Heat shock induction of HSP 89 is regulated in cellular aging

Induction of heat shock proteins (HSPs) was evaluated as a function of age of the IMR-90 human diploid fibroblasts. Heat shock (42 degrees C) markedly increased the synthesis of proteins with apparent molecular weights of 98, 89, 72, 50, 42 and 25 KDa, with HSP 89 and 72 being most prominent. This heat shock induction of HSPs was inversely correlated to the population doubling level (PDL) of the cell cultures used. For example, the synthesis rate of HSP 89 increased from a basal heat shock of young cells (PDL 18); in the old cells (PDL 51), the increase was from 1% to a maximum of 4% at 10-12 hrs after initiation of the heat shock. Western blot analysis showed that HSP 89 constituted approximately 2 and 10% of total cellular proteins in control and heat shocked (42 degrees C, 12-24 hrs) young cells; corresponding values for the old cells were 2 and 4.5%, respectively. Northern blot quantitation of the amount of mRNA hybridizable to cDNA probes of HSP 89 provided evidence that this age-dependent decrease in induction of HSP 89 in IMR-90 cells was attributable to a transcriptional/pre-translational mechanism.