Altered membrane NTPase activity in Lesch-Nyhan disease fibroblasts: comparison with HPRT knockout mice and HPRT-deficient cell lines.
Lesch-Nyhan disease (LND) is a rare disorder caused by a defect of an enzyme in the purine salvage pathway, hypoxanthine phosphoribosyl transferase (HPRT). It is still unknown how the metabolic defect translates into the complex neuropsychiatric phenotype characterized by self-injurious behavior, dystonia and mental retardation. There are abnormalities in purine and pyrimidine nucleotide content in HPRT-deficient cells. We hypothesized that altered nucleotide concentrations in HPRT deficiency change G-protein-mediated signal transduction. Therefore, our original study aim was to examine the high-affinity GTPase activity of G-proteins in membranes from primary human skin and immortalized mouse skin fibroblasts, rat B103 neuroblastoma cells and mouse Neuro-2a neuroblastoma cells. Unexpectedly, in membranes from human fibroblasts, B103- and Neuro-2a cells, V(max) of low-affinity nucleoside 5'-triphosphatase (NTPase) activities was decreased up to 7-fold in HPRT deficiency. In contrast, in membranes from mouse fibroblasts, HPRT deficiency increased NTPase activity up to 4-fold. The various systems analyzed differed from each other in terms of K(m) values for NTPs, absolute V(max) values and K(i) values for nucleoside 5'-[beta,gamma-imido]triphosphates. Our data show that altered membrane NTPase activity is a biochemical hallmark of HPRT deficiency, but species and cell-type differences have to be considered. Thus, future studies on biochemical changes in LND should be conducted in parallel in several HPRT-deficient systems.
Pinto
Cibele S
CS
Department of Pharmacology and Toxicology, University of Kansas, Lawrence, Kansas, USA.
Jinnah
Hyder A
HA
Shirley
Thomas L
TL
Nyhan
William L
WL
Seifert
Roland
R
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D002461:Cell Line, Transformed; D045744:Cell Line, Tumor; D002648:Child; D002675:Child, Preschool; D005110:Extracellular Space / Q000201:enzymology; D005347:Fibroblasts / Q000166:cytology / Q000201:enzymology*; D020558:GTP Phosphohydrolases / Q000378:metabolism; D006801:Humans; D007041:Hypoxanthine Phosphoribosyltransferase / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism*; D007926:Lesch-Nyhan Syndrome / Q000378:metabolism*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009447:Neuroblastoma; D043583:Nucleoside-Triphosphatase / Q000235:genetics* / Q000378:metabolism*; D051381:Rats; D015398:Signal Transduction / Q000502:physiology; D013045:Species Specificity
D007041:Hypoxanthine Phosphoribosyltransferase; D000251:Adenosine Triphosphatases; D020558:GTP Phosphohydrolases; D043583:Nucleoside-Triphosphatase