JunB mediates basal- and TGFβ1-induced smooth muscle cell contractility

Area of Science:

• Cell Biology
• Physiology
• Molecular Biology

Background:

• Smooth muscle contraction relies on acto-myosin interactions regulated by various proteins.
• The AP-1 transcription factor family influences smooth muscle cell behaviors like growth and migration.
• The precise role of AP-1 in regulating smooth muscle contractility remains unclear.

Purpose of the Study:

• To investigate the role of the AP-1 family member JunB in regulating visceral smooth muscle cell contractility.
• To elucidate the molecular mechanisms by which JunB affects smooth muscle contraction.

Main Methods:

• Utilized RNA interference (RNAi) to silence JunB in primary human bladder smooth muscle cells (pBSMC).
• Assessed cell contractility using gel contraction and traction force microscopy assays.
• Measured protein levels and phosphorylation states of key contractile proteins and signaling molecules, including Rho kinase (ROCK), myosin light chain (MLC20), MYPT1, and cofilin.
• Analyzed the F:G actin ratio to evaluate actin dynamics.

Main Results:

• JunB upregulation was observed downstream of transforming growth factor beta-1 (TGFβ1).
• JunB silencing inhibited both basal and TGFβ1-stimulated contractility in pBSMC.
• JunB knockdown reduced levels of ROCK and MLC20 and attenuated MYPT1 and cofilin phosphorylation.
• JunB silencing decreased the F:G actin ratio, indicating altered actin polymerization.

Conclusions:

• JunB is a novel regulator of visceral smooth muscle cell contractility.
• JunB modulates contractility by affecting myosin light chain phosphorylation and actin cytoskeleton dynamics.
• These findings highlight a new mechanism involving JunB in smooth muscle function, particularly in response to TGFβ1 stimulation.