Proteins have to be secreted and then translated in ribosomes on the rough endoplasmic reticulum. They then enter the lumen of the RER.
The proteins move through the golgi apparatus as normal and are packaged into secretory vesicles.
The secretory vesicles move to and fuse with the plasma membrane releasing the proteins out of the cell.
Many proteins are made as an inactive version of the final product (inactive precursors). They require proteolytic cleavage to produce an active protein.
