Huge thanks to all people involved, @smoa-cbm.bsky.social and flow cytometry facilities from @cniostopcancer.bsky.social and @cbm-csic-uam.bsky.social.

So, to sum up: VCP/p97 ➡️ POLA/PRIM on chromatin ➡️ priming ➡️ basal RSR activation! This work was led by @emlecona.bsky.social from @cbm-csic-uam.bsky.social in collaboration with Juan Mendez' group from @cniostopcancer.bsky.social. Want to dive a little bit more in our work? Click here! rdcu.be/eu1yo

And the activation of the RSR induced by VCPi is relevant, as the phosphorylation of CHK1 leads to an arrest in G2/M. More importantly, CHK1 activation is lost when we block the priming action of POLA/PRIM.

What are the consequences of more POLA/PRIM on chromatin? We observed that the inhibition of VCP/p97 also increased priming by POLA/PRIM, as observed in the EdU comet assay.

In fact, we showed that VCP/p97 and POLA/PRIM do interact. Interestingly, VCP/p97 inhibition could not induce the accumulation of POLA/PRIM on chromatin if origin firing is inhibited with CDC7i.

It struck our attention that the increased activation of the RSR induced when VCP/p97 is inhibited is mirrored by the accumulation of POLA/PRIM on chromatin. Could our two guests be working together?

First, we found that VCP/p97 is necessary for DNA replication and its inhibition leads to defects in fork progression and origin firing that result in the activation of the RSR.