Aurora Kinase C Protein

Aurora Kinase C Protein

Overview

<table class="infobox infobox-protein">
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<th class="infobox-header" colspan="2">Aurora Kinase C Protein</th>
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<tr>
<td class="label">Symbol</td>
<td><strong>AURORA-KINASE-C</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Aurora Kinase C</td>
</tr>
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<td class="label">Type</td>
<td>Protein</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/?query=AURORA-KINASE-C" target="_blank">Search UniProt</a></td>
</tr>
</table>

Aurora Kinase C (AURKC) is a serine/threonine protein kinase that plays essential roles in meiotic cell division and is crucial for male and female gametogenesis. While initially characterized as a testis-specific and meiosis-specific kinase, AURKC has also been implicated in various pathological conditions including male infertility, cancer progression, and certain neurodegenerative processes. The protein belongs to the Aurora kinase family, which also includes Aurora Kinase A (AURKA) and Aurora Kinase B (AURKB), each with distinct but overlapping functions in cell division.

Aurora Kinase C Protein

Overview

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">Aurora Kinase C Protein</th>
</tr>
<tr>
<td class="label">Symbol</td>
<td><strong>AURORA-KINASE-C</strong></td>
</tr>
<tr>
<td class="label">Full Name</td>
<td>Aurora Kinase C</td>
</tr>
<tr>
<td class="label">Type</td>
<td>Protein</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/?query=AURORA-KINASE-C" target="_blank">Search UniProt</a></td>
</tr>
</table>

Aurora Kinase C (AURKC) is a serine/threonine protein kinase that plays essential roles in meiotic cell division and is crucial for male and female gametogenesis. While initially characterized as a testis-specific and meiosis-specific kinase, AURKC has also been implicated in various pathological conditions including male infertility, cancer progression, and certain neurodegenerative processes. The protein belongs to the Aurora kinase family, which also includes Aurora Kinase A (AURKA) and Aurora Kinase B (AURKB), each with distinct but overlapping functions in cell division.

The unique expression pattern of AURKC, being primarily restricted to germ cells and certain cancer types, makes it an attractive therapeutic target with potentially limited side effects[@goldenson2015]. Unlike its widely expressed family members AURKA and AURKB, AURKC's meiosis-specific function has generated significant interest in understanding its role in reproductive biology and its potential involvement in diseases characterized by aberrant cell cycle regulation[@nguyen2018]. Research has also begun to explore potential links between AURKC and neurodegenerative conditions, although these associations remain less well characterized than those with cancer and infertility.

Structure

AURKC possesses the characteristic bilobal kinase architecture common to all Aurora kinases, consisting of an N-terminal domain involved in protein-protein interactions and a C-terminal catalytic kinase domain responsible for enzymatic activity[@cheetham2002]. The protein is approximately 309 amino acids in length and shares significant structural homology with AURKA and AURKB, particularly in the catalytic domain where the canonical serine/threonine protein kinase motifs are conserved[@liu2006]. The ATP-binding pocket, located in the cleft between the N and C lobes, contains the characteristic Lys-Gly-Gly-Phe motif and the activation loop that undergoes phosphorylation for catalytic activation.

The C-terminal regulatory region of AURKC contains a destruction box (D-box) and a KEN box, which are recognized by the anaphase-promoting complex/cyclosome (APC/C) ubiquitin ligase for regulated degradation[@visintin2001]. This degradation ensures that AURKC levels fall after meiosis I, allowing proper progression through meiosis II. The N-terminal domain, while less conserved than the catalytic domain, contains docking sites for protein substrates and regulatory partners that confer specificity to AURKC function[@rannou2008]. Additionally, AURKC can form homodimers through its N-terminal domain, a property that may be important for its localization and function at the centrosome and meiotic spindle[@yu2011].

Expression Pattern

AURKC demonstrates a highly restricted expression pattern in normal adult tissues, with the highest levels detected in testis and, to a lesser extent, in thymus[@tsou2011]. Within the testis, AURKC is expressed primarily in spermatogonia, spermatocytes, and round spermatids, with peak expression during the meiotic divisions[@tang2006]. In female tissues, AURKC expression is detected in oocytes, where it participates in meiotic spindle assembly and chromosome segregation during meiosis I and II[@sun2013]. This germ cell-specific expression pattern contrasts sharply with the broader tissue distribution of AURKA and AURKB, which are expressed in proliferating somatic cells throughout the body.

During embryonic development, AURKC expression is more widespread and can be detected in various fetal tissues including brain, lung, and kidney[@aprelikova2005]. This developmental expression pattern suggests that AURKC may play roles in embryonic cell division that are compensated by other Aurora kinases in adult tissues. The reexpression of AURKC in various cancers, including colorectal, breast, and prostate cancers, represents a pathological recurrence of this developmental expression program[@tsou2011a]. Understanding the mechanisms that restrict AURKC expression in normal tissues and those that allow its reexpression in cancer may reveal novel therapeutic opportunities.

Catalytic Mechanism

Activation by Phosphorylation

Like other Aurora kinases, AURKC requires phosphorylation of a conserved threonine residue in its activation loop for full catalytic activity[@walter2000]. The activating phosphorylation site in AURKC corresponds to Thr177, analogous to Thr288 in AURKA and Thr232 in AURKB. Autophosphorylation at this site, likely facilitated by dimerization or trans-autophosphorylation, converts AURKC from a low-activity to a high-activity state capable of phosphorylating substrate proteins[@katagiri2000]. The phosphorylation state of AURKC is dynamically regulated throughout meiosis, with peak activity during metaphase-anaphase transition.

Substrate Specificity

AURKC phosphorylates a subset of substrates shared with AURKB, as well as unique germ cell-specific targets[@demidova2014]. Key substrates include histone H3 (Ser10), which is phosphorylated during chromosome condensation in meiosis, and the chromosomal passenger complex component INCENP, which helps target AURKC to centromeric regions[@varma2010]. Other important substrates include proteins involved in spindle assembly (TPX2, kinesin-5), cytokinesis (MgcRacGAP, Ect2), and centromere function (CENP-A, Borealin)[@goto2003]. The specificity of AURKC for meiotic substrates is determined partly by its unique localization patterns and partly by interaction with testis-specific regulatory proteins.

Function in Meiosis

Spermatogenesis

AURKC is essential for male meiosis and spermatogenesis, as demonstrated by the male infertility phenotype of AURKC-deficient mice and humans[@dieter2012]. During meiosis I, AURKC localizes to centromeres and is required for proper chromosome condensation, spindle attachment, and accurate chromosome segregation. Knockout of AURKC in mice results in arrest at the pachytene stage of meiosis I, failure to proceed to metaphase, and subsequent [apoptosis](/entities/apoptosis) of spermatocytes[@kimmins2004]. These findings demonstrate a non-redundant function of AURKC in male meiosis that cannot be fully compensated by AURKA or AURKB.

The mechanism by which AURKC ensures accurate chromosome segregation in meiosis involves phosphorylation of several key substrates. Phosphorylation of histone H3 at Ser10 promotes chromosome condensation, while phosphorylation of the chromosomal passenger complex components regulates kinetochore-microtubule attachments[@li2004]. AURKC also phosphorylates proteins involved in sister chromatid cohesion, including REC8, which must be cleaved to allow homologous chromosome separation in anaphase I[@lee2009]. These functions ensure that meiosis I proceeds with high fidelity, preventing aneuploidy in haploid gametes.

Oogenesis

In female meiosis, AURKC plays equally important but somewhat distinct roles compared to spermatogenesis[@liu2012]. AURKC is expressed in oocytes and localizes to the meiotic spindle, where it participates in chromosome alignment and segregation during meiosis I and II. Disruption of AURKC function in oocytes leads to metaphase I arrest, abnormal spindle assembly, and chromosome misalignment[@shindo2008]. The importance of AURKC in female meiosis is highlighted by studies showing that AURKC mutations are associated with female infertility in humans, although this phenotype is less severe than in males.

AURKC function in oocytes is regulated by both phosphorylation and protein-protein interactions. The protein forms a chromosomal passenger complex with INCENP, Survivin, and Borealin that targets it to centromeres and regulates its activity during the cell cycle[@ruchaud2007]. During oocyte maturation, AURKC phosphorylation increases dramatically, coinciding with germinal vesicle breakdown and spindle assembly. This activation is essential for proper meiotic progression, and inhibition of AURKC activity blocks oocyte maturation at the germinal vesicle breakdown stage[@uzbekova2009].

Disease Associations

Male Infertility

AURKC mutations represent a significant cause of male infertility, particularly in men with severe oligospermia or azoospermia[@el2015]. Multiple pathogenic mutations have been identified, including missense mutations that reduce kinase activity, nonsense mutations that produce truncated proteins, and splice site mutations that disrupt proper mRNA processing. The most common AURKC mutation in infertile men results in a protein with reduced catalytic activity that cannot properly phosphorylate substrates required for meiotic progression[@fellner2015].

The mechanism of infertility involves impaired spermatogenesis due to defective meiosis I. Spermatocytes with AURKC mutations arrest at the pachytene or metaphase I stage and undergo apoptosis, resulting in decreased numbers of post-meiotic spermatids[@bourchis2008]. Testicular histology in affected individuals shows spermatogenic arrest at the primary spermatocyte stage, with occasional presence of vacuolized seminiferous tubules. The specificity of AURKC mutations for male infertility, compared to other Aurora kinases, reflects the non-redundant function of AURKC in male meiosis that cannot be compensated by AURKA or AURKB[@ben2011].

Cancer

Aberrant expression of AURKC has been documented in multiple cancer types, including colorectal cancer, breast cancer, prostate cancer, and non-small cell lung cancer[@tsou2011b][@khan2015]. In these cancers, AURKC expression is associated with increased proliferation, genomic instability, and poor prognosis. The reexpression of AURKC in somatic cancers appears to involve demethylation of the AURKC promoter or loss of transcriptional repressors that normally silence AURKC in adult somatic tissues[@xu2015].

Functional studies demonstrate that AURKC can promote cancer cell proliferation and survival through phosphorylation of oncogenic substrates. AURKC contributes to cell cycle progression by phosphorylating proteins involved in chromosome segregation and cytokinesis, and can also enhance cell survival by inhibiting apoptotic pathways[@ditchfield2003]. Additionally, AURKC expression may contribute to chemotherapy resistance in some cancer types, making it an attractive target for combination therapy approaches.

Neurodegeneration

Emerging evidence suggests potential links between AURKC and neurodegenerative processes, although these associations are less well established than for cancer and infertility[@liu2012a]. The observation that AURKC can be expressed in certain neuronal populations under pathological conditions raises the possibility that dysregulated AURKC activity could contribute to aberrant cell cycle re-entry in [neurons](/entities/neurons), a phenomenon associated with [Alzheimer's disease](/diseases/alzheimers-disease) and other neurodegenerative conditions. However, more research is needed to establish the significance of AURKC in neurodegeneration.

Therapeutic Implications

The restricted expression pattern of AURKC in normal tissues makes it an attractive therapeutic target for male infertility and cancer treatment[@liu2014]. In male infertility, small molecule activators of AURKC could potentially enhance meiotic progression and improve sperm production. Several AURKC-specific activators have been identified that promote AURKC autophosphorylation and activity in vitro[@fancelli2006]. However, delivering these compounds to the testes while avoiding systemic side effects remains a significant challenge.

In cancer therapy, AURKC represents a potential target for Aurora kinase inhibitors that are currently in clinical development[@dar2007]. While these inhibitors primarily target AURKA and AURKB, some have significant activity against AURKC as well. The expression of AURKC in cancer but not in most normal tissues suggests that AURKC inhibition could provide therapeutic benefit with reduced toxicity compared to targeting more widely expressed Aurora kinases[@goh2015]. Clinical trials of Aurora kinase inhibitors in AURKC-expressing cancers are ongoing to evaluate this hypothesis.

Key Publications

Cross-links

• [AURKC Gene](/genes/aurkc)
• [Cell Cycle](/mechanisms/cell-cycle-arrest)
• [Meiosis](/mechanisms/meiosis)
• [Male Infertility](/diseases/male-infertility)
• [Cancer Biology](/mechanisms/onco-neurobiology)
• [Spermatogenesis](/mechanisms/spermatogenesis)

See Also

• [Cell Cycle](/mechanisms/cell-cycle-arrest)
• [Meiosis](/mechanisms/meiosis)
• [Male Infertility](/diseases/male-infertility)
• [Cancer Biology](/mechanisms/onco-neurobiology)
• [Spermatogenesis](/mechanisms/spermatogenesis)

External Links

• [PubMed](https://pubmed.ncbi.nlm.nih.gov/)
• [KEGG Pathways](https://www.genome.jp/kegg/pathway.html)

References