Investigating regulatory mechanisms within the Akt signaling network

Abstract

Insulin is a key cellular signal which initiates a signaling cascade to control blood glucose levels. It is essential that insulin signaling is tightly regulated, as if it does not work properly, diseases such as diabetes ensue. Consequently, cells contain a variety of regulatory mechanisms to control signal flow and ensure signal fidelity. However, it is poorly understood what these mechanisms are and where the breakpoints lie. During my PhD candidature we have discovered novel regulatory mechanisms within the insulin signaling network which are critical for ensuring appropriate signal propagation. First, using molecular biology we have shown that Akt2, a key protein kinase activated downstream of insulin, is regulated by phosphorylation at Serine 474. In 3T3-L1 adipocytes we established that this phosphorylation event is required for maximal insulin-stimulated biological processes, including glucose uptake into the cell (Kearney et al., Journal of Biological Chemistry, 2019). Second, using advanced live cell microscopy we have identified a powerful negative feedback loop that works to limit signal propagation within the insulin signaling network. We delineated the precise molecular mechanism that forms this loop by showing it is driven by Akt-mediated phosphorylation of insulin receptor substrate (IRS) proteins (Kearney et al., eLife, 2021). Using mass spectrometry-based proteomics we obtained a holistic view of 3T3-L1 adipocytes to discover that Akt-mediated negative feedback has far-reaching and unexpected consequences throughout signaling networks. Collectively, these findings illuminate key regulatory mechanisms within the Akt signaling network and will guide future endeavours to fine-tune insulin signaling in pathological settings