The accessory proteins REEP5 and REEP6 refine CXCR1-mediated cellular responses and lung cancer progression
Cho Rong Park1, Dong-Joo You1, Sumi Park1
1Graduate School of Medicine, Korea University, Seongbuk-gu, Seoul 02841, Republic of Korea.
Abstract:
Some G-protein-coupled receptors have been reported to require accessory proteins with specificity for proper functional expression. In this study, we found that CXCR1 interacted with REEP5 and REEP6, but CXCR2 did not. Overexpression of REEP5 and REEP6 enhanced IL-8-stimulated cellular responses through CXCR1, whereas depletion of the proteins led to the downregulation of the responses. Although REEPs enhanced the expression of a subset of GPCRs, in the absence of REEP5 and REEP6, CXCR1 was expressed in the plasma membrane, but receptor internalization and intracellular clustering of β-arrestin2 following IL-8 treatment were impaired, suggesting that REEP5 and REEP6 might be involved in the ligand-stimulated endocytosis of CXCR1 rather than membrane expression, which resulted in strong cellular responses. In A549 lung cancer cells, which endogenously express CXCR1, the depletion of REEP5 and REEP6 significantly reduced growth and invasion by downregulating IL-8-stimulated ERK phosphorylation, actin polymerization and the expression of genes related to metastasis. Furthermore, an in vivo xenograft model showed that proliferation and metastasis of A549 cells lacking REEP5 and REEP6 were markedly decreased compared to the control group. Thus, REEP5 and REEP6 could be novel regulators of G-protein-coupled receptor signaling whose functional mechanisms differ from other accessory proteins.
Insights
Receptor Expression Enhancing Proteins 5 and 6 (REEP5 and REEP6) regulate CXCR1 function, impacting cellular responses and cancer progression. Their depletion impairs CXCR1 signaling and reduces lung cancer cell growth and metastasis.
Area of Science:
- Cell Biology
- Molecular Biology
- Oncology
Background:
- G-protein-coupled receptors (GPCRs) often require accessory proteins for proper functional expression.
- The specific roles of accessory proteins in GPCR signaling pathways remain an active area of research.
Purpose of the Study:
- To investigate the interaction of REEP5 and REEP6 with chemokine receptors CXCR1 and CXCR2.
- To elucidate the functional impact of REEP5 and REEP6 on CXCR1-mediated cellular responses and lung cancer progression.
Main Methods:
- Co-immunoprecipitation assays to determine protein interactions.
- Overexpression and depletion studies using cell culture models.
- Analysis of IL-8-stimulated cellular signaling pathways (ERK phosphorylation, actin polymerization).
- In vitro and in vivo assays using A549 lung cancer cells and xenograft models.
Main Results:
- REEP5 and REEP6 specifically interact with CXCR1, not CXCR2.
- Overexpression of REEP5/6 enhances IL-8/CXCR1 signaling; depletion impairs it.
- REEP5/6 are crucial for ligand-stimulated CXCR1 internalization and β-arrestin2 clustering.
- Depletion of REEP5/6 in A549 cells reduces proliferation, invasion, and metastasis by downregulating IL-8/CXCR1 signaling.
- REEP5/6 depletion significantly decreases tumor growth and metastasis in vivo.
Conclusions:
- REEP5 and REEP6 are novel regulators of CXCR1 signaling, distinct from other accessory proteins.
- REEP5 and REEP6 play critical roles in CXCR1-mediated cellular responses, including endocytosis and downstream signaling.
- REEP5 and REEP6 are potential therapeutic targets for inhibiting lung cancer progression driven by CXCR1 signaling.
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