Faculty Members

A Novel Mechanism of Protein Degradation

Protein degradation is a basic process in the living cell. A large fraction of onco- and tumor suppressor proteins are regulated at the level of their stability. Therefore investigation of the mechanisms of proteasomal protein degradation has attracted much attention. For example the p53 level is controlled by the rate of its proteasomal degradation, a process regulated by the Mdm2-ubiquitin-proteasome degradation pathway. We have found a novel pathway that regulates p53 stability. This pathway is regulated by NAD(P)H: quinone oxidoreductase 1 (NQO1). Pharmacological and genetic inhibition of NQO1 induces p53 proteasomal degradation and inhibits p53-mediated apoptosis. NQO1 regulates degradation of p53 by a mechanism that is independent of both Mdm2 and ubiquitin. This pathway is not exclusive for p53. A limited number of other short-lived proteins such as p73 and ODC are regulated by NQO1. Studies have indicated that this pathway may play a role in oncogenesis. The underlying molecular mechanism of this process of protein destabilization is under study.

Tumor Suppressors and DNA Damage

We study the molecular basis of cell response to DNA damage, in particular double strand break (DSB). We have characterized a novel signaling-pathway that is initiated by DSB and triggers activation of the non-receptor tyrosine kinase c-Abl. This kinase in turn tyrosine phosphorylates the intimately associated p73, a member of p53 tumor suppressor family. This process often elicits apoptosis unless the damage has been repaired or the DNA fragments have been excluded. Thus, the repair machinery and DNA fragments regulate the apoptosis pathway. The nature and composition of this process is under study.

The Molecular Mechanisms of Virus Host-Cell Interaction

Viruses in order to propagate have to invade cells and to occupy the relevant cellular machinery. How, a given virus with a very limited number of genes can do so is a very basic question but the answers await understanding of the virus genes from one hand and the cellular machineries from other. Hepatitis B virus (HBV) is a common infectious agent worldwide, hence provides an excellent model. HBV is a liver specific virus. Our study revealed that this tropism is determined at the level of both receptor and post-receptor levels, and identified the molecular basis of these processes. We found that the small pX regulatory protein of HBV manipulates the cellular transcription machinery at all possible levels, namely chromatin, enhancer and the basal promoter binding proteins. Cellular proteins, the targets of pX were identified but the list has not been completed.

" Synthetic Viruses" and Gene Therapy

Gene therapy has attracted much attention but proved partially successful. Viruses that are used for DNA transduction are unsafe. Our aim is to generate non-infectious virus like particles. The individual components are prepared in heterogonous systems and assembled in tube. These particles are expected to be safe and their production is highly reproducible. These " synthetic virions " may revolutionize the whole field of gene transfer technology.

Recent References

Ori, A. Zauberman, A., Doitsh, G., Paran N., Oren, M. and Shaul, Y. (1998). p53 binds and represses the HBV enhancer: an adjacent enhancer element can reverse the transcription effect of p53. EMBO J 17, 544-553. PDF Version

Haviv, I., Shamay M., Doitsh, G. and Shaul, Y. (1998). Hepatitis B virus pX targets TFIIB in transcription coactivation. Mol. Cell. Biol. 18,1562-1569 PDF Version

Haviv, I., Matza, Y. and Shaul, Y. (1998). pX, the HBV encoded coactivator, suppresses the phenotypes of TBP and TAF_II250 mutants. Genes and Dev 12, 1217-1226. PDF Version

Agami, R. and Shaul, Y. (1998). The kinase activity of c-Abl but not v-Abl is potentiated by direct interaction with RFX1, a protein that binds the enhancers of several viruses and cell- cycle regulated genes. Oncogene 16, 1779-1788. PDF Version

Agami, R., Blandino, G., Oren, M. and Shaul, Y. (1999). Interaction of c-Abl and p73alpha and their collaboration to induce apoptosis. Nature 399, 809-813. PDF Version

Katan-Khaykovich, Y., Spiegel, I. and Shaul, Y. (1999). The dimerization/repression domain of RFX1 is related to a conserved region of its yeast homologues Crt1 and Sak1: a new function for an ancient motif. J. Mol. Biol. 294, 121-137. PDF Version

Doitsh, G. and Shaul, Y. (1999). HBV transcription repression in response to genotoxic stress is p53-dependent and abrogated by pX. Oncogene 18, 7506-7513. PDF Version

Paran, N, Ori, A., Haviv, I. and Shaul, Y. (2000). A composite polyadenylation signal with TATA box function. Mol. Cell. Biol. 20, 834-841. PDF Version

Asher, G., Lotem, J., Cohen, B., Sachs, L. and Shaul, Y. (2001). Regulation of p53 stability and p53-dependent apoptosis by NADH quinone oxidoreductase 1. Proc. Natl. Acad. Sci. USA. 98, 1188-1193. PDF Version

Barak, O., Aronheim, A. and Shaul, Y. (2001). HBV X protein targets HIV Tat-binding protein 1. Virology 283, 110-120. PDF Version

Katan-Khaykovich, Y. and Shaul, Y. (2001). Nuclear import and DNA-binding activity of RFX1. Evidence for an autoinhibitory mechanism. Eur. J. Biochem. 268, 3108-3116. PDF Version

Paran, N, Geiger, B. and Shaul, Y. (2001). HBV infection of cell culture: evidence for multivalent and cooperative attachment. EMBO J. 20, 4443-4453. PDF Version

Shamay, M., Agami, R. and Shaul, Y. (2001). HBV integrants of hepatocellular carcinoma cell lines contain an active enhancer. Oncogene 20, 6811-6819. PDF Version

Shamay, M., Barak, O., Doitsh, G., Ben-Dor, I. and Shaul, Y. (2002). Hepatitis B virus pX interacts with HBXAP, a PHD finger protein to coactivate transcription. J. Biol. Chem. 277, 9982-9988. PDF Version

Asher, G., Lotem, J., Kama, R., Sachs, L. and Shaul, Y. (2002). NQO1 stabilizes p53 through a distinct pathway. Proc. Natl. Acad. Sci. USA. 99, 3099-3104. PDF Version

Shamay, M., Barak, O. and Shaul, Y. (2002). HBXAP, a novel PHD finger protein, Pssesses transcription repression activity. Genomics 79, 523-529. PDF Version

Asher, G., Lotem, J., Sachs, L., Kahana, C. and Shaul, Y. (2002). Mdm-2 and ubiquitin- independent p53 proteasomal degradation regulated by NQO1. Proc Natl Acad Sci U S A. 99, 13125- 13130. PDF Version

Shlomai, A. and Shaul, Y. (2003). Inhibition of hepatitis B virus expression and replication by RNA interference. Hepatology. 37, 764-770. PDF Version

Doitsh, G. and Shaul, Y. (2003). A long HBV transcript encoding pX is inefficiently exported from the nucleus. Virology. 309, 339-349. PDF Version

Ben-Yehoyada, M., Ben-Dor, I. and Shaul, Y. (2003). c-Abl tyrosine kinase selectively regulates p73 nuclear matrix association. J Biol Chem. 278, 34475-34482. PDF Version

Asher, G., Lotem, J., Tsvetkov, P., Reiss, V., Sachs, L. and Shaul, Y. (2003). P53 hot-spot mutants are resistant to ubiquitin-independent degradation by increased binding to NAD(P)H: quinone oxidoreductase 1. Proc Natl Acad Sci U S A. 100, 15065-15070. PDF Version

Doitsh, G. and Shaul, Y. (2004). Enhancer I predominance in hepatitis B virus gene expression. Mol Cell Biol. 24, 1799-1808. PDF Version

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Department of Molecular Genetics
Weizmann Institute of Science
Rehovot
Israel

Tel: 972-8-934-3970
Fax: 972-8-934-4108

e-mail: lgmichal@wicc.weizmann.ac.il

Last Updated: 14 March 2004