Regulation of Cellular Oxygen Sensing Pathways by VHL

Erythropoiesis represents a vital physiologic process that can be adjusted to combat compromised oxygen availability, otherwise known as hypoxia. The canonical response to adapt to hypoxia is mediated by the transcription factor hypoxia-inducible factor-1 (HIF-1). When oxygen is available HIFalpha subunits are hydroxylated by prolyl hydroxylase enzymes (PHD1-3) to allow for binding to the von Hippel-Lindau (VHL) tumour suppressor protein, which serves as the substrate recognition subunit of an E3-ubiquitin ligase complex that ultimately targets proteins for proteasome-mediated degradation. The work presented in this thesis demonstrates a novel role of VHL in recruiting DCNL1 to initiate E3-ubiquitin ligase enzymatic activity which, in essence, allows for the degradation of HIFalpha to commence. In hypoxia, hydroxylation does not take place and as a result HIFalpha can promote the transactivation of a repertoire of genes that aid in adaptation to hypoxia including one which encodes the glycoprotein hormone erythropoietin (EPO). EPO binds to EPO receptor (EPOR) expressed on erythroid progenitor cells to promote their proliferation and differentiation into red blood cells. An erythroid specific oxygen sensing pathway is elucidated in this thesis wherein EPOR is hydroxylated by PHD3 to promote VHL-mediated degradation in a manner analogous to HIFalpha. Combined, these findings build upon our fundamental understanding of how cells detect and counter hypoxic stress.Ph.D.2017-03-31 00:00:0