O-GlcNAcylation promotes Palbociclib resistance in breast cancer by regulating MITF nuclear translocation

Cyclin-dependent kinases 4 and 6 (CDK4/6) are essential drivers of the cell cycle and are also critical for the initiation and progression of diverse malignancies. Pharmacological inhibitors targeting CDK4/6 have demonstrated significant activity against various tumor types such as breast cancer. However, resistance to CDK4/6 inhibitors (CDK4/6i) (such as palbociclib) remains an immense obstacle in clinical and the underlying mechanisms have not been fully understood. Using quantitative high-throughput combinational screen (qHTCS) and genomic sequencing, we report that the Microphthalmia-associated transcription factor (MITF), was significantly elevated in palbociclib-resistance cells. Inhibition of MITF can enhance the therapeutic efficacy of Palbociclib and surmount Palbociclib resistance both in vitro and in vivo. Mechanistically, we found that O-GlcNAc transferase (OGT) modifies MITF with O-GlcNAcylation at Serine 49 (Ser49) within its nuclear localization signal (NLS), thereby promoting MITF binding to importin α/ β and facilitating its nuclear transportation, which is crucial in regulating senescence.