Nardone Christopher, Gao Jingjing, Seo Hyuk-Soo, Mintseris Julian, Ort Lucy, Yip Matthew C J, Negasi Milen, Besschetnova Anna K, Kamitaki Nolan, Gygi Steven P, Dhe-Paganon Sirano, Munshi Nikhil C, Fulciniti Mariateresa, Greenberg Michael E, Shao Sichen, Elledge Stephen J, Gu Xin
Department of Genetics, Harvard Medical School, Boston, MA 02115, USA; Division of Genetics, Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115, USA; Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.
Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.
Mol Cell. 2025 Jul 3;85(13):2597-2609.e11. doi: 10.1016/j.molcel.2025.05.030. Epub 2025 Jun 17.
The midnolin-proteasome pathway degrades many nuclear proteins without ubiquitination, but how it operates mechanistically remains unclear. Here, we present structures of the midnolin-proteasome complex, revealing how established proteasomal components are repurposed to enable a unique form of proteolysis. While the proteasomal subunit PSMD2/Rpn1 binds to ubiquitinated or ubiquitin-like (Ubl) proteins, we discover that it also interacts with the midnolin nuclear localization sequence, elucidating how midnolin's activity is confined to the nucleus. Likewise, PSMD14/Rpn11, an enzyme that normally cleaves ubiquitin chains, surprisingly functions non-enzymatically as a receptor for the midnolin Ubl domain, positioning the substrate-binding Catch domain directly above the proteasomal entry site to guide substrates into the proteasome. Moreover, we demonstrate that midnolin downregulation is critical for the survival of myeloma cells by stabilizing the transcription factor substrate IRF4. Our findings uncover the mechanisms underlying the midnolin-proteasome pathway and midnolin downregulation as a driver of multiple myeloma.
Midnolin-蛋白酶体途径可降解许多无泛素化修饰的核蛋白，但其作用机制尚不清楚。在此，我们展示了Midnolin-蛋白酶体复合物的结构，揭示了已确定的蛋白酶体组分是如何被重新利用以实现独特形式的蛋白水解的。虽然蛋白酶体亚基PSMD2/Rpn1与泛素化或类泛素（Ubl）蛋白结合，但我们发现它也与Midnolin核定位序列相互作用，阐明了Midnolin的活性如何局限于细胞核。同样，通常切割泛素链的酶PSMD14/Rpn11，出人意料地作为Midnolin Ubl结构域的受体发挥非酶促功能，将底物结合捕获结构域直接定位在蛋白酶体入口位点上方，以引导底物进入蛋白酶体。此外，我们证明Midnolin的下调通过稳定转录因子底物IRF4对骨髓瘤细胞的存活至关重要。我们的研究结果揭示了Midnolin-蛋白酶体途径的潜在机制以及Midnolin下调作为多发性骨髓瘤驱动因素的机制。
