Growth factor regulation of the novel class II phosphoinositide 3-kinases.

It is well established that the class-I phosphoinositide (PI) 3-kinases play a crucial role in growth factor signalling pathways. However, evidence has recently emerged that the alpha isoform of the class-II PI 3-kinase (PI 3K-C2alpha) is activated by growth factors, although the consequences of this are poorly understood. Here we demonstrate that the activation of PI 3K-C2alpha is not associated with a change in subcellular localization. Furthermore, we provide the first evidence that PI 3K-C2beta is activated by insulin, albeit with slower kinetics than activation of PI 3K-C2alpha. These findings suggest that both these class-II PI 3-kinase isoforms are likely to participate in insulin-signalling pathways in the cell.