CHANGES IN THE EXPRESSION OF THE HEME-REGULATED EIF-2-ALPHA KINASE AND HEAT-SHOCK PROTEINS IN RABBIT RETICULOCYTES MATURING DURING RECOVERYFROM ANEMIA

Changes in the expression of the heme-regulated eIF-2 alpha kinase (HR I), heat shock proteins (Hsps, Hsp90, and 70) and their associated coh orts (p60 and p23) were studied in maturing rabbit reticulocytes durin g recovery from anemia. Reticulocytosis was induced by injection of N- acetylphenylhydrazine or by phlebotomy from the ear vein, and circulat ing red blood cells were fractionated on histopaque density gradients. Northern and Western blot analyses indicated that HRI and hsps mRNA a nd protein content gradually decreased during maturation of reticulocy tes into erythrocytes. Reduction in levels of hsps and HRI was also ob served when cells of same age group (density) were compared as the ani mals recovered from the anemia. Low hematocrits correlated with high l evels of hsps expression and with increasing hematocrits hsps expressi on decreased. Under the conditions used to quantify these protein leve ls, Hsc70 and p60 were detected in erythrocytes of fully recovered ani mals. Maintenance of Hsc70 and p60 suggests important ongoing roles fo r these hsps in protecting the structure and function of proteins in e rythrocytes lacking transcriptional and translational machinery. (C) 1 998 Academic Press.