SPC25

SPC25 is a core subunit of the NDC80 kinetochore complex that functions in chromosome alignment, spindle assembly, and spindle checkpoint signaling during cell division, and additionally serves as a scaffolding platform for oncogenic signaling complexes in multiple cancer contexts. At the kinetochore, SPC25 partners with NDC80, NUF2, and SPC24 to ensure faithful chromosome segregation; its perturbation in mouse oocytes causes spindle disruption and chromosome misalignment (PMID:21084868), and the SPC25/NUF2 interaction drives cancer cell proliferation and glycolysis (PMID:39755832). Beyond mitosis, SPC25 assembles a trimeric SPC25/RIOK1/MYH9 complex that activates Wnt/β-catenin signaling through RIOK1-mediated phosphorylation of MYH9, promoting cancer stemness and platinum resistance (PMID:39488790), and it stabilizes E2F1 by blocking MDM2-mediated ubiquitination, thereby upregulating CCND1 (PMID:39919356). SPC25 expression is transcriptionally activated by E2F8 and TFDP1, linking its regulation to cell-cycle transcription factor networks, and its downstream effects include activation of FAK/PI3K/AKT and DNA-PK/AKT/Notch1 cascades, promotion of glycolysis, suppression of ferroptosis, and modulation of anti-tumor immunity through glutamine metabolism (PMID:39829079, PMID:36147467, PMID:39558547).

1. 2010 Medium

   Establishing SPC25 as a functional NDC80 complex subunit required for chromosome alignment and spindle checkpoint signaling resolved its role in cell division beyond sequence-based complex assignment.

   Evidence Overexpression and siRNA knockdown in mouse oocytes with immunofluorescent spindle/chromosome phenotyping

   PMID:21084868

   Open questions at the time

   • Role in somatic mitosis not directly tested
   • Structural basis of SPC25 integration into the NDC80 complex not resolved
   • Whether SPC25 has functions independent of the NDC80 complex was unknown
2. 2022 Medium

   Identification of SPC25 as an activator of FAK/PI3K/AKT signaling through ITGB4 upregulation and of DNA-PK/AKT/Notch1 signaling targeting SOX2/NANOG revealed extra-kinetochore oncogenic functions in hepatocellular carcinoma.

   Evidence siRNA silencing, microarray profiling, ITGB4 rescue, Western blotting, in vivo models, and transcriptional assays in HCC cell lines

   PMID:35293598 PMID:36147467

   Open questions at the time

   • Direct physical interaction between SPC25 and ITGB4 or DNA-PK not demonstrated
   • Whether these pathways operate simultaneously or context-dependently is unclear
   • Mechanism by which a kinetochore protein reaches integrin/AKT signaling nodes not explained
3. 2024 High

   Reconstitution of a trimeric SPC25/RIOK1/MYH9 complex with a defined phosphorylation event (MYH9 Ser1943) driving nuclear MYH9 accumulation and Wnt/β-catenin activation established SPC25 as a bona fide signaling scaffold, not merely a kinetochore structural component.

   Evidence Co-IP of trimeric complex, phosphorylation site mapping, nuclear fractionation, competitive inhibitory peptide (CBP1), patient-derived organoids, and in vivo models in epithelial ovarian cancer

   PMID:39488790

   Open questions at the time

   • Whether the trimeric complex assembles at kinetochores or in the cytoplasm is unresolved
   • Structural details of SPC25-RIOK1 and SPC25-MYH9 binding interfaces are lacking
   • Generalizability of the CBP1 peptide disruption strategy to other cancer types untested
4. 2024 Medium

   Demonstration that SPC25 promotes aerobic glycolysis (Warburg effect) and that this glycolytic activity suppresses ferroptosis expanded its metabolic functions beyond signaling pathway activation.

   Evidence Seahorse XF metabolic flux analysis, glucose uptake/lactate assays, lipid ROS and Fe²⁺ measurement, 2-DG rescue in prostate cancer cells

   PMID:39558547

   Open questions at the time

   • Direct molecular target through which SPC25 enhances glycolysis is not identified
   • Whether ferroptosis suppression is relevant in non-cancer cells is unknown
5. 2025 Medium

   Discovery that SPC25 stabilizes E2F1 by physically blocking MDM2-mediated ubiquitination, with downstream CCND1 upregulation, provided a direct protein-level mechanism for SPC25's pro-proliferative effects distinct from kinase cascade activation.

   Evidence Ubiquitination assays, MDM2 binding assays, CCND1 rescue, in vitro and in vivo esophageal squamous cell carcinoma models

   PMID:39919356

   Open questions at the time

   • Binding site on MDM2 and whether SPC25 competes with E2F1 for the same interface are unresolved
   • Whether SPC25-MDM2 interaction occurs in non-cancer cell cycle contexts is untested
6. 2025 Medium

   Identification of E2F8 and TFDP1 as direct transcriptional activators of SPC25, coupled with SPC25-driven glutamine metabolism and NK cell immune evasion, placed SPC25 within a cell-cycle transcription factor–metabolic immunity circuit.

   Evidence ChIP and dual-luciferase reporter assays for promoter binding, glutamine metabolism measurements, NK cell co-culture and flow cytometry in lung adenocarcinoma

   PMID:39829079 PMID:40552366

   Open questions at the time

   • Whether E2F8 and TFDP1 cooperate on the SPC25 promoter or act independently is unresolved
   • Specific glutamine metabolic enzyme(s) regulated by SPC25 not identified
   • NK cell immune evasion mechanism downstream of glutamine metabolism remains indirect
7. 2025 Medium

   Confirmation of a functional SPC25/NUF2 axis outside the kinetochore context—driving NSCLC growth, invasion, and glycolysis—showed that NDC80 sub-complex interactions are co-opted in cancer signaling.

   Evidence Co-IP, FISH, NUF2 overexpression rescue of SPC25 knockdown, xenograft models in NSCLC

   PMID:39755832

   Open questions at the time

   • Whether SPC25/NUF2 cancer function requires the full NDC80 tetramer or operates as a dimer is unknown
   • Downstream effectors of the SPC25/NUF2 glycolytic axis not molecularly defined

• The mechanism by which a kinetochore protein accesses cytoplasmic and nuclear signaling compartments to scaffold diverse oncogenic complexes remains structurally and spatiotemporally undefined.
• No structural model of SPC25 outside the NDC80 complex context exists
• Cell-cycle phase dependency of extra-kinetochore SPC25 functions is unexplored
• Whether interphase SPC25 pools are regulated by degradation or sequestration is unknown