Cytotoxic activities of several Golgi-dispersing compounds including AMF-26/M-COPA, brefeldin A and golgicide A have previously been shown to induce autophagy or apoptosis. Here, we demonstrate that these Golgi disruptors also trigger ferroptosis, a non-apoptotic form of cell death characterized by iron-dependent oxidative degradation of lipids. Inhibitors of ferroptosis not only counteract cell death, but they also protect from Golgi dispersal and inhibition of protein secretion in response to several Golgi stress agents. Furthermore, the application of sublethal doses of ferroptosis-inducers such as erastin and sorafenib, low cystine growth conditions, or genetic knockdown of SLC7A11 and GPX4 all similarly protect cells from Golgi stress and lead to modulation of ACSL4, SLC7A5, SLC7A11 or GPX4 levels. Collectively, this study suggests a previously unrecognized function of the Golgi apparatus, which involves cellular redox control and prevents ferroptotic cell death.

Tether complexes play important roles in endocytic and exocytic trafficking of lipids and proteins. In yeast, the multisubunit transport protein particle (TRAPP) tether regulates endoplasmic reticulum (ER)-to-Golgi and intra-Golgi transport and is also implicated in autophagy. In addition, the TRAPP complex acts as a guanine nucleotide exchange factor (GEF) for Ypt1, which is homologous to human Rab1a and Rab1b. Here, we show that human TRAPPC13 and other TRAPP subunits are critically involved in the survival response to several Golgi-disrupting agents. Loss of TRAPPC13 partially preserves the secretory pathway and viability in response to brefeldin A, in a manner that is dependent on ARF1 and the large GEF GBF1, and concomitant with reduced caspase activation and ER stress marker induction. TRAPPC13 depletion reduces Rab1a and Rab1b activity, impairs autophagy and leads to increased infectivity to the pathogenic bacterium Shigella flexneri in response to brefeldin A. Thus, our results lend support for the existence of a mammalian TRAPPIII complex containing TRAPPC13, which is important for autophagic flux under certain stress conditions.

The secretory pathway is a major determinant of cellular homoeostasis. While research into secretory stress signaling has so far mostly focused on the ER, emerging data suggests that the Golgi itself serves as an important signaling hub capable of initiating stress responses. To systematically identify novel Golgi stress mediators, we performed a transcriptomic analysis of cells exposed to three different pharmacological compounds known to elicit Golgi fragmentation: brefeldin A (BFA), golgicide A (GCA) and monensin (MON). Subsequent gene set enrichment analysis revealed a significant contribution of the ETS family transcription factors ELK1, GABPA/B and ETS1 to the control of gene expression following compound treatment. Induction of Golgi stress leads to a late activation of the ETS upstream kinases MEK1/2 and ERK1/2 resulting in enhanced ETS factor activity and the transcription of ETS-family target genes related to spliceosome function and cell death induction via alternate MCL1 splicing. Further genetic analyses using loss- as well as gain-of-function experiments suggest that these transcription factors operate in parallel.

Disruption of the Golgi apparatus can induce a distinct form of programmed cell death that has not been thoroughly characterized. We found that pharmacological application of Golgi stress leads to induction of death receptors (DRs) 4 and 5. DR4 appears to be primarily responsible for the initiation of cell death downstream of Golgi stress, whereas DR5 seems to be more important for cell death triggered by endoplasmic reticulum (ER) stress in specific cancer cell lines. DR induction downstream of either Golgi or ER stress mainly causes intracellular accumulation of DR4 presumably at the Golgi, rather than increased expression on the cell surface. Nevertheless, cells treated with secretory pathway stressors displayed an increased susceptibility to TRAIL (tumor necrosis factor related apoptosis inducing ligand), the endogenous ligand of DR4/5, probably due to intracellular sequestration of the caspase-8 regulator CFLAR (caspase-8 and FADD-like apoptosis regulator). These findings have implications for the treatment of cancer with DR agonists and our general understanding of DR signaling while highlighting the role of the Golgi apparatus as a cell death signaling platform.