[NEGATIVE REGULATORS OF TUMOR SUPPRESSOR P53 IN THE CONTEXT OF ANTICANCER THERAPY].

P53 protein is considered to be the major tumor suppressor in human cells. Cancer cells do not survive if the p53-mediated signaling pathways function properly. However, about half of all malignancies still express wild type p53. One of the explanations to this is that p53 is suppressed by overexpression of p53-specific E3-ubiquitin ligases: Mdm2, MdmX, Pirh2 and Cop1. Pharmacological inhibition of protein-protein interactions between p53 and these negative regulators is a promising therapeutic approach to treat cancers retaining wild type p53. To date, a series of chemical inhibitors of p53 interactions with Mdm2 and MdmX E3-ubiquitin ligases have been discovered and characterized. Several of them are in the early stages of clinical trials. Despite this fact, their clinical efficacy may be hampered by a number of reasons, including tumor-specific expression of multiple isoforms of the target E3-ligases, which become inert to treatment with small molecules. This and other biochemical mechanisms of possible resistance of tumor cells with wild type p53 to small molecules against its negative regulators will be discussed in this review.

[Features of structural organization of chromatin from various sources]. / Issledovanie osobennostei strukturnoi organizatsii khormatina iz razlichnykh istochnikov.

The conformational peculiarities of DNA and histones of chromatins of different origin have been studied using circular dichroism (CD). The chromatins were isolated from pigeon brain, rat thymus and liver, ascitic hepatoma 22A, C3HA mouse liver, pigeon erythrocytes and sea urchin sperm. The functional peculiarities of the chromatins were found to correlate with their compactness and the nucleosomal DNA repeat length. Analysis of chromatin CD spectra made it possible to define the degree of DNA compactness in oligonucleosomes and the secondary structure of their linker histones of the H1 family. It was found that in low ionic strength solutions the structures of chromatosomes are formed in erythrocyte and thymus chromatins, but not in sea urchin sperm chromatin. The size of the compact part of the DNA in the nucleosomes of transcriptionally active chromatins of brain and ascitic hepatoma 22A are less than the length of the DNA of the core particles under identical conditions. The secondary structure of the H1 histone from sea urchin sperm chromatin, unlike other linker histones of the H1 family, contains an additional alpha-helical segment in the C-terminal part. Analysis of structural changes of the both chromatin components during condensation of their oligonucleosomal chains with an increase in the ionic strength has been carried out.

[Comparative study of nucleosome particles in chromatin from normal and tumor cells. I. Structural parameters]. / Sravnitel'noe issledovanie nukleosomnykh chastits khromatina normal'nykh i opukholevykh kletok. I. Strukturnye parametry.

The composition and structure of nucleosomic fragments isolated from the ascitic hepatoma 22A cells, liver and from cells of C3HA mice in norm and after partial hepatectomy were investigated. Via electrophoresis in 1.5% agarose gel with the emplogment of reperic restrictive DNA fragments and with the help of mathematical processing, the value of the nucleosomic DNA repeat in ascitic hepatoma 22A was calculated to be 187 b.p., and in regenerating liver--196 b.p. The absence of the H1 degree subfraction in chromatin of ascitic hepatoma 22A cells was found. Lower electrophoretic mobility in 5% polyacrylamid gel of nucleosomic chromatin fragments of ascitic hepatoma 22A as compared with their counterparts from healthy mice liver was established. The method of circular dichroism allowed to reveal differences in the RNA and protein structural state in nucleosomes of normal and tumour cells. The structure of nucleosomes of regenerating mice liver of the C3HA strain did not differ from that of normal liver of the same mice.

[Comparative study of nucleosome particles in chromatin from normal and tumor cells. II. Reconstitution, compaction and association induced by ionic strength of a solution]. / Sravnitel'noe issledovanie nukleosomnykh chastits khromatina normal'nykh i opukholevykh kletok. II. Rekonstruktsiia, kompaktizatsiia i assotsiiatsiia pod deistviem ionnoi sily rastvora.

The method of circular dichroism (CD) has been used to investigate the reconstitution of mononucleosomes from C3HA mice liver and ascitic hepatoma 22A cells chromatin. It has been revealed that the more unfolding state of DNA in ascitic nucleosomes (discovered earlier) is determined by the peculiarities of the interactions between DNA and the dimers H2A-H2B, as well as by the linker histones of the H1 group. The investigation of the DNA folding in the oligonucleosome chains with increasing ionic strength has shown complete invariability of the DNA compactness in the ascitic chromatin up to 100 mM NaCl, while in liver nucleosomes an additional folding of the linker portion of the DNA was observed within the range of 20-40 mM NaCl. Oligonucleosomes from ascitic chromatin are less inclined to association upon increasing ionic strength, as compared with those from liver chromatin.

[Structure of illexine I2 and its complexes with DNA]. / Issledovanie struktury illeksina I2 i ego kompleksov s DNK.

Conformational peculiarities of illexine I2 both in the solution and in the complexes with DNA were studied by circular dichroism, UV-spectroscopy and spectrophotometric melting. IIlexine I2 is shown to have an extended left-handed helical conformation of poly-L-proline II type, that are stable in a wide range of experimental conditions. Upon interaction of illexine I2 with DNA, the parameters of conformation are somewhat distorted but the main peculiarities remain. The DNA double helix changes from B- to the divection of C-form at its interaction with illexine I2. The interaction of illexine I2 with DNA at low ionic strength is non-cooperative and is characterized by some specificity to A--T sequences of DNA. Illexine I2 strongly affects the DNA stability by increasing the melting temperature of DNA.

[Characteristics of the structural state of DNA in chromatin with short linker]. / Osobennosti strukturnogo sostoianiia DNK v khromatine s korotkim linkerom.

Various fragments of pigeon brain neuron chromatin with very short linker DNA have been studied by circular dichroism (CD). The DNA structure in core particles of the brain and thymus chromatins is very similar. Linker DNA and a part of core DNA in the mononucleosomes of brain chromatin is extended. This conclusion follows from increasing CD amplitude of the brain mononucleosomes as compared with the corresponding value for thymus mononucleosomes. The internucleosome interactions stabilized the compactness of core DNA in the brain oligonucleosomes. The whole linker DNA of the brain chromatin unlike thymus chromatin is extended at low ionic strength. This fact can explain the brain chromatin ability to form a compact structure with increasing ionic strength.

[Optical and hydrodynamic properties of DNA complexes with histones H1 from the calf thymus and sea urchin sperm]. / Issledovanie opticheskikh i gidrodinamicheskikh svo'istv kompleksov DNK s gistonami H1 is timusa telenka i spermiev morskogo ezha.

A comparative study of the complexes between DNA and H1 histones from calf thymus (H1-T) and sea urchin sperm (H1-S) has been performed using methods of flow birefringence, viscometry and circular dichroism (CD). Both nucleohistone complexes undergo a conformational transition with the increase of protein content. A two-fold drop of intrinsic viscosity was observed when the histone content in the complex increased up to 9-12%. The transition is not accompanied by essential changes in the nucleohistone anisotropy, the latter coincides with the anisotropy of DNA in H1-T containing complexes and is close to that in H1-S containing complexes. CD spectra of the two types of complexes are not the same. For the H1-S containing complexes the decrease of the amplitude of the CD positive band and the shift of its maximum to the longwave region are observed while the spectrum of H1-T containing complex coincides with that of DNA. The spectral changes are partly due to slight aggregation of the H1-S containing complexes. It is also possible that changes in the local structure of DNA within the H1-S containing nucleohistone complexes take place.

[Comparative study of synthetic peptide fragments of histones H2B]. / Sravnitel'noe issledovanie sinteticheskikh peptidnykh fragmentov gistona H2B.

Oligopeptides of the N-terminal end of H2B histone with different molecular weights and amino acid sequences are studied by the CD method and X-ray analysis. Characteristic peculiarities of CD-spectra and position of diffraction maximums in X-ray diagrams in all the studied oligopeptides show that their conformation by the structure is similar to the extended left--handed helix of polyproline II. The investigation of CD-spectra under different conditions showed the dependence of the stability of "proII" conformation on the oligopeptide chain length. Their spectral and conformational properties may be due to peculiarities of their amino acid composition.