Hide and seek

Agrowth factor hides from its receptor in a different membrane domain, as demonstrated by Paola Vermeer, Michael Welsh (University of Iowa, Iowa City, IA), and colleagues. The separation normally prevents receptor activation, but can be overcome rapidly when activation is necessary.

The sneaky receptor is erbB2, whose activation by the ligand heregulin stimulates cellular migration and proliferation. Although both erbB2 and heregulin are expressed in airway epithelial cells, the slow division rate of these cells suggests that erbB receptors are not signaling. The Iowa group now shows that erbB2 is inactive because it is separated from its ligand by tight junctions. Whereas heregulin was found in the apical membrane of the epithelial cells, erbB2 resided on the basolateral surface.

The spatial barrier offers a quick fix for damaged epithelia....