Inhibition by interleukin-1 of the action of erythropoietin on erythroid precursors and its possible role in the pathogenesis of hypoplastic anaemias

Coordination of iron homeostasis by bone morphogenetic proteins: Current understanding and unanswered questions

Iron homeostasis is tightly regulated to balance the iron requirement for erythropoiesis and other vital cellular functions, while preventing cellular injury from iron excess. The liver hormone hepcidin is the master regulator of systemic iron balance by controlling the degradation and function of the sole known mammalian iron exporter ferroportin. Liver hepcidin expression is coordinately regulated by several signals that indicate the need for more or less iron, including plasma and tissue iron levels, inflammation, and erythropoietic drive. Most of these signals regulate hepcidin expression by modulating the activity of the bone morphogenetic protein (BMP)-SMAD pathway, which controls hepcidin transcription. Genetic disorders of iron overload and iron deficiency have identified several hepatocyte membrane proteins that play a critical role in mediating the BMP-SMAD and hepcidin regulatory response to iron. However, the precise molecular mechanisms by which serum and tissue iron levels are sensed to regulate BMP ligand production and promote the physical and/or functional interaction of these proteins to modulate SMAD signaling and hepcidin expression remain uncertain. This critical commentary will focus on the current understanding and key unanswered questions regarding how the liver senses iron levels to regulate BMP-SMAD signaling and thereby hepcidin expression to control systemic iron homeostasis.

Inhibition of erythropoietin gene expression signaling involves the transcription factors GATA-2 and NF-kappaB

The anemia of chronic inflammatory and malignant diseases is partly due to impaired synthesis of the hormone erythropoietin (Epo). The proinflammatory cytokines interleukin-1 (IL-1) and tumor necrosis factor a (TNF-alpha) suppress in vitro Epo gene expression and Epo protein secretion. However, the molecular mechanisms of this inhibition are poorly understood. The human Epo promoter and the 5' flanking region contain several recognition sequences for transcription factors acting either positively or negatively. Herein, we investigated the roles of the transcription factors GATA-2 and NF-kappaB in the modulation of Epo gene expression by IL-1beta and TNF-alpha in the human hepatoma cell line HepG2. Electrophoretic mobility shift assays revealed increased GATA-2 and NF-kappaB DNA binding in cells treated with IL-1beta or TNF-alpha. Reporter gene assays with a sequence from the Epo promoter in front of the firefly luciferase gene showed that the cytokines reduced Epo reporter gene activity. Functional inactivation of GATA-2 and NF-kappaB by oligo-decoy techniques prevented the inhibition of Epo production by IL-1beta and TNF-alpha. In HepG2 cells stably transfected with a dominant-negative form of IkappaBalpha, the activation of NF-kappaB was inhibited, while Epo mRNA levels and Epo secretion increased. Thus, both GATA-2 and NF-kappaB seem to be involved in the suppression of Epo gene expression by IL-1beta and TNF-alpha in vitro and may be responsible for impaired Epo synthesis in inflammatory diseases in vivo.