Site specific differential activation of ras/raf/ERK signaling in rabbit isoproterenol-induced left ventricular hypertrophy

To understand better the mediating role of ras/raf/ERK signaling pathway in development of cardiac hypertrophy and cerebrovascular events in vivo, the molecular mechanism of the pathway in heart and cerebral arteries after isoproterenol (ISO) induced β-adrenergic receptor (βAR) stimulation was examined in rabbit as animal model. Compared with the heart, our findings indicate that ISO-stimulation results in increase in mRNA levels of ras, raf, and immediate-early genes in the cerebral arteries. Conversely, the ras and raf protein expression levels (determined by Western blot) and the ras-GTP level (determined by pull-down assay) in the heart, but not the cerebral arteries, are markedly elevated after treatment. In addition, despite constant ERK1/2 abundance, phosphorylated ERK (pERK) activity was elevated at both sites with prominent effect on heart following stimulation. Opposing to the PKA and PKC, as upstream contributors in the pathway, which seem to be similarly affected at both sites following ISO-stimulation, the results imply that the downstream candidates ras and raf, as well as immediate-early genes, have different responses at both sites post-stimulation. The results provide an evidence of site-dependent differential response of ras/raf/ERK pathway after cardiac hypertrophy-induced by ISO-stimulation. This varied response may account for underlying mechanisms of development of cardiac hypertrophy and cerebrovascular events in heart and cerebral arteries, respectively.