CHIP phosphorylation by protein kinase G enhances protein quality control and attenuates cardiac ischemic injury

Abstract

Proteotoxicity from insufficient clearance of misfolded/damaged proteins underlies many diseases. Carboxyl terminus of Hsc70-interacting protein (CHIP) is an important regulator of proteostasis in many cells, having E3-ligase and chaperone functions and often directing damaged proteins towards proteasome recycling. While enhancing CHIP functionality has broad therapeutic potential, prior efforts have all relied on genetic upregulation. Here we report that CHIP-mediated protein turnover is markedly post-translationally enhanced by direct protein kinase G (PKG) phosphorylation at S20 (mouse, S19 human). This increases CHIP binding affinity to Hsc70, CHIP protein half-life, and consequent clearance of stress-induced ubiquitinated-insoluble proteins. PKG-mediated CHIP-pS20 or expressing CHIP-S20E (phosphomimetic) reduces ischemic proteo- and cytotoxicity, whereas a phospho-silenced CHIP-S20A amplifies both. In vivo, depressing PKG activity lowers CHIP-S20 phosphorylation and protein, exacerbating proteotoxicity and heart dysfunction after ischemic injury. CHIP-S20E knock-in mice better clear ubiquitinated proteins and are cardio-protected. PKG activation provides post-translational enhancement of protein quality control via CHIP.

Xbp1s-FoxO1 axis governs lipid accumulation and contractile performance in heart failure with preserved ejection fraction

“…Therefore, the identification of negative upstream regulators of FoxO1 such as STUB1 might result in valuable therapeutic targets to diminish FoxO1 activation and its negative metabolic consequences. Indeed, strategies aiming to enhance STUB1 functionality for therapeutic applications in cardiovascular disease have been proposed recently 43 , supporting the potential feasibility of targeting STUB1 for clinical gain.…”

It's not just a phase; ubiquitination in cytosolic protein quality control

“…In combination with its chaperone partners, CHIP targets substrates for degradation via proteasomal degradation [ 59 ]. The phosphorylation of CHIP by Protein Kinase G has also recently been shown to increase the activity of the E3 ligase by enhancing its association with chaperones [ 60 ]. CHIP does not exclusively tag proteins for destruction however, it also coordinates misfolded protein aggregation in concert with its chaperone partners upon proteasome inhibition, although this may be an indirect effect [ 61 ].…”

Cytosolic protein quality control machinery: Interactions of Hsp70 with a network of co-chaperones and substrates

“…87 A recent study of posttranslational modifications of CHIP identified that serine phosphorylation of CHIP also serves to stabilize the interactions between CHIP and Hsp70 and positively influences CHIP-mediated ubiquitination and subsequent proteasomal degradation. 88…”