Hsp90 chaperone code and the tumor suppressor VHL cooperatively regulate the mitotic checkpoint

Area of Science:

• Molecular Biology
• Cell Biology
• Cancer Biology

Background:

• Heat shock protein-90 (Hsp90) is a crucial molecular chaperone in eukaryotes, maintaining the stability and function of signaling proteins, particularly in tumors.
• Hsp90 is essential for the stability and activity of the mitotic checkpoint kinase Mps1, influencing mitotic arrest and exit.
• The Hsp90 'Chaperone Code' refers to its post-translational regulation, impacting its chaperone function.

Purpose of the Study:

• To investigate the role of the von Hippel-Lindau (VHL) E3 enzyme in the regulation of Mps1 kinase activity and its impact on mitosis.
• To elucidate the interplay between Hsp90 chaperone machinery and VHL-mediated protein degradation in controlling cell cycle progression through mitosis.

Main Methods:

• Ubiquitination assays to identify ubiquitination sites on Mps1.
• Proteasomal degradation assays to assess Mps1 stability.
• Cell cycle analysis to determine the effect on mitotic exit.

Main Results:

• Active Mps1 kinase is specifically ubiquitinated on lysine residues K86, K827, and K848 by the VHL E3 enzyme.
• This ubiquitination occurs independently of prolyl hydroxylation and targets Mps1 for proteasomal degradation.
• VHL-mediated degradation of Mps1 regulates the cell's exit from the mitotic checkpoint.

Conclusions:

• The study reveals a novel mechanism where the VHL E3 ligase targets active Mps1 for degradation, thereby controlling mitotic exit.
• This highlights a critical interplay between the Hsp90 chaperone system and the VHL ubiquitin-proteasome system in the regulation of mitosis.
• Understanding this crosstalk is vital for comprehending cell cycle control and has implications for cancer therapy.