The precise role of myosin VI (MyoVI) in the DNA damage response (DDR) remains unresolved. Dysregulated DDR pathways are exploited in cancer and contribute to relapse in breast and cervical malignancies. This thesis examines nuclear functions of MyoVI in breast and cervical models to clarify its impact on genome maintenance and therapeutic response.
Immunofluorescence microscopy showed dynamic nuclear translocation of MyoVI in HeLa, MCF7, MCF10-CA1, MCF10-DCIS, and non-cancerous MCF10A cells after exposure to cisplatin, bleomycin, or irradiation. The magnitude of the response varied by cell line and damage modality: cisplatin and bleomycin were associated with pronounced nuclear accumulation, whereas irradiation produced a significant but more variable increase, consistent with modality-specific regulation and the practical constraints of suspension irradiation and replating.
Transcriptomic analysis in HeLa cells identified about 4,100 differentially expressed genes following cisplatin treatment. MyoVI knockdown altered pathways associated with adhesion, extracellular matrix organisation, and cytokine signalling. Notably, IL6, IGFBP3, and DUSP4 showed opposite regulation compared to cisplatin alone, suggesting a non-canonical role for MyoVI in transcriptional stress adaptation.
Proteomic interactome analysis in HEK293T cells revealed isoform-specific nuclear functions. The large- and small-insert isoforms associated with non-homologous end-joining repair components XRCC6 (Ku70), PRKDC, and POLD1, whereas the non-insert isoform was linked to RNA processing and ribosome biogenesis.
Pharmacological inhibition of MyoVI with TIP reduced nuclear accumulation, delayed the resolution of γH2AX foci, and increased persistent DNA damage in cancer cells. TIP sensitised HeLa and MCF7 cells to cisplatin, enhancing apoptosis, while MCF10A cells repaired DNA efficiently within four hours.
Together, this work identifies MyoVI as a key responder in early DDR and proposes it as a potential biomarker and co-target to improve genotoxic cancer therapies.
