Identification of degradation pathways for HSP90 client proteins

Li, Zhaobo (2017) Identification of degradation pathways for HSP90 client proteins. Doctoral thesis (PhD), University of Sussex.

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Abstract

Heat shock protein 90 (HSP90) is an ATP-dependent molecular chaperone that
plays critical roles in regulating the folding, stabilization, post-translational
modification, activation and maturation of its various client proteins, of which many are
oncoproteins. Impairing the function of HSP90 by the inhibition of its ATPase cycle
with inhibitors such as AUY922 promotes the ubiquitylation and proteasomal
degradation of its client proteins. However, we currently do not fully understand the
mechanism for ATPase-inhibited triggered degradation of client proteins, and which E3
ligase systems are involved.
Although previous studies revealed a number of E3 ligases including CHIP and
CUL5 as potentially E3 ligases involved in the degradation of HSP90-dependent client
protein, these have often used cancer cells that may have dysregulated systems.
Additionally, other components of such E3 ligase systems have not been well
characterised.
Using a Reverse Transfection Format (RTF) siRNA screen system we identified
two E3 ligases that are involved in two independent pathways for mediating
proteasomal degradation of the HSP90-dependent protein kinase CRAF in HEK293
cells. The elongin BC-CUL5-SOCS-box protein (ECS) complex operates one pathway
for the degradation of CRAF, while a novel but poorly described HECTD3 from the
HECT-family was identified as the main E3 ligase for degrading CRAF following the
pharmaceutical inhibition of HSP90. We revealed a potential complexes consisting of
CRAF, HSP90 and HECTD3, which may contribute towards identifying the pathway
for the degrading of such HSP90-dependent client protein kinases. We were also able to
show that depriving access of CRAF to CDC37 and therefore HSP90 resulted in an
HECTD3 and CUL5 independent degradation pathway. These studies form the basis of
establishing the complex network of pathways that help to regulate CRAF protein levels.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Life Sciences > Biochemistry
Subjects: Q Science > QD Chemistry > QD0241 Organic chemistry > QD0415 Biochemistry
Depositing User: Library Cataloguing
Date Deposited: 27 Mar 2017 15:45
Last Modified: 27 Mar 2017 15:45
URI: http://sro.sussex.ac.uk/id/eprint/67006

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