Mutations in nuclear pore genes NUP93, NUP205 and XPO5 cause steroid-resistant nephrotic syndrome

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Abstract
Friedhelm Hildebrandt and colleagues identify mutations in NUP93, NUP205 or XPO5 in patients with steroid-resistant nephrotic syndrome. They show that NUP93 and XPO5 interact with SMAD4 and that NUP93 mutations interfere with BMP7-SMAD4 signaling in podocytes. Nucleoporins are essential components of the nuclear pore complex (NPC)1. Only a few diseases have been attributed to NPC dysfunction2,3,4. Steroid-resistant nephrotic syndrome (SRNS), a frequent cause of chronic kidney disease, is caused by dysfunction of glomerular podocytes5. Here we identify in eight families with SRNS mutations in NUP93, its interaction partner NUP205 or XPO5 (encoding exportin 5) as hitherto unrecognized monogenic causes of SRNS. NUP93 mutations caused disrupted NPC assembly. NUP93 knockdown reduced the presence of NUP205 in the NPC, and, reciprocally, a NUP205 alteration abrogated NUP93 interaction. We demonstrate that NUP93 and exportin 5 interact with the signaling protein SMAD4 and that NUP93 mutations abrogated interaction with SMAD4. Notably, NUP93 mutations interfered with BMP7-induced SMAD transcriptional reporter activity. We hereby demonstrate that mutations of NUP genes cause a distinct renal disease and identify aberrant SMAD signaling as a new disease mechanism of SRNS, opening a potential new avenue for treatment.

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