Hepcidin is the principal iron-regulatory hormone and a pathogenic factor in anemia of inflammation. Patients with multiple myeloma (MM) frequently present with anemia. We showed that MM patients had increased serum hepcidin, which inversely correlated with hemoglobin, suggesting that hepcidin contributes to MMrelated anemia. Searching for hepcidininducing cytokines in MM, we quantified the stimulation of hepcidin promoterluciferase activity in HuH7 cells by MM sera. MM sera activated the hepcidin promoter significantly more than did normal sera. We then examined the role of bone morphogenetic proteins (BMPs) and interleukin-6 (IL-6), the major transcriptional regulators of hepcidin. Mutations in both BMP-responsive elements abrogated the activation dramatically, while mutations in the IL-6-responsive signal transducer and activator of transcription 3-binding site (STAT3-BS) had only a minor effect. Cotreatment with anti-BMP-2/4 or noggin-Fc blocked the promoter induction with all MM sera, anti-IL-6 blocked it with a minority of sera, whereas anti-BMP-4, -6, or -9 antibodies had no effect. BMP-2-immunodepleted MM sera had decreased promoter stimulatory capacity, and BMP-2 concentrations in MM sera were significantly higher than in normal sera. Our results demonstrate that BMP-2 is a major mediator of the hepcidin stimulatory activity of MM sera. (Blood.
2010;116(18):3635-3644) IntroductionMultiple myeloma (MM) is a malignant plasma cell disorder that accounts for approximately 10% of all hematologic cancers. 1 The disease is characterized by monoclonal proliferation of plasma cells together with overproduction of a monoclonal antibody, 2 often accompanied by anemia, hypercalcemia, renal insufficiency, or bone lesions. 3 Approximately 97% of MM patients develop anemia during the course of their illness, and 70% are anemic at diagnosis. The anemia is usually normocytic/normochromic, 4 serum-iron levels are normal to low, serum ferritin is high, and hemosiderin is prominent in bone marrow macrophages. 5 This suggests than iron release from reticuloendothelial macrophages is impaired, consistent with anemia of inflammation. 6 The main mediator of anemia of inflammation is the ironregulatory hormone, hepcidin. Hepcidin is produced by hepatocytes and acts on the iron exporter, ferroportin. Binding of hepcidin to ferroportin induces the internalization and degradation of ferroportin, thereby preventing cellular iron efflux and causing retention of iron, mainly inside enterocytes, macrophages, and hepatocytes. 7 Pathologic induction of hepcidin by inflammation causes hypoferremia, restricting the iron supply for erythropoiesis and, eventually, causing anemia. The interleukin-6 (IL-6)-hepcidin axis was shown to be important for inflammation-related hypoferremia. 8 However, in chronic inflammation, IL-6-independent pathways may also induce hepcidin mRNA. 9 Recently, 2 studies described the involvement of hepcidin in anemia of MM in humans. We reported that patients with stage III MM (n Ï 44) at diagnosis had higher urinar...