[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.

Using intravascular autoradiography for an estimation of proliferative activity of rat mesenteric microvessel endothelial cells during the first month of postnatal development.

BACKGROUND/METHODS: We applied a novel method for studying endothelial cells (EC) by using autoradiography of cells labeled by 3H-thymidine: photo emulsion was administered into the vascular bed. In the flat transparent organ, this method allows to compare the mitotic activity of endothelium (MAE) depending on vessel diameter and animal age. RESULTS: The number of the labeled ECs in animals was found to be almost equal in all vessels at the same age. The amount of labeled vessels and the density of the labeled nuclei increase towards near-capillary vessels of a diameter < or =10 microm. With age, MAE decreases in all categories of vessels. However, in 12-day-old animals, MAE temporarily increases. It was noted that high MAE in the bed of these rats precedes or coincides with the period of accelerated weight gain of the digestive system supplied by an increase in organ blood flow. CONCLUSIONS: By using the endothelial autoradiography method that we developed, we obtained the following evidence: (1) the number of ECs in the synthetic phase of the mitotic cycle in mesenterial vessels is approximately identical in animals of the same age, and (2) this number decreases with age, except during the period of accelerated organ growth, when MAE increases.

Non-compact nucleocapsid protein multimers in influenza-virus-infected cells.

We have previously shown that protease-resistant and highly immunoreactive compact NP oligomers, dissociating at +80 degrees C and possessing properties of folded proteins, are post-translationally formed in influenza-virus-infected cells. In this study we demonstrate that, in addition to compact NP oligomers, incompletely folded NP multimers are detected intracellularly by SDS/PAGE carried out under weak dissociating conditions. In cells infected with avian, human A(H2N2), and human A(H3N2) viruses, NP multimers are detected in the stacking gel of SDS/PAGE as retarded and loose structures dissociating at +50 degrees C. NP multimers are more sensitive to proteolysis than NP oligomers, but they are more resistant to proteolysis than NP monomers. In contrast to compact NP oligomers, NP multimers possess a weak immunoreactivity to some monoclonal antibodies. Pulse-chase experiments have shown that NP multimers appear at early stages of NP synthesis and are partially converted post-translationally into faster-migrating compact NP oligomers. In the course of infection, the excess NP multimers not converted into compact NP oligomers accumulate in cells and degrade. Under weak dissociating conditions, intracellular NP multimers are relatively stable in avian, human A(H2N2) and human A(H3N2) viruses and unstable in human A(H1N1) viruses, dissociating into monomers. NP multimers presumably serve to bring nascent unfolded NP molecules into close contact with each other for further oligomerization, to protect NP monomers from proteolysis, and to serve as intermediates in the posttranslational folding of NP.