Cell-specific expression of heat shock proteins in chicken reticulocytes and lymphocytes.

Abstract

Chicken reticulocytes respond to elevated temperatures by the induction of only 1 heat shock protein, HSP70, whereas lymphocytes induce the synthesis of all 4 heat shock proteins (89,000 MW, HSP89; 70,000 MW, HSP70; 23,000 MW, HSP23; and 22,000 MW, HSP22). The synthesis of HSP70 in lymphocytes was rapidly induced by small increases in temperature (2.degree.-3.degree. C) and blocked by preincubation with actinomycin D. Proteins normally translated at control temperatures in reticulocytes or lymphocytes were not efficiently translated after incubation at elevated temperatures. The preferential translation of mRNA that encodes the heat shock proteins paralleled a block in the translation of other cellular proteins. This effect was most prominently observed in reticulocytes where heat shock almost completely repressed .alpha.- and .beta.-globin synthesis. HSP70 is one of the major nonglobin proteins in chicken reticulocytes, present in the non-heat-shocked cell at .apprx. 3 .times. 106 molecules per cell. HSP70 from normal and heat-shocked reticulocytes was compared by 2-dimensional gel electrophoresis and by digestion with Staphylococcus aureus V8 protease and found no detectable differences to suggest that the P70 in the normal cell is different from the heat shock-induced protein, HSP70. P70 separated by isoelectric focusing gel electrophoresis into 2 major protein spots, an acidic P70A (apparent pI [isoelectric point] = 5.95) and a basic p70B (apparent pI = 6.2). A tissue-specific expression of P70A and P70B was observed in lymphocytes and reticulocytes. In lymphocytes, P70A is the major 70,000 MW protein synthesized at normal temperatures, whereas only P70B is synthesized at normal temperatures in reticulocytes. Following incubation at elevated temperatures, the synthesis of both HSP70A and HSP70B was rapidly induced in lymphocytes, but synthesis of only HSP70B was induced in reticulocytes.