Richard N. Day, PhD
Cellular assembly of transcription factor and nuclear receptor-coregulatory protein complexes and regulation of gene transcription
Cells respond to environmental cues through signaling pathways that function to orchestrate the recruitment and assembly of regulatory protein complexes. There is a dynamic equilibrium between the formation and disassembly of these regulatory complexes, and cellular architecture plays a critical role in controlling this. The contribution of cell architecture, however, is lost during traditional biochemical analysis. Understanding how the living cell assembles signaling protein complexes is critical to unraveling disease processes, and to the design of therapeutic strategies. The broad aim of the studies in the Day laboratory is to define the role of transcription factor and co-regulatory protein interactions with nuclear architectural proteins in specifying pituitary endocrine cell differentiation, and to determine how these interactions function to control proliferation, transformation and tumorigenesis. The approach is to combine biochemical and molecular analysis with live cell imaging approaches to define the interactions of cell-specific transcription factors with their co-regulatory protein partners. The laboratory has pioneered the use of both multi-color imaging to detect the co-localization of proteins, and the technique of fluorescence resonance energy transfer (FRET) microscopy to acquire quantitative measurements of protein kinetics, molecular mobility (diffusion, aggregation) and protein structural information from the living cell.
The results from studies using the combined approaches demonstrated that some transcription factors function as architectural proteins that direct the assembly of protein complexes at specific sites within the cell nucleus. Importantly, they also showed how specific mutations disrupted the final intranuclear positioning of the protein complexes. Recent studies have implicated high mobility group (HMG) protein family members in endocrine cell development, proliferation and tumorigenesis. The over-expression of the HMG proteins in transgenic mice led to the formation of anterior pituitary tumors. These observations raise important questions about the functional role of nuclear architectural proteins, which on the one hand are critical for the formation of multiprotein transcription complexes, but can also drive inappropriate cell proliferation, tumor progression and metastasis. Importantly, this system provides a disease-relevant model that lends itself to analysis through the combination of engineered cell models, new molecular imaging probes and live-cell imaging techniques.