Normal cells will commit suicide if they lose strong attachments to neighboring cells or extracellular matrix. Cancer cells overcome this checkpoint and grow in an anchorage-independent manner. A recent study shows that the p600 protein may connect external cellular signals and the decision to die (Proc. Natl. Acad. Sci. USA 102, 15093–15098).

Yoshihiro Nakatani et al. found that p600 was expressed throughout the cell, overlapping with cytoskeletal proteins in the cytoplasm and nucleus (shown here: p600 in green, microtubules in red, and actin in blue). Loss of p600 resulted in reduced membrane ruffling and cellular adhesion and increased cell death, suggesting the involvement of p600 in survival pathways possibly related to membrane attachments.

p600 may have additional functions in the nucleus, where it interacted with the tumor suppressor protein retinoblastoma. Other recent studies have shown that p600 binds the human papilloma virus protein E7—which also interacts with retinoblastoma and triggers its degradation. Knockdown of p600 diminishes anchorage-independent growth in human papilloma virus–infected cells, suggesting that p600 may have a vital role in antitumor defense (Proc. Natl. Acad. Sci. USA 102, 11486–11491; 11492–11497).