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A farnesyltransferase inhibitor attenuates cardiac myocyte hypertrophy and gene expression
A Calderone1, N Abdelaziz, F Colombo
1Université de Montréal, Departément de Physiologie et Biochimie, et l'Institut de Cardiologie de Montréal, Québec, Canada. calderon@icm.umontreal.ca
Abstract:
The overexpression of either oncogenic ras or calmodulin in cardiac myocytes can elicit a hypertrophic response, albeit their recruitment by physiologically relevant stimuli remains unresolved. The present study utilized a pharmacological approach to examine the role of ras and calmodulin in norepinephrine- and endothelin-1-stimulated hypertrophy of neonatal rat cardiac myocytes. The pretreatment of cardiac myocytes with the farnesyltransferase inhibitor BMS-191563 (25 microM) increased the level of unfarnesylated ras in the cytosolic fraction, and caused a concomitant 42 +/- 2% decrease in immunodetectable farnesylated ras in the particulate fraction. In parallel, BMS-191563 pretreatment inhibited norepinephrine-mediated 3H-leucine uptake (80 +/- 10% decrease: n = 6; P<0.01), whereas a significant but less pronounced effect on the endothelin-1 response (46 +/- 6% decrease: n = 6; P<0.05) was observed. The calmodulin inhibitor W7 caused a 50 +/- 10% decrease (n = 8; P<0.05) of norepinephrine stimulated protein synthesis, whereas the endothelin-1 response was unaffected. Consistent with the recruitment of ras, BMS-191563 pretreatment attenuated norepinephrine and endothelin-1-stimulated extracellular signal-regulated kinase (ERK) activity. However, PD098059-mediated inhibition of MEK-dependent stimulation of ERK did not alter the hypertrophic response of either agonist. At the molecular level, the pretreatment with either BMS-191563 or W7 attenuated the norepinephrine-mediated increase of prepro-ANP and -BNP mRNA. Likewise, BMS-191563 caused a significant decrease of endothelin-1-mediated expression of the natriuretic peptide mRNAs, but to a lesser extent, as compared to norepinephrine. Thus, the present study has shown the treatment of neonatal rat cardiac myocytes with a farnesyltransferase inhibitor can attenuate the hypertrophic phenotype in response to physiologically relevant stimuli, thereby supporting a role of the small GTP-binding protein ras. Moreover, these data further suggest alternative ras-independent signaling pathways are also implicated in the hypertrophic response, albeit, there appears to exist a stimulus-specific heterogeneity in their recruitment.
Insights
This study shows that inhibiting farnesyltransferase reduces cardiac myocyte hypertrophy stimulated by norepinephrine and endothelin-1, highlighting the role of ras signaling. It also suggests stimulus-specific, ras-independent pathways contribute to this response.
Area of Science:
- Cardiovascular Biology
- Molecular Cardiology
- Cell Signaling
Background:
- Cardiac myocyte hypertrophy can be induced by oncogenic ras or calmodulin overexpression.
- The involvement of ras and calmodulin in physiologically stimulated cardiac hypertrophy is not fully understood.
Purpose of the Study:
- To investigate the roles of ras and calmodulin in norepinephrine- and endothelin-1-induced cardiac hypertrophy in neonatal rat myocytes.
- To explore the signaling pathways, including ERK, involved in these hypertrophic responses.
Main Methods:
- Pharmacological inhibition of farnesyltransferase (using BMS-191563) and calmodulin (using W7).
- Measurement of 3H-leucine uptake and protein synthesis as indicators of hypertrophy.
- Assessment of extracellular signal-regulated kinase (ERK) activity and natriuretic peptide mRNA expression (prepro-ANP, -BNP).
Main Results:
- Farnesyltransferase inhibition significantly decreased norepinephrine- and endothelin-1-stimulated hypertrophy and ERK activity.
- Calmodulin inhibition reduced norepinephrine-stimulated hypertrophy but not endothelin-1-stimulated hypertrophy.
- Both inhibitors attenuated norepinephrine-induced natriuretic peptide mRNA expression, with BMS-191563 also affecting endothelin-1 responses to a lesser extent.
Conclusions:
- The small GTP-binding protein ras plays a role in mediating cardiac hypertrophy in response to physiological stimuli like norepinephrine and endothelin-1.
- Ras-independent signaling pathways are also involved in cardiac hypertrophy, with their recruitment being stimulus-specific.