A His-155 to Tyr polymorphism confers gain-of-function to the human P2X7 receptor of human leukemic lymphocytes.
The P2X(7)R is an ATP-gated cation channel expressed in hemopoietic cells that participates in both cell proliferation and apoptosis. Expression and function of the P2X(7)R have been associated with the clinical course of patients affected by chronic lymphocytic leukemia (CLL). Functional variants causing loss-of-function of the P2X(7)R have been identified, namely, polymorphisms 1513A>C (E496A), 1729T>A (I568N), and 946G>A (R307Q). Here we investigated other nonsynonymous polymorphisms located either in the extracellular portion of the receptor, such as the 489C>T (H155Y) variant, or in the long cytoplasmic tail of the receptor, such as the 1068G>A (A348T), 1096C>G (T357S), and 1405A>G (Q460R) variants. P2X(7)R function was monitored by measuring ATP-induced Ca(2+) influx in PBL of patients affected by CLL and in recombinant human embryonic kidney (HEK) 293 cells stably transfected with each single P2X(7) allelic variant. Ca(2+) influx was markedly reduced in association with the 1513C allele, whereas variants located in the same intracellular domain, such as the 1068A, 1096G, or 1405G variants, were associated with a minor functional decrease. Significant Ca(2+) flux increase was observed in lymphocytes from CLL patients bearing the 489C/T and 489T/T genotypes in association with the 1513A/A genotype. Functional analysis in recombinant HEK293 cells expressing P2X(7)R confirmed an increased ATP-dependent activation of the P2X(7) 489T mutant with respect to the wild type receptor, as assessed by both by [Ca(2+)](i) influx and ethidium uptake experiments. These data identify the 489C>T as a gain-of-function polymorphism of the P2X(7)R.
Cabrini
Giulio
G
Section of General Pathology, Department of Experimental and Diagnostic Medicine, University of Ferrara, Italy. giulio.cabrini@azosp.vr.it
Falzoni
Simonetta
S
Forchap
Sylvia L
SL
Pellegatti
Patrizia
P
Balboni
Alessandra
A
Agostini
Paola
P
Cuneo
Antonio
A
Castoldi
Gianluigi
G
Baricordi
O Roberto
OR
Di Virgilio
Francesco
F
D000255:Adenosine Triphosphate / Q000378:metabolism; D000483:Alleles; D019943:Amino Acid Substitution; D001483:Base Sequence; D020013:Calcium Signaling; D016022:Case-Control Studies; D002460:Cell Line; D004273:DNA, Neoplasm / Q000235:genetics; D005787:Gene Frequency; D005838:Genotype; D006801:Humans; D007700:Kinetics; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000235:genetics* / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D011110:Polymorphism, Genetic; D020641:Polymorphism, Single Nucleotide; D018048:Receptors, Purinergic P2 / Q000235:genetics* / Q000378:metabolism*; D058486:Receptors, Purinergic P2X7; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D014162:Transfection
D004273:DNA, Neoplasm; C546468:P2RX7 protein, human; D018048:Receptors, Purinergic P2; D058486:Receptors, Purinergic P2X7; D011994:Recombinant Proteins; D000255:Adenosine Triphosphate