RELL1 inhibits autophagy pathway and regulates Mycobacterium tuberculosis survival in macrophages.

Tuberculosis is a chronic infectious disease caused by Mycobacterium tuberculosis (Mtb). It leads to approximately 1 million deaths annually. Receptor expressed in lymphoid tissues-like protein 1 (RELL1) is a homologous binding partner of receptor expressed in lymphoid tissues (RELT), member of the human tumor necrosis factor receptor family. Genome-wide analysis screening revealed that downregulation of RELL1 in macrophages notably reduces Mtb survival within macrophages. However, the underlying mechanism is not clear. Here, we show that RELL1 expression in macrophages significantly decreased upon Mtb infection. Mtb survival increased in RAW264.7 cells with upregulated RELL1 expression. However, the proinflammatory cytokines TNF-α and IL-6 responsible for Mtb clearance were increased. Further, RELL 1 enhanced mTOR activity and inhibited autophagy through direct interaction. Hence, the reduced autophagy may antagonize increased inflammation in RELL1 upregulated macrophages and promote Mtb survival in macrophages. Together, our results suggest that the reduction of RELL1 expression upon Mtb infection may enhance autophagy and facilitate bacterial clearance, providing a new target for Mtb treatment.