Bag1-Hsp70 mediates a physiological stress signalling pathway that regulates Raf-1/ERK and cell growth

Area of Science:

• Cellular Biology
• Molecular Biology
• Stress Response Signaling

Background:

• Cell survival under stress necessitates coordinated signaling for biosynthesis and survival pathways.
• Heat-shock protein 70 (Hsp70) plays a crucial role in cellular stress responses.

Purpose of the Study:

• To elucidate the role of Bag1, an Hsp70 co-chaperone, in coordinating cell growth signals in response to cellular stress.
• To investigate the interaction between Bag1, Hsp70, and Raf-1 kinase in regulating cell proliferation.

Main Methods:

• Investigated the binding interactions between Bag1, Hsp70, and Raf-1 kinase.
• Utilized mutant forms of Bag1 and Hsp70 to assess their functional impact on signaling pathways.
• Monitored DNA synthesis and Raf-1/ERK kinase activity under various stress conditions.

Main Results:

• Bag1 binds to and activates Raf-1 kinase, promoting downstream ERK signaling and cell growth.
• Elevated Hsp70 levels displace Raf-1 from Bag1, leading to the inhibition of Raf-1/ERK signaling and arrest of DNA synthesis.
• Mutant Bag1 proteins unable to bind Hsp70 constitutively activated Raf-1/ERK signaling, unaffected by Hsp70.
• Mutant Hsp70 proteins unable to bind Bag1 failed to repress Bag1-mediated Raf-1/ERK activation.

Conclusions:

• Bag1 acts as a crucial coordinator of cell growth signals and mitogenesis during the heat-shock response.
• Hsp70 functions as a critical sensor in cellular stress signaling pathways, modulating Bag1's regulatory function.
• The interplay between Bag1 and Hsp70 is essential for regulating cell proliferation under stress conditions.