Investigating the role of protein phosphatase 5 (PP5) in the heat shock protein (Hsp) 70/90 chaperone complex

Ayesha Elias, Purdue University

Abstract

Heat shock proteins 90 and 70 (Hsp90 and Hsp70) are important cellular chaperones that function both independently and in tandem, along with several co-chaperones, in the folding of a multitude of proteins involved in various cellular processes such as cell proliferation, differentiation and apoptosis. Deregulation of these chaperone complexes leads to the accumulation of misfolded proteins, overexpression of mutant proteins, and disruption of various signaling networks resulting in diseased states such as cancer and various neurodegenerative disorders. Several observations indicate that the serine/threonine protein phosphatase 5 (PP5) complexes with Hsp90 and Hsp70 and may play a role in the regulation of the chaperone complex, regulating either the components of the complex or the Hsp90 and Hsp70 clients. To define the role of PP5 in the Hsp90 and Hsp70 chaperone complexes and identify proteins in these complexes that may be substrates for PP5, mass spectrometry, immunoprecipitation and western blot analyses were performed on PP5 immunoprecipitate samples. Several Hsp70 and Hsp90 co-chaperones were identified in the PP5 immunocomplexes ranging from those that bind the chaperone complexes in the earlier stages of the chaperone cycle to those that function at later stages, suggesting that PP5 may participate in the overall regulation of the complexes during client folding. This study shows that Hsp90, Hsp70 and Hsp70/90 organizing protein (HOP) bind differentially to either wildtype or catalytically inactive PP5 in vivo. Heat shock protein 70, like Hsp90, elevates PP5 phosphatase activity in vitro, suggesting that Hsp70 is a potential physiological activator of PP5. In the mass spectrometry and western blot analyses chaperonins that work independent of the Hsp70/90 complex were identified in association with PP5 indicating that PP5 may play a wider role in regulation of protein folding. Given the importance of chaperones in maintaining the proteome, determining the role of PP5 within these complexes will provide insights into the intricate regulation of chaperone function and protein maturation that can provide avenues for the development of novel therapeutic strategies against diseased cells.

Degree

Ph.D.

Advisors

Rossie, Purdue University.

Subject Area

Molecular biology

COinS