Epstein-Barr virus nuclear antigen 3C facilitates G1-S transition by stabilizing and enhancing the function of cyclin D1

• Published in: PLoS pathogens Vol. 7; no. 2; p. e1001275
• Main Authors: Saha, Abhik, Halder, Sabyasachi, Upadhyay, Santosh K, Lu, Jie, Kumar, Pankaj, Murakami, Masanao, Cai, Qiliang, Robertson, Erle S
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 01.02.2011; Public Library of Science (PLoS)
• Subjects: Antigens, Viral - chemistry; Antigens, Viral - genetics; Antigens, Viral - metabolism; Antigens, Viral - physiology; Apoptosis; Cell division; Cell growth; Cell Transformation, Viral - genetics; Cells; Cells, Cultured; Colleges & universities; Cyclin D proteins; Cyclin D1 - genetics; Cyclin D1 - metabolism; Cyclin D1 - physiology; Epstein-Barr virus; Epstein-Barr Virus Infections - genetics; Epstein-Barr Virus Nuclear Antigens; Experiments; G1 Phase - genetics; Gene expression; Gene Expression Regulation; Genetic aspects; Genetic engineering; Health aspects; Herpes viruses; Herpesvirus 4, Human - physiology; Humans; Infections; Infectious Diseases/Viral Infections; Kinases; Microbiology/Cellular Microbiology and Pathogenesis; Oncology/Hematological Malignancies; Phase transitions; Physiological aspects; Protein Binding; Protein Processing, Post-Translational - genetics; Protein Processing, Post-Translational - physiology; Protein Stability; Protein Structure, Tertiary - physiology; Proteins; S Phase - genetics; Ubiquitination; Up-Regulation - genetics; Virology/Viruses and Cancer; United States; Japan
• ISSN: 1553-7374; 1553-7366; 1553-7374
• DOI: 10.1371/journal.ppat.1001275

EBNA3C, one of the Epstein-Barr virus (EBV)-encoded latent antigens, is essential for primary B-cell transformation. Cyclin D1, a key regulator of G1 to S phase progression, is tightly associated and aberrantly expressed in numerous human cancers. Previously, EBNA3C was shown to bind to Cyclin D1 in vitro along with Cyclin A and Cyclin E. In the present study, we provide evidence which demonstrates that EBNA3C forms a complex with Cyclin D1 in human cells. Detailed mapping experiments show that a small N-terminal region which lies between amino acids 130-160 of EBNA3C binds to two different sites of Cyclin D1- the N-terminal pRb binding domain (residues 1-50), and C-terminal domain (residues 171-240), known to regulate Cyclin D1 stability. Cyclin D1 is short-lived and ubiquitin-mediated proteasomal degradation has been targeted as a means of therapeutic intervention. Here, we show that EBNA3C stabilizes Cyclin D1 through inhibition of its poly-ubiquitination, and also increases its nuclear localization by blocking GSK3β activity. We further show that EBNA3C enhances the kinase activity of Cyclin D1/CDK6 which enables subsequent ubiquitination and degradation of pRb. EBNA3C together with Cyclin D1-CDK6 complex also efficiently nullifies the inhibitory effect of pRb on cell growth. Moreover, an sh-RNA based strategy for knock-down of both cyclin D1 and EBNA3C genes in EBV transformed lymphoblastoid cell lines (LCLs) shows a significant reduction in cell-growth. Based on these results, we propose that EBNA3C can stabilize as well as enhance the functional activity of Cyclin D1 thereby facilitating the G1-S transition in EBV transformed lymphoblastoid cell lines.