• Principal Investigator: Vedrana Filić Mileta
• Funding Agency: Croatian Science Foundation
• Call: Research Projects (Call identifier: IP-02-2020)
• Funding: 985.000,00 HRK
• Project duration: 15/02/2021 – 14/02/2025

Project summary: Large-scale endocytosis is clathrin-independent, actin-driven bulk endocytosis. The term collectively describes particle uptake or phagocytosis and nonselective bulk uptake of fluid or macropinocytosis. For unicellular organisms like amoeba Dictyostelium, large-scale endocytosis is an exclusive way of feeding, while for metazoan cells it is one of several, not preferred, pathways of nutrient uptake.

Images of fluorescently labelled IqgC (upper panel, yellow) and IqgD (lower panel, green) in live cells acquired using fluorescent confocal microscope.

However, mammalian cells use both types of large-scale endocytosis for other physiological functions, besides feeding. The best example are cells of the immune system that use both phagocytosis and macropinocytosis for removal of apoptotic cells and pathogens from tissues and to scan extracellular fluids for the presence of foreign antigens. Large-scale endocytosis is also linked to several pathological conditions like neurodegenerative diseases, atherosclerosis and cancer.

This project aims to investigate the role of two IQGAP-related proteins, IqgC and IqgD, in regulation of large-scale endocytosis in Dictyostelium, which has become the leading model in macropinocytosis research. Our previous results identified IqgC as a negative regulator of Ras activity during large-scale endocytosis in stages of endosome formation. However, further preliminary data suggest that IqgC plays additional roles during endosome maturation, probably via interactors other than Ras.

We aim to elucidate these functions by tackling its phospholipid interactions and by determining requirements for its membrane recruitment. The second part of the project will focus on biological roles of IqgD. Our preliminary data show cortical localization of IqgD, including macropinosomes. This localization, along with the presence of an actin-binding domain in its sequence, strongly suggests mechanistic role for IqgD in macropinocytosis via regulation of actin cytoskeleton. Our goal is to identify direct binding partners of IqgD and determine how it regulates large-scale endocytosis.