The Role of Paxillin in Regulating Rab5 through Modulating Microtubule Acetylation

Abstract

Cell migration is vital to many cellular processes such as development, immune surveillance and wound healing. Cells interact with and move along the extracellular matrix by utilizing transmembrane integrin receptors and large macromolecular structures, called focal adhesions. Focal adhesions are comprised of many signaling and scaffolding proteins, and these complexes constantly undergo formation and turnover. The trafficking of focal adhesion components is mediated by RabGTPases, which are essential in regulating cell migration. Defects in Rab-associated vesicle trafficking have been implicated in diseases such as cancer cell migration. Understanding the mechanisms contributing to vesicle trafficking is vital to the development of therapeutics to treat diseases. The focal adhesion adaptor protein, paxillin, plays a central role in regulating focal adhesion dynamics and cell migration. Recent studies have implicated paxillin in regulating vesicle trafficking. Paxillin, through regulation of microtubule acetylation via modulation of HDAC6 activity, regulates anterograde trafficking of ts-VSVG to the plasma membrane. Additionally, paxillin interacts with components of endocytic machinery, suggesting it may also regulate retrograde trafficking. Further studies are needed to characterize paxillin's role in regulating vesicle trafficking. Herein, this thesis identifies a role for paxillin in regulating the RabGTPase, Rab5, in a HDAC6-dependent manner. Through modulation of HDAC6 activity, paxillin regulates Rab5 vesicle size and distribution, Rab5 activity and dynein-mediated retrograde Rab5 vesicle motility in MDA-MB-231 cells and paxillin (-/-) fibroblasts. In addition to its role in regulating Rab5, paxillin was also shown to promote Rab7 vesicle size and co-localization with Rab5-positive vesicles. Co-localization analysis revealed that the distribution of active β1 integrin at zyxin-positive focal adhesions was disrupted upon paxillin depletion but was rescued upon inhibition of HDAC6 activity. Altogether, this work expands on a recently identified role of paxillin regulating vesicle trafficking in both normal and transformed cancer cells.