Regulators of The Unfolded Protein Response Signaling - Project Summary/Abstract: The endoplasmic reticulum (ER) provides the platform for protein folding and secretion. In cases when proteins fail to fold correctly or misfold, they accumulate inside the ER, leading to the activation of a signaling network known as the unfolded protein response (UPR). This response involves three major ER-resident sensors: activating transcription factor 6 (ATF6), inositol requiring enzyme 1 (Ire1), and protein kinase RNA-activated-like ER kinase (PERK).Each sensor activates a distinct signaling pathway that leads to the activation of specific transcription factors, which are responsible for the activation of genes encoding protein-folding enzymes. These coordinated processes enhance the protein-folding capacity of cells. Emerging biological data, such as transcriptome, proteome and interactome information, have revealed that a large-scale regulatory crosstalk exists between the UPR and the other intracellular signaling pathways. For example, the phosphoinositide 3-kinase (PI3K) pathway and the mitogen-activated protein kinase (MAPK) pathways cross talk with UPR. However, the precise extent and mechanisms of crosstalk have not yet been clearly defined. Therefore, it is still unclear how the UPR pathways are connected to form networks, how specific information is processed as it flows through intermediate components, and how the network is tuned by various regulatory inputs. The dysfunctional UPR has been associated with the development of many neurological and metabolic diseases such as diabetes, arthritis, and certain cancers. Consequently, a pressing need is to better understand the UPR to explore the therapeutic interventions targeting the UPR components for the treatment of these diseases. The Ire1 pathway is the sole UPR pathway in the budding yeast S. cerevisiae. In this proposal, we will use S. cerevisiae as a model organism to investigate the regulatory UPR network that contributes to ER proteostasis. Here, we have delineated two specific aims, involving three protein kinases: Pkh1 (human ortholog of PDK1, phosphoinositide-dependent kinase 1), Ypk1 [a substrate of Ypk1, human ortholog of serum and glucocorticoid-regulated kinase 1 (SGK1)] and Slt2 (human ortholog of MAPK ERK5). We will initially characterize the roles kinases Pkh1, Ypk1 and Slt2 in the yeast UPR mediated by Ire1. Building on our findings in yeast cells, we will understand the roles of human PDK1, SGK1 and ERK5 in human UPR. Collectively, our study will unveil a new biological nexus between the PI3K, MAPK and UPR pathways.
