Plk3 Functions as an Essential Component of the Hypoxia Regulatory Pathway by Direct Phosphorylation of HIF-1α

Abstract

Polo-like kinase 3 (Plk3) plays an important role in the regulation of cell cycle progression and stress responses. Plk3 also has a tumor-suppressing activity as aging PLK3-null mice develop tumors in multiple organs. The growth of highly vascularized tumors in PLK3-null mice suggests a role for Plk3 in angiogenesis and cellular responses to hypoxia. By studying primary isogenic murine embryonic fibroblasts, we tested the hypothesis that Plk3 functions as a component in the hypoxia signaling pathway. PLK3 ؊/؊ murine embryonic fibroblasts contained an enhanced level of HIF-1␣ under hypoxic conditions. Immunoprecipitation and pulldown analyses revealed that Plk3 physically interacted with HIF-1␣ under hypoxia. Purified recombinant Plk3, but not a kinase-defective mutant, phosphorylated HIF-1␣ in vitro, resulting in a major mobility shift. Mass spectrometry identified two unique serine residues that were phosphorylated by Plk3. Moreover, ectopic expression followed by cycloheximide or pulse-chase treatment demonstrated that phospho-mutants exhibited a much longer halflife than the wild-type counterpart, strongly suggesting that Plk3 directly regulates HIF-1␣ stability in vivo. Combined, our study identifies Plk3 as a new and essential player in the regulation of the hypoxia signaling pathway.

Transcription Factor YY1 Contributes to Tumor Growth by Stabilizing Hypoxia Factor HIF-1α in a p53-Independent Manner

“…S8H and S8I), indicating that the regulation of HIF-1a degradation induced by YY1 silencing occurs mainly not through the hydroxylation of proline 564. Indeed, recent reports showed that besides hydroxylation, regulation of HIF-1a protein is also mediated by multiple modification pathways (5), such as phosphorylation, SUMOylation, and degradation in cytosol (28)(29)(30)(31). Whether YY1 silencing mediated HIF-1a regulation occurs through one of these pathways, or through other pathways, which has not been reported, requires further detailed investigations.…”

CDK1 stabilizes HIF-1α via direct phosphorylation of Ser668 to promote tumor growth

“…The Ser657 site was previously identified as a target of PLK3, and mutation of this residue to an Ala enhances the stability of HIF-1α. 19 Therefore, we focused on the other candidate site, Ser668. Sequence alignment revealed that the Ser668 residue is highly conserved in lower species, indicating that it may be of functional importance to HIF-1α (Fig.…”

“…16 It has also been reported that phosphorylation by glycogen synthase kinase 3 (GSK3) and Polo-like kinase 3 (PLK3) promote HIF-1α degradation, while binding to the cellular chaperone, HSP90, stabilizes HIF-1α. [17][18][19] Thus, HIF-1α expression and the transcriptional activation of HIF-1 are controlled by both oxygen-dependent and oxygen-independent mechanisms in response to extracellular stimuli and the conditions of the cellular microenvironment. The identification of novel mechanisms that regulate HIF-1α expression is extremely valuable in the effort to understand tumor progression as well as to target HIF-1 as an anti-cancer therapeutic strategy.…”

Cyclin-dependent kinases regulate lysosomal degradation of hypoxia-inducible factor 1α to promote cell-cycle progression

“…HIF-2, which is composed of HIF-2α and HIF-1β subunits, is regulated by oxygen in a similar manner, although HIF-2 has a more limited tissue distribution and in some cases regulates distinct target genes (15). Mechanisms by which HIF-1α is regulated in an O 2 -independent manner have also been identified (16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26). In addition to proteasome-dependent pathways for HIF-1α degradation, we identified a pathway by which HIF-1α can be targeted for lysosomal degradation through chaperonemediated autophagy (27), which subsequently was confirmed by others (28)(29)(30).…”