Continuing with the challenge of overcoming acquired resistance in BLCA, we discovered that the transcription factor E2F1 is not only highly expressed in GEM-resistant cells but is also directly induced by chemotherapy exposure. Patients with elevated E2F1 expression exhibited poorer prognoses, suggesting that E2F1 stability is a key factor in therapeutic failure.

To date, E2F1 has been primarily studied as a cell cycle regulator. However, the mechanisms by which it modulates lipid metabolism to confer drug resistance have remained elusive. Here, we determine that E2F1 promotes GEM resistance by activating cholesterol biosynthesis and that its stability is tightly controlled by USP43.

In this study, we further explored the molecular mechanism of USP43 in BLCA. We identified a mechanism by which USP43 regulates GEM resistance mediated by the stabilization of E2F1. Specifically, as shown in the Figure above, USP43 interacts with E2F1 and functions as a deubiquitinase, removing ubiquitin chains to prevent E2F1 proteasomal degradation. The stabilized E2F1 then transcriptionally activates NSDHL, a key enzyme in cholesterol biosynthesis. This leads to intracellular cholesterol accumulation, which subsequently enhances drug efflux via ABC transporters and suppresses ferroptosis.

Finally, a USP43-E2F1-NSDHL axis is established, which accelerates the development of chemoresistance. Overall, our study identifies USP43 as a promoter of GEM resistance via a cholesterol-dependent mechanism and suggests its potential as a therapeutic target for BLCA.

Reference

[1] Li M, Liu T, Shi J, Zhou F, Deng Z, Luo Y, Tu S, Jiang W, Wang G, Qian K, Zhang Y, Xiao Y, Wang X, Liu T, Ju L. USP43 promotes gemcitabine resistance by regulating cholesterol homeostasis through E2F1 stabilization in bladder cancer. J Exp Clin Cancer Res. 2025 Dec 23. doi: 10.1186/s13046-025-03621-2.