Drivers and Mechanisms of Golgi Fragmentation as a Modulator of Disease

Abstract

The Golgi apparatus plays a pivotal role in post-translational modification, trafficking, and secretion of proteins, ensuring proper cellular function. As a result, its fragmentation has been implicated in multiple pathological conditions, including alcohol-induced liver injury and prostate cancer (PCa). Despite its known impact on cellular homeostasis, the molecular mechanisms governing Golgi fragmentation remain to be clarified. Additionally, we have only just begun to understand the vast consequences of Golgi disorganization on disease progression. This dissertation investigates the drivers and mechanisms of Golgi fragmentation, with a focus on its role as a modulator of disease. Using both in vitro and in vivo models, I demonstrate that chronic alcohol exposure triggers Golgiphagy (a selective form of autophagy that degrades Golgi membranes) through downregulation of the Rab GTPase, Rab3D. The loss of Rab3D results in p230 extension and dissociation of NMIIB from the Golgi. Ultimately, NMIIB dissociation gives way for NMIIA to associate with the Golgi and promote autophagy of the Golgi membranes. This Golgi disorganization leads to endoplasmic reticulum (ER) stress by activating the activating transcription factor 6 (ATF6)-mediated unfolded protein response (UPR). Additionally, the glycosyltransferase MGAT3 loses Golgi localization, but its competitor MGAT5 remains. This results in abnormal integrin glycosylation and binding to Galectin-3, increasing cluster formation and retention on the plasma membrane (PM). In addition to MGAT5-mediated glycosylation, underglycosylated integrins arrive at the PM carrying high-Man glycans due to alternative trafficking. This non-canonical route bypasses the Golgi and depends on STIM1- and ORP5-mediated ER-PM contact sites, which are involved in relieving ER stress and maintaining Golgi architecture. The findings presented in this dissertation underscore a novel link between Golgi fragmentation, ER stress, and alternative protein trafficking routes, revealing how these pathways contribute to disease pathogenesis. I demonstrate that Golgi integrity can be restored by autophagy inhibition with hydroxychloroquine (HCQ) and ER stress inhibition by ATF6 depletion. Importantly, by restoring compact Golgi morphology, I have reduced tumor growth and progression of alcohol-induced liver injury. These results highlight Golgi disorganization as both a driver of pathology and a potential therapeutic target, offering new insights into the development of interventions for alcohol-related liver disease and aggressive PCa