Czech National Centre of the European Research Infrastructure Consortium INSTRUCT ERIC

Nedd4-2 is a key enzyme involved in regulating sodium levels by controlling the removal of sodium channels from cell membranes. This function is essential for the regulation of blood pressure and osmotic balance, and its disruption has been linked to diseases such as hypertension, kidney disease and some cancers. A new study by a team from the Institute of Physiology of the CAS and the Faculty of Science of Charles University has for the first time described in detail the structure of the entire Nedd4-2 enzyme and explained the mechanism of its regulation. Using advanced imaging and biochemical methods, the researchers found that the function of Nedd4-2 is blocked by interactions between its domains. The enzyme remains inactive until it binds to the cell membrane in the presence of calcium ions. This leads to the release of inter-domain interactions and the activation of Nedd4-2. The study also showed that the 14-3-3 proteins, which respond to hormonal signals and by their binding block both the enzymatic activity of Nedd4-2 and its ability to bind to the membrane, are also involved in the regulation of Nedd4-2.

Replication stress, particularly in hard-to-replicate regions such as telomeres and centromeres, leads to the accumulation of replication intermediates that must be processed to ensure proper chromosome segregation. In this study, we identify a critical role for the interaction between RECQ4 and MUS81 in managing such stress. We show that RECQ4 physically interacts with MUS81, targeting it to specific DNA substrates and enhancing its endonuclease activity. Loss of this interaction, results in significant chromosomal segregation defects, including the accumulation of micronuclei, anaphase bridges, and ultrafine bridges (UFBs). Our data further demonstrate that the RECQ4-MUS81 interaction plays an important role in ALT-positive cells, where MUS81 foci primarily colocalise with telomeres, highlighting its role in telomere maintenance. We also observe that a mutation associated with Rothmund-Thomson syndrome, which produces a truncated RECQ4 unable to interact with MUS81, recapitulates these chromosome instability phenotypes. This underscores the importance of RECQ4-MUS81 in safeguarding genome integrity and suggests potential implications for human disease. Our findings demonstrate the RECQ4-MUS81 interaction as a key mechanism in alleviating replication stress at hard-to-replicate regions and highlight its relevance in pathological conditions such as RTS.