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Cdk5 is involved in BDNF-stimulated dendritic growth in hippocampal neurons.

Cheung ZH, Chin WH, Chen Y, Ng YP, Ip NY - PLoS Biol. (2007)

Bottom Line: Interestingly, attenuation of Cdk5 activity or overexpression of a TrkB mutant lacking the Cdk5 phosphorylation site essentially abolishes brain-derived neurotrophic factor (BDNF)-triggered dendritic growth in primary hippocampal neurons.In addition, we found that Cdk5 is involved in BDNF-induced activation of Rho GTPase Cdc42, which is essential for BDNF-triggered dendritic growth.Our observations therefore reveal an unanticipated role of Cdk5 in TrkB-mediated regulation of dendritic growth through modulation of BDNF-induced Cdc42 activation.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, Biotechnology Research Institute and Molecular Neuroscience Center, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.

ABSTRACT
Neurotrophins are key regulators of neuronal survival and differentiation during development. Activation of their cognate receptors, Trk receptors, a family of receptor tyrosine kinases (RTKs), is pivotal for mediating the downstream functions of neurotrophins. Recent studies reveal that cyclin-dependent kinase 5 (Cdk5), a serine/threonine kinase, may modulate RTK signaling through phosphorylation of the receptor. Given the abundant expression of both Cdk5 and Trk receptors in the nervous system, and their mutual involvement in the regulation of neuronal architecture and synaptic functions, it is of interest to investigate if Cdk5 may also modulate Trk signaling. In the current study, we report the identification of TrkB as a Cdk5 substrate. Cdk5 phosphorylates TrkB at Ser478 at the intracellular juxtamembrane region of TrkB. Interestingly, attenuation of Cdk5 activity or overexpression of a TrkB mutant lacking the Cdk5 phosphorylation site essentially abolishes brain-derived neurotrophic factor (BDNF)-triggered dendritic growth in primary hippocampal neurons. In addition, we found that Cdk5 is involved in BDNF-induced activation of Rho GTPase Cdc42, which is essential for BDNF-triggered dendritic growth. Our observations therefore reveal an unanticipated role of Cdk5 in TrkB-mediated regulation of dendritic growth through modulation of BDNF-induced Cdc42 activation.

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Ser478 Phosphorylation of TrkB Required Cdk5 Activity In Vivo(A) BDNF stimulation resulted in an increase in p-Ser478 TrkB (p-Ser TrkB) levels in cortical neurons. Treatment with Cdk5 selective inhibitor Ros (25 μM) inhibited the BDNF-induced increase in p-Ser478 TrkB, although Ros treatment also resulted in a slight increase in basal p-Ser478 TrkB.(B) cdk5+/+ and cdk5−/− brain lysates were immunoblotted against TrkB, phospho-TrkB at Ser478, and β-actin as loading control. p-Ser478 TrkB was almost completely absent in cdk5−/− brain, indicating the importance of Cdk5 in the phosphorylation of TrkB at Ser478 in vivo.(C) Cortical neurons isolated from cdk5+/+ and cdk5−/− brain were treated with BDNF for different periods. Interestingly, while BDNF enhanced TrkB Ser478 phosphorylation in cdk5+/+ cortical neurons, TrkB Ser478 phosphorylation was not detected in cdk5−/− neurons, nor did BDNF stimulation enhance Ser478 phosphorylation, indicating that BDNF-stimulated increase in TrkB Ser478 phosphorylation requires Cdk5 activity.
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pbio-0050063-g003: Ser478 Phosphorylation of TrkB Required Cdk5 Activity In Vivo(A) BDNF stimulation resulted in an increase in p-Ser478 TrkB (p-Ser TrkB) levels in cortical neurons. Treatment with Cdk5 selective inhibitor Ros (25 μM) inhibited the BDNF-induced increase in p-Ser478 TrkB, although Ros treatment also resulted in a slight increase in basal p-Ser478 TrkB.(B) cdk5+/+ and cdk5−/− brain lysates were immunoblotted against TrkB, phospho-TrkB at Ser478, and β-actin as loading control. p-Ser478 TrkB was almost completely absent in cdk5−/− brain, indicating the importance of Cdk5 in the phosphorylation of TrkB at Ser478 in vivo.(C) Cortical neurons isolated from cdk5+/+ and cdk5−/− brain were treated with BDNF for different periods. Interestingly, while BDNF enhanced TrkB Ser478 phosphorylation in cdk5+/+ cortical neurons, TrkB Ser478 phosphorylation was not detected in cdk5−/− neurons, nor did BDNF stimulation enhance Ser478 phosphorylation, indicating that BDNF-stimulated increase in TrkB Ser478 phosphorylation requires Cdk5 activity.

Mentions: To further examine if Cdk5 is essential for phosphorylation of TrkB at Ser478 in vivo, we examined the effect of inhibiting Cdk5 activity on phospho-Ser478 (p-Ser478) TrkB levels in cortical neurons. We found that at basal level, TrkB was weakly phosphorylated at Ser478. Interestingly, stimulation with BDNF led to a marked increase in p-Ser478 TrkB levels, indicating that phosphorylation of TrkB at Ser478 was at least in part ligand dependent. Remarkably, treatment with Cdk5 selective inhibitor roscovitine (Ros) almost abrogated the BDNF-triggered increase in p-Ser478 TrkB levels (Figure 3A), suggesting that Cdk5 was involved in the BDNF-stimulated component of TrkB Ser478 phosphorylation. To further establish the involvement of Cdk5 in Ser478 phosphorylation of TrkB in vivo, the levels of p-Ser478 TrkB in cdk5+/+ and cdk5−/− brain lysates were examined. Importantly, we found that Ser478-phosphorylated TrkB was basically undetectable in Cdk5−/− brain lysates (Figure 3B). Similarly, cortical neurons prepared from Cdk5−/− brains exhibited undetectable levels of p-Ser478 TrkB. In addition, BDNF stimulation failed to trigger an increase in p-Ser478 TrkB levels (Figure 3C). These observations strongly suggest that Cdk5 is essential for phosphorylation of TrkB at Ser478 in vivo, and that BDNF-stimulated increase in Ser478 phosphorylation of TrkB requires Cdk5 activity.


Cdk5 is involved in BDNF-stimulated dendritic growth in hippocampal neurons.

Cheung ZH, Chin WH, Chen Y, Ng YP, Ip NY - PLoS Biol. (2007)

Ser478 Phosphorylation of TrkB Required Cdk5 Activity In Vivo(A) BDNF stimulation resulted in an increase in p-Ser478 TrkB (p-Ser TrkB) levels in cortical neurons. Treatment with Cdk5 selective inhibitor Ros (25 μM) inhibited the BDNF-induced increase in p-Ser478 TrkB, although Ros treatment also resulted in a slight increase in basal p-Ser478 TrkB.(B) cdk5+/+ and cdk5−/− brain lysates were immunoblotted against TrkB, phospho-TrkB at Ser478, and β-actin as loading control. p-Ser478 TrkB was almost completely absent in cdk5−/− brain, indicating the importance of Cdk5 in the phosphorylation of TrkB at Ser478 in vivo.(C) Cortical neurons isolated from cdk5+/+ and cdk5−/− brain were treated with BDNF for different periods. Interestingly, while BDNF enhanced TrkB Ser478 phosphorylation in cdk5+/+ cortical neurons, TrkB Ser478 phosphorylation was not detected in cdk5−/− neurons, nor did BDNF stimulation enhance Ser478 phosphorylation, indicating that BDNF-stimulated increase in TrkB Ser478 phosphorylation requires Cdk5 activity.
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Related In: Results  -  Collection

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pbio-0050063-g003: Ser478 Phosphorylation of TrkB Required Cdk5 Activity In Vivo(A) BDNF stimulation resulted in an increase in p-Ser478 TrkB (p-Ser TrkB) levels in cortical neurons. Treatment with Cdk5 selective inhibitor Ros (25 μM) inhibited the BDNF-induced increase in p-Ser478 TrkB, although Ros treatment also resulted in a slight increase in basal p-Ser478 TrkB.(B) cdk5+/+ and cdk5−/− brain lysates were immunoblotted against TrkB, phospho-TrkB at Ser478, and β-actin as loading control. p-Ser478 TrkB was almost completely absent in cdk5−/− brain, indicating the importance of Cdk5 in the phosphorylation of TrkB at Ser478 in vivo.(C) Cortical neurons isolated from cdk5+/+ and cdk5−/− brain were treated with BDNF for different periods. Interestingly, while BDNF enhanced TrkB Ser478 phosphorylation in cdk5+/+ cortical neurons, TrkB Ser478 phosphorylation was not detected in cdk5−/− neurons, nor did BDNF stimulation enhance Ser478 phosphorylation, indicating that BDNF-stimulated increase in TrkB Ser478 phosphorylation requires Cdk5 activity.
Mentions: To further examine if Cdk5 is essential for phosphorylation of TrkB at Ser478 in vivo, we examined the effect of inhibiting Cdk5 activity on phospho-Ser478 (p-Ser478) TrkB levels in cortical neurons. We found that at basal level, TrkB was weakly phosphorylated at Ser478. Interestingly, stimulation with BDNF led to a marked increase in p-Ser478 TrkB levels, indicating that phosphorylation of TrkB at Ser478 was at least in part ligand dependent. Remarkably, treatment with Cdk5 selective inhibitor roscovitine (Ros) almost abrogated the BDNF-triggered increase in p-Ser478 TrkB levels (Figure 3A), suggesting that Cdk5 was involved in the BDNF-stimulated component of TrkB Ser478 phosphorylation. To further establish the involvement of Cdk5 in Ser478 phosphorylation of TrkB in vivo, the levels of p-Ser478 TrkB in cdk5+/+ and cdk5−/− brain lysates were examined. Importantly, we found that Ser478-phosphorylated TrkB was basically undetectable in Cdk5−/− brain lysates (Figure 3B). Similarly, cortical neurons prepared from Cdk5−/− brains exhibited undetectable levels of p-Ser478 TrkB. In addition, BDNF stimulation failed to trigger an increase in p-Ser478 TrkB levels (Figure 3C). These observations strongly suggest that Cdk5 is essential for phosphorylation of TrkB at Ser478 in vivo, and that BDNF-stimulated increase in Ser478 phosphorylation of TrkB requires Cdk5 activity.

Bottom Line: Interestingly, attenuation of Cdk5 activity or overexpression of a TrkB mutant lacking the Cdk5 phosphorylation site essentially abolishes brain-derived neurotrophic factor (BDNF)-triggered dendritic growth in primary hippocampal neurons.In addition, we found that Cdk5 is involved in BDNF-induced activation of Rho GTPase Cdc42, which is essential for BDNF-triggered dendritic growth.Our observations therefore reveal an unanticipated role of Cdk5 in TrkB-mediated regulation of dendritic growth through modulation of BDNF-induced Cdc42 activation.

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry, Biotechnology Research Institute and Molecular Neuroscience Center, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China.

ABSTRACT
Neurotrophins are key regulators of neuronal survival and differentiation during development. Activation of their cognate receptors, Trk receptors, a family of receptor tyrosine kinases (RTKs), is pivotal for mediating the downstream functions of neurotrophins. Recent studies reveal that cyclin-dependent kinase 5 (Cdk5), a serine/threonine kinase, may modulate RTK signaling through phosphorylation of the receptor. Given the abundant expression of both Cdk5 and Trk receptors in the nervous system, and their mutual involvement in the regulation of neuronal architecture and synaptic functions, it is of interest to investigate if Cdk5 may also modulate Trk signaling. In the current study, we report the identification of TrkB as a Cdk5 substrate. Cdk5 phosphorylates TrkB at Ser478 at the intracellular juxtamembrane region of TrkB. Interestingly, attenuation of Cdk5 activity or overexpression of a TrkB mutant lacking the Cdk5 phosphorylation site essentially abolishes brain-derived neurotrophic factor (BDNF)-triggered dendritic growth in primary hippocampal neurons. In addition, we found that Cdk5 is involved in BDNF-induced activation of Rho GTPase Cdc42, which is essential for BDNF-triggered dendritic growth. Our observations therefore reveal an unanticipated role of Cdk5 in TrkB-mediated regulation of dendritic growth through modulation of BDNF-induced Cdc42 activation.

Show MeSH