have been carried out on several classes of mutants revealing defects in specific ion channels in some cases. Mutants have proven very useful to analyze channel properties, to unravel interactions between channels and to discover the function of these channels in a variety of cellular processes. Some important channels are located in the ciliary membranes and cilia as well as ciliary membranes can now be purified in high purity and reasonable yield. These fractions have been used recently in a variety of biochemical approaches to gain insight into the molecular components of the excitation machinery. Specific alterations in some minor membrane proteins have been found in two mutants as well as a specific defect in sphingolipids in a third mutant. Those alterations had to be distinguished from large scale variations in membrane proteins and lipids that occur in this organism in response to modifications in growth conditions. Several other recent biochemical developments are reviewed and the advantages as well as the difficulties of the genetic approach to the molecular study of biological processes are discussed.     

Ubiquitin Signaling Regulates RNA Biogenesis,Processing, and Metabolism

The fate of eukaryotic proteins, from their synthesis to destruction, is supervised by the ubiquitin–proteasome system (UPS). The UPS is the primary pathway responsible for selective proteolysis of intracellular proteins, which is guided by covalent attachment of ubiquitin to target proteins by E1 (activating), E2 (conjugating), and E3 (ligating) enzymes in a process known as ubiquitylation. The UPS can also regulate protein synthesis by influencing multiple steps of RNA (ribonucleic acid) metabolism. Here, recent publications concerning the interplay between the UPS and different types of RNA are reviewed. This interplay mainly involves specific RNA-binding E3 ligases that link RNA-dependent processes with protein ubiquitylation. The emerging understanding of their modes of RNA binding, their RNA targets, and their molecular and cellular functions are primarily focused on. It is discussed how the UPS adapted to interact with different types of RNA and how RNA molecules influence the ubiquitin signaling components.