Protein homeostasis is tightly controlled by the coordinated actions of E3 ubiquitin ligases and deubiquitinases (DUBs). We previously identified Spindlin-4 (SPIN4), a histone H3K4me3 reader, as a degradation substrate of DCAF16. In this study, we confirmed this degradation pathway using an E3 ligase-focused CRISPR-Cas9 knockout screen. Furthermore, through a DUB-focused CRISPR-Cas9 knockout screen and biochemical analyses, we demonstrated that the deubiquitinase BAP1 interacts with and stabilizes SPIN4 via its deubiquitination activity. Inhibition or loss of BAP1 reduces SPIN4 levels, highlighting its critical role in maintaining SPIN4 homeostasis. Proteomics and interactome analyses further support this regulatory axis. These findings reveal a dynamic balance controlling SPIN4 stability, with potential implications for epigenetic regulation and disease processes.

Lactate is a vital metabolite in cancer, significantly impacting tumor progression, metastasis, and overall survival. The CD147-monocarboxylate transporter 1 (MCT1) complex, a major lactate transporter, has emerged as a promising therapeutic target. However, no effective protein-protein interaction (PPI) inhibitors targeting the CD147-MCT1 complex have been identified. In this study, we found that the small-molecule inhibitor crizotinib effectively disrupts the CD147-MCT1 interaction, leading to reduced lactate secretion from melanoma cells and decreased lactate uptake by macrophages. In vivo studies demonstrated that crizotinib treatment significantly suppressed tumor growth and enhanced responsiveness to immune checkpoint blockade therapy. Flow cytometry revealed that this metabolic intervention inhibits M2 polarization and reshapes the tumor immune microenvironment. Transcriptomic analysis further revealed that lactate induces C-X-C motif chemokine ligand 13 (CXCL13) expression in macrophages, which enhances melanoma invasiveness and impairs immune cell-mediated cytotoxicity. Importantly, crizotinib suppresses CXCL13 expression by blocking lactate-driven histone lactylation, thereby reversing the transcriptional reprogramming induced by lactate, as evidenced by reduced histone H3 lysine 18 lactylation (H3K18la) enrichment at the CXCL13 promoter. Taken together, these findings provide new insights into targeting metabolic-immune crosstalk and highlight the value of disrupting CD147-MCT1 interactions to improve immunotherapeutic responses in patients with melanoma.
© 2025 The Author(s). MedComm published by Sichuan International Medical Exchange & Promotion Association (SCIMEA) and John Wiley & Sons Australia, Ltd.

The transforming growth factor-beta (TGFβ) signaling pathway plays crucial roles in the establishment of an immunosuppressive tumor microenvironment, making anti-TGFβ agents a significant area of interest in cancer immunotherapy. However, the clinical translation of current anti-TGFβ agents that target upstream cytokines and receptors remains challenging. Therefore, the development of small-molecule inhibitors specifically targeting SMAD4, the downstream master regulator of the TGFβ pathway, would offer an alternative approach with significant therapeutic potential for anti-TGFβ signaling. In this study, we present the development of a cell lysate-based multiplexed time-resolved fluorescence resonance energy transfer (TR-FRET) assay in an ultrahigh-throughput screening (uHTS) 1536-well plate format. This assay enables simultaneous monitoring of the protein‒protein interaction between SMAD4 and SMAD3, as well as the protein‒DNA interaction between SMADs and their consensus DNA-binding motif. The multiplexed TR-FRET assay exhibits high sensitivity, allowing the dynamic analysis of the SMAD4-SMAD3-DNA complex at single-amino acid resolution. Moreover, the multiplexed uHTS assay demonstrates robustness for screening small-molecule inhibitors. Through a pilot screening of an FDA-approved bioactive compound library, we identified gambogic acid and gambogenic acid as potential hit compounds. These proof-of-concept findings underscore the utility of our optimized multiplexed TR-FRET platform for large-scale screening to discover small-molecule inhibitors that target the SMAD4-SMAD3-DNA complex as novel anti-TGFβ signaling agents.
© The Author(s) (2023). Published by Oxford University Press on behalf of Journal of Molecular Cell Biology, CEMCS, CAS.

Molecular radiotherapy combines the advantages of systemic administration of highly specific antibodies or peptides and the localized potency of ionizing radiation. A potential target for molecular radiotherapy is the cell surface antigen CD44v6, which is overexpressed in numerous cancers, with limited expression in normal tissues. The aim of the present study was to generate and characterize a panel of human anti-CD44v6 antibodies and identify a suitable candidate for future use in molecular radiotherapy of CD44v6-expressing cancers. Binders were first isolated from large synthetic phage display libraries containing human scFv and Fab antibody fragments. The antibodies were extensively analyzed through in vitro investigations of binding kinetics, affinity, off-target binding, and cell binding. Lead candidates were further subjected to in vivo biodistribution studies in mice bearing anaplastic thyroid cancer xenografts that express high levels of CD44v6. Additionally, antigen-dependent tumor uptake of the lead candidate was verified in additional xenograft models with varying levels of target expression. Interestingly, although only small differences were observed among the top antibody candidates in vitro, significant differences in tumor uptake and retention were uncovered in in vivo experiments. A high-affinity anti-CD44v6 lead drug candidate was identified, mAb UU-40, which exhibited favorable target binding properties and in vivo distribution. In conclusion, a panel of human anti-CD44v6 antibodies was successfully generated and characterized in this study. Through comprehensive evaluation, mAb UU-40 was identified as a promising lead candidate for future molecular radiotherapy of CD44v6-expressing cancers due to its high affinity, excellent target binding properties, and desirable in vivo distribution characteristics.
© 2023. The Author(s).

Tumor suppressor genes represent a major class of oncogenic drivers. However, direct targeting of loss-of-function tumor suppressors remains challenging. To address this gap, we explored a variant-directed chemical biology approach to reverse the lost function of tumor suppressors using SMAD4 as an example. SMAD4, a central mediator of the TGF-β pathway, is recurrently mutated in many tumors. Here, we report the development of a TR-FRET technology that recapitulated the dynamic differential interaction of SMAD4 and SMAD4R361H with SMAD3 and identified Ro-31-8220, a bisindolylmaleimide derivative, as a SMAD4R361H/SMAD3 interaction inducer. Ro-31-8220 reactivated the dormant SMAD4R361H-mediated transcriptional activity and restored TGF-β-induced tumor suppression activity in SMAD4 mutant cancer cells. Thus, demonstration of Ro-31-8220 as a SMAD4R361H/SMAD3 interaction inducer illustrates a general strategy to reverse the lost function of tumor suppressors with hypomorph mutations and supports a systematic approach to develop small-molecule protein-protein interaction (PPI) molecular glues for biological insights and therapeutic discovery.
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