F. Suheda Karci

Research Overview

We want to understand what happens when cells choose to be physical with their environment. In particular, how their eating (endocytosis) habits are influenced, and how this affects various cellular functions. We are also motivated by determining cells' mechanical properties and predicting what they are programmed to do in their near future (e.g., divide, move, commit suicide) by characterizing their eating pattern.

o Clathrin-mediated endocytosis (CME) is the most prominent internalization mechanism of membrane lipids and proteins from the cell surface. Over the past decades, a multitude of biophysical and biochemical methodologies have been employed to elucidate structural and dynamic properties of endocytic clathrin coats. However, the fundamental aspects of clathrin-mediated endocytosis remain controversial due to the lack of experimental approaches that allow correlation of ultra-structural and dynamic properties of clathrin coats. We develop innovative experimental and analytical approaches for studying structural and dynamic properties of clathrin-coated structures in vitro (isolated cells in culture) and in vivo (tissues of multicellular organisms).

o Dynamics and structures of endocytic clathrin coats are remarkably divergent across different cell types, cells within the same culture, or even distinct surfaces of the same cell. We have shown that spatiotemporal heterogeneity in CME dynamics is particularly prominent during cell division, migration and spreading. Alterations in CME rates give rise to increased proliferation, migration and metastasis of cancer cells. The origin of this astounding heterogeneity, which regulates the rate of endocytosis during central cellular and developmental processes, is yet to be elucidated. We focus on AP2, FCHo and CALM adaptors of clathrin to test our hypotheses. Our research involves determining i) recruitment dynamics (and stoichiometric ratios) of adaptors to clathrin coats at distinct membrane tension levels, ii) differential roles of curvature generating clathrin adaptors in maintaining CME at distinct tension levels, and iii) enabling roles of spatiotemporal CME heterogeneity in cell migration, spreading and division.

o Clathrin triskelions can assemble into membrane-bound coats (i.e., polyhedral cages and lattices) in seemingly infinite number of geometries. Regardless of shape and size, formation of endocytic vesicles require curvature generation during the lifespan of clathrin coats. When and how a clathrin coat develops the curvature is still an open question. Electron microscopy provides high-resolution snapshots of clathrin-coated structures at different curvature levels. However, due to the lack of temporal dimension, electron micrographs fail to provide a direct evidence on the mechanism of clathrin-driven curvature generation. We use various superresolution fluorescence approaches to characterize curvature formation by distinct classes of clathrin-coated structures in live cells and tissues.