Transcriptional and translational analysis of the murine 84- and 86-kDa heat shock proteins.

The mammalian 85-90-kDa heat shock protein(s) (hsp) have been shown to exist as two species of 84 and 86 kDa (Ullrich, S. J., Robinson, E. A., Law, L. W., Willingham, M., and Appella, E. (1986) Proc. Natl. Acad. Sci. U. S. A. 83, 3121-3125). Two cDNA clones corresponding to the two forms have been isolated which specifically hybridize to either a 2.85- or a 3.0-kilobase pair transcript corresponding to hsp 84 and 86, respectively (Moore, S. K., Kozak, C., Robinson, E. A., Ullrich, S. J., and Appella, E. (1987) Gene (Amst.) 56, 29-40, and this paper). The regulation of these hsp were examined in nontransformed NIH-3T3 and chemically transformed Meth A cells. The basal level of the hsp 84 mRNA transcript was approximately 2.5-fold greater than the hsp 86 transcript, with a corresponding ratio of hsp 84 to hsp 86 protein synthesis of approximately 2.5:1. After a transient heat shock (10 min, 44 degrees C), the rate of transcription of hsp 84 and 86 increased approximately 4.5- and approximately 7-fold, respectively, within 0.5 h and remained elevated for approximately 2 h. Northern blot analysis performed on NIH-3T3 and Meth A cells, during recovery from a transient heat shock, indicated that in both cells mRNA levels of both hsp increased rapidly, peaking at 5 h post-heat shock; hsp 84 and 86 transcripts were 1.5- and 2-fold higher than in non-heat-shocked cells, respectively. The increased rate of hsp synthesis after heat shock correlated with the increased levels of each transcript in both cell lines. In the transformed Meth A cells the basal mRNA, hsp synthesis, and steady state levels of each hsp in vitro were 2-3-fold higher than in the nontransformed NIH-3T3 cells. In Meth A tumors in vivo, the steady state level of hsp 84 was reduced compared to in vitro levels. Thus, in normal and in transformed murine cells, both hsp are heat-inducible, transcriptionally and translationally, with the transformed cells expressing higher levels of synthesis of both hsp 84 and 86. The data suggest that hsp 84 and 86 syntheses are primarily transcriptionally regulated.