A bacterial cytotoxin identifies the RhoA exchange factor Net1 as a key effector in the response to DNA damage.
BACKGROUND
Exposure of adherent cells to DNA damaging agents, such as the bacterial cytolethal distending toxin (CDT) or ionizing radiations (IR), activates the small GTPase RhoA, which promotes the formation of actin stress fibers and delays cell death. The signalling intermediates that regulate RhoA activation and promote cell survival are unknown.


RESULTS
We demonstrate that the nuclear RhoA-specific Guanine nucleotide Exchange Factor (GEF) Net1 becomes dephosphorylated at a critical inhibitory site in cells exposed to CDT or IR. Expression of a dominant negative Net1 or Net1 knock down by iRNA prevented RhoA activation, inhibited the formation of stress fibers, and enhanced cell death, indicating that Net1 activation is required for this RhoA-mediated responses to genotoxic stress. The Net1 and RhoA-dependent signals involved activation of the Mitogen-Activated Protein Kinase p38 and its downstream target MAPK-activated protein kinase 2.


CONCLUSIONS
Our data highlight the importance of Net1 in controlling RhoA and p38 MAPK mediated cell survival in cells exposed to DNA damaging agents and illustrate a molecular pathway whereby chronic exposure to a bacterial toxin may promote genomic instability.
Department of Cell and Molecular Biology, Karolinska Institutet, Stockholm, Sweden.
Lina
L
Guerra
Heather S
HS
Carr
Agneta
A
Richter-Dahlfors
Maria G
MG
Masucci
Monica
M
Thelestam
Jeffrey A
JA
Frost
Teresa
T
Frisan
D000199:Actins / Q000378:metabolism; D001419:Bacteria / Q000378:metabolism*; D001427:Bacterial Toxins / Q000633:toxicity*; D001483:Base Sequence; D002460:Cell Line; D004249:DNA Damage; D006801:Humans; D015513:Oncogene Proteins; D012313:RNA / Q000235:genetics; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D000199:Actins; D001427:Bacterial Toxins; C099763:NET1 protein, human; D015513:Oncogene Proteins; C067044:cytolethal distending toxin; D012313:RNA; D048051:p38 Mitogen-Activated Protein Kinases