Identification of the Nucleotidase Responsible for the AMP Hydrolysing Hyperactivity Associated with Neurological and Developmental Disorders

Abstract

Nucleoside monophosphate phosphohydrolases comprise a family of enzymes dephosphorylating nucleotides both in intracellular and extracellular compartments. Members of this family exhibit different sequence, location, substrate specificity and regulation. Besides the ectosolic 5'-nucleotidase, several cytosolic and one mitochondrial enzymes have been described. Nevertheless, researchers refer any AMP-dephosphorylating activity to as 5'-nucleotidase, lacking a more accurate identification. Increase of AMP hydrolysing activity has been associated with neurological and developmental disorders. The identification of the specific enzyme involved in these pathologies would be fundamental for the comprehension of the linkage between the enzyme activity alteration and brain functions. We demonstrate that the described neurological symptoms are associated with increased ectosolic 5'-nucleotidase activity on the basis of radiochemical assays and immunoblotting analysis. Furthermore, present data evidence that the assay conditions normally applied for the determination of cytosolic 5'-nucleotidases activity in crude extracts are affected by the presence of solubilised ectosolic nucleotidase.

Neurological Disorders of Purine and Pyrimidine Metabolism

“…The gene involved in this disease has not been identified yet. The increased nucleotidase activity measured in the fibroblasts of one patient was associated to the hyperexpression of the e-N form; this finding was recently confirmed by kinetic characterization and specific antibody cross reaction [133]. The gene coding for e-N (NT5E) has been mapped to 6q14-q21.…”

“…CD38 has been demonstrated to induce a rapid export of CD73 from an intracellular pool to the cell surface [134], thus suggesting some connection between NAD breakdown and this purine disorder. Normal NAD(P) concentration was found in fibroblasts from patients with 5'NT hyperactivity [133]. The mechanism whereby nucleotidase hyperactivity causes NAPDD is unknown.…”

5'-Nucleotidases, Nucleosides and their Distribution in the Brain: Pathological and Therapeutic Implications

“…Increased cN-II (in Lesch-Nyhan patients with HGPRT deficiency) and Abbreviations: A1 receptor/A2A receptor/A2B receptor/A3 receptor: A1/A2A/A2B/A3 subtype of adenosine receptors; ADA: adenosine deaminase; ADK: adenosine kinase; Ado: adenosine; CNT transporters: concentrative nucleoside transporters; ENT transporters: equilibrative nucleoside transporters; GDA: guanine deaminase; Guo: guanosine; Ino: inosine; PNP: purine nucleoside phosphorylase; Urd: uridine; XO: xanthine oxidase e5'NT (in nucleotidase-associated pervasive developmental disorders) activity are associated with neurological symptoms, such as seizures and ataxia [35,37,38,87,[336][337][338]. Increased serum 5'NT (enhanced AMP hydrolysis by e.g., glycosylphosphatidyl-inositol anchored and mainly soluble extracellular form of e5'NT) [82,200] activity have also been shown in a chronic animal model of electroconvulsive shock [339], in patients with epilepsy and in clozapinetreated schizophrenic patients [72,73] and in pentylenetetrazol-induced seizures [74,75].…”

IMP–GMP specific cytosolic 5′-nucleotidase regulates nucleotide pool and prodrug metabolism

“…It is conceivable that this discrepancy depends on an over-estimation of the phosphatase activity in control cells. In fact, while the phosphotransferase assay is specific for cN-II [30], the phosphatase activity, measured as the rate of IMP hydrolysis, even in the presence of an ectosolic-5′-nucleotidase inhibitor, depends not only on cN-II, but also on other cytosolic 5′-nucleotidases or aspecific phosphatases [52,53]. To assess the effect of cN-II over-expression on the viability of HEK 293 cells, we measured the viability of cells after 48 h of ponasterone exposure finding no significant differences between over-expressing and control cells.…”