Pathways to Cancer: Releasing the protein

The newly made proteins leave the endoplasmic reticulum wrapped in a layer of membrane called a vesicle. They travel toward the Golgi apparatus (on the right) where the proteins are modified and sorted for transport. The Golgi is busy with protein traffic moving in and out. The vesicle fuses with the membrane at one end of the Golgi and a new vesicle containing the modified proteins is pinched off the other side. The proteins are transported through the cytoplasm and delivered to where they are needed. Some proteins are used inside the cell. Others, like these growth factors, must be exported to function. The vesicle fuses with the cell membrane, dumping the proteins outside the cell. The released proteins will signal surrounding cells, or, in some pathways to cancer, will coax this cell into further action.