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Blood, 15 May 2008, Vol. 111, No. 10, pp. 5195-5204.
Prepublished online as a Blood First Edition Paper on March 7, 2008; DOI 10.1182/blood-2007-09-111567.
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Submitted September 10, 2007
Accepted February 23, 2008
Hemojuvelin regulates hepcidin expression via a selective subset of BMP ligands and receptors independently of neogenin
Yin Xia, Jodie L Babitt, Yisrael Sidis, Raymond T Chung, and Herbert Y Lin*
Program in Membrane Biology and Division of Nephrology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States
Reproductive Endocrine Unit, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States
Gastrointestinal Unit, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States
* Corresponding author; email: hlin{at}partners.org.
Hemojuvelin (HJV) is a co-receptor for bone morphogenetic protein (BMP) signaling that regulates hepcidin expression and iron metabolism. However, the precise combinations of BMP ligands and receptors used by HJV remain unknown. HJV has also been demonstrated to bind to neogenin, but it is not known whether this interaction has a role in regulating hepcidin expression. In the present study, we show that BMP-2, BMP-4 and BMP-6 are endogenous ligands for HJV in hepatoma-derived cells, and that all three of these ligands are expressed in human liver. We demonstrate in vitro that HJV selectively uses the BMP type II receptors ActRIIA and BMPRII, but not ActRIIB, and HJV enhances utilization of ActRIIA by BMP-2 and BMP-4. Interestingly, ActRIIA is the predominant BMP type II receptor expressed in human liver. While HJV can employ all three BMP type I receptors (ALK2, ALK3 and ALK6) in vitro, only ALK2 and ALK3 are detected in human liver. Finally, we show that HJV-induced BMP signaling and hepcidin expression are not altered by neogenin overexpression or by inhibition of endogenous neogenin expression. Thus, HJV-mediated BMP signaling and hepcidin regulation occur via a distinct subset of BMP ligands and BMP receptors, independently of neogenin.

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