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Updated: Jun 2, 2026
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Published on: January 2, 2026
Prefoldin subunits are protected from ubiquitin-proteasome system-mediated degradation by forming complex with other
Makoto Miyazawa1, Erika Tashiro, Hirotake Kitaura
1Graduate School of Pharmaceutical Sciences, Hokkaido University, Kita-ku, Sapporo, Japan.
Insights
Prefoldin (PFD) subunits mutually regulate their protein levels, preventing degradation and facilitating PFD complex formation. This discovery sheds light on how cells manage PFD subunit homeostasis and assembly.
Area of Science:
- Molecular Biology
- Protein Biochemistry
- Cellular Regulation
Background:
- Prefoldin (PFD) is a molecular chaperone complex essential for protein folding, composed of six subunits (PFD1-PFD6).
- Individual PFD subunits possess functions distinct from the PFD complex, including MM-1α/PFD5's role in suppressing c-Myc transformation activity.
- Mechanisms regulating individual PFD subunit levels and their assembly into the PFD complex remain largely unknown.
Purpose of the Study:
- To investigate the regulatory mechanisms controlling protein levels of individual prefoldin subunits.
- To elucidate how these mechanisms influence the formation of the prefoldin complex.
- To understand the interplay between subunit stability, degradation pathways, and complex assembly.
Main Methods:
- Gene knockdown and transfection experiments to alter PFD subunit expression levels.
- Treatment with MG132, a proteasome inhibitor, to assess protein degradation pathways.
- Analysis of protein levels of endogenous and overexpressed PFD subunits.
- Co-transfection experiments to identify subunit-specific stabilization interactions.
Main Results:
- Knockdown of one PFD subunit led to decreased protein levels of other subunits, indicating mutual regulation.
- Overexpression of PFD subunits (excluding MM-1α/PFD5) increased endogenous MM-1α/PFD5 levels.
- Overexpressed MM-1α/PFD5, but not endogenous MM-1α/PFD5, was degraded by the ubiquitin proteasome system (UPS).
- The UPS degrades monomeric PFD subunits, with varying degradation extents among subunits.
- Specific subunit combinations were identified that enhance mutual stabilization.
Conclusions:
- PFD subunits exhibit mutual regulation of protein levels, contributing to their stability.
- The ubiquitin proteasome system plays a role in degrading individual PFD subunits.
- Specific subunit interactions are crucial for stabilizing PFD monomers and facilitating PFD complex formation.
Abstract:
The molecular chaperone prefoldin (PFD) is a complex comprised of six different subunits, PFD1-PFD6, and delivers newly synthesized unfolded proteins to cytosolic chaperonin TRiC/CCT to facilitate the folding of proteins. PFD subunits also have functions different from the function of the PFD complex. We previously identified MM-1α/PFD5 as a novel c-Myc-binding protein and found that MM-1α suppresses transformation activity of c-Myc. However, it remains unclear how cells regulate protein levels of individual subunits and what mechanisms alter the ratio of their activities between subunits and their complex. In this study, we found that knockdown of one subunit decreased protein levels of other subunits and that transfection of five subunits other than MM-1α into cells increased the level of endogenous MM-1α. We also found that treatment of cells with MG132, a proteasome inhibitor, increased the level of transfected/overexpressed MM-1α but not that of endogenous MM-1α, indicating that overexpressed MM-1α, but not endogenous MM-1α, was degraded by the ubiquitin proteasome system (UPS). Experiments using other PFD subunits showed that the UPS degraded a monomer of PFD subunits, though extents of degradation varied among subunits. Furthermore, the level of one subunit was increased after co-transfection with the respective subunit, indicating that there are specific combinations between subunits to be stabilized. These results suggest mutual regulation of protein levels among PFD subunits and show how individual subunits form the PFD complex without degradation.
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