Figure 9.

Schematic diagram depicting a predicted steady state mechanism for POMC and CgA trafficking in AtT20 cells. POMC and CgA are synthesized and trafficked to the TGN where sorting occurs. SgIII and CPE can facilitate CgA and POMC sorting into the granules of the RSP, because in all cases, reduction of these proteins result in increased constitutive secretion of POMC/ACTH and CgA and accumulation in the TGN. Chronic reduction of SgIII alone prevented a component of POMC/ACTH sorting to the RSP, whereas chronic reduction of CPE enhanced the sorting to the RSP. In contrast, acute KD of CPE prevented a component of POMC/ACTH sorting to the RSP. This suggests that AtT20 cells with long-term reduction of CPE levels have adapted to maintain and even increase the sorting efficiency of POMC/ACTH in AtT20 cells, presumably through the SgIII pathway.