Abstract
Targeting metabolic remodeling represents a potentially promising strategy for hepatocellular carcinoma (HCC) therapy. In-depth understanding on the regulation of the glutamine transporter alanine-serine-cysteine transporter 2 (ASCT2) contributes to the development of novel promising therapeutics. As a developmentally regulated RNA binding protein, RBM45 is capable to shuttle between nucleus and cytoplasm, and directly interacts with proteins. By bioinformatics analysis, we screened out that RBM45 was elevated in the HCC patient specimens and positively correlated with poor prognosis. RBM45 promoted cell proliferation, boosted xenograft tumorigenicity and accelerated HCC progression. Using untargeted metabolomics, it was found that RBM45 interfered with glutamine metabolism. Further results demonstrated that RBM45 positively associated with ASCT2 in human and mouse specimens. Moreover, RBM45 enhanced ASCT2 protein stability by counteracting autophagy-independent lysosomal degradation. Significantly, wild-type ASCT2, instead of phospho-defective mutants, rescued siRBM45-suppressed HCC cell proliferation. Using molecular docking approaches, we found AG-221, a mutant isocitrate dehydrogenase 2 (mIDH2) inhibitor for acute myeloid leukemia therapy, pharmacologically perturbed RBM45-ASCT2 interaction, decreased ASCT2 stability and suppressed HCC progression. These findings provide evidence that RBM45 plays a crucial role in HCC progression via interacting with and counteracting the degradation of ASCT2. Our findings suggest a novel alternative structural sites for the design of ASCT2 inhibitors and the agents interfering with RBM45-ASCT2 interaction may be a potential direction for HCC drug development.

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Data availability
Source data and reagents are available from the corresponding author upon reasonable request.
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Acknowledgements
The study was supported by the National Natural Science Foundation of China (Nos. 82070883, 82273982, 81872892), the Natural Science Foundation of Jiangsu Province, China (BK20221525) and Scientific Research Foundation for high-level faculty, China Pharmaceutical University. We thank all the financial support for this project and Dr. Xin Chen (UCSF) for sharing the oncogene plasmids.
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DYD, MY, MYQ, L Shi and CL performed the research; ZGL, HXW, ZBZ, ZRL, HYL and JP conducted some experiments; JWJ performed molecular docking and MD simulations; HY collected clinical specimens; HF drew the graphical abstract; JX and STY designed the research study; JX and STY contributed essential reagents or tools; DYD, JX, L Sun and MY analyzed the data; JX, DYD and STY wrote the paper.
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Du, D., Qin, M., Shi, L. et al. RNA binding motif protein 45-mediated phosphorylation enhances protein stability of ASCT2 to promote hepatocellular carcinoma progression. Oncogene 42, 3127–3141 (2023). https://doi.org/10.1038/s41388-023-02795-3
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DOI: https://doi.org/10.1038/s41388-023-02795-3