Functional EP₂ receptors on blast cells of patients with acute leukemia

Abstract

Dear Sir,The ability of the lipidic mediator prostaglandin E 2 (PGE 2 ) to regulate the immune system has been widely explored in the past decade.1,2 Numerous studies have highlighted the ability of PGE 2 to regulate monocyte macrophages, dendritic cells, as well as T and B lymphocytes.1,2 The biologic effects of PGE 2 are mediated through interactions with 4 distinct membrane-bound G-protein-coupled EP receptors: EP 1 , EP 2 , EP 3 and EP 4 . EP 1 is coupled to G q/p and ligand binding induces intracellular calcium levels. EP 3 is coupled to G i and inhibits cAMP production. In contrast, EP 2 and EP 4 are coupled to G s and stimulate cAMP production, which leads to gene regulation.1 Freshly isolated blast cells of acute myeloid leukemic (AML) and acute lymphoid leukemic (ALL) patients increase their cAMP synthesis in response to forskolin, a cAMP-induced agonist.3 While the presence of functional EP receptors on mature leukocytes is documented, 4 no results are available concerning their presence on immature ones. In view of the potentially important role of PGE 2 in processes of cancer and leukocyte maturation and function, 1,2 we investigated the presence of EP 2 and EP 4 receptors on freshly isolated blast cells from AML and ALL patients by testing the effect of PGE 2 on their cAMP synthesis.Over a period of 1 year, blood samples recovered on EDTA were obtained from 12 consecutive patients (6 men, 6 women; mean age, 66 years) at diagnosis according to the Helsinki recommendations. Blood samples from patients with more than 85% (range, 85-97%) blast cells as circulating leukocytes were used. Leucocytosis ranged from 11 to 210 G/l. The population (graded according to the French-American-British classification) consisted of 2 AML0, 3 AML1, 2 AML2, 1 AML3, 1 AML4, 1 AML5 and 2 ALL2. Cytogenetic data were available for 11 patients. Six had a normal karyotype. The 5 remaining patients were heterogeneous and comprised one complex karyotype, one with a Philadelphia chromosome, one with a t(15;17), one with an unidentified marker and one with a monosomy 7. Blood mononuclear cells were isolated by separation on a Ficoll gradient and washed 2 times with Hank's balanced salts solution (HBSS). The blast purity (mean, 98%; range, 94-99%) was controlled by flow cytometry analysis (XL II; Coulter, Margency, France). Blast viability (> 95%) was judged by Trypan blue exclusion. Blasts (3 Â 10 6 cells) were stimulated in HBSS with PGE 2 and various EP-specific agonists for 10 min at 378C. In separate sets of experiments, the effect of PGE 2 on cAMP production was investigated in a cell-and timedependent manner. After stimulation, cells were ethanol-extracted and cAMP levels were measured using a commercially available EIA kit (Cayman Chemical, Ann Arbor, MI) according to the manufacturer's instructions. The sensitivity of the assay permits detection of 0.1 pmol cAMP. In another set of experiments, EP 2 receptors were studied by reverse transcription-polymerase chain reaction (RT-PCR).Results indicate that PGE 2 stimulated cAMP...

A Role for Lipid Mediators in Acute Myeloid Leukemia

“…Concordantly, expression levels of EP1 and EP2 have been demonstrated to be increased in cancerous tissues [111]. In AML, Ross et al as well as Yagi et al could demonstrate elevated transcript levels of EP2 in AML blasts in a pediatric cohort [112,113] and Denizot et al could show that AML blasts express functional EP2 receptors [25,114] (Figure 2).…”

Homeobox Protein HB9 Binds to the Prostaglandin E Receptor 2 Promoter and Inhibits Intracellular cAMP Mobilization in Leukemic Cells

“…A coherent functional effect of an altered PTGER2 expression in leukemia is not described yet; however, on myeloid blast cells, only stimulation of PTGER2 has a functional effect compared with the expression of other PTGER receptors (28,29).…”

Bone marrow stroma-derived PGE2 protects BCP-ALL cells from DNA damage-induced p53 accumulation and cell death

“…To our knowledge, very little is known about the role of PGE 2 in haematopoietic malignancies, and we here propose a distinct anti-apoptotic mechanism of PGE 2 in BCP-ALLs compared to what is established in carcinomas. Based on our findings that 1) exposure of BCP-ALL cells to either forskolin, cAMP analogues, PGE 2 , or MSC cocultures inhibits p53 accumulation and cell death in a similar fashion [ 9 - 11 ], 2) MSCs secrete PGE 2 , 3) ALL cells are known to express functional EP2 receptors eliciting a cAMP response [ 24 ], and 4) the effect of MSC cocultures on BCP-ALL p53 levels and cell survival is inhibited by COX or PKA inhibitors, we suggest a model in which BCP-ALL cells are protected from DNA damage-induced p53 accumulation and cell death by BM stromal cells in a PGE 2 -cAMP-PKA-dependent manner (Figure 6 ). Furthermore, it should be noted that we have observed a similar effect of cAMP on p53 in carcinoma and sarcoma cell lines such as MCF-7 [ 10 ], U2-OS [ 10 ], and HCT116 (unpublished results), suggesting that inhibition of the tumour suppression function of wild type p53 by cAMP is not a phenomenon restricted to BCP-ALL.…”

“…BM-MSCs are known to secrete prostaglandin E 2 (PGE 2 ) [ 23 ], and ALL blasts have been demonstrated to express functional EP2 receptors, one of the AC-activating subclasses of PGE 2 receptors [ 24 , 25 ]. The role of tumour stroma-derived PGE 2 has been extensively studied in solid tumours [ 26 ], however, little is known about its potential role in leukaemia physiology.…”