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Pathway Analysis of Dominant CHIP E3 Ligase-Dependent Protein Steady State Changes Highlight a Role in Neuronal Cell Membrane Integrity Linked to the Actin Cytoskeleton

ABSTRACT: Functional integrity of the E3-ubiquitin ligase CHIP is essential for healthy aging in the brain. By virtue of its association with the core molecular chaperone machinery, studies into the physiological role(s) of CHIP have been dominated by its involvement in the quality control and degradation of unfolded, aggregated and/or mutated proteins. To elucidate the dominant CHIP-dependent changes in protein steady state levels in human neurons we conducted an unbiased proteomic analysis in genetically engineered wild-type and CHIP knockout iPSC-derived cortical neurons. Rather than a broad effect on protein homeostasis, pathway analysis highlighted a focused cohort of CHIP-responsive proteins involved in actin cytoskeleton signalling and membrane integrity. In support of the pathway analysis CHIP KO cell-lines had enhanced sensitivity to mechanical and chemical membrane damage. Consistent with recent studies on the identification of a non-canonical HSP-independent E3-activity for CHIP, the lack of general quality control defects in knock-out cells suggests that the major readout of CHIP function in cortical neurons is the regulation of native folded substrates involved in maintaining cellular ‘health’. Thus, CHIP-mediated regulation of the of cytoskeletal- and membrane-related proteins is likely to make a vital contribute to the neuroprotective activity of CHIP.

INSTRUMENT(S): TripleTOF 5600

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Stem Cell

DISEASE(S): Neurodegenerative Disease

SUBMITTER: Lenka Hernychova

LAB HEAD: Prof. Kathryn Ball

PROVIDER: PXD021404 | Pride | 2021-07-29

REPOSITORIES: Pride

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Project description:Interferon-induced transmembrane protein (IFITM1) plays a dual role in restriction of RNA viruses and in metastatic cancer cell growth. The signal transduction events that are orchestrated by IFITM1 are not well defined. We set out to identify IFITM1 interacting proteins to begin to define its mechanism of action. Affinity purification of SBP-tagged IFITM1, coupled to SWATH-mass spectrometry, identified significantly higher confidence interacting proteins from IFN- treated cells, relative to non-treated cells. This promoted an examination of the protein synthetic machinery in order to determine whether IFITM1 can impact on ribosomal proteome from IFN- treated cells. Isogenic ifitm1 null and ifitm1-ifitm3 null-SiHa cell panels were generated using CRISPR gRNAs to define signaling events that are linked to IFN--dependent protein synthesis. Ultracentrifugation sedimentation of cell lysates from interferon gamma treated wt and ifitm1-ifitm3 null-SiHa cells was carried out to isolate ribosomal constituents. Although SWATH-mass spectrometry of the 40S, 60S, and 80S fractions demonstrated changes in selected protein content, a significant reduction in A254 (RNA) in the 80S ribosomal fractions suggested a relatively select defect in 80S ribosomal biogenesis in ifitm1-ifitm3 null cells. The localization of IFITM1 to ribosomal protein components prompted an analysis of IFN--dependent protein synthesis using pulse SILAC. STAT1 and B2M were two dominant proteins whose synthesis increased equivalently in wt or ifitm1-ifitm3 null cells. However, MHC class I molecules and ISG15 were the most highly suppressed IFN--responsive proteins in the ifitm1-ifitm3 double null cells and this was confirmed using ifitm1 single null cells. Transient depletion of IFITM1 using targeted siRNA also depleted MHC class I molecules as well as IFITM3, STAT1, B2M, and ISG15. These data have implications for the function of IFITM1 in mediating IFN--stimulated protein synthesis and associated antigen presentation during either oncogenic or anti-viral signalling.

Dataset Information

Pathway Analysis of Dominant CHIP E3 Ligase-Dependent Protein Steady State Changes Highlight a Role in Neuronal Cell Membrane Integrity Linked to the Actin Cytoskeleton

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