Differential IFNa-stimulated gene expression profiles in PLZF-inducible U937T monocyte cells

Sensitivity to Interferon (IFN) is determined by a complex coordination of genetic and environmental factors. A previous experiment using two renal cancer cell lines differing markedly in their response to IFN were analyzed for their ISG profiles in order to determine gene expression changes associated with IFN sensitivity (Holko M, Williams BR. Functional annotation of IFN-alpha-stimulated gene expression profiles from sensitive and resistant renal cell carcinoma cell lines. J Interferon Cytokine Res 2006 Aug;26(8):534-47). Higher and more persistent expression of a subset of ISGs was noted in the IFN-sensitive RCC1 cells when compared with the relatively IFN-insensitive ACHN cells. A subset of Interferon stimulated genes (ISGs) whose sustained expression correlates with heightened IFN sensitivity were analyzed for functional and sequence similarities. This subset predominately contains genes involved in transcription, and most were found to contain in their promoters binding sites for promyleocytic zinc finger factor (PLZF), a transcriptional repressor identified by virtue of its role in the etiology of Acute Promyelocytic Leukemia (APL). Analysis of gene expression in a lymphoid cell line with inducible PLZF expression reveals that increased expression of immune system related genes including ISGs, depends on PLZF expression. Chromatin Immunoprecipitation assays show direct association between PLZF and in silico identified PLZF binding sites in ISG promoters. This study reveals a novel interaction between PLZF and IFN signaling. A time course of IFNa treatment (0, 6, 16, 24 hrs) was performed in tetetracycline induced PLZF overexpressing and control U937T:PLZF45 cells. For the 0 hr time point, PLZF overexpression (Cy5) was compared with control cells (Cy3). For the 6, 16, and 24 hr IFN treated time points, treated RNA was labelled with Cy5 and non-IFN treated RNA with Cy3. Each IFN treatment time point was performed on control and PLZF-overexpressing cells respectively.