Rab7l1 plays a role in regulating surface expression of toll like receptors and downstream signaling in activated macrophages

Abstract

Rab GTPases are known for controlling intracellular membrane traffic in a GTP-dependent manner. Rab7l1, belonging to family of Rab GTPases, is important for both endosomal sorting and retrograde transport. In our previous study, we identified a novel role of Rab7l1 in phagosome maturation. However, its role in regulating macrophage innate-effector signaling and cytokine response is not clearly understood. In this study, we have demonstrated that upon treatment of Rab7l1-knocked-down (Rab7l1-KD) THP-1 macrophages with lipopolysaccharide (LPS) and Pam₃CSK₄ has led to higher induction levels of tumor necrosis factor-alpha (TNF-α) and interleukin-10 (IL-10) as compared to the control cells that received scrambled shRNA. Similar results were observed in Rab7l1-KD RAW 264.7 and Balb/c peritoneal macrophages. The phospho-ERK 1/2 (extracellular signal-regulated kinase 1/2) and phospho-p38 MAPK (mitogen-activated protein kinase) levels, known to be responsible for higher induction of TNF-α and IL-10 respectively, were higher in Rab7l1-KD THP-1 macrophages which also displayed higher nuclear translocation of p50/p65 nuclear factor kappa B (NF-κB) upon stimulation with LPS. Surface expression levels of toll-like receptor 2 (TLR2), TLR4 and CD14 receptors were higher in Rab7l1-KD THP-1 macrophages as compared to the control cells. However, intracellular levels of these receptors were lower in Rab7l1-KD THP-1 macrophages as compared to the control group. Together, our study suggests that Rab7l1 has a role in regulating MAPK signaling and cytokine effector responses in macrophages by regulating the surface expression of membrane receptors.

Keywords: IL-10/TNF-α; MAP kinase; Macrophages; NF-κB; Rab7l1; TLR2/TLR4.