The Hyposensitive N187D P2X7 Mutant Promotes Malignant Progression in Nude Mice

Abstract

Nucleotides are new players in the intercellular communication network. P2X7 is a member of the P2X family of receptors, which are ATP-gated plasma membrane ion channels with diverse biological functions. Abnormal expression and dysfunction of P2X7 have been reported in leukemias. Here, we report a new P2X7 mutant (an A 559 -to-G substitution causing N187D P2X7) cloned from J6-1 leukemia cells. The characteristics of N187D P2X7 were studied by establishing stably transfected K562 cell lines. Our results show that N187D P2X7 required a higher concentration of agonist for its activation, leading to Ca 2؉ influx (EC 50 ‫؍‬ 293.3 ؎ 6.6 M for the mutant and 93.6 ؎ 2.2 M for wild-type P2X7) and ERK phosphorylation, which were not caused by differential cell-surface expression or related to high ATPase activity on the cell surface and in the extracellular space. K562 cells expressing this N187D mutant showed a proliferative advantage and reduced pro-apoptosis effects in vitro and in vivo. Furthermore, elevated angiogenesis and CD206-positive macrophage infiltration were found in tumor tissues formed by K562-M cells. In addition, higher expression of VEGF and MCP1 could be detected in tumor tissues formed by K562-M cells. Our results suggest that N187D P2X7, representing mutants hyposensitive to agonist, might be a positive regulator in the progression of hematopoietic malignancies.

Expression of P2X7 Receptor IncreasesIn VivoTumor Growth

“…Increased neovascularization of P2X7-expressing tumors was also recently reported by others (47). The recent demonstration that P2X7 expression enhances cancer cell invasiveness in vivo (30) is in keeping with its angiogenetic activity and further stresses the possible role of this receptor in cancer.…”

Targeting Ion Channels in Leukemias: A New Challenge for Treatment

“…The K562 cells transfected with these mutant channels display a proliferative advantage, both in vitro and in immunodepressed mice. Furthermore, elevated angiogenesis and CD206-positive macrophage infiltration were detected in tumor masses formed by mutant K562 cells [51]. Finally, P 2X7 receptors were also functionally expressed in murine erythroelukemia cells, in which their activation seems to be important for induction of apoptotic death and release of microparticles [52].…”

“…Blocking this channel in mice led to long-term loss of T EM cells, with consequent improvement of autoimmune disease symptoms, without concomitant effects on the T-cell population that confers protection against infection and cancers [103]. However, because T EM cells are protective in some cancers [104,105] but not others [106], chronic blockade of K v 1.3 could have overall positive or negative effects depending on cancer [48], [49], [50], [51], [52] The first column (Target) indicates the type of ion channel; the second column (Hemopoietic neoplasia) indicates the tumor (cells or tissues) where the channel has been found to be expressed; the third column (Role) shows the biological effect exerted on leukemia cells by the drugs/molecular tools affecting ion channels, which are reported in the fourth column (Molecular tool). (AML: acute myeloid leukemia; ALL: acute lymphoblastic leukemia; CML: chronic myeloid leukemia; MDS: myelodysplastic syndrome).…”

Organ-Specific Microenvironment Modifies Diverse Functional and Phenotypic Characteristics of Leukemia-Associated Macrophages in Mouse T Cell Acute Lymphoblastic Leukemia

“…The roles of macrophages in the development of hematopoietic malignancies have not been fully elucidated. In fact, accumulation of macrophages was observed in hematopoietic malignant cell-formed tumor tissues, with higher growth potential in nude mice models (40,41). The significance of macrophages in lymph node samples was studied in lymphomas.…”