Endolysosome transport along microtubules and clustering in the perinuclear area are crucial steps for activating specialized phagocyte functions in response to microbes. This process is essential for immune response regulation.
 
The study aims to investigate alternative isoforms of RUN and FYVE domain-containing protein 3 (RUFY3) and their role in endolysosome dynamics. It aims to explore the relationship between RUFY3 isoforms, immune cell activation, and responses to microbes and interferons.
 
We identified and characterized two RUFY3 isoforms based on the presence of a C-terminal FYVE domain and their affinity for PtdIns(3)P on endosomal membranes. The expression of iRUFY3 in immune cells and its up-regulation upon activation by microbes and interferons were analyzed. We also investigated the role of iRUFY3 in endolysosome positioning, macrophage migration, MHC II presentation, responses to Interferon-gamma, and intracellular Salmonella replication.
 
The study found that the FYVE domain-bearing isoform (iRUFY3) was preferentially expressed in immune cells and associated with ARL8b+/LAMP1+ endolysosome positioning at the pericentriolar organelles cloud in LPS-activated macrophages. It also found that iRUFY3 controlled macrophage migration, MHC II presentation, and responses to Interferon-gamma. Additionally, iRUFY3 was required for intracellular Salmonella replication, and the specific inactivation of rufy3 in phagocytes led to aggravated pathologies in mice upon LPS injection or bacterial pneumonia.
 
We highlighted the critical role of iRUFY3 in controlling endolysosome dynamics and its contribution to phagocyte activation and immune response regulation. These findings provide significant insights into the immune system and potential implications for pathologies and infections.