24Mutations in the nuclear trypsin-like serine protease FAM111A cause Caffey syndrome (KCS2) with hypoparathyroidism and skeletal dysplasia, or 26 perinatally lethal osteocraniostenosis (OCS). In addition, FAM111A was identified 27 as a restriction factor for certain host range mutants of the SV40 polyomavirus and 28 VACV orthopoxvirus. However, because FAM111A function is poorly 29 characterized, its roles in restricting viral replication and the etiology of KCS2 and 30 OCS remain undefined. We find that the FAM111A KCS2 and OCS patient 31 mutants are hyperactive, inducing apoptosis-like phenotypes in a protease-32 dependent manner. Similarly, in response to the attempted replication of SV40 33 host range mutants in restrictive cells, FAM111A activity induces the loss of 34 nuclear barrier function and structure. Interestingly, pan-caspase inhibitors do not 35 block FAM111A-dependent phenotypes such as nuclear "leakiness", shrinkage 36 and pore redistribution, implying it acts independently or upstream of caspases. In 37 this regard, we identified nucleoporins and the associated GANP transcription 38 factor as FAM111A interactors and candidate targets. Together our data provide 39 key insight into how FAM111A activation can restrict viral replication, and how its 40 deregulated activity could cause KCS2 and OCS. 41 42 48 2019). Further analysis indicated that FAM111A executes its restrictive function 49 during or following SV40 viral genome replication (Tarnita et al., 2019). 50Expanding the role of FAM111A in protecting against viral challenge, it was 51 identified along with the PCNA clamp-loading complex RFC1-5 as a restriction 52 factor for orthopoxvirus host range mutants lacking the serine protease inhibitor 53 SPI-1 (Panda et al., 2017). Early studies on rabbitpox virus (RPXV) host range 54 mutants lacking SPI-1 suggested that restrictive human A459 cells exhibit 55 apoptosis-like features upon infection, which required RPXV DNA synthesis 56 (Brooks et al., 1995). However, a subsequent study found that the related vaccinia 57 virus (VACV) lacking SPI-1 caused nuclear morphological changes such as 58 chromatin condensation and membrane invagination, without the normal 59 biochemical features of apoptosis (Shisler et al., 1999).60Thus, viruses with diverse life cycles e.g. nuclear replication sites 61 (polyomavirus) versus replication in the cytoplasm (orthopoxvirus) possess a 62 mechanism to overcome the antagonistic effects of FAM111A. However, how 63 FAM111A combats viral challenges remains poorly characterized, but its activity is likely triggered during viral replication (Panda et al., 2017, Luttge and Moyer, 2005, 65 Tarnita et al., 2019). 66Consistent with its apparent replication-dependent role in viral restriction, 67FAM111A was identified in high-throughput screens as a protein enriched on 68 nascent chromatin i.e. replication forks (Alabert et al., 2014, Wessel et al., 2019. 69Exogenous FAM111A was found to associate with replication sites via a PCNA 70 interacting motif (Alabert e...

Activity-dependent gene expression is critical for synapse development and plasticity. To elucidate novel mechanisms linking neuronal activity to changes in transcription, we compared the nuclear proteomes of tetrodotoxin-silenced and bicuculline-stimulated cultured rodent neurons using nuclear-localized APEX2 proximity biotinylation and mass spectrometry. The tumor suppressor protein PDCD4 was enriched in the silenced nuclear proteome, and PDCD4 levels rapidly decreased in the nucleus and cytoplasm of stimulated neurons. The activity-dependent decrease of PDCD4 was prevented by inhibitors of both PKC and proteasome activity and by a phospho-incompetent mutation of Ser71 in the βTRCP ubiquitin ligase-binding motif of PDCD4. We compared the activity-dependent transcriptomes of neurons expressing wildtype or degradation-resistant (S71A) PDCD4. We identified 91 genes as PDCD4 targets at the transcriptional level, including genes encoding proteins critical for synapse formation, remodeling, and transmission. Our findings indicate that regulated degradation of nuclear PDCD4 facilitates activity-dependent transcription in neurons.