TTC28

TTC28 is a tetratricopeptide repeat (TPR) protein that regulates microtubule dynamics during cell division and thereby safeguards chromosomal stability (PMID:29738714, PMID:39630868). Through its TPR motifs, TTC28 binds the intracellular domain of the atypical cadherin Dchs1b, an interaction that controls its subcellular distribution; in zebrafish, excess Ttc28 impairs embryonic cleavage and reduces microtubule turnover, while loss of ttc28 increases turnover and suppresses the cleavage furrow and midzone microtubule defects of dchs1b mutants, placing TTC28 within an Aurora B–sensitive pathway governing cytokinesis (PMID:29738714). In human cancer cells, TTC28 levels are set by chaperone-mediated and microautophagy: its TPR domains bind the C-terminal PTIEEVD motif of HSPA8 (Hsc70) and it engages LAMP2A, routing the protein for degradation; TTC28 loss triples micronucleus frequency and elevates DNA damage markers, while re-expression rescues this, establishing TTC28 as a regulator of mitosis and cytokinesis whose autophagic turnover modulates chromosomal instability (PMID:39630868). Independently of its protein function, the TTC28 genomic locus harbors an active LINE-1 retrotransposon that undergoes frequent somatic 3' transduction events in colorectal and ovarian cancers (PMID:24553397, PMID:29032825).

1. 2014 Medium

   Before this work it was unclear which genomic loci act as active LINE-1 source elements in human tumors; this study established the TTC28 locus as a recurrent source of somatic L1-mediated 3' transductions, defining a cancer-relevant genomic property of the gene independent of its protein function.

   Evidence Deep whole-genome sequencing of 92 colorectal tumor-normal pairs with PCR validation of insertion events

   PMID:24553397

   Open questions at the time

   • Does not address the function of the TTC28 protein
   • Mechanism linking L1 activation at this locus to tumorigenesis not established
2. 2017 Medium

   It was unknown whether TTC28-L1 transposition was confined to colorectal cancer or occurred early in tumor evolution; clonal transduction events across multiple tumor samplings showed TTC28 L1 activation occurs early in ovarian carcinoma development and extends beyond colorectal cancer.

   Evidence Whole genome sequencing with PCR and capillary sequencing validation across multiple anatomical tumor sites in endometrioid and clear cell ovarian carcinomas

   PMID:29032825

   Open questions at the time

   • Functional consequence of transduction events on tumor biology not determined
   • No link to the TTC28 protein's role
3. 2018 High

   The molecular function of the TTC28 protein was uncharacterized; this work showed Ttc28 binds the atypical cadherin Dchs1b via its TPR motifs and regulates microtubule turnover, cleavage, and midzone microtubule assembly, defining a Dchs1b–Ttc28 axis controlling cell division.

   Evidence Co-IP/pulldown, maternal-zygotic zebrafish mutants, gain- and loss-of-function, Aurora B inhibitor sensitivity, and genetic epistasis (double-mutant rescue)

   PMID:29738714

   Open questions at the time

   • Direct biochemical link between Ttc28 and microtubules not resolved
   • Relationship to Aurora B is inferred from inhibitor sensitivity, not direct binding
   • Human/mammalian relevance not tested in this study
4. 2024 High

   How TTC28 levels are controlled and whether it functions in chromosomal stability in human cells was unknown; this study showed TTC28 binds HSPA8 (via the PTIEEVD motif) and LAMP2A and is degraded by chaperone-mediated autophagy, with TTC28 loss tripling micronucleus frequency, establishing it as an autophagy-regulated guardian of chromosomal stability acting through mitosis and cytokinesis.

   Evidence Reciprocal Co-IP defining domain-level binding, TTC28 knockout and rescue in cancer cells, micronuclei quantification, γH2AX and comet assays, TCGA analysis

   PMID:39630868

   Open questions at the time

   • Direct substrate or molecular effector of TTC28 in mitosis not identified
   • How TTC28 mechanistically influences cytokinesis at the molecular level unresolved
   • Structural basis of TPR–PTIEEVD binding not determined
5. 2025 Medium

   This follow-up reinforced that CMA-mediated degradation through the TTC28–HSPA8 axis is the master regulator of TTC28 levels and that its downregulation drives chromosomal instability in cancer.

   Evidence Serial functional experiments and bioinformatics (follow-up/commentary on the 2024 study)

   PMID:39893561

   Open questions at the time

   • Single-lab follow-up adding conceptual confirmation rather than new orthogonal evidence
   • Does not resolve the downstream molecular target of TTC28
6. 2025 Medium

   Whether the Dchs1b–Ttc28 axis acts beyond cleavage stages was unknown; loss of ttc28 was shown to suppress epiboly and yolk-cell microtubule dynamics defects of dchs1b mutants, extending the regulatory axis into gastrulation.

   Evidence Genetic epistasis (dchs1b/ttc28 double mutants), Dchs1b-GFP knock-in, live microtubule imaging, transcriptomics (preprint)

   PMID:40463075

   Open questions at the time

   • Preprint, single-lab and not peer-reviewed
   • Direct effect of Ttc28 on microtubule polymerization not biochemically demonstrated

• The direct molecular effector through which TTC28 modulates microtubule dynamics and cytokinesis, and whether its developmental function in zebrafish and its CMA-regulated tumor-suppressive role in human cells reflect one unified mechanism, remain unresolved.
• No identified direct microtubule-binding or regulatory substrate
• No structural model of TTC28
• Integration of developmental and oncogenic/genome-stability roles not established