Regulation of intermicrovillar adhesion and microvillar dynamics in epithelial cells by a JAM family adhesion molecule

• Applicant: Professor Dr. Klaus Thomas Ebnet
• Subject Area: Cell Biology
• Term: from 2019 to 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 425854143

Epithelial sheets play important roles in human physiology by forming mechanical and physiological barriers between compartments. The mechanical barriers maintain the integrity of the organs when subjected to mechanical forces, the physiological barriers allow a controlled uptake of soluble factors. This intercellular barrier function is regulated by cell adhesion molecules, which sense and resist forces and which mediate selectivity in paracellular permeability. Interestingly, similar cell adhesion molecules are localized at the apical domain of various epithelial cells and mediate the interaction between microvilli or between stereocilia, F-actin-rich protrusions of absoptive epithelial cells and sensory epithelial cells in the cochlear/vestibular system, respectively. The role of these adhesion molecules is much less understood. Similar to adhesion molecules at intercellular junctions, the adhesion molecules at intermicrovillar junctions are spatially restricted to specific (submicrovillar) locations and are involved in mechanosensing. The focus of our work are Junctional Adhesion Molecules (JAMs). We have recently found that a novel member of the JAM family of adhesion molecules, called JAM-M, is localized at microvilli of intestinal epithelial cells and is specifically expressed by intestinal tuft cells in mice. We found that JAM-M is enriched at the middle to basal region of microvilli and is absent form the distal tip region. Using a yeast-two hybrid approach and biochemical experiments, we found that JAM-M interacts with two PDZ domain-containing scaffolding proteins present at microvilli, i.e. NHERF1 and NHERF2 in PDZ domain-dependent manner. Finally, using an inducible system allowing ectopic microvilli formation, we observed that JAM-M is recruited to microvilli in a PDZ-domain-dependent manner. Our findings thus point to the existence of a novel intermicrovillar adhesion complex that is localized at the basal region of microvilli. The aim of this study is to understand the role of this adhesion complex in microvillus formation. We will biochemically characterize the complex in detail, and we will analyze the role of this complex in regulating the localization and activity of ezrin, a plasma membrane - cytoskeleton cross-linking protein required for microvilli formation. We will analyze the influence of JAM-M on the dynamics of NHERF1 and NHERF2 as well as its influence on the dynamics of microvilli. We will also analyze the biochemical and biophysical porperties of JAM-M as adhesion molecule. Finally, we will generate two animal models in which we will study the role of JAM-M during intestinal development and its role in the formation and function of tuft cells. From our studies we expect a deeper understanding of the molecular mechanisms underlying the formation and regulation of microvilli in intestinal epithelial cells.

• DFG Programme: Research Grants