Submitted on December 10, 2003
Accepted on April 9, 2004
ANP-INDUCED DECREASE OF IRON REGULATORY PROTEIN ACTIVITY IS INDEPENDENT OF HO-1 INDUCTION
Alexandra K. Kiemer1*, Anke C. Fornges1, Kostas Pantopoulos2, Manfred Bilzer3, Bill Andriopoulos2, Tobias Gerwig1, Silke Kenngott3, Alexander L. Gerbes3, and Angelika M. Vollmar4
1 Department of Pharmacy, University of Munich, Munich, Germany; Department of Medicine II, University of Munich, Munich, Germany
2 Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital, Montreal, Quebec, Canada
3 Department of Medicine II, University of Munich, Munich, Germany
4 Department of Pharmacy, University of Munich, Munich, Germany
* To whom correspondence should be addressed. E-mail: kiemer{at}scripps.edu.
ANP-preconditioned livers are protected from ischemia/reperfusion injury. ANP-treated organs
show increased expression of HO-1. Since HO-1 liberates bound iron, aim of our study was to
determine whether ANP affects iron regulatory protein (IRP) activity and thus the levels of
ferritin. Methods: Rat livers were perfused with KH-buffer (± ANP, 8-Br-cGMP, SnPP, 20 min),
stored in UW-solution (4°C, 24 h), and reperfused (120 min). IRP activity was assessed by
gelshift assays; ferritin, IRP phosphorylation, and PKC localization by Western blot. Results:
Control livers displayed decreased IRP activity at the end of ischemia but no change in ferritin
content during ischemia and reperfusion. ANP-pretreated livers showed reduced IRP activity, an
effect mimicked by 8-Br-cGMP. Ferritin levels were increased in ANP-pretreated organs.
Simultaneous perfusion of livers with ANP and SnPP did not reduce ANP-induced action arguing
against a role of HO-1 for the changes in IRP activity. ANP and 8-Br-cGMP decreased
membrane localization of PKC
and 
, but this modulation of PKC seems not related to inhibition
of IRP binding. Conclusion: This work shows the cGMP-mediated attenuation of IRP binding
activity by ANP which results in increased hepatic ferritin levels. This change in IRPs is
independent of ANP-induced HO-1 and reduced PKC activation.
