A bacterial cytotoxin identifies the RhoA exchange factor Net1 as a key effector in the response to DNA damage

Area of Science:

• Cellular biology
• Molecular mechanisms of DNA damage response

Background:

• DNA damaging agents like bacterial cytolethal distending toxin (CDT) and ionizing radiation (IR) activate RhoA.
• Activated RhoA promotes actin stress fiber formation and delays cell death.
• Signaling intermediates regulating RhoA activation and cell survival remain unidentified.

Purpose of the Study:

• To identify signaling intermediates that regulate RhoA activation and promote cell survival upon DNA damage.
• To elucidate the molecular pathway linking genotoxic stress to RhoA-mediated cell survival.

Main Methods:

• Investigated the role of Net1, a nuclear RhoA-specific Guanine nucleotide Exchange Factor (GEF).
• Utilized dominant-negative Net1 expression and Net1 knockdown via RNA interference (RNAi).
• Assessed RhoA activation, actin stress fiber formation, cell death, and activation of p38 MAPK and MAPK-activated protein kinase 2.

Main Results:

• Net1 dephosphorylation at an inhibitory site occurred upon exposure to CDT or IR.
• Net1 knockdown or dominant-negative expression blocked RhoA activation and stress fiber formation, increasing cell death.
• Net1 and RhoA signaling involved the activation of p38 MAPK and MAPK-activated protein kinase 2.

Conclusions:

• Net1 is critical for controlling RhoA and p38 MAPK-mediated cell survival in response to DNA damaging agents.
• This pathway highlights how chronic exposure to bacterial toxins may contribute to genomic instability.