CLONING OF THE HUMAN PUROMYCIN-SENSITIVE AMINOPEPTIDASE AND EVIDENCE FOR EXPRESSION IN NEURONS

The puromycin-sensitive aminopeptidase (PSA) is thought to contribute to the degradation of enkephalins. Besides being the most abundant ami nopeptidase in the brain, PSA is expressed in other organs as well. Fr om a human fetal brain cDNA library, we have isolated a cDNA encoding the human PSA (huPSA) protein. The isolated cDNA gave rise to a protei n with a molecular mass of 99 kDa. Compared with mouse PSA, homology a t the amino acid and cDNA level was 98 and 93%, respectively. Translat ion of the huPSA was found to be initiated at the second of two possib le start codons, as shown by studies with antibodies directed against peptide sequences of both potential N-terminal regions. Northern blot analysis with RNA isolated from different human organs demonstrated th at the huPSA transcript is strongest but not exclusively expressed in the brain. Vesicular stomatitis virus epitope-tagged huPSA protein was expressed in HeLa cells and found to be localized in the cytoplasm, e specially in the perinuclear region. By in situ hybridization, huPSA t ranscript could be identified in cortical and cerebellar neurons, wher eas glial cells and blood vessels remained negative.