Deubiquitinating Enzyme UCHL1 Modulates FHL2 to Block Ferroptosis and Counteract CD8 + T Cell Anti‐Tumour Immunity in Lung Adenocarcinoma

ABSTRACT A pivotal strategy in immuno‐oncology is the initiation and modulation of adaptive immune responses. Ubiquitin carboxyl‐terminal hydrolase L1 (UCHL1), known for its role in protein homeostasis and functionality, is implicated in tumorigenesis. However, its part in the antitumor immunity mediated by CD8 + T cells in lung adenocarcinoma (LUAD) is not yet clear. We harnessed bioinformatics to evaluate the clinical relevance of UCHL1 in LUAD, performed IHC to detect the expression of UCHL1 in LUAD tissue, and utilised qPCR to assess UCHL1 levels in LUAD cells, exploring its correlation with the presence of CD8 + T cells. The effects of UCHL1 on CD8 + T cell vigour have been investigated using lactate dehydrogenase and enzyme‐linked immunosorbent assay kits, as well as flow cytometry. The contribution of UCHL1 to ferroptosis was examined with ferrous ion and manganese dioxide assay kits, alongside western blot. Furthermore, we utilised bioinformatics software UbiBrowser and Hdock, in conjunction with co‐immunoprecipitation (Co‐IP), immunofluorescence, and IP methods, to dissect the interaction between UCHL1 and FHL2. Rescue experiments further clarified the mechanism by which UCHL1 modulates FHL2 in tumour immunity. In vivo experiments confirmed the promoting effect of UCHL1 on tumour growth. Elevated UCHL1 levels in LUAD tissues and cells were observed. Dampening UCHL1 triggered ferroptosis in LUAD cells, which in turn ramped up CD8 + T cell activity and enhanced their tumour‐killing potential. Mechanistically, UCHL1 was shown to deubiquitinate the downstream factor FHL2, and knocking down FHL2 could counteract the immunosuppressive effects induced by high UCHL1 levels on CD8 + T cells. UCHL1 inhibitor LDN57444 significantly inhibited tumour growth in mice. Therapies aimed at the UCHL1/FHL2 axis could be effectively paired with immunotherapies, opening new avenues in cancer treatment strategies.