Investigation of the cellular mechanisims underlying the Carboxypeptidase E mutation

Kaşıkçı, Feride
Carboxypeptidase E (CPE) is an enzyme expressed in both endocrine and neuroendocrine cells functioning as both an exopeptidase and a sorting receptor. Recently, it has been reported that CPE plays a role in preventing neuronal cell death in the CA3 hippocampus so as to maintain normal cognitive function in the adult brain. Studies on CPE-knockout mice showed total degeneration of neurons in the CA3 region of the hippocampus in adult mice 4 weeks of age and older. Additionally, increased CPE expression was involved in protecting hippocampal neurons from oxidative stress-induced apoptosis. The neuroprotective role of CPE prompted us to search for possible mutations in the human CPE gene that might be linked to human neurodegenerative diseases. A non-redundant nucleotide sequence database search with the human CPE nucleotide sequence as queries identified an EST sequence entry from Alzheimer cortex tissue that had three adenosine inserts. This introduces 9 amino acids in the first beta-pleated sheet after the pro-domain of the mutant CPE protein, herein called QQ CPE due to the presence of two glutamine residues in the new sequence. The studies demonstrate that mutant CPE cannot perform its enzymatic functions and at the same time it interferes with the wild type CPE activity. Expression studies in neuroblastoma cells (N2A) demonstrated that QQ CPE was made but failed to be secreted and instead degraded in the both proteosomes and lysosomes. The percent rescue of QQ CPE was higher in proteosomes compared to lysosomes, hence, QQ CPE was primarily degraded in proteosomes. Co-expression of WT and QQ CPE in N2A cell showed additive effects of degradation both in proteosomes and lysosomes.
Citation Formats
F. Kaşıkçı, “Investigation of the cellular mechanisims underlying the Carboxypeptidase E mutation,” M.S. - Master of Science, Middle East Technical University, 2014.