Ras regulates NFAT3 activity in cardiac myocytes

Area of Science:

• Cardiology
• Molecular Biology
• Cell Signaling

Background:

• Cardiac myocyte hypertrophy involves distinct signal transduction pathways.
• Key pathways include Ras superfamily small GTPases and calcineurin-NFAT3 signaling.

Purpose of the Study:

• To investigate the functional interaction between Ras-regulated and calcineurin-regulated pathways in cardiac myocytes.
• To elucidate the role of Ras proteins in regulating NFAT3 activity and cardiac hypertrophy.

Main Methods:

• Expression of constitutively active and dominant-negative Ras mutants in neonatal myocytes.
• Assessing NFAT activity and nuclear translocation of NFAT3 fusion proteins.
• Utilizing pharmacological inhibitors (cyclosporin A, MEK1 inhibitor) and dominant-negative forms of Raf and ERK2.

Main Results:

• Constitutively active Ras (V12ras) increased NFAT activity and NFAT3 nuclear translocation, unlike other small GTPases.
• Dominant-negative Ras blocked phenylephrine-stimulated NFAT activity and NFAT3 nuclear localization.
• Ras appears upstream of calcineurin; MEK1/Raf/ERK pathway inhibition blocked NFAT3 activation, while their activation stimulated NFAT activity.

Conclusions:

• A functional interaction exists between Ras-regulated and calcineurin-regulated pathways in cardiac myocytes.
• Ras proteins regulate NFAT3 activity, likely via a pathway involving mitogen-activated protein kinase (MAPK).
• These findings suggest a novel Ras-MAPK-NFAT3 axis in cardiac myocyte hypertrophy.