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AKT and CDK5/p35 mediate brain-derived neurotrophic factor induction of DARPP-32 in medium size spiny neurons in
Alexey Bogush1, Steve Pedrini, Joshua Pelta-Heller
1Farber Institute for Neurosciences and Department of Neurology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
Abstract:
Mature striatal medium size spiny neurons express the dopamine and cyclic AMP-regulated phosphoprotein, 32 kDa (DARPP-32), but little is known about the mechanisms regulating its levels or the specification of fully differentiated neuronal subtypes. Cell extrinsic molecules that increase DARPP-32 mRNA and/or protein levels include brain-derived neurotrophic factor (BDNF), retinoic acid, and estrogen. DARPP-32 induction by BDNF in vitro requires phosphatidylinositide 3-kinase (PI3K), but inhibition of phosphorylation of protein kinase B/Akt does not entirely abolish expression of DARPP-32. Moreover, the requirement for Akt has not been established. Using pharmacologic inhibitors of PI3K, Akt, and cyclin-dependent kinase 5 (cdk5) and constitutively active and dominant negative PI3K, Akt, cdk5, and p35 viruses in cultured striatal neurons, we measured BDNF-induced levels of DARPP-32 protein and/or mRNA. We demonstrated that both the PI3K/Akt/mammalian target of rapamycin and the cdk5/p35 signal transduction pathways contribute to the induction of DARPP-32 protein levels by BDNF and that the effects are on both the transcriptional and translational levels. It also appears that PI3K is upstream of cdk5/p35, and its activation can lead to an increase in p35 protein levels. These data support the presence of multiple signal transduction pathways mediating expression of DARPP-32 in vitro, including a novel, important pathway via by which PI3K regulates the contribution of cdk5/p35.
Insights
Brain-derived neurotrophic factor (BDNF) regulates dopamine and cyclic AMP-regulated phosphoprotein, 32 kDa (DARPP-32) levels in neurons. Multiple signaling pathways, including PI3K/Akt/mTOR and cdk5/p35, mediate this BDNF-induced DARPP-32 expression.
Area of Science:
- Neuroscience
- Molecular Biology
- Cell Signaling
Background:
- Mature striatal medium spiny neurons express DARPP-32, crucial for neuronal function.
- Mechanisms regulating DARPP-32 levels and neuronal subtype specification are not fully understood.
- Brain-derived neurotrophic factor (BDNF) is known to increase DARPP-32 expression.
Purpose of the Study:
- To elucidate the signaling pathways involved in BDNF-induced DARPP-32 expression in cultured striatal neurons.
- To investigate the roles of phosphatidylinositide 3-kinase (PI3K)/protein kinase B/Akt and cyclin-dependent kinase 5 (cdk5) pathways.
- To determine if BDNF affects DARPP-32 at transcriptional and/or translational levels.
Main Methods:
- Utilized pharmacologic inhibitors and viral vectors for PI3K, Akt, cdk5, and p35 in cultured striatal neurons.
- Measured BDNF-induced changes in DARPP-32 protein and mRNA levels.
- Investigated the upstream/downstream relationships between signaling molecules.
Main Results:
- Both PI3K/Akt/mTOR and cdk5/p35 pathways contribute to BDNF-induced DARPP-32 protein levels.
- BDNF's effects on DARPP-32 occur at both transcriptional and translational levels.
- PI3K acts upstream of cdk5/p35, potentially increasing p35 protein levels.
Conclusions:
- Multiple signal transduction pathways mediate BDNF-induced DARPP-32 expression in vitro.
- A novel pathway exists where PI3K regulates the contribution of cdk5/p35 to DARPP-32 expression.
- These findings advance understanding of DARPP-32 regulation and neuronal differentiation.
