THG-1/TSC22D4 Promotes IL-1 Signaling through Stabilization of TRAF6 in Squamous Cell Carcinoma.

Abstract

Malignant neoplasms arise within a region of chronic inflammation, which is a key factor in all aspects of tumorigenesis including initiation, proliferation, invasion, angiogenesis, and metastasis. IL-1 plays critical functions in tumor development by influencing the tumor microenvironment and promoting cancer progression. However, the mechanism of continuous activation of the IL-1-mediated inflammatory pathway in tumors has not been fully elucidated. This study provides a novel mechanism of the autocrine activation of IL-1 signaling in squamous cell carcinoma (SCC) through a novel oncoprotein, TSC-22 homologous gene-1 (THG-1, also known as TSC22D4). The RNA sequencing analysis revealed that THG-1 overexpression enhances the transcription of NF-κB targets including IL1A, IL1B, TNFA, and IL8. Furthermore, THG-1 knockdown reduced the responsiveness to IL-1 through the suppression of NF-κB nuclear translocation. To elucidate the mechanism, we focused on a THG-1 interacting protein, NRBP1. We found that NRBP1 facilitates the degradation of TNF receptor-associated factor 6 (TRAF6) through its E3 ubiquitin ligase activity. THG-1 bound to NRBP1 and suppressed the degradation of TRAF6. Furthermore, THG-1 knockdown reduced TRAF6 abundance and NF-κB activity in SCC cells. Public database analyses of head and neck SCC revealed that high expression of THG-1 is associated with the activation of the IL-1 and TNF pathways, which share TRAF6 in the signal transductions. Finally, THG-1 abundance in laryngeal SCC specimens is elevated in patients with recurrence. These results indicated that THG-1 drives the self-sufficiency of IL-1-mediated inflammatory pathway, which could contribute to the future diagnosis and immunotherapy of SCCs. Implications: An oncoprotein, THG-1/TSC22D4 activates the IL-1-mediated inflammatory pathway through the suppression of TRAF6 degradation, which mediates the continuous inflammation in tumors.