FAM111 protease activity undermines cellular fitness and is amplified by gain‐of‐function mutations in human disease

Abstract

Dominant missense mutations in the human serine protease FAM111A underlie perinatally lethal gracile bone dysplasia and Kenny-Caffey syndrome, yet how FAM111A mutations lead to disease is not known. We show that FAM111A proteolytic activity suppresses DNA replication and transcription by displacing key effectors of these processes from chromatin, triggering rapid programmed cell death by Caspase-dependent apoptosis to potently undermine cell viability. Patient-associated point mutations in FAM111A exacerbate these phenotypes by hyperactivating its intrinsic protease activity. Moreover, FAM111A forms a complex with the uncharacterized homologous serine protease FAM111B, point mutations in which cause a hereditary fibrosing poikiloderma syndrome, and we demonstrate that disease-associated FAM111B mutants display amplified proteolytic activity and phenocopy the cellular impact of deregulated FAM111A catalytic activity. Thus, patient-associated FAM111A and FAM111B mutations may drive multisystem disorders via a common gain-of-function mechanism that relieves inhibitory constraints on their protease activities to powerfully undermine cellular fitness.

FAM111A induces nuclear dysfunction in disease and viral restriction

“…Together, our results demonstrate that FAM111A exhibits protease‐dependent cytotoxicity, which is amplified by the KCS2 and OCS patient mutants, consistent with recent studies (Kojima et al , 2020; Hoffmann et al , 2020). Thus, FAM111A hyperactivity can explain the dominant effects of FAM111A R569H and FAM111A S342del over wild‐type in the heterozygous disease state (Unger et al , 2013).…”

“…Given that hyperactive FAM111A R569H disrupts cellular DNA replication, we envisioned that FAM111A could directly inhibit viral replication by degrading key replication factors. Crucially however, although others and we have identified replication factors as FAM111A interactors, to date none appear to be targets of its protease activity (Hoffmann et al , 2020). Instead, FAM111A causes nuclear barrier dysfunction, among other phenotypes, when SV40 HR mutants attempt to replicate in restrictive cells.…”

“…Consistent with its S phase localization, FAM111A is in close proximity to DNA replication factors such as RFC1 and PCNA, but these do not appear to be targets of FAM111A protease activity (see also Hoffmann et al , 2020). Instead, FAM111A likely cooperates with PCNA and RFC1‐5 at both cellular and viral genome replication sites.…”

Report of a novel variant in the FAM111A gene in a fetus with multiple anomalies including gracile bones, hypoplastic spleen, and hypomineralized skull

“…The fetus in this report shows phenotypic overlap with previously reported cases and the Y562S variant shares multiple similarities with previous reported pathogenic variants, including the well‐established pathogenic R569H mutation (Abraham et al, 2017; Isojima et al, 2014; Nikkel et al, 2014; Unger et al, 2013). Like the R569H variant, Y562S is a single nucleotide missense mutation resulting in a single amino acid change located in the C‐terminus, an evolutionarily conserved region of the protein that appears to be a hotspot for mutations (Abraham et al, 2017; Hoffmann et al, 2020; Isojima et al, 2014; Unger et al, 2013).…”

“…Given this evidence, it has been theorized that FAM111A mutations cause phenotypic features by altering the protein's intermolecular interactions (Isojima et al, 2014; Unger et al, 2013). A recent study showed altered peptidase activity and gain of function mechanism as pathophysiology for FAM111A‐ related disorders (Hoffmann et al, 2020). Pathogenic mutations increased proteolytic activity of the protein resulting in decreased DNA replication and transcription ultimately resulting in programmed cell death (Hoffmann et al, 2020).…”