Detection and sequencing analysis of IL-18 expression in J(6-1_ leukemic cells

Expression of IL-18 and its receptor in human leukemia cells

The importance of IL-18, although clearly established in solid tumors, has not been fully elucidated in human hematopoietic neoplasms. Here we examined the mRNA and protein for IL-18 in eight human hematopoietic cell lines representing different lineages and neoplasms including leukemia, lymphoma and others. Our results revealed that IL-18 mRNA was expressed in these cells and that the corresponding protein was found in the cytoplasm. Seven of eight cell lines were also found to express two subunits of the IL-18 receptor (IL-18R) at varied levels. Furthermore, 29 out of 51 leukemia patients tested were observed to express IL-18R with 18/29 (62%) co-expression of both receptor and ligand. By blocking the IL-18 loop using specific antisense oligodeoxynucleotide (ASON) for IL-18 mRNA or anti-human IL-18R monoclonal antibody (McAbR), we were not able to demonstrate a marked inhibition on the most leukemic cell lines growth. Moreover, the potential proliferation in vitro of primary AML cells co-expressing IL-18 and its receptor was not significantly enhanced by recombinant human IL-18, suggesting that IL-18 is not apparently implicated in the proliferation of the leukemia cells via an autocrine loop. Additionally, we also found the effective modulating effect of M-CSF, IFN-alpha and TNF-alpha on IL-18R expression, implying an important in vivo effect of cytokines on IL-18-induced reaction. Moreover, the modulation of IL-18R expression was possibly irrelevant to IFN-gamma secretion induced by these cytokines.

Clinical significance of IL-18 gene over-expression in AML

Little is known about the clinical significance of interleukin (IL)-18, a novel immunoregulatory cytokine, in acute myeloid leukemia (AML). Using reverse transcriptase polymerase chain reaction (RT-PCR) analysis, levels of IL-18 mRNA were assessed in bone marrow mononuclear cells (BMMC) from 47 adult patients with de novo or CR AML in order to explore the clinical significance of IL-18. The relationship between expression levels and the established prognostic factors such as age, cytogenetic aberrations, CD34 expression and FAB subtypes was investigated. Either disease status, age or CD34 expression were found to significantly correlate with the expression of IL-18. With respect to FAB cytotypes, expression of IL-18 gene in M4/M5 (n=15) was statistically higher than that in other subtypes (n=32, P<0.001). Moreover, a significant difference in IL-18 gene expression was obtained between the high risk group and the intermediate risk group (0.5627 versus 0.3111, P=0.038). In addition, a relationship between IL-18 expression of BMMC and initial white blood cell (WBC) was clearly demonstrated by a statistical analysis (r=0.806, P<0.001). These observations suggest that IL-18 gene over-expression might reflect the convergence of several important unfavorable prognostic factors in AML.

Clone and expression of mutant M-CSF and its receptor from human leukemic cell line J6-1

Macrophage colony-stimulating factor (M-CSF) plays important roles in hematopoietic and immunologic systems. Some isoforms or mutations have been demonstrated including membrane-bound and cellular M-CSF, which associated with some leukemia, lymphoma and other solid tumors. We previously reported that the M-CSF-like membrane-associated factor (MAF-J6-1) and its receptor was found from human leukemic cell line J6-1. In this report, the cDNA of MAF-J6-1 and its receptor were cloned. The cDNA sequence of MAF-J6-1 shows a 768bp open reading frame (ORF) with 99.2% homology to m-M-CSF, but six site mutations, including two synonymous mutations and four missense mutations. The cDNA of MAF-J6-1-R has a 2916bp ORF shared 99.6% homology with M-CSF-R, but 13 site mutations, including six synonymous mutations and seven missense mutations. At the same time, a 1662bp mutant s-M-CSF cDNA, which has 10 site mutations including three synonymous mutations and seven missense mutations, was cloned from J6-1 cells. The cDNAs of MAF-J6-1 and MAF-J6-1-R were inserted into a mammalian expression plasmid pTARGET and were expressed in COS-7 cells that demonstrated by their specific MAb. COS-7 cells transfected with MAF-J6-1-R show obvious protein tyrosine kinase (PTK) activity. Our present work shows that MAF-J6-1 and its receptor are mutations of M-CSF and its receptor.