Identification of the soluble granulocyte-macrophage colony stimulating factor receptor protein in vivo

Abstract

On the basis of the finding of alternatively spliced mRNAs, the -subunit of the receptor for GM-CSF is thought to exist in both a membrane spanning (tmGMR) and a soluble form (solGMR). However, only limited data has been available to support that the solGMR protein product exists in vivo. We hypothesized that hematopoietic cells bearing tmGMR would have the potential to also produce solGMR. To test this hypothesis we examined media conditioned by candidate cells using functional, biochemical, and immunologic means. Three human leukemic cell lines that express tmGMR (HL60, U937, THP1) were shown to secrete GM-CSF binding activity and a solGMR-specific band by Western blot, whereas a tmGMR-negative cell line (K562) did not. By the same analyses, leukapheresis products collected for autologous and allogeneic stem cell transplants and media conditioned by freshly isolated human neutrophils also contained solGMR. The solGMR protein in vivo displayed the same dissociation constant (Kd = 2-5 nmol) as that of recombinant solGMR. A human solGMR ELISA was developed that confirmed the presence of solGMR in supernatant conditioned by the tmGMR-positive leukemic cell lines, hematopoietic progenitor cells, and neutrophils. Furthermore, the ELISA demonstrated a steady state level of solGMR in normal human plasma (36 ± 17 pmol) and provided data suggesting that plasma solGMR levels can be elevated in acute myeloid leukemias.

Differential regulation of c‐Jun N‐terminal kinase and NF‐κB pathway by caffeic acid phenethyl ester in astroglial and monocytic cells

“…1999). The CRT‐MG human astroglial cells and U937 human monocytic cells were maintained in RPMI 1640 medium with 10 mmol/L HEPES (pH 7.2) supplemented with 2 mmol/L l ‐glutamine, 100 U/mL penicillin, 100 μg/mL streptomycin (Gibco BRL, Grand Island, NY, USA), and 10% heat‐inactivated fetal bovine serum, as previously described (Sayani et al. 2000; Choi et al.…”

Neutrophil apoptosis pathways and their modifications in inflammation

“…Death receptors and perhaps other surface molecules are able to activate SHP‐1, which can also inhibit survival factor signaling. Moreover, survival factor‐mediated effects can be reduced by soluble cytokine receptors (117) or anti‐inflammatory cytokines and elimination of the pathogen results in reduced survival factor production. Finally, anti‐inflammatory drugs often modify the production of pro‐inflammatory cytokines.…”

Clinical manifestations associated with the aberrant expression of the soluble granulocyte–macrophage colony‐stimulating factor receptor in patients presenting with haematological malignancies

“…It has previously been demonstrated that solGMRα was found in serum samples obtained from healthy donors with a normal range of 10–85 pmol/l (Sayani et al, 2000). In the same study, four of five patients with AML demonstrated elevated solGMRα levels (Sayani et al, 2000). The elevated solGMRα levels in that small cohort of AML patients suggested a pathophysiological role for solGMRα in leukaemia.…”

“…The distribution of solGMRα levels in serum has been determined in the normal population (Sayani et al, 2000) and has a range of 10–85 pmol/l. In our study, solGMRα levels less than 10 pmol/l were considered low and levels greater than 85 pmol/l were considered high.…”

“…In‐vitro, solGMRα can also form a unique high‐affinity cell‐surface complex with βc which may serve as a decoy receptor for GM‐CSF, thus providing a second mechanism of antagonism (Murray et al , 1996, 1998; Prevost et al, 2000). solGMRα circulates as a normal serum constituent (Sayani et al, 2000); however, the cellular sources and mechanisms of regulation of solGMRα production are just beginning to be elucidated.…”