Scientists Discover Ubiquitin-Independent Mechanism for Proteasome Activation and Regulation
Researchers used pulsed-SILAC proteomics to systematically map proteins degraded by the proteasome without ubiquitin tagging, identifying two key activation factors, ZFAND5 and ZFAND6. The ubiquitin-proteasome system is the cell's primary mechanism for selective protein disposal, but ubiquitin-independent routes have been poorly characterized. The findings reveal an unexpected feedback loop connecting proteasome activation to inflammatory signaling via the TLR4 pathway.
A new preprint study on bioRxiv reports a systematic investigation of ubiquitin-independent proteasomal degradation (UbInPD) using pulsed-SILAC proteomics, a technique that tracks protein turnover rates across the proteome. The researchers identified ZFAND5 and ZFAND6 as paralogous proteasome activation factors, with ZFAND5 containing a specific degron sequence that simultaneously triggers its own rapid degradation and allosterically activates the proteasome. This dual function supports a feedback model in which the proteasome's own activators are consumed as part of the activation process. Beyond proteasome regulation, the study links ZFAND5/6 and the scaffold protein p62 to restraining NF-κB activation in the TLR4 innate immune signaling pathway. This restraint appears to operate through the degradation of UBCH5c, an E2 ubiquitin-conjugating enzyme that initiates ubiquitin chain synthesis. Together, the findings broaden the known scope of UbInPD and draw previously unrecognized connections between proteasome biology, E2 enzyme regulation, and inflammatory responses.
What's missing
As a preprint, this work has not yet undergone formal peer review, so findings should be treated as preliminary. The study does not address whether ZFAND5/6-mediated regulation of NF-κB is physiologically relevant in specific disease contexts (e.g., chronic inflammation or infection models in vivo). The generalizability of the pulsed-SILAC screen across different cell types or stress conditions is also not established.
What different sources said
- bioRxivCenter
Regulation of proteasome activation by a ubiquitin-independent feedback mechanism
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