Cellular control of macropinososome formation and maturation

Macropinocytosis is an endocytosis mechanism which allows cells to take up body fluids and dissolved molecules. This process is also called “cellular drinking” since it allows the cells to take up large amounts of extracellular fluid. Macropinocytosis is an important process in the immune system where it can serve as “early warning system” for intruders. Many immune cells take up large amounts of body fluids, which they then sample for foreign materials, such as viruses and bacteria. If pathogens are detected, the immune system is activated and can respond to the pathogen. However, this process is also exploited by pathogens. Many viruses and bacteria, like SARS-CoV2 and Ebola viruses or Salmonella bacteria, use this process to effectively infiltrate and infect cells. Many pathogens can even force cells to perform macropinocytosis to enhance their uptake. In addition, many cancer cells upregulate macropinocytosis and take up body fluids to gain additional nutrients, which allows these cells to grow faster. Despite these important functions for human health, extraordinarily little is known how cells regulate macropinocytosis and which proteins are involved in this process. In this project, we will investigate the molecular mechanism that control macropinocytosis. We will investigate which proteins and which cellular signaling processes are controlling macropinocytosis. We have recently identified a new regulator of macropinocytosis, the protein Phafin2. We found that Phafin2 is important for early timepoints of macropinosome formation and that it locally regulates the actin cytoskeleton. Moreover, we found that pancreatic cancer cells need Phafin2 for effective uptake of extracellular nutrients. Formation of macropinosomes is controlled by the actin cytoskeleton, which also controls the shape if cells. We have found that specific cell shapes appear to be more prone to produce macropinosomes. In order to understand the underlying bio-mechanical principles, we have established micropatterning techniques which allows us to force cells to adapt specific shapes. Using these micropatterns, we are able to control where cells form new macropinosomes, which will allow us to investigate the underlying molecular mechanisms. We will also investigate how viruses and bacteria exploit this mechanism to infect cells and which cellular proteins are needed for this. This can provide new target proteins for drug development.

Macropinocytosis is an endocytosis mechanism that leads to the formation of large vesicle filled with extracellular fluids and soluble macromolecules. Immune cells like dendritic cells and macrophages use this bulk uptake mechanism to sample the environment for foreign antigens. It is also exploited by many pathogens, which subvert this mechanism for cellular uptake and invasion. Moreover, cancer cells use macropinosomes as amino acids supply route to fuel their metabolism. In order to understand how this basal cellular mechanism works and to identify how cancer and pathogens exploit this mechanism, it is important to develop a deeper understanding how early steps of macropinocytosis work on a molecular level and how they are regulated. We will use state-of-the-art cell biological techniques, coupled with advanced microscopy, to investigate how macropinosomes are formed, how they enter the cell and how they get their endosomal identity. We will also address the role of macropinocytosis during pathogen infection and investigate how pathogens exploit cellular protein components to enter cells in order to replicate and to evade the immune system. This will allow us to generate a comprehensive cell biological and biomechanical model of the requirements to form a new vesicle. It will also allow us to better understand how pathogens are able invade cells and how tumors are able to gain enough nutrients to support their fast growth.