VCF1 is a p97/VCP cofactor promoting recognition of ubiquitylated p97-UFD1-NPL4 substrates.

The hexameric AAA+ ATPase p97/VCP functions as an essential mediator of ubiquitin-dependent cellular processes, extracting ubiquitylated proteins from macromolecular complexes or membranes by catalyzing their unfolding. p97 is directed to ubiquitylated client proteins via multiple cofactors, most of which interact with the p97 N-domain. Here, we discover that FAM104A, a protein of unknown function also named VCF1 (VCP/p97 nuclear Cofactor Family member 1), acts as a p97 cofactor in human cells. Detailed structure-function studies reveal that VCF1 directly binds p97 via a conserved α-helical motif that recognizes the p97 N-domain with unusually high affinity, exceeding that of other cofactors. We show that VCF1 engages in joint p97 complex formation with the heterodimeric primary p97 cofactor UFD1-NPL4 and promotes p97-UFD1-NPL4-dependent proteasomal degradation of ubiquitylated substrates in cells. Mechanistically, VCF1 indirectly stimulates UFD1-NPL4 interactions with ubiquitin conjugates via its binding to p97 but has no intrinsic affinity for ubiquitin. Collectively, our findings establish VCF1 as an unconventional p97 cofactor that promotes p97-dependent protein turnover by facilitating p97-UFD1-NPL4 recruitment to ubiquitylated targets.

Sustainability and molecular biology: An interview with Prof. Niels Mailand and Ann Schirin Mirsanaye.

Prof. Niels Mailand and Ann Schirin Mirsanaye share with Molecular Cell some of their thoughts on making molecular biology more sustainable, outline their first-hand experiences of having their lab LEAF (Laboratory Efficiency Assessment Framework) certified, and impart some advice to our readers who are considering doing the same.

Ubiquitylation at Stressed Replication Forks: Mechanisms and Functions.

Accurate duplication of chromosomal DNA is vital for faithful transmission of the genome during cell division. However, DNA replication integrity is frequently challenged by genotoxic insults that compromise the progression and stability of replication forks, posing a threat to genome stability. It is becoming clear that the organization of the replisome displays remarkable flexibility in responding to and overcoming a wide spectrum of fork-stalling insults, and that these transactions are dynamically orchestrated and regulated by protein post-translational modifications (PTMs) including ubiquitylation. In this review, we highlight and discuss important recent advances on how ubiquitin-mediated signaling at the replication fork plays a crucial multifaceted role in regulating replisome composition and remodeling its configuration upon replication stress, thereby ensuring high-fidelity duplication of the genome.

Membrane capacitance recordings resolve dynamics and complexity of receptor-mediated endocytosis in Wnt signalling.

Receptor-mediated endocytosis is an essential process in signalling pathways for activation of intracellular signalling cascades. One example is the Wnt signalling pathway that seems to depend on endocytosis of the ligand-receptor complex for initiation of Wnt signal transduction. To date, the roles of different endocytic pathways in Wnt signalling, molecular players and the kinetics of the process remain unclear. Here, we monitored endocytosis in Wnt3a and Wnt5a-mediated signalling with membrane capacitance recordings of HEK293 cells. Our measurements revealed a swift and substantial increase in the number of endocytic vesicles. Extracellular Wnt ligands specifically triggered endocytotic activity, which started immediately upon ligand binding and ceased within a period of ten minutes. By using specific inhibitors, we were able to separate Wnt-induced endocytosis into two independent pathways. We demonstrate that canonical Wnt3a is taken up mainly by clathrin-independent endocytosis whereas noncanonical Wnt5a is exclusively regulated via clathrin-mediated endocytosis. Our findings show that membrane capacitance recordings allow the resolution of complex cellular processes in plasma membrane signalling pathways in great detail.