Striking Oxygen Sensitivity of the Peptidylglycine α-Amidating Monooxygenase (PAM) in Neuroendocrine Cells

Interactions between biological pathways and molecular oxygen require robust mechanisms for detecting and responding to changes in cellular oxygen availability, to support oxygen homeostasis. Peptidylglycine α-amidating monooxygenase (PAM) catalyzes a two-step reaction resulting in the C-terminal amidation of peptides, a process important for their stability and biological activity. Here we show that in human, mouse, and insect cells, peptide amidation is exquisitely sensitive to hypoxia. Different amidation events on chromogranin A, and on peptides processed from proopiomelanocortin, manifest similar striking sensitivity to hypoxia in a range of neuroendocrine cells, being progressively inhibited from mild (7% O2) to severe (1% O2) hypoxia. In developing Drosophila melanogaster larvae, FMRF amidation in thoracic ventral (Tv) neurons is strikingly suppressed by hypoxia. Our findings have thus defined a novel monooxygenase-based oxygen sensing mechanism that has the capacity to signal changes in oxygen availability to peptidergic pathways. Background: Peptidylglycine α-Amidating Monooxygenase (PAM) is solely responsible for catalysis of amidation, a biologically important post-translational modification. Results: Modification-specific antibodies reveal that peptide substrate amidation is strikingly sensitive to the exposure of cells to moderate hypoxia. Conclusion: PAM-dependent amidation has the potential to signal oxygen levels in the same range as the hypoxia-inducible factor (HIF) system. Significance: Physiological effects of hypoxia may be PAM-dependent.