title: Upregulation of the cell-cycle regulator RGC-32 in Epstein-Barr virus-immortalized cells.
abstract: Epstein-Barr virus (EBV) is implicated in the pathogenesis of multiple human tumours of lymphoid and epithelial origin. The virus infects and immortalizes B cells establishing a persistent latent infection characterized by varying patterns of EBV latent gene expression (latency 0, I, II and III). The CDK1 activator, Response Gene to Complement-32 (RGC-32, C13ORF15), is overexpressed in colon, breast and ovarian cancer tissues and we have detected selective high-level RGC-32 protein expression in EBV-immortalized latency III cells. Significantly, we show that overexpression of RGC-32 in B cells is sufficient to disrupt G2 cell-cycle arrest consistent with activation of CDK1, implicating RGC-32 in the EBV transformation process. Surprisingly, RGC-32 mRNA is expressed at high levels in latency I Burkitt's lymphoma (BL) cells and in some EBV-negative BL cell-lines, although RGC-32 protein expression is not detectable. We show that RGC-32 mRNA expression is elevated in latency I cells due to transcriptional activation by high levels of the differentially expressed RUNX1c transcription factor. We found that proteosomal degradation or blocked cytoplasmic export of the RGC-32 message were not responsible for the lack of RGC-32 protein expression in latency I cells. Significantly, analysis of the ribosomal association of the RGC-32 mRNA in latency I and latency III cells revealed that RGC-32 transcripts were associated with multiple ribosomes in both cell-types implicating post-initiation translational repression mechanisms in the block to RGC-32 protein production in latency I cells. In summary, our results are the first to demonstrate RGC-32 protein upregulation in cells transformed by a human tumour virus and to identify post-initiation translational mechanisms as an expression control point for this key cell-cycle regulator.
authors.affiliation: School of Life Sciences, University of Sussex, Falmer, Brighton, United Kingdom.
authors.forename: Sandra N
authors.initials: SN
authors.lastname: Schlick
authors.forename: C David
authors.initials: CD
authors.lastname: Wood
authors.forename: Andrea
authors.initials: A
authors.lastname: Gunnell
authors.forename: Helen M
authors.initials: HM
authors.lastname: Webb
authors.forename: Sarika
authors.initials: S
authors.lastname: Khasnis
authors.forename: Aloys
authors.initials: A
authors.lastname: Schepers
authors.forename: Michelle J
authors.initials: MJ
authors.lastname: West
mesh_terms: D001402:B-Lymphocytes / Q000378:metabolism / Q000821:virology; D016203:CDC2 Protein Kinase / Q000096:biosynthesis; D018797:Cell Cycle Proteins / Q000096:biosynthesis*; D045744:Cell Line, Tumor; D050676:Core Binding Factor Alpha 2 Subunit / Q000096:biosynthesis; D005434:Flow Cytometry / Q000379:methods; D016195:G2 Phase; D020869:Gene Expression Profiling; D004854:Herpesvirus 4, Human / Q000378:metabolism*; D006801:Humans; D009124:Muscle Proteins / Q000096:biosynthesis*; D009419:Nerve Tissue Proteins / Q000096:biosynthesis*; D010957:Plasmids / Q000378:metabolism; D011132:Polyribosomes / Q000378:metabolism; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000378:metabolism; D014158:Transcription, Genetic; D015854:Up-Regulation
chemical_list: D018797:Cell Cycle Proteins; D050676:Core Binding Factor Alpha 2 Subunit; D009124:Muscle Proteins; D009419:Nerve Tissue Proteins; C115049:RGCC protein, human; D012333:RNA, Messenger; C493728:RUNX1 protein, human; D016203:CDC2 Protein Kinase