Effect of cytosol on the regulation of expression of myosin heavy chain genes during cardiac hypertrophy.

In vitro translation of RNA transported from the rat heart nuclei has suggested that the transport of translatable messages from hypertrophic heart nuclei is greater than from sham-operated heart nuclei. An increased translation activity was observed in cell-free system with RNA transported from sham-operated heart nuclei in presence of hypertrophic heart cytosol, than from sham-operated heart cytosol. Similar results were obtained when myosin heavy chain (MHC) mRNA in the transported RNA was analyzed by slot-blot hybridization using beta cDNA probe. Immunoprecipitation analysis of the translated products using beta MHC isozyme specific antibody indicated that the increased levels of beta MHC specific mRNA in the RNA transported from sham-operated heart nuclei in presence of hypertrophic heart cytosol than sham-operated heart cytosol. Direct quantitation of alpha and beta MHC messengers by slot-blot hybridization analysis of transported RNA using oligomeric probes corresponding to the 3' untranslated regions of alpha and beta MHC mRNAs revealed that an increased transport of both alpha and beta MHC specific mRNAs from sham-operated heart nuclei in the presence of hypertrophic heart cytosol occurs, of which beta MHC mRNA is more than that of alpha MHC. In contrast, slot-blot hybridization analysis of the radioactive RNA synthesized during transcription in vitro in nuclei obtained from sham-operated as well as hypertrophic hearts has shown an increased synthesis of alpha in sham nuclei and that of beta in hypertrophic heart nuclei. These results suggest that both transcriptional and post-transcriptional regulation may be operative in the expression of alpha and beta MHC genes during the development of cardiac hypertrophy.