Disrupted function of cytoplasmically oriented nucleoporins leads to a stress-induced traffic jam in nuclear pore channels

NUP214 and NUP358 are two large nucleoporins exclusively found on the cytoplasmic side of the nuclear pore complex (NPC). Mutations in the human genes encoding these proteins cause rare inherited diseases involving neurodevelopmental regression and severe damage to the central nervous system. Dominant mutations in NUP358 cause infection-induced acute necrotizing encephalopathy (ANE), while recessive missense mutations in NUP214 cause acute febrile encephalopathy (AFE).

We have used patient-derived fibroblasts, induced pluripotent stem cells differentiated into neurons, and an auxin-induced degron system to assess the function of these nucleoporins. Based on clinical disease features, we combined these cell-based models with an exposure to heat shock (HS) stress. Our results show that disrupting the function of NUP214 or NUP358 leads to increased sensitivity to HS and decreased survival in cell culture. Direct surface imaging of individual NPCs by scanning electron microscopy demonstrates an accumulation of large central channel particles, also known as ‘‘plugs’’, in NPC channels. This suggests that large cargoes may be delayed in passage or release from the central NPC channel. The “plugs” that accumulate following HS exposure contain a prominent RNase-sensitive component and the expression of key regulators of the heat shock response is critically delayed in AFE patient-derived fibroblasts.

Taken together, our results suggest that pathogenic changes in certain nucleoporins can lead to the formation of a stress-induced traffic jam in NPC channels. This notion will be discussed in a wider context of early and late onset neurodegenerative disorders that have recently been linked to defects in nucleocytoplasmic transport.