RAP1 moonlights to activate NF-κB and Notch in ALT.

Cancer cells activate either telomerase or telomere recombination (ALT) to maintain telomere length and achieve immortalization. In this issue of Science Signaling, Robinson et al. reveal an unanticipated role of the protein SLX4IP in the SUMOylation of RAP1, which enhances its extratelomeric function in activating an NF-κB-Notch signaling axis that favors ALT.