Epstein-Barr Virus Latent Membrane Protein 1 (CAO) Up-regulates VEGF and TGFα Concomitant with Hyperlasia, with Subsequent Up-regulation of p16 and MMP9

Abstract

EBV latent membrane protein 1 (LMP1) is an oncoprotein frequently expressed in nasopharyngeal carcinoma. We have generated transgenic mice expressing the nasopharyngeal carcinoma-derived CAO strain of LMP1 and LMP1 of the B95-8 strain, using the viral ED-L2 promoter for epithelial expression. LMP1(CAO) and LMP1(B95-8) induce transforming growth factor alpha expression and epidermal hyperplasia. However, levels of total epidermal growth factor receptor (EGFR) decline with the appearance of phosphorylated EGFR products, suggesting that the negative feedback loop upon EGFR expression is intact or that there is faster turnover at these early stages of carcinogenesis. In the L2LMP1(CAO) mice, increased levels of vascular endothelial growth factor are also seen at an early stage in the skin. As the phenotype worsens, with increasing hyperplasia and vascularization leading to keratoacanthoma, p16(INK4a) and matrix metalloproteinase 9 expression is induced. The lesions can progress spontaneously to carcinoma. Carcinoma cell lines developed from these mice show high levels of total and phosphorylated EGFR. These data show that the induction of signaling through EGFR by LMP1 is an early event in carcinogenesis and that any inhibition upon EGFR expression is lifted during progression. Furthermore, expression of LMP1 is not sufficient to inhibit induction of p16(INK4a) in response to abnormal proliferation. These data are consistent with the cooperative effects seen between LMP1 and loss of the INK4a locus in transgenic mice and with the frequency of loss of this locus in EBV-associated nasopharyngeal carcinoma.

Epstein–Barr virus-encoded LMP1 induces a hyperproliferative and inflammatory gene expression programme in cultured keratinocytes

“…Of particular interest was that many fell into the categories of inflammatory and wound-response genes (Table 1, Figs 3 and 6). Increased expression of many of these classes has been reported in hyperproliferative and inflamed epidermis and is consistent with previous observations demonstrating that LMP1 induces hyperproliferative lesions in transgenic murine epidermis (Stevenson et al, 2005;Wilson et al, 1990). The induction of several of these genes (IL6, IL8, VEGF, CXCL1, 2, 3, CSF2, CCL5, CCL20, BIRC3, TNFAIP3, NFKBIA and IER3) ( Table 1, Fig.…”

Modulation of LMP1 protein expression by EBV-encoded microRNAs

“…The lack of LMP1 protein expression in some NPC samples may not accurately reflect the contribution of LMP1 to the pathology of NPC. In the transgenic mouse model, LMP1 expression led to epithelial hyperplasia, and yet LMP1 protein could not be readily detected with standard extraction methods (31). Here, we found that very small amounts of LMP1 that may be difficult to detect with currently available reagents, are sufficient to activate NF-B.…”

LMP1 Promotes Expression of Insulin-Like Growth Factor 1 (IGF1) To Selectively Activate IGF1 Receptor and Drive Cell Proliferation

“…In epithelial cells, the CTAR1 domain of LMP1 signals through protein kinase C ␦ (PKC␦) and STAT3 to induce EGFR expression via a unique form of NF-B signaling wherein p50 dimers bind to BCL3 to regulate gene transcription (10,(16)(17)(18). Although LMP1 increases the transcription of the EGFR ligand, transforming growth factor-␣ (TGF-␣), TGF-␣ does not appear to be necessary for EGFR phosphorylation (19). Hence, it is unclear how LMP1 regulates EGFR activation.…”