The Interferon Consensus Sequence-binding Protein (ICSBP/IRF8) Represses PTPN13 Gene Transcription in Differentiating Myeloid Cells

Abstract

The interferon consensus sequence-binding protein (ICSBP/ IRF8) is an interferon regulatory factor that is expressed in myeloid and B-cells. ICSBP-deficient mice develop a myeloproliferative disorder characterized by cytokine hypersensitivity and apoptosis resistance. To identify ICSBP target genes involved in these effects, we screened a CpG island microarray with chromatin that co-immunoprecipitated with ICSBP from myeloid cells. Using this technique, we identified PTPN13 as an ICSBP target gene. PTPN13 encodes Fas-associated phosphatase 1 (Fap-1), a ubiquitously expressed protein-tyrosine phosphatase. This was of interest because interaction of Fap-1 with Fas results in Fas dephosphorylation and inhibition of Fas-induced apoptosis. In this study, we found that ICSBP influenced Fas-induced apoptosis in a Fap-1-dependent manner. We also found that ICSBP interacted with a cis element in the proximal PTPN13 promoter and repressed transcription. This interaction increased during myeloid differentiation and was regulated by phosphorylation of conserved tyrosine residues in the interferon regulatory factor domain of ICSBP. ICSBP deficiency was present in human myeloid malignancies, including chronic myeloid leukemia. Therefore, these studies identified a mechanism for increased survival of mature myeloid cells in the ICSBP-deficient murine model and in human myeloid malignancies with decreased ICSBP expression.

Increased Fanconi C expression contributes to the emergency granulopoiesis response

“…This set included genes that terminate cytokine-induced proliferation (NF1 and GAS2), increase sensitivity of phagocytes to Fas-induced apoptosis (PTPN13), and are involved in DNA repair (FANCF) (14)(15)(16)(17). We found that IRF8 activated FANCF (the gene encoding Fanconi F) in bone marrow progenitor cells that were stimulated with differentiating cytokines (17).…”

“…The PCR product was sequenced to assure that no mutations were present. IRF8-specific shRNAs were designed and subcloned into the pLKO expression vector, as previously described (15,16). These shRNAs consistently reduce IRF8 expression in U937 cells by 70% (15,16).…”

“…The human myelomonocytic leukemia cell line U937 (32) was obtained from Andrew Kraft (Hollings Cancer Center, University of South Carolina, Charleston, South Carolina, USA). Cells were maintained as described previously (14)(15)(16)(17).…”

Role of IRF6 in epithelial cell-mediated host defence and inflammation

“…Macrophages, monocytes, DCs and T cells from these mice also showed functional abnormalities, with resistance to apoptosis and hypersensitivity to cytokines (Huang, Zhu et al 2008). These defects indicate the importance of IRF8 in myelopoiesis.…”

“…Specific IRF family members have well-established functions in development of immune cell lineages. IRF8 plays an important role in development of immune cells including macrophages, monocytes, DCs, natural killer (NK) cells, CD4 + and CD8 + T cells , Turcotte, Gauthier et al 2005, Greeneltch, Schneider et al 2007, Huang, Zhu et al 2008). IRF8 knockout mice showed impaired myeloid cell differentiation, and also developed a syndrome similar to human chronic or acute myelogenous leukemia (Holtschke, Lohler et al 1996).…”