The Insulin Receptor Adaptor IRS2 is an APC/C Substrate That Promotes Cell Cycle Protein Expression and a Robust Spindle Assembly Checkpoint

We report a chemical proteomic screen to uncover substrates of the APC/C, a ubiquitin ligase that controls cell division. We found that IRS2, a component of the insulin receptor signaling network that is required for normal metabolic homeostasis, is a direct APC/C substrate during G1. Analysis of IRS2 knockout cells revealed depletion of cell cycle regulatory proteins and a weakened spindle assembly checkpoint. Thus, IRS2 is a component of the cell cycle control system in addition to acting as a metabolic regulator. [Display omitted] Highlights •Chemical proteomics in G1 cells treated with small molecule APC/C inhibitors reveals novel putative APC/C substrates.•The insulin receptor adaptor IRS2 is an APC/C substrate that is targeted for degradation by APC/CCdh1.•Quantitative proteomics in IRS2 knockout cells reveals a deficiency in cell cycle related protein expression.•IRS2 promotes a robust spindle assembly checkpoint (SAC) during M-phase. Insulin receptor substrate 2 (IRS2) is an essential adaptor that mediates signaling downstream of the insulin receptor and other receptor tyrosine kinases. Transduction through IRS2-dependent pathways is important for coordinating metabolic homeostasis, and dysregulation of IRS2 causes systemic insulin signaling defects. Despite the importance of maintaining proper IRS2 abundance, little is known about what factors mediate its protein stability. We conducted an unbiased proteomic screen to uncover novel substrates of the Anaphase Promoting Complex/Cyclosome (APC/C), a ubiquitin ligase that controls the abundance of key cell cycle regulators. We found that IRS2 levels are regulated by APC/C activity and that IRS2 is a direct APC/C target in G1. Consistent with the APC/C's role in degrading cell cycle regulators, quantitative proteomic analysis of IRS2-null cells revealed a deficiency in proteins involved in cell cycle progression. We further show that cells lacking IRS2 display a weakened spindle assembly checkpoint in cells treated with microtubule inhibitors. Together, these findings reveal a new pathway for IRS2 turnover and indicate that IRS2 is a component of the cell cycle control system in addition to acting as an essential metabolic regulator.