Ubiquilin 1 Inhibits intracellular proliferation of Salmonella enterica serovar Typhimurium through Xenophagy.

Abstract

BACKGROUND: Salmonella enterica serovar Typhimurium is a gram-negative bacterium that infects intestinal cells, causing gastroenteritis in humans and animals. Following infection, the bacteria persist and replicate within a unique cytoplasmic compartment known as the Salmonella-containing vacuole. While the proliferation of most intracellular bacteria is restricted by classical autophagy, Salmonella has evolved mechanisms to evade autophagic intervention. Ubiquilin 1 (Ubqln1) contains an N-terminal ubiquitin-like domain and a C-terminal ubiquitin-associated domain. These domains play crucial roles in cellular protein degradation, autophagosome maturation, and the prevention of starvation-induced apoptosis. OBJECTIVE: This study investigates the regulation of Ubqln1 expression in response to Salmonella infection and elucidates the role of Ubqln1 in modulating Salmonella proliferation and the autophagic process. METHODS: To achieve this, we employed RT-PCR, Western blotting, a Ubqln1 overexpression system, and Ubqln1 knockout cell lines. Confocal microscopy was used to assess the spatiotemporal association between Salmonella, Ubqln1, and autophagic markers such as LC3. RESULTS: Our findings demonstrate that Ubqln1 expression is upregulated in response to treatment with major bacterial antigens (LPS, OmpA) or Salmonella infection. Intracellular proliferation of Salmonella was inhibited in cells overexpressing Ubqln1, whereas it was promoted in Ubqln1 deficient cells. Furthermore, Ubqln1 showed significant recruited to Salmonella and exhibited spatial overlap with the autophagy marker LC3, as confirmed by fluorescence intensity profiling. Notably, Ubqln1 appeared to inhibit the accumulation of LAMP2 around Salmonella. CONCLUSION: Collectively, these results suggest that Ubqln1 plays a critical role in host defense against Salmonella by promoting Xenophagy.