New roles for Notch in tuberous sclerosis.

Tuberous sclerosis complex (TSC) is a dominantly inherited disease that is characterized by the growth of multiple benign tumors that are often difficult to treat. TSC is caused by mutations that inactivate the TSC1 or TSC2 genes, which normally function to inhibit activation of mammalian target of rapamycin signaling. In this issue of the JCI, two studies reported by Karbowniczek et al. and Ma et al. link TSC inactivation with activated Notch signaling (see the related articles beginning on pages 93 and 103, respectively). Using a variety of approaches, both studies show that inactivation of TSC leads to Notch1 activation. Furthermore, studies in tumor cells suggest that inhibiting Notch slows growth of the tumor cells. Although much remains to be learned about the precise mechanisms by which TSC loss leads to Notch activation, the newly identified link of TSC to Notch provides the rationale for testing Notch inhibitors in TSC-associated tumors.