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bioRxiv · 10.1101/2025.11.21.689851

Systematic characterization of cancer-associated SPOP mutants reveals novel and reprogrammable degradative activities

Caldwell, A. G.·Parmar, H.·Jin, X.·Zhou, C.·Zhang, X.
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Abstract

Speckle-type POZ protein (SPOP) functions as the substrate adaptor of the Cullin3-RING ligase (CRL3) complex and is recurrently mutated in multiple cancer types. Among these, F102C and F133L are frequent prostate cancer mutations within the substrate-binding domain, yet their biochemical consequences remain incompletely understood. Using quantitative proteomics, we show that SPOP-F133L, unlike SPOP-F102C, retains degradative activity toward the nuclear basket proteins NUP153 and TPR, indicating substrate-dependent loss-of-function. Moreover, SPOP-F133L induces partial down-regulation of p53 through a CRL-dependent, post-translational mechanism, revealing a potential neo-substrate relationship. Finally, we demonstrate that both SPOP-F102C and SPOP-F133L support targeted protein degradation (TPD) in an engineered cellular system. These findings define the degradative capacities of SPOP mutants and highlight opportunities to repurpose these variants as mutant-selective E3 ligases for therapeutic applications.

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Caldwell, A. G., Parmar, H., Jin, X., Zhou, C., Zhang, X.. 2025-11-23. Systematic characterization of cancer-associated SPOP mutants reveals novel and reprogrammable degradative activities. https://doi.org/10.1101/2025.11.21.689851

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