Roles and Regulation of the bZip Transcription Factor CEBP-1 in Stress Response Pathways

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Project Summary Proper cellular response to stress is vital for organismal survival. Most cellular stress responses involve the action of transcription factors that regulate expression of stress response genes. Determining how transcription factors can initiate differential responses to a variety of stressful inputs is critical for understanding multiple human diseases. The overall goal of this project is to uncover the mechanisms by which a single transcription factor can integrate multiple inputs and direct proper transcriptional responses. CCAAT enhancer binding proteins (C/EBP) family proteins are involved in many forms of stress responses. C/EBPs contain a basic-leucine-zipper DNA binding domain, and transactivating and regulatory domains, which modulate transcriptional activity via specific protein-protein interactions or post-translational modifications. Although C/EBP proteins have been extensively studied, the mechanism of their action under external stimuli is still poorly understood. Studies using Caenorhabditis elegans offer great advantages to investigate multi-level cellular and organismal responses to stress signals. This proposal focuses on examining the molecular function of the conserved C/EBP homologue, CEBP-1, in mediating both development and neuronal stress responses. In neurons, CEBP-1 plays critical roles in response to axon injury and cytoskeleton disruption, acting downstream of the DLK-1 MAP kinase cascade. In animal development CEBP-1 is negatively controlled by the Tribbles family protein, NIPI-3, and in turn activates a different MAP kinase cascade. Using powerful forward genetic screening, I have identified a distinct functional domain in the N-terminus of CEBP-1 that is crucial for its activity. Here, I propose to test the hypothesis that this domain, in conjunction with differential protein-protein interaction, endows transactivating regulation to initiate transcriptional responses to different stressful inputs. The goals of this study will be accomplished through the following specific aims: Aim 1: To identify CEBP-1 binding proteins using IP- mass spectrometry and to demonstrate that the N-terminal region contains transactivating activity. Aim 2: To determine the mechanism of transcriptional regulation of CEBP-1 by NIPI-3; and Aim 3: to Identify new genetic players in NIPi-3/Tribbles and CEBP-1 pathway. The completion of this proposal will provide a deeper understanding of the general process of stress response to various external stimuli. Understanding the mechanism of this control could allow for development of targeted treatments for diseases affecting cellular stress response and repair.