MAPping tubulin mutations

MAP7 drives EMT and cisplatin resistance in ovarian cancer via wnt/β-catenin signaling

Methods

Our approach encompasses analyzing MAP7's expression levels across various datasets and clinical specimens, evaluating its association with patient outcomes, and probing its influence on ovarian cancer cell dynamics such as proliferation, migration, invasion, and apoptosis.

Results

We have identified significant upregulation of MAP7 in ovarian cancer tissues, which correlates with advanced disease stages, higher pathological grades, and unfavorable prognoses. Functionally, the inhibition of MAP7 suppresses cancer cell proliferation, migration, and invasion while promoting apoptosis. Notably, the silencing of MAP7 attenuates the epithelial-mesenchymal transition (EMT) and disrupts Wnt/β-catenin pathway signaling-two critical processes implicated in metastasis and chemoresistance. In cisplatin-resistant A2780-DDP cells, the downregulation of MAP7 effectively reverses their resistance to cisplatin. Furthermore, the nuclear localization of MAP7 in these cells underscores its pivotal role in driving cisplatin resistance by modulating the transcriptional regulation and interaction dynamics of β-catenin.

Conclusion

Our findings position MAP7 as a pivotal element in ovarian cancer advancement and cisplatin resistance, primarily through its modulation of EMT and the Wnt/β-catenin pathway. Its association with poor clinical outcomes underscores its potential as both a prognostic marker and a therapeutic target. Strategies aimed at MAP7 could represent a new frontier in combating chemotherapy resistance in ovarian cancer, emphasizing its significance in crafting complementary treatments for this disease.

Loss-of-function of kinesin-5 KIF11 causes microcephaly, chorioretinopathy, and developmental disorders through chromosome instability and cell cycle arrest

Kinesin motors play a fundamental role in development by controlling intracellular transport, spindle assembly, and microtubule organization. In humans, patients carrying mutations in KIF11 suffer from an autosomal dominant inheritable disease called microcephaly with or without chorioretinopathy, lymphoedema, or mental retardation (MCLMR). While mitotic functions of KIF11 proteins have been well documented in centrosome separation and spindle assembly, cellular mechanisms underlying KIF11 dysfunction and MCLMR remain unclear. In this study, we generate KIF11-inhibition chick and zebrafish models and find that KIF11 inhibition results in microcephaly, chorioretinopathy, and severe developmental defects in vivo. Notably, loss-of-function of KIF11 causes the formation of monopolar spindle and chromosome misalignment, which finally contribute to cell cycle arrest, chromosome instability, and cell death. Our results demonstrate that KIF11 is crucial for spindle assembly, chromosome alignment, and cell cycle progression of progenitor stem cells, indicating a potential link between polyploidy and MCLMR. Our data have revealed that KIF11 inhibition cause microcephaly, chorioretinopathy, and development disorders through the formation of monopolar spindle, polyploid, and cell cycle arrest.

Tubulin CFEOM mutations both inhibit or activate kinesin motor activity

Kinesin-mediated transport along microtubules is critical for axon development and health. Mutations in the kinesin Kif21a, or the microtubule subunit β-tubulin, inhibit axon growth and/or maintenance resulting in the eye-movement disorder congenital fibrosis of the extraocular muscles (CFEOM). While most examined CFEOM-causing β-tubulin mutations inhibit kinesin-microtubule interactions, Kif21a mutations activate the motor protein. These contrasting observations have led to opposed models of inhibited or hyperactive Kif21a in CFEOM. We show that, contrary to other CFEOM-causing β-tubulin mutations, R380C enhances kinesin activity. Expression of β-tubulin-R380C increases kinesin-mediated peroxisome transport in S2 cells. The binding frequency, percent motile engagements, run length and plus-end dwell time of Kif21a are also elevated on β-tubulin-R380C compared with wildtype microtubules in vitro. This conserved effect persists across tubulins from multiple species and kinesins from different families. The enhanced activity is independent of tail-mediated kinesin autoinhibition and thus utilizes a mechanism distinct from CFEOM-causing Kif21a mutations. Using molecular dynamics, we visualize how β-tubulin-R380C allosterically alters critical structural elements within the kinesin motor domain, suggesting a basis for the enhanced motility. These findings resolve the disparate models and confirm that inhibited or increased kinesin activity can both contribute to CFEOM. They also demonstrate the microtubule's role in regulating kinesins and highlight the importance of balanced transport for cellular and organismal health.

Taxol acts differently on different tubulin isotypes

Taxol is a small molecule effector that allosterically locks tubulin into the microtubule lattice. We show here that taxol has different effects on different single-isotype microtubule lattices. Using in vitro reconstitution, we demonstrate that single-isotype α1β4 GDP-tubulin lattices are stabilised and expanded by 10 µM taxol, as reported by accelerated microtubule gliding in kinesin motility assays, whereas single-isotype α1β3 GDP-tubulin lattices are stabilised but not expanded. This isotype-specific action of taxol drives gliding of segmented-isotype GDP-taxol microtubules along convoluted, sinusoidal paths, because their expanded α1β4 segments try to glide faster than their compacted α1β3 segments. In GMPCPP, single-isotype α1β3 and α1β4 lattices both show accelerated gliding, indicating that both can in principle be driven to expand. We therefore propose that taxol-induced lattice expansion requires a higher taxol occupancy than taxol-induced stabilisation, and that higher taxol occupancies are accessible to α1β4 but not α1β3 single-isotype lattices.