FAM111A induces nuclear dysfunction in disease and viral restriction

Mutations in the nuclear trypsin-like serine protease FAM111A cause Kenny–Caffey syndrome (KCS2) with hypoparathyroidism and skeletal dysplasia or perinatally lethal osteocraniostenosis (OCS). In addition, FAM111A was identified as a restriction factor for certain host range mutants of the SV40 polyomavirus and VACV orthopoxvirus. However, because FAM111A function is poorly characterized, its roles in restricting viral replication and the etiology of KCS2 and OCS remain undefined. We find that FAM111A KCS2 and OCS patient mutants are hyperactive and cytotoxic, inducing apoptosis-like phenotypes such as disruption of nuclear structure and pore distribution, in a protease-dependent manner. Moreover, wild-type FAM111A activity causes similar nuclear phenotypes, including the loss of nuclear barrier function, when SV40 host range mutants attempt to replicate in restrictive cells. Interestingly, pan-caspase inhibitors do not block these FAM111A-induced phenotypes, implying it acts independently or upstream of caspases. In this regard, we identify nucleoporins and the associated GANP transcription/replication factor as FAM111A interactors and candidate targets. Overall, we reveal a potentially unifying mechanism through which deregulated FAM111A activity restricts viral replication and causes KCS2 and OCS. SYNOPSIS FAM111A is a nuclear trypsin-like protease that was identified as an antiviral restriction factor, and as the gene mutated in two debilitating syndromes, KCS2 and OCS. Patient mutations and polyomavirus replication in restrictive cells hyperactivate FAM111A, which then compromises nuclear barrier function, DNA replication, and cell viability. FAM111A protease activity is hyperactivated by patient-associated mutations, and upon the attempted replication of host range mutants of SV40 in restrictive cells. Hyperactive FAM111A is cytotoxic, disrupting nuclear barrier function and DNA replication. FAM111A interacts with DNA replication and nuclear pore-associated factors, with the latter being identified as candidate targets of its protease activity. Graphical Abstract The protease FAM111A was identified as an antiviral restriction factor, and as the gene mutated in two multisystem human syndromes, KCS2 and OCS. Patient mutations and polyomavirus replication in restrictive cells hyperactivate FAM111A, resulting in compromised nuclear barrier function, DNA replication, and cell viability.