Effects of RGMc on BMP2 and BMP6-mediated Gene Expression in Hep3B Liver Cells

Mutations in repulsive guidance molecule c (RGMc) / hemojuvelin (HJV) cause juvenile hemochromatosis, an aggravated iron overload disorder that presents early in life. Patients with juvenile hemochromatosis, and RGMc knockout mice, have diminished expression of the key iron-regulatory peptide, hepcidin. This suggests that RGMc plays a critical role in the regulation of iron homeostasis; however the mechanisms of RGMc actions are unknown. Recent studies have shown that RGMc directly binds to the growth factors, bone morphogenetic protein 2 and 6 (BMP2 and BMP6), and it is possible that this interaction regulates aspects of iron metabolism. We used microarrays to examine the effects of RGMc on BMP2- and BMP6-mediated gene expression. In our experimental model we treated Hep3B liver cells that had been serum starved for 16 hours as follows: (1) un-treated, (2) BMP2, (3) BMP2 + 10-fold molar excess of Noggin (a potent BMP2 inhibitor), (4) BMP2 + 20-fold molar excess of RGMc, (5) BMP6, (6) BMP6 + 10-fold molar excess of Noggin, (7) BMP6 + 20-fold molar excess of RGMc. Binding was allowed to proceed for BMP and Noggin or RGMc for 3 hr at 20°C prior to treatment of Hep3B cells. Treatment time was 4 hr at which cells were collected for RNA isolation.