A thermosensitive PCNA allele underlies an ataxia- telangiectasia-like disorder

Proliferating cell nuclear antigen (PCNA) is a sliding clamp protein that coordinates DNA replication with various DNA maintenance events that are critical for human health. Recently, a hypomorphic homozygous serine to isoleucine (S228I) substitu-tion in PCNA was described to underlie a rare DNA repair dis-order known as PCNA-associated DNA repair disorder (PARD). PARD symptoms range from UV sensitivity, neurodegeneration, telangiectasia, and premature aging. We, and others, previously showed that the S228I variant changes the protein-binding pocket of PCNA to a conformation that impairs interactions with specific partners. Here, we report a second PCNA substitution (C148S) that also causes PARD. Unlike PCNA-S228I, PCNA-C148S has WT-like structure and affinity toward partners. In contrast, both disease-associated variants possess a thermostability defect. Furthermore, patient-derived cells homozygous for the C148S allele exhibit low levels of chromatin-bound PCNA and display temperature-dependent phenotypes. The stability defect of both PARD variants indicates that PCNA levels are likely an important driver of PARD disease. These results significantly advance our understanding of PARD and will likely stimulate additional work focused on clinical, diagnostic, and therapeutic aspects of this severe disease.

Automated summary

PCNA is a crucial protein involved in DNA replication and maintenance. Two variants, S228I and C148S, have been identified to cause a rare DNA repair disorder called PARD. While S228I affects protein interactions, C148S does not change the structure or affinity of PCNA. However, both variants exhibit a thermostability defect. This study advances our understanding of PARD and highlights the importance of PCNA levels in the disease.