Role of mechanosensors and Hippo pathway signaling in controlling cell fate decisions

The main interest of my lab is in understanding how the Hippo signaling pathway controls cellular responses to mechanical forces. The Hippo pathway is a protein kinase-mediated network that regulates cell proliferation, contact inhibition, apoptosis, stem cell maintenance and differentiation, and tissue regeneration. Misregulation of this pathway has deleterious effects on cells and organisms and can lead to cancer.  In the canonical pathway, MST1/2 kinases activate the LATS1/2 kinases, which in turn phosphorylate and inhibit the transcriptional co-activator YAP by causing its translocation from the nucleus to the cytoplasm. In the nucleus, YAP promotes cell survival and proliferation. YAP nuclear localization is regulated by diverse stimuli that affect the mechanical environment of the cell such as cell crowding, substrate stiffness, tension, and cell detachment. The ability to sense these types of changes to the mechanical environment is crucial for regulation of stem cell niches, wound healing, and contact inhibition of growth.

The Hippo pathway is known to monitor the mechanical environment both indirectly through the effects of various stimuli on the actin cytoskeleton, and more directly by sensing tension across tissues. My lab’s focus has been on determining how F-actin levels and tension at cell-cell junctions are sensed, and how these signals are transduced to control Hippo signaling. We identified the angiomotin proteins as candidate Hippo pathway sensors for F-actin levels. Our studies have also uncovered new Hippo pathway regulators at cell-cell junctions that may directly sense tension across tissues. Current research in the lab is focusing on understanding the molecular mechanisms underlying F-actin and tension sensing, and how signals from separate sensors are integrated to generate cellular responses to mechanical stimuli.

Rotation Projects

Analog sensitive LATS kinase:  The goal of this project is to use CRISPR based genome modification to make mutations in the endogenous LATS kinase that cause it to be inhibited by a synthetic ATP analog. This will allow LATS kinase activity to be turned on and off using the ATP analog. The analog sensitive cell line will be a valuable tool for studying Hippo pathway responses to various stimuli and will be used to test whether dephosphorylation of LATS substrates is an important regulatory mechanism. This project will also set the stage for future experiments to create mice that have analog sensitive versions of LATS. These mice will be used to test whether LATS inhibition is a viable treatment for regenerative therapies for the heart, gut, pancreas and other organs.

TRIP6 and Angiomotin interacting proteins: We know that cells monitor their mechanical environment by sensing F-actin levels and by measuring tension at cell-cell junctions. We have identified angiomotins as sensors for F-actin and the TRIP6 protein as part of a tension sensor at cell-cell junctions. However, to understand how these sensors work, we need know the network of proteins that they each interact with, and how those networks change in response to mechanical perturbations. To do this we will fuse each sensor to the promiscuous biotin ligase protein BirA, and express the fusion proteins in cells under various conditions. The biotin ligase will label proteins in close proximity with biotin. Labeled proteins will be purified and analyzed by mass spectrometry, and the spectrum of interacting partners under different conditions will be compared.

A postdoctoral position is available to study in this laboratory. Contact Dr. McCollum for additional details.