Preventing evolution of chronic hepatitis B to hepatocellular carcinoma: from an interaction between HBV X protein with the cellular protein DDB1 toward a therapeutic agent

F Bergametti, D Sitterlin, PhD, J. Bianchi, C Transy, PhD

Inserm U163, Institut Pasteur, Paris, France

Aims: Due to the lack of fully efficient treatments of chronic hepatitis B, the 350 million persistent HBV carriers have a high risk of developing liver cancer. In this regard, targeting the X regulatory protein encoded by HBV would be of therapeutic interest. Indeed X protein is not only essential for infection but it also exerts deleterious effects on the host cell, contributing to HBV-induced carcinogenesis. We earlier showed that X activity requires productive interaction with DDB1 p127, one of the two subunits of the DDB complex, which is involved in cellular genome global repair (Sitterlin et al., Oncogene (2000)). We therefore focus on this interaction to: (i) elucidate its role at the molecular level and (ii) develop inhibitors interfering with X function. Methods and Results: Using co-expression experiments, we show that: (i) DDB1 dramatically increases the half-life of X protein by interfering with its proteasome-dependent degradation. (ii) Stabilization of X requires its efficient interaction with DDB1. (iii) The stabilization effect is observed with an irrelevant short-lived protein fused to the DDB1-binding domain of X. (iv) X stabilization is partially reversed by co-expression of DDB2, a cullin 4A target, which associates with DDB1 to form the DDB complex. Furthermore, using the two-hybrid system, we narrowed the DDB1-binding domain of X down to a 15-aminoacid region. We therefore expect the corresponding peptide to compete with X for DDB1-binding, resulting in inhibition of X-mediated transactivation and apoptosis. This assumption is currently under investigation. Conclusions: By showing the role of DDB1 in X stability and delineating the DDB1-binding domain to a short region amenable to chemical synthesis, our results further emphasize the usefulness and feasibility of targeting X-DDB1 interaction for therapeutic purposes.

KEY WORDS: hepatocellular carcinoma, therapeutic peptide.

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Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Prevention.