Akt is a major downstream target of PI3-kinase involved in angiotensin II-induced proliferation

Area of Science:

• Molecular Biology
• Cell Signaling
• Cardiovascular Research

Background:

• Angiotensin II (Ang II) is known to mediate cell growth through various signal transduction pathways.
• Key pathways implicated include extracellular signal-regulated kinase 1/2 (ERK1/2) and phosphatidylinositol 3-kinase (PI3K).
• The precise downstream targets of PI3K in Ang II-induced proliferation require further elucidation.

Purpose of the Study:

• To identify downstream targets of the PI3K pathway involved in Ang II-mediated cell proliferation.
• To investigate the role of Akt signaling in Ang II-induced cell growth.
• To determine the involvement of Gq protein coupling and intracellular calcium in Akt activation.

Main Methods:

• Utilized rat aortic smooth muscle (RASM) cells and CHO cells expressing the rat AT1A receptor.
• Employed specific Akt inhibitors and a dominant-negative Akt mutant.
• Investigated signaling using an AT1 receptor mutant (AT1AD74E) and intracellular calcium chelator BAPTA-AM.

Main Results:

• Both ERK1/2 and PI3K pathways were independently activated by Ang II, contributing to DNA synthesis and cell proliferation.
• Inhibition or dominant-negative mutation of Akt blocked Ang II-induced proliferation.
• Akt activation by Ang II was found to be Gq protein-dependent but calcium-independent.

Conclusions:

• Akt plays a specific and necessary role in Ang II-induced proliferation.
• The signaling pathway involves Gq protein coupling but does not rely on intracellular calcium elevation.
• These findings clarify a critical downstream mechanism of Ang II-mediated cell growth.