Prolyl 4-hydroxylase-1 mediates O₂ signaling during development of Dictyostelium

Development in multicellular organisms is subject to both environmental and internal signals. In Dictyostelium, starvation induces amoebae to form migratory slugs that translocate from subterranean areas to exposed sites, where they culminate to form sessile fruiting bodies. Culmination, thought to be regulated by anterior tip cells, is selectively suppressed by mild hypoxia by a mechanism that can be partially overridden by another environmental signal, overhead light, or genetic activation of protein kinase A. Dictyostelium expresses, in all cells, an O₂-dependent prolyl 4-hydroxylase (P4H1) required for O-glycosylation of Skp1, a subunit of E3^SCF-Ub-ligases. P4H1-null cells differentiate the basic pre-stalk and pre-spore cell types but exhibit a selectively increased O₂ requirement for culmination, from 12% to near or above ambient (21%) levels. Overexpression of P4H1 reduces the O₂ requirement to <5%. The requirement for P4H1 can be met by forced expression of the active enzyme in either pre-stalk (anterior) or pre-spore (posterior) cells, or replaced by protein kinase A activation or addition of small numbers of wild-type cells. P4H1-expressing cells accumulate at the anterior end, suggesting that P4H1 enables transcellular signaling by the tip. The evidence provides novel genetic support for the animal-derived O₂-sensor model of prolyl 4-hydroxylase function, in an organism that lacks the canonical HIF transcriptional factor subunit substrate target that is a feature of animal hypoxic signaling.