Nuclear RhoA Activation Regulates Nucleus Size and DNA Content via Nuclear Activation of ROCK and pErk

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• RhoA is a key regulator of the actin cytoskeleton.
• The specific role of RhoA within the cell nucleus remains largely unknown.

Purpose of the Study:

• To investigate the distinct functions of nuclear versus cytoplasmic RhoA.
• To elucidate the molecular mechanisms underlying nuclear RhoA activity.

Main Methods:

• Engineered various RhoA forms (wildtype, constitutively active, dominant negative) with localization tags.
• Established a platform to differentiate nuclear and cytoplasmic RhoA functions.
• Utilized ROCK and Erk pathway inhibitors.

Main Results:

• Nuclear RhoA activation, not cytoplasmic, controls DNA amount and nuclear size.
• This regulation is mediated by sequential activation of nuclear ROCK and Erk kinases.
• GDP-bound RhoA, not activated RhoA, enters the nucleus, suggesting distinct signaling pools.
• Nuclear RhoA activation does not significantly increase nuclear F-actin levels.

Conclusions:

• Nuclear RhoA signaling, through ROCK and Erk, plays a critical role in regulating cell proliferation and nuclear morphology.
• Cytoplasmic and nuclear RhoA signaling pathways are largely separated.
• RhoA's role in nuclear F-actin formation is minimal.