The Epstein-Barr virus bZIP transcription factor Zta causes G(0)/G(1) cell cycle arrest through induction of cyclin-dependent kinase inhibitors

While oncoproteins encoded by small DNA tumor viruses and Epstein-Barr virus (EBV) latent antigens facilitate G(1)/S progression, the EBV lytic switch transactivator Zta was found to inhibit growth by causing cell cycle arrest in G(0)/G(1) in several epithelial tumor cell lines. Expression of Zta results in induction of the tumor suppressor protein, p53, and the cyclin-dependent kinase inhibitors, p21 and p27, as well as accumulation of hypophosphorylated pRb. Up-regulation of p53 and p27 occurs by post-transcriptional mechanisms while expression of p21 is induced at the RNA level in a p53-dependent manner. Inactivation of pRb by transient overexpression of the human papillomavirus E7 oncoprotein indicates that pRb or pRb-related proteins are key mediators of the growth-inhibitory function of Zta. These findings suggest that EBV plays an active role in redirecting epithelial cell physiology to facilitate the viral replicative program through a Zta-mediated growth arrest function.