Related Experiment Videos
Nerve growth factor activates extracellular signal-regulated kinase and p38 mitogen-activated protein kinase pathways
J Xing1, J M Kornhauser, Z Xia
1Department of Neurobiology, Harvard Medical School, Children's Hospital, Boston, Massachusetts 02115, USA.
Abstract:
The mechanisms by which growth factor-induced signals are propagated to the nucleus, leading to the activation of the transcription factor CREB, have been characterized. Nerve growth factor (NGF) was found to activate multiple signaling pathways that mediate the phosphorylation of CREB at the critical regulatory site, serine 133 (Ser-133). NGF activates the extracellular signal-regulated kinase (ERK) mitogen-activated protein kinases (MAPKs), which in turn activate the pp90 ribosomal S6 kinase (RSK) family of Ser/Thr kinases, all three members of which were found to catalyze CREB Ser-133 phosphorylation in vitro and in vivo. In addition to the ERK/RSK pathway, we found that NGF activated the p38 MAPK and its downstream effector, MAPK-activated protein kinase 2 (MAPKAP kinase 2), resulting in phosphorylation of CREB at Ser-133. Inhibition of either the ERK/RSK or the p38/MAPKAP kinase 2 pathway only partially blocked NGF-induced CREB Ser-133 phosphorylation, suggesting that either pathway alone is sufficient for coupling the NGF signal to CREB activation. However, inhibition of both the ERK/RSK and the p38/MAPKAP kinase 2 pathways completely abolished NGF-induced CREB Ser-133 phosphorylation. These findings indicate that NGF activates two distinct MAPK pathways, both of which contribute to the phosphorylation of the transcription factor CREB and the activation of immediate-early genes.
Insights
Nerve growth factor (NGF) activates two distinct mitogen-activated protein kinase (MAPK) pathways, extracellular signal-regulated kinase/ribosomal S6 kinase (ERK/RSK) and p38/MAPK-activated protein kinase 2 (MAPKAP kinase 2). Both pathways are crucial for phosphorylating the transcription factor CREB at serine 133, leading to gene activation.
Area of Science:
- Cellular signaling and molecular biology
- Neuroscience and signal transduction
Background:
- Growth factors like Nerve Growth Factor (NGF) regulate gene expression by activating transcription factors.
- The transcription factor CREB (cAMP response element-binding protein) is a key mediator of cellular responses to various stimuli, including growth factors.
- Understanding the precise signaling cascades that lead to CREB activation is crucial for deciphering gene regulation.
Purpose of the Study:
- To elucidate the specific signaling pathways by which NGF induces the phosphorylation and activation of CREB at serine 133.
- To determine the contribution of different mitogen-activated protein kinase (MAPK) pathways in mediating NGF-induced CREB activation.
Main Methods:
- Investigated NGF-induced signaling using in vitro and in vivo assays.
- Utilized specific inhibitors to block the extracellular signal-regulated kinase (ERK)/ribosomal S6 kinase (RSK) pathway and the p38 MAPK/MAPK-activated protein kinase 2 (MAPKAP kinase 2) pathway.
- Assessed the phosphorylation of CREB at serine 133 in response to NGF and pathway inhibition.
Main Results:
- NGF activates both the ERK/RSK and p38/MAPKAP kinase 2 signaling pathways.
- Both pathways independently contribute to the phosphorylation of CREB at serine 133.
- Complete inhibition of both pathways abolished NGF-induced CREB phosphorylation, indicating their synergistic role.
Conclusions:
- NGF employs two parallel MAPK pathways, ERK/RSK and p38/MAPKAP kinase 2, to achieve CREB phosphorylation at Ser-133.
- These findings reveal a complex but coordinated signaling mechanism for NGF-mediated gene activation.
- The identified pathways are critical for coupling extracellular NGF signals to nuclear events, including the activation of immediate-early genes.