O-GlcNAcylation is a mitochondrial-nuclear signal that regulates passive transport through the nuclear pore complex.

The nuclear pore complex (NPC) is the single gateway between the nucleus and the cytoplasm, and in healthy cells there is a size threshold for passive diffusion across the NPC. In aging and disease, the NPC deteriorates, leading to promiscuous passive transport. We have previously showed that NPC protein expression is required for biguanide-induced lifespan extension, mTOR inhibition, and further that biguanide treatment leads to restriction of passive nuclear transport, but the underlying changes leading to this restriction were not identified. Here, we use fluorescent dextran transport and biochemical assays in HeLa cells to clarify the mechanism by which biguanide phenformin alters NPC permeability. We find phenformin treatment in HeLa cells leads to restricted passive nuclear transport in a dose and time-dependent manner. Multiple inhibitors of the mitochondrial electron transport chain (ETC) also restrict passive nucleocytoplasmic transport. Critically, phenformin reduced expression of O-GlcNAc transferase (OGT), lowering global O-GlcNAcylation and locally decreasing O-GlcNAcylation of Nup98. OGT inhibition alone restricts passive transport, while increasing O-GlcNAcylation reverses phenformin's effects. These results identify O-GlcNAc as a mitochondrial-nuclear signal and show that ETC inhibition rapidly modulates nucleocytoplasmic transport via NPC post-translational modification in human cancer cells.