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.

The EBV Latent Antigen 3C Inhibits Apoptosis through Targeted Regulation of Interferon Regulatory Factors 4 and 8

“…Previous studies suggested that the oncogenic transcription factor c-Myc has a crucial role in cell growth, metabolism and proliferation [57], Cyclin dependent kinase 6 (CDK6) overexpression was implicated in the pathogenesis of B-cell malignancies [58], and also aberrant expression of the cell cycle regulatory protein Cyclin B1 has been detected in different lymphomas and EBV-immortalized cells [59], [60]. Earlier studies also demonstrated that these molecules are direct targets of IRF4 [44], [61].…”

Modulation of Enhancer Looping and Differential Gene Targeting by Epstein-Barr Virus Transcription Factors Directs Cellular Reprogramming

“…EBV infection results in the deregulation of the cell-cycle, with EBNA 3C playing a key role in overriding G1/S, G2/M and mitotic checkpoints through numerous potential mechanisms that include transcriptional repression and the regulation of protein stability [83]–[84]. Disruption of the G2/M checkpoint may be mediated through effects on the Chk2 kinase and we have recently described upregulation of an activator of CDK1, RGC-32, in EBV-infected cells [69], [85]. Although Wee1 has not previously been implicated in EBV-mediated cell-cycle disruption, a recent microarray study identified WEE1 as the fourth most regulated gene in the ‘cell proliferation’ gene ontology category in newly EBV-infected hyperproliferating B-cells [86].…”

Response gene to complement 32 (RGC-32) expression on M2-polarized and tumor-associated macrophages is M-CSF-dependent and enhanced by tumor-derived IL-4

“…This protein forms complexes with cyclin-dependent kinase p34CDC2 to enhance kinase activity and induce Sphase entry and mitosis. 14,15 Moreover, RGC-32 promotes cell migration, inhibits angiogenesis and induces smooth muscle cell differentiation. [16][17][18][19] Interestingly, RGC-32 is abnormally expressed in the peripheral blood mononuclear cells of patients with hyper-immunoglobulin E syndrome and multiple sclerosis.…”