Dissecting signalling pathways underlying hepcidin regulation
Current project members:
- Flavia d’Allesio (PhD student)
From the plasma membrane to the nucleus: how proteins associated with hereditary hemochromatosis regulate hepcidin expression - Guillem Casanovas (PhD student)
Identification of regulatory elements in the hepcidin promoter - Kasia Mleczko-Sanecka (PhD student)
Identification of novel regulators of hepcidin expression by a genome-wide siRNA knock-down approach
Previous lab member:
Maria Vittoria Verga Falzacappa
From the plasma membrane to the nucleus: how proteins associated with hereditary hemochromatosis regulate hepcidin expression.
Flavia d’Allesio
The HH associated proteins HFE, TfR2 and HJV are membrane proteins that positively regulate hepcidin expression to maintain tissue iron homeostasis. The molecular mechanism(s) how these proteins sense systemic iron levels and transmit the signal to regulate hepcidin production is not yet understood. A common model suggests that HFE and TfR2 are integral parts of a protein complex that monitors systemic iron availability via iron bound to serum transferrin and transmits the signal to the nucleus to regulate hepcidin transcription. Competition of HFE binding to TfR1 and TfR2 may play a role in this process. Furthermore, HJV acts as a bone morphogenetic protein (BMP) co-receptor to stimulate hepcidin expression via the SMAD signalling pathway.
In my PhD project I will apply biochemical and fluorescent microscopy based techniques to understand whether the HH-associated proteins HFE, TfR2 and HJV form a protein complex on the plasma membrane of transfected cells and whether complex formation is affected by the addition of iron-bound transferrin. Furthermore, I will analyze whether overexpression of specific HH proteins alters the expression of the endogenous HH proteins and/or amplifies BMP signalling or activates hepcidin transcription via alternative pathways.
Identification of regulatory elements in the hepcidin promoter
Guillem Casanovas
The aim of my work is to dissect the pathways that regulate hepcidin expression and to discover new elements in the hepcidin promoter that control its transcription. Specifically, my research is focused on the analyses of the cross-talk between the HJV/BMP and the IL-6/STAT3 pathways that were shown previously to regulate hepcidin promoter activity.
IL-6 is a pro-inflammatory cytokine secreted by T-cells and macrophages. It induces hepcidin transcription via the JAK/STAT pathway and a STAT3 responsive element that we and others identified at position –64/–72 of the hepcidin promoter. Increased hepcidin levels in response to IL6 reduce plasma iron levels to limit iron availability to pathogens. If increased hepcidin expression persists in the case of chronic infectious and inflammatory processes, anemia will develop.
Additional work in our group identified a functional Bone Morphogenetic Protein-responsive element (BMP-RE) within the hepcidin promoter. The hemochromatosis protein hemojuvelin (Hjv), a BMP co-receptor regulates hepcidin expression through this element, which is located very close to the STAT3 responsive element. Interestingly, mutation of this element impairs hepcidin activation in response to IL-6, uncovering a link between the IL-6/STAT3 and the HJV/BMP pathways. By combining siRNA knock-down technology with hepcidin promoter assays, I am currently characterising the cross-talk between these two pathways, and I am searching for novel functional elements present within the hepcidin promoter.
Identification of novel regulators of hepcidin expression by a genome-wide siRNA knock-down approach
Kasia Mleczko-Sanecka
Although hepcidin is a key regulator of mammalian iron homeostasis, only few proteins, including the hemochromatosis proteins Hfe, transferrin receptor 2 (TfR2) and hemojuvelin (Hjv) were so far identified as critical regulators of its expression. The aim of my PhD project is to discover novel genes involved in regulation of hepcidin expression using the hepatocyte cell line Huh7, hepcidin promoter-driven reporter constructs and a genome-wide siRNA knock-down approach. Experiments are being performed in collaboration with Michael Boutros (DKFZ), where this technology is well established.
Project-related publications:
Casanovas G, Mleczko-Sanecka K, Altamura S, Hentze MW, Muckenthaler MU. Bone morphogenetic protein (BMP)-responsive elements located in the proximal and distal hepcidin promoter are critical for its response to HJV/BMP/SMAD. *J Mol Med* (2009)
Verga Falzacappa MV, Casanovas G, Hentze MW and Muckenthaler MU. A bone morphogenetic protein (BMP)-responsive element in the hepcidin promoter controls HFE2-mediated hepatic hepcidin expression and its response to IL-6 in cultured cells. J Mol Med. 86(5):531-40; 2008
Braliou GG, Verga Falzacappa MV, Chachami G, Casanovas G, Muckenthaler MU, Simos G. 2-Oxoglutarate-dependent oxygenases control hepcidin gene expression. J Hepatol. 48(5):801-10; 2008
- Maria Vittoria Verga Falzacappa*, Maja Vujić Spasić*, Regina Kessler, Jens Stolte, Matthias W. Hentze, and Martina U. Muckenthaler STAT3 mediates hepatic hepcidin expression and its inflammatory stimulation. Blood 109 (1): 353-358; 2007 (*equal contribution)
