The Role of the Cullin-5 E3 Ubiquitin Ligase in the Regulation of Insulin Receptor Substrate-1

Abstract

Background. SOCS proteins are known to negatively regulate insulin signaling by inhibiting insulin receptor substrate-1 (IRS1). IRS1 has been reported to be a substrate for ubiquitin-dependent proteasomal degradation. Given that SOCS proteins can function as substrate receptor subunits of Cullin-5 E3 ubiquitin ligases, we examined whether Cullin-5 dependent ubiquitination is involved in the regulation of basal IRS1 protein stability and signal-induced IRS1 degradation. Findings. Our results indicate that basal IRS1 stability varies between cell types. However, the Cullin-5 E3 ligase does not play a major role in mediating IRS1 ubiquitination under basal conditions. Protein kinase C activation triggered pronounced IRS1 destabilization. However, this effect was also independent of the function of Cullin-5 E3 ubiquitin ligases. Conclusions. In conclusion, SOCS proteins do not exert a negative regulatory effect on IRS1 by functioning as substrate receptors for Cullin-5-based E3 ubiquitin ligases both under basal conditions and when IRS1 degradation is induced by protein kinase C activation.

A CRISPR-Based Genome-Wide Screen for Adipogenesis Reveals New Insights into Mitotic Expansion and Lipogenesis

“…We propose that this CRL is composed of CUL5 and ELOB/ELOC. Based on our proteomics analysis and previously published data (Hu, et al, 2012), we further propose that IRS1 is a critical substrate of this CRL. We note that our proteomics analysis identified several other components of insulin signaling which are also stabilized as a consequence of neddylation inhibition, including PIK3R1, SRFBP1, PHIP, and IGFBP3.…”

“…S6D, purple and teal). IRS1 has previously been identified as a substrate for CRLs in other cell contexts (Scheufele, et al, 2014;Hu, et al, 2012;Xu, et al, 2012). Immunoblot staining confirmed that inhibition of neddylation resulted in activation of insulin signaling within hours of treatment, as assessed by staining for phosphorylated IRS1 and AKT (Fig.…”

A CRISPR-based genome-wide screen for adipogenesis reveals new insights into mitotic expansion and lipogenesis

“…S6D, purple and teal). IRS1 has previously been identified as a substrate for CRLs in other cell contexts (Scheufele, et al, 2014;Hu, et al, 2012;Xu, et al, 2012). Immunoblot staining confirmed that inhibition of neddylation resulted in activation of insulin signaling within hours of treatment, as assessed by staining for phosphorylated IRS1 and AKT ( Fig.…”