Modulation of Histone Acetyltransferase Activity through Interaction of Epstein-Barr Nuclear Antigen 3C with Prothymosin Alpha

Abstract

The Epstein-Barr virus (EBV) nuclear antigen 3C (EBNA3C) is essential for EBV-dependent immortalization of human primary B lymphocytes. Genetic analysis indicated that amino acids 365 to 992 are important for EBV-mediated immortalization of B lymphocytes. We demonstrate that this region of EBNA3C critical for immortalization interacts with prothymosin alpha (ProT␣), a cellular protein previously identified to be important for cell division and proliferation. This interaction maps to a region downstream of amino acid 365 known to be involved in transcription regulation and critical for EBV-mediated transformation of primary B lymphocytes. Additionally, we show that EBNA3C also interacts with p300, a cellular acetyltransferase. This interaction suggests a possible role in regulation of histone acetylation and chromatin remodeling. An increase in histone acetylation was observed in EBV-transformed lymphoblastoid cell lines, which is consistent with increased cellular gene expression. These cells express the entire repertoire of latent nuclear antigens, including EBNA3C. Expression of EBNA3C in cells with increased acetyltransferase activity mediated by the EBV transactivator EBNA2 results in down-modulation of this activity in a dose-responsive manner. The interactions of EBNA3C with ProT␣ and p300 provide new evidence implicating this essential EBV protein EBNA3C in modulating the acetylation of cellular factors, including histones. Hence, EBNA3C plays a critical role in balancing cellular transcriptional events by linking the biological property of mediating inhibition of EBNA2 transcription activation and the observed histone acetyltransferase activity, thereby orchestrating immortalization of EBV-infected cells.Epstein-Barr Virus (EBV) is a human gammaherpesvirus predominantly infecting epithelial cells of the oropharynx and human primary B lymphocytes (41,63). EBV is the etiological agent of infectious mononucleosis and is also associated with various human malignancies, including Burkitt's lymphoma, nasopharyngeal carcinoma, non-Hodgkin's disease, AIDS immunoblastic lymphomas, and lymphoproliferative disease (3,63). Infection of the oropharyngeal epithelium is predominantly a lytic type of infection with the production of progeny virus (33,61,63,73). Infection of human primary B lymphocytes by EBV transforms them into continuously proliferating lymphoblastoid cell lines (LCLs) in vitro (11,29). Recent studies have demonstrated that EBV utilizes two major cellular signaling pathways for transforming B cells, the NOTCH1 signaling pathway and the TNF signaling pathway (6, 34, 57).After initial infection of B lymphocytes, EBV typically establishes a latent infection with the expression of 11 viral transcripts (41, 63). These genes are the six EBV nuclear antigens (EBNAs), three latent membrane proteins (LMPs), and the EBV early RNAs (41). Only a selected number of these genes are necessary for EBV-mediated immortalization of B lymphocytes (65). EBNA2, EBNA3A, EBNA3C, and LMP1 are essential for EBV-induced immorta...

Macromolecular Translocation Inhibitor II (Zn2+-binding Protein, Parathymosin) Interacts with the Glucocorticoid Receptor and Enhances Transcription in Vivo

“…As mentioned above, PT␣ has been reported to interact with CBP, Epstein-Barr virus nuclear antigen 3C, and p300 (37)(38)(39)(40). These results indicate that PT␣ is a coactivator of transcriptional activation.…”

“…Recently, it has been reported that PT␣ interacts with CBP and enhances the transcriptional potential of CBP (37). In addition, PT␣ interacts with the Epstein-Barr virus nuclear antigen 3C and p300, and cooperatively regulates the acetylation (38,39) and deacetylation (40) of histones. Moreover, PT␣ selectively enhances the transcriptional activity of the estrogen receptor (ER) but not the transcriptional activity of other nuclear receptors (41).…”

Regulation of apoptosis by the p8/prothymosin α complex

“…ProT␣ is a small ubiquitous protein, generally abundant, and present both in nucleus and cytoplasm. It is involved in the proliferation of mammalian cells (19), in transcription (20), in chromatin remodeling, and in protection against apoptosis (22). The molecular mechanisms are unknown, except for the antiapoptotic activity of ProT␣, which occurs through inhibition of apoptosome formation (22).…”

“…ProT␣ was associated with cellular proliferation and carcinogenesis (18,19), cellular and viral transcription (19,20), and remodeling of chromatin (21). More recently, ProT␣ was shown to inhibit caspase 9 activation by blocking apoptosome formation, which prevents the activation of effector caspases (22) p8 and ProT␣ are two small proteins without stable secondary structure in solution, showing opposite electrostatic charges at neutral pH.…”

Epstein-Barr virus nuclear antigens 3C and 3A maintain lymphoblastoid cell growth by repressing p16 INK4A and p14 ARF expression

“…Indeed, all mutations in EBNA3A or EBNA3C that inhibit association with RBPJ are null for LCL growth (22)(23)(24), whereas EBNA3A or EBNA3C mutations that affect binding to the adenovirus E1a C-terminal binding protein (CtBP) corepressor result in continuous, albeit slower, growth (22)(23)(24)(25)(26). EBNA3C or EBNA3A have many specific and potentially significant interactions with other transcription factors or modifiers, including PU.1, Spi-B, HDAC1, DP103, prothymosin-α, p300, Nm23-H1, SUMO1, and SUMO3, cyclin A, SCF SKP2 ubiquitin ligase, pRb, Chk2, Mdm2, and MRS18-2, and these interactions could be relevant to CDKN2A p16 INK4A or p14 ARF regulation and LCL growth (27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37)(38). Furthermore, EBNA3C upregulates TCL1A and ITGA4, down-regulates JAG1 and NCALD RNAs, and cooperates with EBNA3A in repressing Bim, a proapoptotic Bcl-2 family protein (24,(39)(40)(41).…”