A Gold-PROTAC Degrades the Oncogenic Tyrosine Kinase MERTK: Insights into the Degradome from a Steady-State System

TL;DR

This study introduces a covalent gold-based PROTAC that degrades the cancer-related protein MERTK and identifies its targets using a steady-state cell system.

Contribution

The paper presents a novel covalent gold-based PROTAC and a steady-state system for unbiased degradome profiling.

Findings

The AuPROTAC degrades MERTK and TXNL1, with degradation rescued by proteasome inhibition.

The AuPROTAC degrades 95 proteins, showing higher selectivity compared to ACBI2, which degrades 221 proteins.

Abstract

Proteolysis targeting
chimeras (PROTACs) are bifunctional molecules
designed to induce the degradation of specific proteins within a cell.
While most PROTACs are noncovalent interactors, covalent PROTACs may
benefit from improved selectivity and pharmacodynamics, yet remain
largely understudied. Here, a covalent gold-based PROTAC (AuPROTAC) was synthesized, featuring a Au­(III)-warhead, known to induce cysteine-arylation
in a gold-templated two-step mechanism, linked to a cereblon binding
moiety. The degradome of the AuPROTAC was characterized
by establishing a cycloheximide chase assay in a nonproliferative
steady-state HL-60 cell culture, enabling the identification of PROTAC
degradation targets uncoupled from confounding effects originating
from cell-cycle-dependent translational patterns. The method was verified
using the known SMARCA2 and PBRM1-degrader ACBI2. AuPROTAC could degrade the oncogenic tyrosine kinase MERTK and the thioredoxin-like
1 protein TXNL1. Their degradation was successfully rescued by proteasome
inhibition. Proteome-wide degradation selectivity was further characterized
by ranking the degraded targets according to the reduction extent
of their protein half-lives. Interestingly, the AuPROTAC degraded a relatively limited number of proteins (95) when compared
to ACBI2 (221).

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