KGF impedes TRIM21-enhanced stabilization of keratin 10 mediating differentiation in hypopharyngeal cancer

Abstract

KGF, also known as FGF7, is a member of the fibroblast growth factor (FGF) family that binds with high affinity to the FGF receptor 2b (FGFR2b) and regulates various cellular processes, including cell proliferation and differentiation in a variety of tumors. However, its potential role in hypopharyngeal cancer (HPC) remains largely unknown. In our study, we observed increased expression of FGFR2b in HPC. KGF treatment inhibited the expression of the differentiation marker keratin 10 (K10) protein at the post-transcriptional level in FaDu cells. Furthermore, treatment with the proteasome inhibitor MG132 was found to attenuate KGF-induced K10 reduction, suggesting the involvement of the ubiquitin-proteasome system. Using mass spectrometry and immunoprecipitation analysis, we identified the E3 ubiquitin ligase TRIM21 as a K10-interacting protein. Unexpectedly, instead of causing degradation, TRIM21 enhanced K10 protein stability through K6-linked ubiquitination of K10 at lysine 163 (K163) in the context of KGF exposure. Meanwhile, KGF treatment decreased TRIM21 protein levels, which were regulated by the p38 MAPK pathway, leading to K48-linked ubiquitination-mediated degradation of TRIM21. Notably, TRIM21 knockdown significantly promoted proliferation, inhibited differentiation and migration of FaDu cells, whereas TRIM21 overexpression had opposite effects in vitro and suppressed xenograft tumor growth in vivo. Our study demonstrates that TRIM21 may act as a tumor suppressor in HPC. However, TRIM21 overexpression decreased the sensitivity of FaDu cells to 5-fluorouracil, whereas TRIM21 knockdown or KGF administration significantly increased 5-fluorouracil sensitivity. Taken together, these findings highlight the intricate balance between protein stabilization and degradation orchestrated by KGF. This ubiquitination-mediated non-degradation mechanism of TRIM21 may provide novel therapeutic strategies for HPC and other cancers.