Research

We focus on p53-dependent mechanisms of proliferation control and maintenance of genetic stability. One direction of our research involves study of recently identified antioxidant activity of p53 which represents a major component of tumor suppressor function of p53. The goal of our second research direction is developing approaches for functional restoration of the p53-dependent pathway in human cancer. The third direction is devoted to the study of novel nuclear single-polypeptide RNA polymerase IV (siRNAP-IV) which we recently discovered in humans and animals. In addition, we are developing approaches for functional analysis of the genome using genome-wide lentivirus-based siRNA libraries and transcriptional reporters.  

Antioxidant activity of the p53 tumor suppressor 

It is widely accepted that the function of the tumor suppressor p53 is mediated through restriction of proliferation of abnormal cells. Recently we have shown that in addition p53 protects the genome from excessive oxidation by reactive oxygen species (ROS), a major cause for DNA damage and mutations. We found that p53-regulated sestrins (PA26 and Hi95) function as antioxidant enzymes. Sestrins participate in regeneration of overoxidized peroxoredoxins, which are the peroxidases responsible for removal of H 2 O 2 produced during signaling. We found that in the absence of severe stresses relatively low levels of p53 are sufficient for transcriptional up-regulation of several antioxidant genes, including glutathione peroxidase and sestrins, leading to a substantial decrease in intracellular ROS levels. Inhibition of p53 results in the increase in intracellular ROS, excessive oxidation to DNA, and increased mutation rate, which are completely reversed by incubation with antioxidants.  In p53-knockout mice application of antioxidant N-acetylcysteine improves significantly karyotype stability and inhibits formation of thymic lymphomas. We are studying mechanisms of sestrin-mediated protection of nuclei and genome from peroxide bursts by analyzing composition, intracellular localization and enzymatic activity of sestrin-containing protein complexes.  

Reactivation of broken p53 tumor suppressor pathway in human cancer.  

The p53 gene is mutated in almost half of cancer cases. In the other half, the p53 pathway is disrupted by other mechanisms. The absence of p53 tumor suppressor activity increases genetic instability and abrogates apoptotic programs that prevent survival of abnormal cells. Reactivation of p53 pathway would lead to massive death of tumor cells representing an attractive therapeutic approach. In cervical carcinomas p53 is blocked by protein product of human papilloma virus (HPV), while all the rest components of the pathway stay structurally intact. We are screening for small molecules that interfere with the HPV-mediated block of p53 pathway. The obtained result suggest that such molecules can reestablish p53 function and result in apoptosis of carcinoma cells. Similarly, we are searching for small molecules that reactivate suppressor activity of p53 destroyed by point mutations. We obtained several classes of such compounds and currently are studying mechanisms of their stimulative effects on the p53 pathway.  

Identification of novel nuclear RNA polymerase IV 

Recently in human cells we identified transcripts that are stimulated after treatment with RNA polymerase II inhibitor alpha-amanitin. We have found that such transcripts represent protein-coding mRNAs and that their synthesis depends on functional POLRMT gene encoding mitochondrial RNA polymerase (mtRNAP). We established that an alternatively spliced transcript from the POLRMT gene encodes a truncated protein isoform devoid of mitochondria targeting signal. The protein is localized to the nuclei where it drives expression of several nuclear genes. Therefore, the alternative product of the POLRMT gene represents novel nuclear single-polypeptide RNA polymerase (spRNAP-IV). The promoters for spRNAP-IV differ substantially from those utilized by RNAP-II, do not respond to transcriptional enhancers, and contain a common functional sequence motif. We are exploring functions of novel spRNAP-IV in biogenesis of RNAs, and its potential roles in other nuclear processes.