Enhancer Control of MicroRNA miR-155 Expression in Epstein-Barr Virus-Infected B Cells.

The oncogenic microRNA (miRNA) miR-155 is the most frequently upregulated miRNA in Epstein-Barr virus (EBV)-positive B cell malignancies and is upregulated in other nonviral lymphomas. Both EBV nuclear antigen 2 (EBNA2) and the B cell transcription factor interferon regulatory factor 4 (IRF4) are known to activate transcription of the host cell gene from which miR-155 is processed (miR-155HG; BIC). EBNA2 also activates IRF4 transcription, indicating that EBV may upregulate miR-155 through direct and indirect mechanisms. The mechanism of transcriptional regulation of IRF4 and miR-155HG by EBNA2, however, has not been defined. We demonstrate that EBNA2 can activate IRF4 and miR-155HG expression through specific upstream enhancers that are dependent on the Notch signaling transcription factor RBPJ, a known binding partner of EBNA2. We demonstrate that in addition to the activation of the miR-155HG promoter, IRF4 can also activate miR-155HG via the upstream enhancer also targeted by EBNA2. Gene editing to remove the EBNA2- and IRF4-responsive miR-155HG enhancer located 60 kb upstream of miR-155HG led to reduced miR-155HG expression in EBV-infected cells. Our data therefore demonstrate that specific RBPJ-dependent enhancers regulate the IRF4-miR-155 expression network and play a key role in the maintenance of miR-155 expression in EBV-infected B cells. These findings provide important insights that will improve our understanding of miR-155 control in B cell malignancies.IMPORTANCE MicroRNA miR-155 is expressed at high levels in many human cancers, particularly lymphomas. Epstein-Barr virus (EBV) infects human B cells and drives the development of numerous lymphomas. Two genes carried by EBV (LMP1 and EBNA2) upregulate miR-155 expression, and miR-155 expression is required for the growth of EBV-infected B cells. We show that the EBV transcription factor EBNA2 upregulates miR-155 expression by activating an enhancer upstream from the miR-155 host gene (miR-155HG) from which miR-155 is derived. We show that EBNA2 also indirectly activates miR-155 expression through enhancer-mediated activation of IRF4 IRF4 then activates both the miR-155HG promoter and the upstream enhancer, independently of EBNA2. Gene editing to remove the miR-155HG enhancer leads to a reduction in miR-155HG expression. We therefore identify enhancer-mediated activation of miR-155HG as a critical step in promoting B cell growth and a likely contributor to lymphoma development.

Expedient iron-catalyzed coupling of alkyl, benzyl and allyl halides with arylboronic esters.

While attractive, the iron-catalyzed coupling of arylboron reagents with alkyl halides typically requires expensive or synthetically challenging diphosphine ligands. Herein, we show that primary and secondary alkyl bromides and chlorides, as well as benzyl and allyl halides, can be coupled with arylboronic esters, activated with alkyllithium reagents, by using very simple iron-based catalysts. The catalysts used were either adducts of inexpensive and widely available diphosphines or, in a large number of cases, simply [Fe(acac)3] with no added co-ligands. In the former case, preliminary mechanistic studies highlight the likely involvement of iron(I)-phosphine intermediates.