atrial-natriuretic-factor and Astrocytoma

The content of membrane peptidases has been compared in the human astrocytoma clone D384 and the human neuroblastoma line SH-SY5Y. Endopeptidase-24.11 (neutral endopeptidase, EC 3.4.24.11) was detectable only on the astrocytoma cells whereas angiotensin-converting enzyme (EC 3.4.15.1) was selectively expressed on the neuroblastoma line. Dipeptidyl peptidase IV (EC 3.4.14.5) was also abundant on the astrocytoma line. The presence of both endopeptidase-24.11 and dipeptidyl peptidase IV on D384 cells was confirmed by immunohistochemistry. A membrane preparation from D384 cells hydrolyzed both atrial natriuretic peptide and brain natriuretic peptide and, in both cases, the pattern of metabolism was similar to that seen with purified endopeptidase-24.11. The endopeptidase-24.11 inhibitor, phosphoramidon, at 1 microM abolished natriuretic peptide metabolism. The neuroblastoma line, which lacked endopeptidase-24.11, failed to metabolise atrial natriuretic peptide and brain natriuretic peptide, emphasizing the key role of the endopeptidase in hydrolyzing these regulatory peptides at the cell surface.

Topics: Astrocytoma; Atrial Natriuretic Factor; Cell Membrane; Dipeptidyl Peptidase 4; Dipeptidyl-Peptidases and Tripeptidyl-Peptidases; Fluorescent Antibody Technique; Humans; Hydrolysis; Natriuretic Peptide, Brain; Neprilysin; Nerve Tissue Proteins; Neuroblastoma; Peptidyl-Dipeptidase A; Tumor Cells, Cultured

Topics: Astrocytoma; Atrial Natriuretic Factor; Cell Line; Cell Membrane; Clone Cells; Endopeptidases; Humans; Hydrolysis; Natriuretic Peptide, Brain; Nerve Tissue Proteins; Neuroblastoma

Specific high-affinity binding sites (dissociation constant 100 pmol/l) for atrial natriuretic peptide (ANP) have been identified in the clone D384 derived from the human astrocytoma cell line G-CCM. Unrelated peptides such as angiotensin II, vasopressin and bradykinin did not compete for these sites. Of the atrial natriuretic peptides studied, both the human and rat ANP competed equally, while peptides with either C- or N-terminal residue missing or with no internal -S-S-bond either competed less effectively or did not compete at all. Human ANP stimulated the cells to increase their intracellular level of cyclic GMP in a time- and dose-dependent manner with maximum stimulation being approached but not reached at concentrations of 1 mumol/l. These results support both the notion that ANP has an important functional role within the brain and the concept of neurotransmitter/neuromodulator communication between neurones and glia.

Topics: Astrocytoma; Atrial Natriuretic Factor; Binding Sites; Brain Neoplasms; Cyclic GMP; Humans; Receptors, Atrial Natriuretic Factor; Receptors, Cell Surface; Tumor Cells, Cultured