Phosphoinositides and membrane traffic at the trans-Golgi network.

Cargo proteins moving along the secretory pathway are sorted at the TGN (trans-Golgi network) into distinct carriers for delivery to the plasma membrane or endosomes. Recent studies in yeast and mammals have shown that formation of these carriers is regulated by PtdIns(4)P. This phosphoinositide is abundant at the TGN and acts to recruit components required for carrier formation to the membrane. Other phosphoinositides are also present on the TGN, but the extent to which they regulate trafficking is less clear. Further characterization of phosphoinositide kinases and phosphatases together with identification of new TGN-associated phosphoinositide-binding proteins will reveal the extent to which different phosphoinositides regulate TGN trafficking, and help define the molecular mechanisms involved.