PROTAC: targeted drug strategy. Principles and limitations

The PROTAC (PROteolysis TArgeting Chimera) technology is a method of targeting intracellular proteins previously considered undruggable. This technology utilizes the ubiquitin-proteasome system in cells to specifically degrade target proteins, thereby offering significant advantages over conventional small-molecule inhibitors of the enzymatic function. Preclinical and preliminary clinical trials of PROTAC-based compounds (degraders) are presented. The review considers the general principles of the design of degraders. Advances and challenges of the PROTAC technology are discussed.

Dynamic behavior of Arabidopsis eIF4A-III, putative core protein of exon junction complex: fast relocation to nucleolus and splicing speckles under hypoxia

Here, we identify the Arabidopsis thaliana ortholog of the mammalian DEAD box helicase, eIF4A-III, the putative anchor protein of exon junction complex (EJC) on mRNA. Arabidopsis eIF4A-III interacts with an ortholog of the core EJC component, ALY/Ref, and colocalizes with other EJC components, such as Mago, Y14, and RNPS1, suggesting a similar function in EJC assembly to animal eIF4A-III. A green fluorescent protein (GFP)-eIF4A-III fusion protein showed localization to several subnuclear domains: to the nucleoplasm during normal growth and to the nucleolus and splicing speckles in response to hypoxia. Treatment with the respiratory inhibitor sodium azide produced an identical response to the hypoxia stress. Treatment with the proteasome inhibitor MG132 led to accumulation of GFP-eIF4A-III mainly in the nucleolus, suggesting that transition of eIF4A-III between subnuclear domains and/or accumulation in nuclear speckles is controlled by proteolysis-labile factors. As revealed by fluorescence recovery after photobleaching analysis, the nucleoplasmic fraction was highly mobile, while the speckles were the least mobile fractions, and the nucleolar fraction had an intermediate mobility. Sequestration of eIF4A-III into nuclear pools with different mobility is likely to reflect the transcriptional and mRNA processing state of the cell.

[Various forms of water in the rat myocardium and liver during blood loss and the early postresuscitation period]

Different forms of water content were studied in myocardium and liver of male rats at 2-h hypotension and during the early postreanimation period. The phenomenon of redistribution of free and bound water was found. Comparison of water balance during the postreanimation period in the myocardium and liver revealed that normalization of different forms of water occured in myocardium. In hepatocytes oedema remained over the whole period studied.

Biochemical characteristics and water exchange in the surface layer of human joint cartilage

We compared the contents of collagen, glycosaminoglycans, and various forms of water in the surface layer and whole tissue of joint cartilages of different localization. It was found that the surface layer is characterized by reduced content of glycosaminoglycans compared to the whole tissue and higher water-holding capacity due high content of bound water.

Source-sink coupling in young barley plants and control of phloem loading

Phloem loading of carbohydrate within a mature exporting leaf of a barley seedling is shown to respond quickly to a change in the temperature of the root and the shoot meristem. This is interpreted as a close coupling between source supply and sink demand for carbohydrate, through the hydrostatic pressure gradient linking source and sink generated by the solute concentration within the sieve tubes. This interpretation was tested by using anoxia to alter solute concentration within the sieve tubes of one region of a leaf while observing phloem loading in an adjacent region. Responses to anoxia could not be explained by the above model, suggesting that either this model is incorrect or other signalling pathways are involved. There is evidence in the literature for coarse control of phloem loading but no evidence was found of fine control by solute content of the loaded sieve elements.

Some biochemical characteristics and water exchange in human articular cartilage in osteoarthrosis

Rearrangement of intra- and intermolecular bonds in collagen molecule, disaggregation of proteoglycans and their elimination from cartilage involved in osteoarthrosis are responsible for water accumulation and its increased mobility in cartilage.

[Changes in biochemical characteristics of collagen and the cartilage water in osteoarthritis]

The stability of collagen molecules and moisture capacity of human normal and osteoarthrotic (OA) cartilage were studied before and after extraction of glycosaminoglycans (GAG) by 4M guanidinum chloride. The content and nature of water were determined by Fisher titration, DSC and analysis of sorbtion-desorbtion processes of water vapour in cartilage. The stability of collagen molecules was determined by the degree of enzymatic hydrolysis: collagenase, pronase and pepsin. It was found that weakening of bonds between main compounds of the cartilage matrix and decrease of GAG quantities in the OA cartilage were accompanied by structural disorganization of the collagen network, which is manifested by breakdowns of intramolecular bonds in telopeptides and intermolecular bonds in the spiral part of collagen molecules, these changes may contribute to increase of total water in OA cartilage. The correlation of free and bound water fractions in cartilage was increased from 5 to 44 in OA cartilage. These results can be used as a criterion of pathological condition of human articular cartilage.

[Water-exchange processes in hyaline cartilage and its basic components in a normal state and in osteoarthritis]

The content of different forms of tissue water was studied in the normal articular cartilage and osteoarthrosis cartilage and its structural components: collagen, potassium hyaluronate, sodium chondroitinsulphate and its complexes. In the components of cartilage matrix a few of fractions of bound water different in the strength of binding are present. At the maximal humidity, all water in collagen binds with the active groups of biopolymers and in the glycosaminoglycans, in addition to bound water, are present, two crystal forms of freezing water (free water) at least. The quantity of free water in the collagen-chondroitin sulphat membrane, is increased with the increase of chondroitin sulphate. In the collagen-hyaluronate complex, fraction of free water is found only at the low concentration of hyaluronate kalium. It was shown that in the hyalin cartilage, in different from the other connective tissue (skin, achilles tendon), the most part of water is free water and its quantity is increased in the osteoarthrosis. It is supposed that the rearrangement of binding and free-water fractions in the osteoarthrosis is the result of deficiency of hyaluronic acid and therefore this may be regarded in the improvement of methods of treatment. This scientific and methodical approach allow to receive information on the forms and binding energy of water in the biological tissues, which is absorbed from fluids and steam phase and determine characters of the pathological changes.

Identification of a new glucosinolate-rich cell type in Arabidopsis flower stalk

Distribution of K, Ca, Cl, S, and P in freeze-dried sections of Arabidopsis flower stalk was analyzed by energy dispersive x-ray imaging. Concentrations of these elements in different cell types were quantified by microanalysis of single-cell samples and phloem exudates. Results showed a differential pattern of distribution for all five elements. K concentration was found to be highest in the parenchymatous tissue around vascular bundles. Ca and Cl were present mainly in the central part of the flower stalk. P was largely located in the bundles and in the parenchyma surrounding them. S signal was extraordinary high in groups of cells (S-cells) situated between the phloem of every vascular bundle and the endodermis. Enzymatic hydrolysis by thioglucosidase of cell sap collected from S-cells using a glass microcapillary resulted in the release of glucose, indicating that these cells contain glucosinolates at high (> 100 mM) concentration, which is consistent with the concentration of S (> 200 mM) estimated by x-ray analysis of cell sap samples. Since their position outside of the phloem is ideally suited for protecting the long-distance transport system from feeding insects, the possible roles of these cells as components of a plant defense system are discussed.

[The effect of ionizing radiation on human muscle tissue]

The effect of ionizing radiation (gamma-irradiation of 60Co, doses from 10 Gy to 15 kGy) on human muscle tissue was studied using a biopsy material. Destructive alterations in muscle proteins were observed beginning from the dose of 1.0 kGy: appearance of new protein fractions with molecular mass 68-160 kDa and 18-36 kDa. Resistance of muscle proteins to the trypsin effect was unaltered, while the rate of pronase-induced hydrolysis was slightly increased, about 1.2-fold. Content of water and biomechanical properties of the tissue were unaltered, but the modulus of elasticity was decreased approximately 3-fold after treatment with maximal doses of the ionizing radiation used.

[The structure and physicochemical properties of human hyaline cartilage in the disorganization of the carbohydrate-protein complexes of the ground substance]

In the experiments in vitro we studied the influence of the process of disorganization of the carbohydrate-protein complexes of the ground substance on the structure, water content and biomechanical properties of the human hyaline cartilage. It was shown that the disorganization process of the cartilage ground substance and the subsequent removal of the formed products resulted in the increasing porosity of the cartilaginous tissue. This is expressed in the exposure of the fibrillar frame of the cartilage and formation of cavities of various volumes between its elements. The mentioned changes of the cartilage structure are followed by the reduction of the amount of monomolecular-bound water and simultaneous increase in swelling in water and water vapor sorption at maximal relative humidity. The removal of about 25% of glycosaminoglycanes of the ground substance resulted in the reduction of the rigidity of the cartilagenous tissue, and the increase in the residual deformation. The examination of the hyaline cartilage did not reveal any interrelation between the contents of proteoglycanes and the water content of the cartilagenous tissue.

[Effect of ionizing radiation on the structure of the collagen fibers of human tendons]

In studying the effect of ionizing radiation on the properties of human Achilles tendon collagen fibres, the following parameters were analyzed: hydrothermal contraction temperature, module of elasticity, the number of cross-links, free and bound water levels, acids-soluble fraction content, and ultrastructure. With radiation doses of 2-10 Gy no changes in the collagen status were noted. An increased (from 5 to 25 Gy) radiation dose caused changes in physicochemical properties which was indicative of the formation, in the connective tissue collagen, of radiation-induced intermolecular cross-links stabilizing the biopolymer structure.

[Effect of autolysis on the physico-chemical properties of mammalian skin]

Alterations in physico-chemical properties and in content of several biochemical components were found in skin during postmortal storage of the tissue at the temperature 22 degrees and 5 degrees and relative moisture 92%. Within 96-120 hrs of the postmortal storage a decrease in content of hydrate-bound water and of glycosaminoglycans occurred in the tissue. The alterations were accompanied by an increase in temperature of hydrothermic denaturation and in module of elasticity of the skin. As a result of autolysis solubility of collagen in water was increased at 65 degrees and its acid soluble fractions tended to become denatured although the content of hydroxyproline was unaltered. The processes occurring in the skin within the first period after death, might be considered as a two-step sequence: formation of additional interstructural hydrogen bonds and structure transformation of both collagen and glycosaminoglycans due to the effect of proteinases.