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p21-activated kinase links Rac/Cdc42 signaling to merlin
Guang-Hui Xiao1, Alexander Beeser, Jonathan Chernoff
1Human Genetics Program, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111, USA.
Abstract:
The neurofibromatosis type 2 tumor suppressor gene, NF2, is mutated in the germ line of NF2 patients and predisposes affected individuals to intracranial and spinal tumors. Moreover, somatic mutations of NF2 can occur in the sporadic counterparts of these neurological tumor types as well as in certain neoplasms of non-neuroectodermal origin, such as malignant mesothelioma and melanoma. NF2 encodes a 595-amino acid protein, merlin, which exhibits significant homology to the ezrin-radixin-moesin family of proteins. However, the mechanism by which merlin exerts its tumor suppressor activity is not well understood. In this investigation, we show that merlin is phosphorylated in response to expression of activated Rac and activated Cdc42 in mammalian cells. Furthermore, we demonstrate that merlin phosphorylation is mediated by p21-activated kinase (Pak), a common downstream target of both Rac and Cdc42. Both in vivo and in vitro kinase assays demonstrated that Pak can directly phosphorylate merlin at serine 518, a site that affects merlin activity and localization. These biochemical investigations provide insights into the regulation of merlin function and establish a framework for elucidating tumorigenic mechanisms involved in neoplasms associated with merlin inactivation.
Insights
The neurofibromatosis type 2 (NF2) tumor suppressor merlin protein is phosphorylated by p21-activated kinase (Pak). This phosphorylation, occurring at serine 518, impacts merlin
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- Neurofibromatosis type 2 (NF2) is a genetic disorder predisposing individuals to tumors.
- The NF2 gene encodes the merlin protein, a tumor suppressor with homology to the ezrin-radixin-moesin family.
- The precise mechanism of merlin's tumor suppressor activity and its regulation remain incompletely understood.
Purpose of the Study:
- To investigate the regulation of merlin's tumor suppressor function.
- To identify signaling pathways that modulate merlin activity.
- To elucidate the role of merlin phosphorylation in tumorigenesis.
Main Methods:
- Mammalian cell culture to study merlin phosphorylation.
- Expression of activated Rac and Cdc42 to induce merlin phosphorylation.
- In vitro and in vivo kinase assays to identify the responsible kinase.
- Site-directed mutagenesis to pinpoint the phosphorylation site.
Main Results:
- Merlin phosphorylation is induced by activated Rac and Cdc42.
- p21-activated kinase (Pak) directly phosphorylates merlin at serine 518.
- Phosphorylation at serine 518 influences merlin's activity and cellular localization.
Conclusions:
- Merlin function is regulated by Pak-mediated phosphorylation at serine 518.
- This finding provides insight into the molecular mechanisms underlying NF2-associated tumors.
- Establishes a framework for understanding tumorigenesis in neoplasms with merlin inactivation.