The down-regulation (top) of Rac1 activity (colored) at cell contact sites is lost if Fak is inhibited (bottom).

On page 283, Yano et al. show how some cells use signals from cell-matrix contacts to maintain cell–cell contacts as they migrate.

Although most cells travel in isolation, some epithelial cell types migrate as a sheet, as during gastrulation or in carcinoma metastasis. Yano et al. find that HeLa cells (derived from a carcinoma) need the focal adhesion proteins Fak and paxillin to maintain their N-cadherin–based cell contacts.

When integrins at focal adhesions bind to the matrix, paxillin joins the complex. The new results suggest that paxillin recruits Fak to focal adhesions. Then, activated Fak somehow down-regulates only the Rac1 at sites of cell contact, although the direct Fak substrates are not yet known. When either paxillin or Fak was inhibited, the resulting Rac1 activity caused large overactive membrane protrusions and reduced the number of N-cadherin–based cell–cell adhesions. The mechanism is unclear, but perhaps the strong membrane motion caused by Rac1 makes cadherin bond formation unlikely.

Fak inhibition also increased migration rates and disrupted wound healing because cells broke away from the sheet. The studies were done using cancer cells, and Fak inhibition has the opposite effect on fibroblast migration, so the authors next need to see if their studies extend to normal epithelial cells. ▪