Individual gene programs must be expressed at the right time and in the right place (cell or tissue type). Control of gene expression occurs primarily at the level of transcription. How and when each gene is transcribed is thus a central question in biology. It is also of great importance to human health: abnormal transcription causes or exacerbates many human diseases, including cancers, metabolic syndrome, neurodegenerative diseases, and developmental disorders. Vice versa, transcriptional regulators are important pharmacological targets in many diseases.
We study how transcriptional regulators modulate gene programs in response to nutritional cues and various types of stress. These metabolic and stress adaptation pathways are of great biomedical relevance. For example, transcriptional activation of stress response programs helps cancers to grow in hostile microenvironments featuring oxidative stress, starvation, and hypoxia.
In this context, our research focuses on Mediator, a multi-protein complex that is evolutionarily conserved and vital for eukaryotic transcription. Individual Mediator subunits affect specific gene programs and can thus selectively implement biological processes. We use the nematode Caenorhabditis elegans and the house mouse as genetically tractable model organisms to delineate Mediator function. This way we have found important roles for the C. elegans Mediator subunit MDT-15 in fatty acid metabolism, oxidative stress responses, starvation adaptation, prevention of endoplasmic reticulum (ER) stress, xenobiotic/drug detoxification, and trace metal homeostasis. These responses are enabled by the specific physical interaction of MDT-15 with the nuclear hormone receptor NHR-49/HNF4, the master redox regulator SKN-1/Nrf, and other evolutionarily conserved transcription factors. We also showed that another Mediator subunit, the kinase CDK-8, restrains MDT-15 function, serving as a negative regulatory circuit within Mediator.
Dissecting the roles of this important homeostatic network, mapping its functions and interactions, and exploring how these can be targeted pharmacologically to benefit human health is our overall goal. Small molecules drugs that target the human and yeast ortholog of MDT-15 have already been developed by other groups and have powerful anti-obesity and anti-fungal properties, suggesting that our vision is promising and feasible.
Specific projects include:
- Identifying and characterizing the TFs that physically and functionally interact with MDT-15 to implement specific stress and drug response programs; this primarily involves C. elegans functional genomics and genetic analysis and molecular/biochemical interaction mapping.
- Define whether and how C. elegans MDT-15 and its partner TFs such as NHR-49 are themselves regulated by stress; to map pertinent molecular signaling pathways; and to test whether similar mechanisms and stimuli regulate mammalian MED15 by means of cell culture models.
- To test whether mammalian MED15 is required for the development and/or function of metabolically relevant tissues such as the pancreas, liver, and adipose, using tissue-specific knockout mouse models.
C. elegans is a powerful model organism for genetic research
These are immunofluorescent images of wild-type 8 week old mouse pancreas sections stained for: Green – Glucose transporter GLUT2 (note membrane localization), Red – Transcription factor which marks pancreatic lineage PDX1, and Blue – DNA staining (to mark nucleus) TOPRO. GLUT2 is of high importance during beta cell development as it allows these cells to sense how much glucose is in the blood stream and lets them know how much insulin to output.
Immunofluorescent staining of: Green – Insulin processing enzyme ERO1LB, Red – Insulin, Blue – TOPRO. ERO1LB is important to study as it is found in the endoplasmic reticulum (ER) and allows proper processing of insulin into granules. Its name stands for ER oxidoreductase like 1 beta and marks the ER in beta cells.
Immunofluorescent staining of: Green – Mature beta cell specific transcription factor NKX6.1 (note nuclear localization), Red – Insulin, Blue – TOPRO. NKX6.1 is an important transcription factor which is mainly found in mature beta cells. It plays a role in controlling the expression of GLUT2, ERO1LB, Insulin, and many other important beta cell factors.