Role of pGlu-serpinin, a novel chromogranin A-derived peptide in inhibition of cell death.

Chromogranin A (CgA) is a member of the granin family of molecules found in secretory granules of endocrine and neuro-endocrine cells. Here, we have identified a new 23-mer CgA-derived peptide secreted from pituitary AtT-20 cells, which we named pyroGlu-serpinin (pGlu-serpinin). LC-MS studies of peptides in conditioned medium of AtT-20 cells indicate that pGlu-serpinin is derived from initial processing of mouse CgA at paired basic residues, Arg461-Arg462 and Arg433-Arg434, to yield a previously described 26 amino acid peptide, serpinin. Three amino acids are then cleaved from the N terminus of serpinin, yielding a peptide with an N-terminal glutamine, which is then subsequently pyroglutaminated. Immunocytochemistry showed co-localization of pGlu-serpinin with adrenocorticotropic hormone in secretory granules of AtT-20 cells, and it was released in an activity-dependent manner. Functional studies demonstrated that pGlu-serpinin was able to prevent radical oxygen species (hydrogen peroxide)-induced cell death of AtT-20 cells and cultured rat cerebral cortical neurons at a concentration of 1 and 10 nM, respectively. These data indicate that pGlu-serpinin has anti-apoptotic effects that may be important in neuroprotection of central nervous system neurons and pituitary cells. Furthermore, pGlu-serpinin added to the media of AtT-20 cells up-regulated the transcription of the serine protease inhibitor, protease nexin-1 (PN-1) mRNA. pGlu-serpinin's ability to increase levels of PN-1, a potent inhibitor of plasmin released during inflammatory processes causing cell death, may play a role in protecting cells under adverse pathophysiological conditions.