The Rac activator Tiam1 prevents keratinocyte apoptosis by controlling ROS-mediated ERK phosphorylation.
Tiam1 is a ubiquitously expressed activator of the small GTPase Rac. Previously, we found that Tiam1 knockout (KO) mice are resistant to DMBA-induced skin tumorigenicity, which correlated with increased apoptosis in keratinocytes of the skin epidermis. Here, we have studied the mechanisms by which Tiam1 protects against apoptosis. We found that Tiam1-KO keratinocytes show increased apoptosis in response to apoptotic stimuli, including growth factor deprivation and heat-shock treatment. Expression of catalytically active Tiam1, but not inactive Tiam1, rescues the apoptosis susceptibility of Tiam1-KO keratinocytes, indicating that this defect is caused by impaired Tiam1-mediated Rac activation. Apoptosis induced by growth factor starvation correlates with impaired ERK phosphorylation in Tiam1-KO keratinocytes. Moreover, Tiam1-KO keratinocytes contain lower levels of intracellular reactive oxygen species (ROS) when compared with wild-type cells. The ROS content of keratinocytes is dependent on both Tiam1 and the activity of NADPH oxidase (Nox), and is required for ERK-mediated survival signaling. Indeed, Tiam1 deficiency or the inhibition of intracellular ROS production blocks ERK phosphorylation and sensitizes wild-type keratinocytes to apoptotic stimuli. Our results indicate that the Rac activator Tiam1 controls the intracellular redox balance by Nox-mediated ROS production, which regulates ERK phosphorylation and the susceptibility of keratinocytes to apoptotic signaling.
Rygiel
Tomasz P
TP
Division of Cell Biology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
Mertens
Alexander E
AE
Strumane
Kristin
K
van der Kammen
Rob
R
Collard
John G
JG
D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis / Q000187:drug effects*; D002470:Cell Survival; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism / Q000502:physiology*; D015603:Keratinocytes / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D010766:Phosphorylation; D017382:Reactive Oxygen Species / Q000378:metabolism; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1
D020662:Guanine Nucleotide Exchange Factors; D017382:Reactive Oxygen Species; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; C513260:Tiam1 protein, mouse; D048049:Extracellular Signal-Regulated MAP Kinases