Distinct roles of COPI proteins attenuated with cell senescence

Cellular senescence is characterized by persistent cell cycle arrest, apoptosis resistance, and widespread changes in gene expression. Although the functional alterations in organelles like mitochondria and lysosomes are well characterized, senescence-associated changes in the structure and function of the Golgi apparatus remain poorly understood. The Golgi apparatus orchestrates intracellular transport processes that rely heavily on the coating of vesicles with Coatomer Protein Complex I (COPI) proteins (COPA, COPB1, COPB2, COPD, COPE, COPG1, and COPZ1). Based on an earlier RNA interference (RNAi) screen showing that silencing COPI subunits reduced extracellular vesicle (EV) uptake in human diploid WI-38 fibroblasts, and that EV uptake was diminished in senescent WI-38 cells, we sought to functionally analyze COPI proteins in senescent cells. In proliferating cells, individually silencing COPA, COPB1, COPB2, or COPD induced ATF4 production and disrupted autophagy, apoptosis, and cytokine signaling—hallmarks of impaired Golgi-to-ER transport—while individually silencing COPG1, COPE, or COPZ1 altered extracellular matrix organization and GTPase activity. Silencing of any COPI subunit reduced mitochondrial respiration and EV uptake. Proteomic analysis revealed that individual COPI proteins associate with both Golgi and endosomal components, supporting their role in vesicular trafficking. Importantly, the phenotypic effects observed in proliferating cells were not observed in senescent cells, which appeared refractory to further COPI reduction. Our findings underscore the distinct, multifunctional actions of individual COPI proteins and suggest that they are key factors in the intracellular transport networks that sustain homeostatic responses, which become attenuated during senescence.