ENZYMES INVOLVED IN HYPOXIA RESPONSE, ACTA UNIVERSITATIS OULUENSIS D Medica 1055

Oxygen homeostasis is critical to all animals, as both excess (hyperoxia) and reduced (hypoxia)\nlevels of oxygen can result in pathological changes and ultimately in the loss of cellular and\norganismal viability. Complex systems have evolved to sense and adapt to changes in cellular\noxygen availability, and the hypoxia-inducible factor HIF plays a pivotal role in this elaborate\nmolecular network. In normoxic conditions the á-subunit of HIF becomes hydroxylated by HIF\nprolyl 4-hydroxylases (HIF-P4Hs 1-3), earmarking HIF-á for proteasomal degradation.\nAdditionally, in the presence of oxygen the hydroxylation of an asparagine residue by the HIF\nasparaginyl hydroxylase FIH inhibits the transactivation of HIF-target genes by blocking the\ninteraction of HIF-á with a transcriptional coactivator. In addition to being a feature of an\norganism’s normal life, hypoxia is also characteristic of many common diseases such as severe\nanemia and myocardial infarction, and it notably decreases these hydroxylation reactions, as HIFP4Hs\nand FIH have an absolute requirement for oxygen as a cosubstrate. HIF-á thus escapes\ndegradation and translocates into the nucleus, where it dimerizes with HIF-â and recruits\ntranscriptional coactivators to the hypoxia-response elements of target genes, inducing their\ntranscription and triggering the hypoxia response aimed at restoring cellular oxygen homeostasis.\nIn this study we generated a genetically modified HIF-P4H-2 hypomorphic mouse line that\nexpresses only 8% of the wild-type HIF-P4H-2 mRNA in the heart. We showed that chronic\ncardiac HIF-P4H-2 deficiency leads to stabilization of HIF-1á and HIF-2á and protects the heart\nagainst acute ischemia-reperfusion injury without causing any adverse effects.\nFurthermore, we identified and cloned a novel human transmembrane prolyl 4-hydroxylase\nP4H-TM and showed that it regulates HIF-1á protein levels in cellulo and hydroxylates HIF-1á in\nvitro similarly to the HIF-P4Hs, but may also have other physiological substrates. Using forward\ngenetic tools we showed that lack of P4H-TM during development leads to basement membrane\ndefects and compromised kidney function in zebrafish embryos.\nFinally, we demonstrated that FIH displays substrate selectivity in terms of hydroxylation and\nbinding of HIF-1á and novel substrates Notch1-3. We showed that FIH has higher affinity for\noxygen with Notch1 than with HIF-1á as a substrate, implying that FIH-mediated hydroxylation\nof Notch can continue in oxygen concentrations where HIF-1á hydroxylation would be markedly\nreduced.

ISBN-10:
978-951-42-6193-0
Kieli:
eng.
Sivumäärä:
184 s.
Tekijät:
Hyvärinen Jaana
Tuotekoodi 013971
22,50 €