IRON-RESPONSIVE ELEMENT-BINDING PROTEIN IN HEMOCHROMATOSIS LIVER AND INTESTINE

Iron-responsive element-binding protein (IRE-BP) activity was studied in liver and intestinal samples of hemochromatosis and control patient s using a short P-32-IRE-RNA probe on ''retardation'' nondenaturing po lyacrylamide gels. IRE-BP activity was assessed in liver biopsy specim ens in 36 patients-16 hemochromatosis homozygotes, 4 hemochromatosis h eterozygotes, 6 patients with secondary iron overload, and 10 control patients with normal hepatic iron concentrations. Intestinal IRE-BP ac tivity was assessed in 14 hemochromatosis homozygotes and 16 normal su bjects. Endogenous IRE-BP activity was determined from P-32 retarded o n the gel, and total IRE-BP activity was assessed after reducing tissu e samples with 2-mercaptoethanol. Hepatic endogenous IRE-BP activity w as inversely related to hepatic iron concentration (r = -.59, P <.0002 ). Mean hepatic endogenous IRE-BP activity in the hemochromatosis homo zygotes, 0.25 +/- 0.04 pmol/mg protein, was significantly decreased co mpared with values in the normal controls, 0.45 +/- 0.06 pmol/mg prote in, P <.05. Hepatic total IRE-BP was also significantly decreased in t he hemochromatosis patients by gel retardation assay and Western blott ing with anti-IRE-BP antibody. Intestinal endogenous IRE-BP activity, total IRE-BP activity, and iron concentration did not significantly di ffer between hemochromatosis patients and normal control subjects. Thi s suggests that both endogenous IRE-BP activity and the total amount o f the protein are downregulated in the liver by tissue iron, Intestina l IRE-BP activity that regulates intestinal transferrin receptor expre ssion is normal in hemochromatosis and appropriate for the intracellul ar iron concentration.