A novel role for a familiar protein in apoptosis induced by proteasome inhibition.

In this issue of Cancer Cell, Nickeleit et al. (2008) identify a new proteasome inhibitor, argyrin A, and show that it induces apoptosis and inhibits angiogenesis via p27-dependent mechanisms. Their observations challenge current thinking about how this class of promising cancer therapies works and why they selectively kill cancer cells.