IRF4 downregulation suppresses the gene expression network of MYC in ALCL. (A) Gene expression profiling after IRF4 knockdown in K299, DEL, and FE-PD cells. Changes of gene expression were profiled at the indicated time points after induction of IRF4 shRNA #1. Gene expression changes are depicted according to the color scale shown. Genes that are involved in critical biological processes are highlighted. (B) Gene set enrichment analysis of a previously described MYC gene expression signature. The MYC signature is significantly enriched with genes that are downregulated after IRF4 knockdown. (C) IRF4 shRNA #1 and #2 downregulate MYC mRNA in K299, JB6, and FE-PD cells 48 hours after shRNA induction as measured by quantitative PCR. MYC mRNA levels were normalized to expression of GAPDH. Error bars indicate the standard deviation. (D) IRF4 shRNA #1 and #2 downregulate MYC protein in K299, JB6, and FE-PD cells 48 hours after shRNA induction as measured by western blotting. (E) Chromatin immunoprecipitation quantitative PCR analysis of IRF4 binding in the MYC promoter and at a control locus in DEL (ALK⁺) and FE-PD (ALK⁻) cells. The control locus is a region on chromosome 7, used as a negative control for IRF4 binding, due to the lack of observable IRF4 binding in previous studies.^24,25  Error bars depict standard error of the mean. **P < .01.