Research Projects

Our overall goal is to understand how transcriptional regulatory complexes regulate biological processes in health and disease. Transcriptional deregulation occurs in many genetic disorders such as cancer and metabolic diseases. We use genetics, biochemistry and molecular biology to study the molecular action and biological role of transcription factors and cofactors, and their potential links to cardiovascular disease and cancer.

BACKGROUND

Many cellular and systemic signaling pathways converge on transcriptional regulators. Dissecting the dynamic complexity in such regulatory networks is important to understand human biology and the progress of diseases. However, studying regulatory circuits in mammals is somewhat limited by their genetic inaccessibility. In contrast, the nematode Caenorhabditis elegans provides a powerful model organism because regulatory pathways can be investigated genetically and pharmacologically on a genome-wide scale, and because many key genes are structurally and functionally related to mammalian genes.

Our research focuses on the Mediator, a multi-protein machinery that regulates transcription. Mediator is evolutionarily conserved from yeast to mammals. Functionally, Mediator affects RNA Polymerase II (PolII) dependent transcription in a global fashion. However, some Mediator subunits selectively implement biological programs. This is exemplified by our findings that the C. elegans Mediator subunit MDT-15 integrates transcription of genes involved in lipid biology and in nutrition-associated stress responses (fasting response, heavy metal response, xenobiotic detoxification, and the oxidative stress response): Worms with mutated or depleted mdt-15 display abnormal fat storage, toxin sensitivity, and a shortened life span. Importantly, the MDT-15 homologues in mammals and in yeast (MED15 and Gal11p, respectively) also impinge on lipid biology and stress responses, suggesting functional conservation.

C. elegans MDT-15 collaborates with numerous transcription factors. Hence, we hypothesize that MDT-15/MED15 is a key component in a conserved regulatory network that coordinates metabolism and the response to ingestion-associated stresses. Due to its implication in these processes, MDT-15/MED15 may be involved in human metabolic conditions such as obesity and diabetes.

CURRENT PROJECTS

1. We are performing gain-of-function and structure function analysis to determine what residues and surfaces specify MDT-15 function in vivo. To this end, we are generating transgenic C. elegans strains that overexpress wild-type or mutant MDT-15 proteins. Additionally, we are testing whether individual MDT-15 associated transcription factors selectively confer MDT-15 regulated processes.

2. What regulates MDT-15's expression and/or activity? Preliminary results indicate that MDT-15's protein levels respond to environmental stimuli (fasting, toxin exposure). Moreover, MDT-15 can interact with components of the ubiquitin-proteasome machinery that degrades proteins, providing a putative mechanism controlling MDT-15 levels. We are testing whether gain- or loss-of-function mutations in components of this machinery affect MDT-15 levels or activity.

3. Given the prominent role of MDT-15 in the regulation of metabolic processes, we are addressing whether MED15, its mammalian homologue, performs similar functions. Using candidate and unbiased genomic approaches we aim to identify MED15's transcriptional targets and biological functions in cultured human cells. In the long-term we plan to generate tissue-specific gain- or loss-of-function MED15 mice, and to study their phenotypes.

4. As genes do not act in an isolated fashion, we intend to discover and characterize the regulatory network centered on C. elegans MDT-15. To this end, we will screen genetically for enhancers and suppressors of the phenotypes exhibited by mdt-15 mutants. Moreover, we will study other Mediator subunits such as the oncogenic Mediator Kinase CDK-8. C. elegans provides a powerful model system for such large-scale screens.

Using C. elegans and mammalian cells allows us to exploit the strengths of each system (genetics, cytology, molecular biology, and biochemistry). Thus, we can gain insight into (metabolic) regulation by MDT-15/MED15. Viewed more broadly, investigating the downstream targets, genetic interactions, and interaction surfaces of Mediator subunits (and other transcriptional coregulators) can yield novel information about their function and their contributions to genetic disorders such as. Applicants interested in any of our research topics are very welcome to contact us.