Where Is PTEN?

A tumor suppressor protein may function in multiple locations inside and outside the originating cell. [Also see Reports by Bassi et al. and Hopkins et al. ] There are plenty of examples in biology of finding things in unexpected places, such as bacteria thriving in the stomach or deep in Earth's crust, or proteins that have acquired “moonlighting” functions when in new cellular locations. On pages 399 and 395 of this issue, two reports describe newly identified aspects of the functions of phosphatase and tensin homolog (PTEN), a tumor suppressor protein. Both studies focus on where these functions are fulfilled. Hopkins et al. ( 1 ) describe a secreted form of PTEN that can be transferred between cells, potentially for intercellular tumor suppression. Bassi et al. ( 2 ) present a new mechanism of PTEN regulation in response to DNA damage that controls PTEN localization in the nucleus. Both discoveries have implications for cancer therapy.