Ph.D Thesis

Ph.D StudentHashmueli Sharon
SubjectStructure Function Analysis of the Interactions among the
DepartmentDepartment of Biotechnology and Food Engineering
Supervisor PROFESSOR EMERITUS Ben-Zion Levi


Interferon Regulatory Factors (IRFs) constitute a family of transcription factors involved in regulation of IFN signaling and immune responses. Targeted gene disruption studies in mice assigned their primary role to the immune system. IRFs transcriptional activities vary and are mediated through protein-protein interactions with other transcription factors. These protein complexes enhance the ability of IRFs to bind DNA and modulate their transcriptional activities. IFN Consensus Sequence Binding Protein (ICSBP/IRF8) is a lymphoid-specific factor and plays a key role in macrophage maturation. Previous research identified a region in ICSBP, termed IRFs association Domain (IAD), which is conserved in all IRFs (excluding IRF1 and IRF2) and is essential for interactions with other IRF proteins. The aim of my study was to characterize the association domains and the interactions they mediate. This study demonstrates that the IAD is a novel and independent domain sufficient to promote protein-protein interactions with IRF and non-IRF transcription factors. Assays with the IAD and full length ICSBP demonstrated the importance of protein-protein as well as DNA-protein interactions in IRFs activity. In addition, the association domain of IRF2 (IAD2), necessary for interaction with ICSBP, was identified and found to be conserved in IRF1. Computer analysis indicated that IAD2 as a PEST motif, with similar characteristics as the PEST domain of PU.1 that enables association with IRF4 and ICSBP. A DN-ICSBP construct (ICSBP defective in its DBD) was generated that could compete with endogenous ICSBP and IRF4 for interactions with other factors, and inhibit or alter their transcriptional activity. Interestingly, expression of DN-ICSBP induced apoptosis in hematopoietic cell line U937, but not non-hematopoietic cell line NIH 3T3. The effect of DN-ICSBP on differentiation of myeloid progenitor cells was also investigated.