Previous data demonstrate that Epstein-Barr Virus Latent Membrane Protein 2A (LMP2A) enhances IL-10 to promote the survival of LMP2A-expressing B cell lymphomas. Since STAT3 is an important regulator of IL-10 production, we hypothesized that LMP2A activates a signal transduction cascade that increases STAT3 phosphorylation to enhance IL-10. Using LMP2A-negative and –positive B cell lines, the data indicate that LMP2A requires the early signaling molecules of the Syk/RAS/PI3K pathway to increase IL-10. Additional studies indicate that the PI3K-regulated kinase, BTK, is responsible for phosphorylating STAT3, which ultimately mediates the LMP2A-dependent increase in IL-10. These data are the first to show that LMP2A signaling results in STAT3 phosphorylation in B cells through a PI3K/BTK-dependent pathway. With the use of BTK and STAT3 inhibitors to treat B cell lymphomas in clinical trials, these findings highlight the possibility of using new pharmaceutical approaches to treat EBV-associated lymphomas that express LMP2A.
The incidence of Hodgkin's lymphoma (HL) is growing due to an increase in Epstein‐Barr virus (EBV)‐associated HL in AIDS patients. The HL tumor microenvironment is vital for the survival of the malignant Hodgkin‐Reed Sternberg (HRS) cells of HL, which express the EBV protein latent membrane protein 2A (LMP2A). While previous work shows that LMP2A mimics B‐cell receptor (BCR) signaling to promote the survival of HRS cells, the ability of LMP2A to establish and maintain the tumor microenvironment through the production of chemokines remains unknown. Since BCR signaling induces the production of the chemokine macrophage inflammatory protein‐1α (MIP‐1α), and since LMP2A is a BCR mimic, we hypothesized that LMP2A increases MIP‐1α levels. A comparison of multiple LMP2A‐negative and ‐positive cell lines demonstrates that LMP2A increases MIP‐1α. Additionally, LMP2A‐mutant cell lines and pharmacologic inhibitors indicate that LMP2A activates a Syk/PI3K/NF‐κB pathway to enhance MIP‐1α. Finally, based on the finding that an NF‐κB inhibitor decreased MIP‐1α RNA/protein in LMP2A‐positive cells, we are the first to demonstrate that LMP2A increases the nuclear localization of the NF‐κB p65 subunit using DNA‐binding assays and confocal microscopy in human B cells. These findings not only have implications for the treatment of HL, but also other LMP2A‐expressing B‐cell tumors that overexpress NF‐κB.
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