Lipopolysaccharide stimulation of RAW264.7 cells is a model for identifying novel clients of Hsc70

Abstract

Heat shock cognate protein 71 kDa (Hsc70, Hspa8, Hspa10, Hsp73) is a member of the heat shock protein 70 kDa family of molecular chaperones. These chaperones function to aid the correct folding of client proteins using an ATP-dependent mechanism. Though Hsc70 is accepted to be a constitutively expressed protein, it has a well-documented function in modulating the induction of the pro-inflammatory cytokine TNFα by the LPS/TLR4 pathway. In this work we attempt to identify protein clients of Hsc70 to gain insight into those which may be responsible for this regulatory effect. RAW264.7 cells were cultured in the absence or presence of 1 μg/mL LPS for 0 to 24 hours. Herein we describe of a large number of newly-categorized Hsc70 clients using immunoprecipitation and nanoLC-MS/MS and we validate several novel Hsc70/client interactions using co-immunoprecipitation. After performing immunoprecipitation using a commercially available antibody, eluted fractions were proteolytically digested either immediately after immunoprecipitation or after separation by SDS-PAGE and sequence analyzed using nanoLC-MS/MS with a Q-Exactive Plus triple-quadrupole/orbitrap mass spectrometer. Using these methods, 292 total unique protein hits were identified with high confidence; 34 of which were only detected in LPS-treated cells.