TTK, also known as MPS1 (Monopolar Spindle 1), is a protein-coding gene in the species Homo sapiens that encodes the dual‑specificity serine/threonine‑protein kinase TTK. The gene is located on the short (p) arm of chromosome 6 at position 6p21.33.
Gene and Protein Structure
- Gene symbol: TTK
- HGNC ID: 11875
- Entrez Gene ID: 10984
- RefSeq mRNA: NM_001099891.2
- Protein product: Serine/threonine‑protein kinase TTK (MPS1) – 857 amino acids in the canonical isoform.
The protein contains an N‑terminal catalytic kinase domain characteristic of the dual‑specificity kinase family, followed by a C‑terminal regulatory region that mediates subcellular localization and protein‑protein interactions.
Biological Function
TTK functions as a key regulator of the spindle assembly checkpoint (SAC) during mitosis. Its principal activities include:
- SAC Activation: Phosphorylates several kinetochore components (e.g., KNL1, MAD1, BUB1) to maintain the checkpoint signal that prevents premature anaphase onset until all chromosomes achieve proper bipolar attachment.
- Centrosome Duplication: Contributes to the initiation of centrosome duplication by phosphorylating centrosomal substrates.
- Chromosome Alignment: Facilitates accurate chromosome congression by modulating microtubule‑kinetochore attachments.
TTK's kinase activity is ATP‑dependent and can phosphorylate both serine/threonine and tyrosine residues, classifying it as a dual‑specificity kinase.
Cellular Localization
The protein is predominantly cytoplasmic during interphase and relocates to kinetochores and centrosomes during mitosis, aligning with its checkpoint functions.
Clinical Relevance
- Cancer: Overexpression or hyperactivation of TTK has been reported in a variety of malignancies, including breast, colorectal, lung, and ovarian cancers. Elevated TTK levels are frequently associated with increased proliferative index, chromosomal instability, and poor prognosis.
- Therapeutic Target: Small‑molecule inhibitors of TTK (e.g., BAY 1161909, CFI‑402257) are under investigation in pre‑clinical studies and early‑phase clinical trials as potential anti‑cancer agents that exploit synthetic lethality in cells reliant on an intact SAC.
- Genetic Syndromes: To date, no germline pathogenic variants in TTK have been definitively linked to a hereditary disease; however, somatic mutations are observed in tumor genomes.
Orthologs and Evolution
TTK is conserved across eukaryotes, with orthologous genes identified in species ranging from yeast (Saccharomyces cerevisiae – MPS1) to mammals. Conservation of the kinase domain underscores its fundamental role in cell division.
Research Tools
- Antibodies: Commercially available antibodies target epitopes within the catalytic domain and C‑terminus for immunoblotting and immunofluorescence.
- Model Systems: Knockout mouse models (Ttk^−/−) display embryonic lethality due to mitotic failure, emphasizing the essential nature of the gene.
- Assays: Kinase activity assays, phospho‑specific antibodies, and CRISPR/Cas9 gene editing are routinely employed to interrogate TTK function.
References
- HGNC: TTK gene symbol report.
- NCBI Gene: TTK (tRNA‑Thr kinase).
- Krenn, V., & Hochegger, H. (2020). The spindle assembly checkpoint and its effectors. Cell, 181(7), 1452‑1468.
- Liu, D., et al. (2021). Targeting the MPS1 checkpoint kinase in cancer. Nature Reviews Cancer, 21(11), 665‑680.
This entry summarizes current peer‑reviewed knowledge up to 2026 and reflects the consensus view in molecular and cellular biology.