Combinatorial regulation by ERK1/2 and CK1 protein kinases leads to HIF-1 association with microtubules and facilitates its symmetrical distribution during mitosis

Hypoxia-inducible factor-1 (HIF-1) is the key transcriptional mediator of the cellular response to hypoxia and is also involved in cancer progression. Regulation of its oxygen-sensitive HIF-1 alpha subunit involves post-translational modifications that control its stability, subcellular localization, and activity. We have previously reported that phosphorylation of the HIF-1 alpha C-terminal domain by ERK1/2 promotes HIF-1 alpha nuclear accumulation and stimulates HIF-1 activity while lack of this modification triggers HIF-1 alpha nuclear export and its association with mitochondria. On the other hand, modification of the N-terminal domain of HIF-1 alpha by CK1 delta impairs HIF-1 activity by obstructing the formation of a HIF-1 alpha/ARNT heterodimer. Investigation of these two antagonistic events by expressing double phospho-site mutants in HIF1A-/- cells under hypoxia revealed independent and additive phosphorylation effects that can create a gradient of HIF-1 alpha subcellular localization and transcriptional activity. Furthermore, modification by CK1 delta caused mitochondrial release of the non-nuclear HIF-1 alpha form and binding to microtubules via its N-terminal domain. In agreement, endogenous HIF-1 alpha could be shown to co-localize with mitotic spindle microtubules and interact with tubulin, both of which were inhibited by CK1 delta silencing or inhibition. Moreover, CK1 delta expression was necessary for equal partitioning of mother cell-produced HIF-1 alpha to the daughter cell nuclei at the end of mitosis. Overall, our results suggest that phosphorylation by CK1 delta stimulates the association of non-nuclear HIF-1 alpha with microtubules, which may serve as a means to establish a symmetric distribution of HIF-1 alpha during cell division under low oxygen conditions.