Expression of P2X₇ purinoceptors on human lymphocytes and monocytes: evidence for nonfunctional P2X₇ receptors

Abstract

Lymphocytes from normal subjects and patients with B-chronic lymphocytic leukemia (B-CLL) show functional responses to extracellular ATP characteristic of the P2X(7) receptor (previously termed P2Z). These responses include opening of a cation-selective channel/pore that allows entry of the fluorescent dye ethidium and activation of a membrane metalloprotease that sheds the adhesion molecule L-selectin. The surface expression of P2X(7) receptors was measured in normal leucocytes, platelets, and B-CLL lymphocytes and correlated with their functional responses. Monocytes showed four- to fivefold greater expression of P2X(7) than B, T, and NK lymphocytes, whereas P2X(7) expression on neutrophils and platelets was weak. All cell types demonstrated abundant intracellular expression of this receptor. All 12 subjects with B-CLL expressed lymphocyte P2X(7) at about the same level as B lymphocytes from normal subjects. P2X(7) function, measured by ATP-induced uptake of ethidium, correlated closely with surface expression of this receptor in normal and B-CLL lymphocytes and monocytes (n = 47, r = 0.70; P < 0.0001). However, in three patients the ATP-induced uptake of ethidium into the malignant B lymphocytes was low or absent. The lack of P2X(7) function in these B lymphocytes was confirmed by the failure of ATP to induce Ba(2+) uptake into their lymphocytes. This lack of function of the P2X(7) receptor resulted in a failure of ATP-induced shedding of L-selectin, an adhesion molecule that directs the recirculation of lymphocytes from blood into the lymph node.

Involvement of P2X receptors in the NAD+-induced rise in [Ca2+]i in human monocytes

“…However as described earlier, monocytes, in contrast to monocyte-derived macrophages, do not form pores in [46,47]. Considering the crucial role of ionic compositions of the extracellular medium in P2X 7 receptor activation by ATP [48][49][50][51], Gudipaty et al [37] showed that replacement of extracellular Na + and Cl − with K + and nonhalide anions strongly facilitated ATP-dependent pore formation in monocytes. In line with their data, we also observed that these ionic conditions resulted in an increased agonist affinity, such that 100 μM ATP was sufficient for the activation of a nonselective pore by P2X 7 receptors.…”

Roles of extracellular nucleotides and P2 receptors in ectodomain shedding

“…Adenosine, ADP and UTP did not cause CD62L shedding, while oxidised ATP inhibited both ATP-and BzATP-induced CD62L shedding from these cells [55]. Furthermore, KN-62 inhibited ATP-induced CD62L shedding from CLL lymphocytes [34,56], while BzATP-induced CD62L shedding was impaired in CLL cells expressing non-functional P2X7 [57]. Collectively, confirming a role for P2X7 in this process.…”

Human neutrophils do not express purinergic P2X7 receptors

“…It has been proposed that activation of neutrophils with the chemo-attractant N-formylmethionyl-leucyl-phenylalanine (fMLP) induced the appearance of purinergic responses [9,43]. Such activation could induce trafficking of purinergic receptors to plasma membrane as was suggested by Gu et al [19]. To test this hypothesis, isolated neutrophils were treated with 1 μM fMLP during 10 min at 37°C and then subjected to patch clamp to measure the ATP-activated currents.…”

“…Although mRNA for P2X 7 as well as P2X 1 and P2X 4 has been detected by some groups in human neutrophils [8,42], others failed to detect both mRNA and protein in whole human neutrophils [31,44]. Furthermore, it has been suggested that most of P2X 7 R are in the cytosol of human neutrophils serving as a reserve to be recruited to the plasma membrane after cell activation [19]. However, treatment of neutrophils with lipopolysaccharide (LPS), which is known to up-regulate P2X 7 R expression in monocytes [22], did not induce P2X 7 R protein expression [44].…”