Microtubule Involvement with the WRAMP Structure, a Mechanism for Rear Membrane Retraction in Mammalian Cells

Abstract

Cellular locomotion involves coordination between membrane protrusions and attachments to extracellular matrix at the front, and membrane retraction and disassembly of attachments at the rear. While Rac‐ and Cdc42‐dependent polymerization of F‐actin to push lamellipodia and filopedia protrusions have been well studied, rear end retraction during cell locomotion is still poorly understood. Our lab has discovered a complex of interacting proteins and membranes known as the Wnt5a‐receptor‐actin‐myosin‐polarity (WRAMP) structure, which forms dynamically and transiently, and is associated with rear membrane retraction and directional cell migration. A remarkable feature of this complex is that it involves endosomes containing the cell surface glycoprotein, melanoma cell adhesion molecule (MCAM, aka CD146/MUC18), suggesting that organelle positioning links to rear‐end retraction. Live images of MCAM‐GFP show that WRAMP structures relocalize intracellularly before cells change direction, suggesting that their placement helps guide the new direction of movement. We hypothesize that microtubules mediate the delivery of endosomes to WRAMP structures, through microtubule binding proteins that contact the plasma membrane. Preliminary experiments using indirect immunofluorescence indeed show colocalization of microtubules with MCAM and F‐actin within WRAMP structures. Ongoing studies are investigating the potential involvement of plus end tracking proteins (+TIPs) such as EB1, and its binding partners, IQGAP1 and ezrin, as potential membrane anchors. Conceivably, recruitment of cortical microtubules via +TIPs may traffic endosomes to the plasma membrane, forming WRAMP structures which in turn control the new direction of migration. In this way, WRAMP structures may provide a mechanism allowing the orientation of cells and direction of movement to be guided from the rear.Support or Funding InformationThis work is supported by the National Institutes of Health (R01GM105997 and T32GM008759).This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.