Absence of Pyridoxine-5‘-Phosphate Oxidase (PNPO) Activity in Neoplastic Cells:  Isolation, Characterization, and Expression of PNPO cDNA

Abstract

Major differences in the metabolism of vitamin B6 in various cancers compared to their normal cellular counterparts have been documented. In particular, pyridoxine- 5'-phosphate oxidase (PNPO), the rate-limiting enzyme in pyridoxal 5'-phosphate (PLP) biosynthesis, is absent in liver and neurally-derived tumors. We show that the expression of PNPO is developmentally regulated not only in liver but also in brain. Specifically, PNPO activity in fetal brain tissue is 7.5-fold lower than that found in adult brain tissue. Furthermore, the isolation and characterization of a PNPO cDNA are described. The isolated cDNA was verified to be the authentic PNPO cDNA on the basis of two criteria. First, the translated product from the PNPO cDNA is immunologically reactive to a polyclonal PNPO antibody. Second, PNPO negative hepatoma cell lines stably transfected with the PNPO cDNA express enzymatically active PNPO protein. The availability of these biological reagents will not only facilitate in depth investigations of the reasons for the absence of PNPO in liver and brain malignancies but also aid in an understanding of the biochemical regulation of B6 metabolism in development.

Pyridoxal phosphate-dependent neonatal epileptic encephalopathy

“…PNPO is the rate-limiting enzyme in the synthesis of pyridoxal from pyridoxine and pyridoxamine. Defective conversion of pyridoxine-5′-phosphate to PLP caused by deficiency of PNPO activity has initially been described in neoplastic cells 6. More recently, homozygous missense, splice site and stop codon mutations were identified in three families with five infants with severe NEE 4.…”

Intraoperative delineation of primary brain tumors using time-resolved fluorescence spectroscopy

“…The PLP mechanism is known to be disturbed in cancers. [24][25][26] Our TR-LIFS studies of gliomas and normal brain tissue show that there is a decrease/absence of the emission peak at 390 nm of wavelength in glioma when compared with normal cortex tissue. We hypothesize that this may be due to altered metabolism in the PLP mechanism that leads to decrease in the PMP levels in the brain.…”

Degradation of Stop Codon Read-through Mutant Proteins via the Ubiquitin-Proteasome System Causes Hereditary Disorders

“…PNPO plays an essential role in brain metabolism, catalyzing the conversion of pyridoxine 5Ј-phosphate and pyridoxamine 5Ј-phosphate to pyridoxal 5Ј-phosphate, a metabolically active form of vitamin B6 (15). Patients with homozygous read-through mutation in the PNPO gene (X262Q) suffer from neonatal epileptic encephalopathy (16) and show no PNPO activity.…”