Targeting fibrinogen-like protein 1 enhances immunotherapy in hepatocellular carcinoma
Mingen Lin, … , Yanping Xu, Lei Lv
Mingen Lin, … , Yanping Xu, Lei Lv
Published May 1, 2023
Citation Information: J Clin Invest. 2023;133(9):e164528. https://doi.org/10.1172/JCI164528.
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Research Article Cell biology Immunology

Targeting fibrinogen-like protein 1 enhances immunotherapy in hepatocellular carcinoma

Abstract

How cancer cells evade the therapeutic effects of immune checkpoint blockade is largely unknown. Here, we report that fibrinogen-like protein 1 (FGL1), a newly identified immune checkpoint ligand, was modified by acetylation at Lys 98 in hepatocellular carcinoma (HCC), which targeted it for proteasomal degradation. Sirtuin 2 (SIRT2) deacetylated and stabilized FGL1, thus promoting immune evasion. Notably, the SIRT2 inhibitor 2-Cyano-3-[5-(2,5-dichlorophenyl)-2-furanyl]-N-5-quinolinyl-2-propenamide (AGK2) enhanced acetylation of FGL1 and reduced FGL1 protein levels in vitro. The combination of AGK2 and programmed death ligand 1 (PD-L1) blockade effectively suppressed tumor growth and improved overall survival of mice. Furthermore, aspirin, an old drug, could directly acetylate FGL1 at Lys 98 and promote its degradation in vitro. Aspirin enhanced the immunotherapeutic efficacy, induced tumor regression, and extended the lifespan of tumor-bearing mice. Furthermore, the SIRT2/FGL1 axis was expressed in HCC specimens. Collectively, these findings unveil an acetylation-mediated regulation of FGL1, identify a potential target for HCC immunotherapy, and provide therapeutic strategies for the clinical treatment of HCC.

Authors

Mingen Lin, Jing He, Xinchao Zhang, Xue Sun, Wenjing Dong, Ruonan Zhang, Yanping Xu, Lei Lv

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Figure 4

Aspirin acetylates FGL1 and promotes its degradation.

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Aspirin acetylates FGL1 and promotes its degradation. (A and B) Recombin...
(A and B) Recombinant His-FGL1 protein was treated or not with aspirin (0.125 mM or 0.25 mM) for 30 minutes in vitro. FGL1 acetylation was assessed by IB using a pan–anti–acetyl-lysine antibody or site-specific anti–FGL1 acetylation antibody. (C) Mass spectrometric detection of Lys 98 acetylation derived from recombinant His-FGL1 protein treated or not with aspirin (0.25 mM) for 30 minutes in vitro. The y ion peaks are shown in red, and the b ion peaks are shown in blue. The mass difference between b6 and b5 is the mass of the acetyl-lysine residue. (D) IB analysis of FGL1 acetylation levels in HEK293T cells stably expressing Flag-FGL1 and treated or not with aspirin (0.25 mM, 12 h). Pan– or site-specific anti–FGL1 acetylation antibodies were used as indicated. (E) IB analysis of FGL1 acetylation levels in HEK293T cells stably expressing Flag-FGL1 and treated with increasing concentrations of aspirin (+, 0.0625 mM; ++, 0.125 mM; +++, 0.25 mM; ++++, 0.5 mM) for 12 hours. (F) IB analysis of FGL1 protein levels in HEK293T cells stably expressing Flag-FGL1 and treated with increasing concentrations of aspirin (+, 0.0625 mM; ++, 0.125mM; +++, 0.25mM; ++++, 0.5 mM) for 24 hours. (G) IB analysis of endogenous FGL1 protein levels in HCCLM3 cells treated with increasing concentrations of aspirin (+, 0.0625 mM; ++, 0.125mM; +++, 0.25mM; ++++, 0.5mM) for 24 hours. (H) IB analysis of endogenous FGL1 protein levels in SMMC-7721 and HCCLM3 cells treated with aspirin (0.25 mM, 24 h) in the presence or absence of MG132 (10 μM, 6 h). (I) IB analysis of FGL1 ubiquitination levels in HEK293T cells stably expressing Flag-FGL1 and treated with 0.25 mM aspirin for 12 hours.