Polo-like kinase 3 (PLK3), encoded by the PLK3 gene on human chromosome 10q24, is a serine/threonine protein kinase belonging to the polo-like kinase family. This family of evolutionarily conserved enzymes regulates critical cellular processes including cell cycle progression, DNA damage responses, and centrosome function. PLK3 is structurally characterized by an N-terminal kinase domain and a C-terminal polo-box domain (PBD), which serves as a protein-protein interaction module. Unlike its more extensively studied homolog PLK1, PLK3 demonstrates broader tissue distribution and plays specialized roles in stress responses and genomic stability maintenance. The protein is expressed at relatively low levels in most tissues but shows enriched expression in the nervous system, making it particularly relevant to neurobiological processes.
Function/Biology
PLK3 functions as a multifaceted signaling hub responding to cellular stress signals, particularly DNA damage and mitotic checkpoint activation. The kinase phosphorylates numerous substrates involved in checkpoint control, including p53-binding protein 1 (53BP1) and other DNA damage response mediators. In the context of the cell cycle, PLK3 regulates G2/M checkpoint integrity by modulating checkpoint kinase signaling pathways. The polo-box domain enables PLK3 to recognize phosphorylated serine/threonine motifs on target proteins, facilitating substrate specificity and localization to damage sites or centrosomes.
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PLK3 Protein
Overview
Polo-like kinase 3 (PLK3), encoded by the PLK3 gene on human chromosome 10q24, is a serine/threonine protein kinase belonging to the polo-like kinase family. This family of evolutionarily conserved enzymes regulates critical cellular processes including cell cycle progression, DNA damage responses, and centrosome function. PLK3 is structurally characterized by an N-terminal kinase domain and a C-terminal polo-box domain (PBD), which serves as a protein-protein interaction module. Unlike its more extensively studied homolog PLK1, PLK3 demonstrates broader tissue distribution and plays specialized roles in stress responses and genomic stability maintenance. The protein is expressed at relatively low levels in most tissues but shows enriched expression in the nervous system, making it particularly relevant to neurobiological processes.
Function/Biology
PLK3 functions as a multifaceted signaling hub responding to cellular stress signals, particularly DNA damage and mitotic checkpoint activation. The kinase phosphorylates numerous substrates involved in checkpoint control, including p53-binding protein 1 (53BP1) and other DNA damage response mediators. In the context of the cell cycle, PLK3 regulates G2/M checkpoint integrity by modulating checkpoint kinase signaling pathways. The polo-box domain enables PLK3 to recognize phosphorylated serine/threonine motifs on target proteins, facilitating substrate specificity and localization to damage sites or centrosomes.
PLK3 also participates in centrosome-associated functions, including centriole duplication and centrosome maturation. Through interactions with centrosomal proteins and regulators of the Aurora A kinase pathway, PLK3 helps coordinate proper spindle apparatus formation. Additionally, PLK3 exhibits roles in cilia-related processes and vesicular trafficking, suggesting broader cytoplasmic functions beyond cell cycle regulation.
Role in Neurodegeneration
PLK3 emerging significance in neurodegeneration stems from its involvement in protein quality control mechanisms and neuronal stress responses. Dysfunction in PLK3-mediated pathways has been implicated in several neurodegenerative conditions characterized by proteostatic collapse and mitochondrial dysfunction. In Parkinson's disease contexts, PLK3 interacts with PINK1 (PTEN-induced kinase 1), a key regulator of mitophagy—the selective autophagy of damaged mitochondria. This interaction facilitates proper clearance of dysfunctional mitochondria, preventing accumulation of oxidative-damaged organelles that drive neuronal toxicity.
PLK3 also phosphorylates and stabilizes p53, promoting apoptosis or cell cycle arrest in neurons with irreparable damage. While protective in limiting propagation of pathological changes, excessive PLK3-mediated apoptosis contributes to neuronal loss in conditions featuring heightened cellular stress. Age-related decline in PLK3 expression and kinase activity may compromise mitochondrial quality control in aging neurons, potentially predisposing to late-onset neurodegeneration.
Molecular Mechanisms
At the molecular level, PLK3 integrates stress signals through upstream kinases including ATM (ataxia telangiectasia mutated) and checkpoint kinase pathways. Upon DNA damage detection or mitochondrial dysfunction, PLK3 undergoes autophosphorylation and relocalization to sites of damage or compromised mitochondria. The kinase phosphorylates multiple substrates in tandem: stabilizing p53 through inhibition of MDM2-mediated ubiquitination, activating autophagy-associated proteins like ULK1, and promoting PINK1-dependent mitophagy initiation.
In mitochondrial contexts, PLK3 phosphorylates PINK1 at specific sites, enhancing its kinase activity and recruitment of E3 ubiquitin ligase Parkin to depolarized mitochondria. This kinase cascade triggers polyubiquitination of outer membrane proteins, marking mitochondria for autophagic degradation. PLK3 additionally modulates mTOR signaling and AMPK pathway components, connecting energy status with autophagy induction.
Clinical/Research Significance
PLK3 represents an emerging therapeutic target for neurodegenerative disease intervention. Enhanced PLK3 activity or stabilization could augment mitochondrial quality control in Parkinson's disease and related conditions. Conversely, PLK3 inhibition may be therapeutically relevant in conditions featuring excessive neuronal apoptosis. Current research employs PLK3 knockout animal models to characterize long-term consequences of PLK3 deficiency on neuronal survival and function.
Related Entities
PLK1, PLK2, PLK4: Other polo-like kinase family members with distinct cellular functions
PINK1/Parkin: Mitophagy pathway components interacting with PLK3
p53: Tumor suppressor substrate of PLK3 with neuroprotective implications
Mitochondrial quality control: Broader cellular process involving PLK3
Neuroinflammation: Potential PLK3 role in microglial activation responses