NSF/MCB-BSF: Mechanism of liquid-liquid phase separation in pathway-specific transcription regulation

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

The objective of this research is to determine how a human cell generates specific biological outcomes in response to a given hormone or growth factor. In animals, cells are exposed to a variety of regulatory hormones and growth factors that act as a signal to cause the cells to adopt different fates, including growth, survival, acquisition of specific functions such as producing insulin, or becoming a special cell type such as a neuron. These hormones or growth factors cannot enter cells and thus rely on a series of proteins inside the cell to transmit the signals into the cell nucleus and orchestrate the changes in gene expression, leading to specific biological outcomes. A key unanswered question is how these signaling proteins activate highly specific sets of genes in response to a hormone. This signaling specificity is essential for normal development and cell function. Disruption of this specificity results in defects in development and other diseases. This research project, a collaborative effort of the Luo lab at UC Berkeley and the Henis lab at Tel Aviv University, will dissect the molecular basis of an important signaling pathway to understand how a single signal can create different cellular outcomes, a long-standing puzzle in signal transduction. The project will also contribute to interdisciplinary education and training of postdoctoral fellows, undergraduate and graduate students, including an underrepresented minority graduate student. Finally, the project is expected to contribute to the broader scientific community through publication of the major findings and sharing of reagents. The Hippo signaling pathway will be used as a model system for this project. Hippo signaling regulates multiple biological processes via two homologous transcription effectors, TAZ and YAP. Although they perform largely non-redundant functions, how this functional specificity is achieved is unknown. Recently a process called liquid-liquid phase separation (LLPS) has been discovered that allows intracellular proteins to form membraneless condensates inside the cells. Our preliminary study has shown that TAZ, but not YAP, forms nuclear condensates via LLPS together with its important functional partners. We propose that TAZ may employ LLPS to compartmenta¬lize its partner proteins that perform similar functions within a physically distinct domain, enabling efficient gene expression and pathway insulation to generate specificity. Biochemical and biophysical studies will be performed to define the molecular basis of TAZ LLPS and to determine the mechanisms of TAZ LLPS assembly. If successful, this research will provide a new paradigm to address the broad question of signaling specificity for multiple intracellular pathways and has many implications for fundamental cell biology. This project is jointly funded by the Cellular Dynamics and Function program and the Genetic Mechanisms program of the Molecular and Cellular Biosciences Division in the Biological Sciences Directorate. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.