IRF4 Deficiency Leads to Altered BCR Signalling Revealed by Enhanced PI3K Pathway, Decreased SHIP Expression and Defected Cytoskeletal Responses

The graded expression of transcription factor interferon regulatory factor 4 (IRF4) regulates B cell development and is critical for plasma cell differentiation. However, the mechanisms, by which IRF4 elicits its crucial tasks, are largely unknown. To characterize the molecular targets of IRF4 in B cells, we established an IRF4-deficient DT40 B cell line. We found that in the absence of IRF4, the expression of several molecules involved in BCR signalling was altered. For example, the expression of B cell adaptor for PI3K (BCAP) was upregulated, whereas the SHIP (SH2-containing Inositol 5?-Phosphatase) expression was downregulated. These molecular unbalances were accompanied by increased BCR-induced calcium signalling, attenuated B cell linker protein (BLNK) and ERK activity and enhanced activity of PI3K/protein kinase B (Akt) pathway. Further, the IRF4-deficient cells showed dramatically diminished cytoskeletal responses to anti-IgM cross-linking. Our results show that IRF4 has an important role in the regulation of BCR signalling and help to shed light on the molecular mechanisms of B cell development and germinal centre response.