AKT and CDK5/p35 Mediate Brain-derived Neurotrophic Factor Induction of DARPP-32 in Medium Size Spiny Neurons in Vitro

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. The medium size spiny neuron (MSN)2 is the primary projection neuron of the striatum (caudate and nucleus accumbens) and accounts for over 95% of the striatal neurons (1). All MSNs receive glutamatergic input from the cortex. In addition, they receive dopamine input from the substantia nigra or ventral tegmental area and are therefore dopaminoceptive, usually expressing only a single dopamine receptor subtype (2, 3). Cellspecific MSN gene transcription is altered during the pathogenesis and treatment of many neuropsychiatric diseases, including Huntington disease, Parkinson disease, drug addiction, affective disorders, attention deficit hyperactivity disorder, and schizophrenia (4 -7). Despite the obvious clinical significance of gene regulation in MSNs and the requirement for cell-specific transcription in the development of the nervous system, few details are available regarding how the MSN phenotype is specified at the molecular level. Indeed, little is known about the molecular mechanisms underlying the specification of most central nervous system neuronal subtypes. Delineation of these pathways presents a major challenge to current molecular neurobiology.DARPP-32 (dopamine and cyclic AMP-regulated phosphoprotein, 32 kDa) is a homologue of protein phosphatase inhibitor-1 that plays a key role in integrating incoming first messenger signals. A host of transmitters and neuropeptides converges upon DARPP-32 and its state of phosphorylation, and in turn, levels of phospho-DARPP-32 provide moment-to-moment control of the signaling "tone" of ov...

Cdk5 activity in the brain – multiple paths of regulation

“…3). In contrast, BDNF stimulates the Erk1/2-EGR1 pathway to increase p35 transcription, as well as the phosphoinositide-3 kinase (PI3K) pathway to increase p35 protein levels in striatal neurons (Bogush et al, 2007) (Fig. 3).…”

“…3). It is not known whether P13K-mediated increase in p35 levels is at transcriptional or posttranslational level (Bogush et al, 2007) (Fig. 3).…”

Huntington's Disease and the Striatal Medium Spiny Neuron: Cell-Autonomous and Non-Cell-Autonomous Mechanisms of Disease

“…This latter study used Emx1-Cre to conditionally delete BDNF in the cortex, and recombination occurs as early as embryonic day 11, long before BDNF is down-regulated in HD. Regulation of transcription by BDNF requires signal transduction systems altered in HD (e.g., phosphatidylinositol-3-kinase and cdk5) [43,178]. Increased BDNF, either by intraventricular injection or prenatal transgenic overexpression, ameliorates the severity of the phenotype in R6 and YAC128 mice, whereas crossing with BDNF heterozygote-null mice exacerbates the phenotype [62,63,179].…”

Single-nucleotide polymorphisms in the promoter of the CDK5 gene and lung cancer risk in a Korean population

“…16 Frequent amplification and overexpression of the CDK5 gene along with multiple epidermal growth factor receptor (EGFR)-family-signaling pathway components, including SHC1, AKT1 and MYC, was recently discovered in non-small cell lung cancer (NSCLC). 17 As it has been known earlier that CDK5/p35 activation by neuregulin subsequently activates PI3K and Akt through ErbB3 and ErbB2 receptors in cultured cortical neurons, 18 the activation of CDK5, along with the other genes, may play a role in NSCLC tumorigenesis.…”