Expression of P2X Family Receptors in Pediatric Acute Leukemia Patients.

Abstract 4417

Nucleotides are new players in intercellular communication network. Abnormal signaling leads to cell dysfunction and diseases. P2X family receptors, consisting of seven members, are ATP-gated plasma membrane ion channels widely distributed in different organs, tissues, and cells with diverse biological functions. Their distribution patterns and significance in pediatric leukemias have not been established though the abnormal expression of P2×7 receptor was reported in leukemias. Here we investigated the expression of P2X family receptors in BMMC samples from 124 Chinese pediatric acute leukemia patients (85 boys and 39 girls; 66 newly diagnosed ALL, 37 newly diagnosed AML, 17 relapsed ALL, and 4 relapsed AML) with the median age of 8 (range, 1-16 years) as well as 20 childhood normal healthy controls. Relative quantitative real-time PCR results showed that P2×1, 4, 5, 7 receptors were simultaneously over expressed in newly diagnosed ALL patients (p=0.04, p<0.001, p=0.007 and p=0.02, respectively), whereas P2×1, 4, 7 receptors were also over expressed in newly diagnosed AML patients (p<0.001, p<0.001 and p=0.018, respectively) when compared with control samples. The P2×2, 3, 6 receptors were absent or marginally expressed in both leukemia and control groups. These results suggested that P2×1, 4, 5, 7 receptors were hematopoiesis-related P2X family receptors. Statistic analysis between their expressions and clinical features in ALL samples, such as sex, leukocyte count, risk group, numerical or structural cytogenetic abnormalities, LDH level, 15 day bone marrow response to induction chemotherapy, was also performed. The results showed that P2×1 was highly expressed in TEL/AML positive B-ALL patients than in negative ones (P = 0.017). Interestingly, the expression of P2×1 receptor was negatively related to age in ALL patients (r = -0.44; p = 0.001), but not in AML or normal controls. Western blot results confirmed the over-expression of these receptors in leukemia samples. It was worth noting that the co-expression feature of them, especially between P2×4 and P2×7 receptors (r=0.63; p<0.0001) could be observed, which raised the speculation that the simultaneously high expression of hematopoiesis-related P2X receptors might change the functional properties of P2X receptors and might have particular roles in pediatric leukemias. The highest expression of P2×1 and P2×7 receptors was detected in both ALL and AML patients with relapse, while highest expression of P2×4 and P2×5 receptors could be detected in ALL patients with relapse. Moreover, concomitant decrease of P2×4, 5, 7 receptor expressions was observed at complete remission stage after chemotherapy in a follow up study of 26 patients (20 ALL and 6 AML). The expression of these receptors was also studied in a Notch1 over-expressing murine T-ALL model, showing all P2X but P2×5 receptors were expressed in mouse bone marrow samples, which is different from the results obtained in human. It's worth noting that elevated expression of P2×7 receptor could be detected in these Notch1-T-ALL leukemia cells and steady increase of its expression was observed in BM samples during the development of leukemia. Functional P2×7 receptor was verified in both human and murine samples by monitoring the intracellular free calcium concentration upon stimulation by its more potent agonist BzATP. These results suggested that P2×1, 4, 5, 7 receptors were hematopoiesis-related P2X family receptors in human, and their signaling, especially for P2×7 receptor, might play important roles in pediatric leukemias. P2X family receptors might co-operatively contribute to the malignant phenotype in human pediatric leukemias.