Role of the Skp1 prolyl-hydroxylation/glycosylation pathway in oxygen dependent submerged development of Dictyostelium
1 Department of Biochemistry and Molecular Biology, Oklahoma Center for Medical Glycobiology, University of Oklahoma Health Sciences Center, 975 NE 10th St., BRC 413, OUHSC, Oklahoma City, OK, 73104, USA
2 current address: Department of Molecular Microbiology, Washington University Medical School Campus, Box 8230, 660 South Euclid Avenue, St. Louis, MO, 63110, USA
BMC Developmental Biology 2012, 12:31 doi:10.1186/1471-213X-12-31Published: 25 October 2012
Oxygen sensing is a near universal signaling modality that, in eukaryotes ranging from protists such as Dictyostelium and Toxoplasma to humans, involves a cytoplasmic prolyl 4-hydroxylase that utilizes oxygen and α-ketoglutarate as potentially rate-limiting substrates. A divergence between the animal and protist mechanisms is the enzymatic target: the animal transcriptional factor subunit hypoxia inducible factor-α whose hydroxylation results in its poly-ubiquitination and proteasomal degradation, and the protist E3SCFubiquitin ligase subunit Skp1 whose hydroxylation might control the stability of other proteins. In Dictyostelium, genetic studies show that hydroxylation of Skp1 by PhyA, and subsequent glycosylation of the hydroxyproline, is required for normal oxygen sensing during multicellular development at an air/water interface. Because it has been difficult to detect an effect of hypoxia on Skp1 hydroxylation itself, the role of Skp1 modification was investigated in a submerged model of Dictyostelium development dependent on atmospheric hyperoxia.
In static isotropic conditions beneath 70-100% atmospheric oxygen, amoebae formed radially symmetrical cyst-like aggregates consisting of a core of spores and undifferentiated cells surrounded by a cortex of stalk cells. Analysis of mutants showed that cyst formation was inhibited by high Skp1 levels via a hydroxylation-dependent mechanism, and spore differentiation required core glycosylation of Skp1 by a mechanism that could be bypassed by excess Skp1. Failure of spores to differentiate at lower oxygen correlated qualitatively with reduced Skp1 hydroxylation.
We propose that, in the physiological range, oxygen or downstream metabolic effectors control the timing of developmental progression via activation of newly synthesized Skp1.