Extracellular NM23 protein promotes the growth and survival of primary cultured human acute myelogenous leukemia cells

Abstract

An elevated serum level of NM23-H1 protein is found in acute myelogenous leukemia (AML), and predicts a poor treatment outcome in AML patients. To investigate the potential pathological link between the elevated serum level of this protein and poor prognosis, we examined the extracellular effects of recombinant NM23-H1 protein on the in vitro growth and survival of primary cultured AML cells at concentrations equivalent to the levels found in the serum of AML patients. Extracellular NM23-H1 protein promoted the in vitro growth and survival of AML cells and this activity was associated with the cytokine production and activation of the MAPK and signal transducers and activators of transcription signaling pathways. Inhibitors specific to MAPK signaling pathways inhibited the growth-and survival-promoting activity of NM23-H1. These findings indicate the novel biological action of extracellular NM23-H1 and its association with poor prognosis, and suggest an important role for extracellular NM23-H1 in the malignant progression of leukemia and a potential therapeutic target for these malignancies. (Cancer Sci 2009; 100: 1885-1894) T he NM23 gene was identified by differential hybridization of a cDNA library with total RNA extracted from slightly and highly metastatic melanoma cell lines.(1) NM23 genes have been identified as a family of genes encoding different isoforms of nucleoside diphosphate kinase (NDPK).(2) NM23 genes play critical roles in cellular proliferation, differentiation, oncogenesis, and tumor metastasis, and the mechanisms of these pleiotropic effects are not well understood. (3,4) Eight isotypes of the human NM23 gene (NM23-H1, NM23-H2, have been identified, (5) of which only NM23-H1 and NM23-H2 have been studied extensively in human cancers. The level of NM23-H1 expression is inversely correlated with the tumor's metastatic potential in experimental rodent cells and in human tumors, such as breast, ovarian, cervical, and gastric cancer, hepatocellular carcinoma, and melanomas.(4) Exogenous overexpression of NM23-H1 reduces the metastatic potential of multiple types of cancer cells and suppresses in vitro tumor cell motility and invasion.(6) NM23-H1 is therefore implicated in the regulation of metastasis in a variety of human cancers and its overexpression predicts a favorable patient prognosis; however, overexpression of the NM23-H1 gene in other neoplasms, including neuroblastoma and hematological malignancies, is indicative of a poor patient prognosis.(7-11) The significance of NM23-H1 overexpression as a prognostic factor is dependent on tumor cell type, although the mechanism of this discrepancy is unknown.We previously reported that a non-differentiating myeloid leukemia cell line produced differentiation-inhibiting factors (12,13) and purified one of these factors as a homologue of mouse NM23-M2. (14) NM23 genes were overexpressed in acute myelogenous leukemia (AML) cells, and a higher level of NM23 expression was correlated with poor prognosis in AML. (10,15,16) The amount of intracellular N...

Nm23-H1 Indirectly Promotes the Survival of Acute Myeloid Leukemia Blast Cells by Binding to More Mature Components of the Leukemic Clone

“…It has been previously documented that expression of Nm23-H1 transcripts, and more so levels of Nm23-H1 protein in serum, provide strong indicators of prognosis with higher values associating with poorer overall survival (7,16). The data of Okabe-Kado and colleagues (17) and our observations here strongly indicate that Nm23-H1 can act as a tumor-derived survival factor in AML, and therefore that these associations with prognosis are causal. However, the influence of this mechanism on patient outcome is likely to have been underestimated because earlier studies were not able to delineate between Nm23-H1 binding AMLs in which the mechanism is likely to be active, from nonbinders in which Nm23-H1 levels are less likely to be of importance.…”

“…Unexpectedly, either IL1b or IL6 was sufficient in all cases tested, with each of the AML samples demonstrating different survival responses to the 2 cytokines. The promoted release of IL1b and IL6 by Nm23-H1 was also observed by Okabe-Kado and colleagues (17). However, their experiments used unsorted cells, and therefore did not show that these cytokines form part of a feedback mechanism within the AML clone.…”

“…Recent data suggest that extracellular Nm23-H1 acts to support AML cell survival (17). To further examine the role of extracellular Nm23-H1 in AML, primary AML cells from 18 patients were cultured in serum-free conditions with and without 2 mg/mL rNm23-H1 and cell survival analyzed at day 5. rNm23-H1 enhanced overall AML cell survival compared with elution buffer control (P < 0.001; Fig.…”

“…Furthermore, patients with high levels of serum Nm23-H1 have significantly lower survival rates than those with low serum levels (16). Recently it has been shown that recombinant Nm23-H1 (rNm23-H1) supports the growth and survival of primary AML cells, indicating a role for extracellular Nm23-H1 in exacerbating the tumor burden (17). The authors showed that the prosurvival activity of Nm23-H1 was associated with activation of p38 mitogen activated protein kinase (MAPK) and STAT pathways, and the release of a number of supportive cytokines including granulocyte macrophage colony stimulating factor (GM-CSF), interleukin 1b (IL1b), and IL6.…”

Cell-Permeable NM23 Blocks the Maintenance and Progression of Established Pulmonary Metastasis

“…Moreover, NM23-H1 functions are not always intracellular, judging from activities mediated by extracellular NM23 (34,35). In particular, the protein is overexpressed in some tumors, including hematologic malignancies, and is present at elevated levels in patient sera, where the protein seems to promote tumor cell growth and survival by autocrine and/or paracrine mechanisms (36)(37)(38)(39). In the present study, we show that NM23-H1 lacking an MTD sequence does not efficiently enter cells.…”