Induction of deltaFosB in the periaqueductal gray by stress promotes active coping responses.

We analyzed the influence of the transcription factor DeltaFosB on learned helplessness, an animal model of affective disorder wherein a subset of mice exposed to inescapable stress (IS) develop a deficit in escape behavior. Repeated IS induces DeltaFosB in the ventrolateral periaqueductal gray (vlPAG), and levels of the protein are highly predictive of an individual's subsequent behavorial deficit-with the strongest DeltaFosB induction observed in the most resilient animals. Induction of DeltaFosB by IS predominates in substance P-positive neurons in the vlPAG, and the substance P gene, a direct target for DeltaFosB, is downregulated upon DeltaFosB induction. Local overexpression of DeltaFosB in the vlPAG using viral-mediated gene transfer dramatically reduces depression-like behaviors and inhibits stress-induced release of substance P. These results indicate that IS-induced accumulation of DeltaFosB in the vlPAG desensitizes substance P neurons enriched in this area and opposes behavioral despair by promoting active defense responses.

Dimerization and DNA-binding properties of the transcription factor DeltaFosB.

The transcription factor, DeltaFosB, a splice isoform of fosB, accumulates in rodents in a brain-region-specific manner in response to chronic administration of drugs of abuse, stress, certain antipsychotic or antidepressant medications, electroconvulsive seizures, and certain lesions. Increasing evidence supports a functional role of such DeltaFosB induction in animal models of several psychiatric and neurologic disorders. Fos family proteins, including DeltaFosB, are known to heterodimerize with Jun family proteins to create active AP-1 transcription-factor complexes, which bind to DNA specifically at AP-1 consensus sites. We show here, using a range of biochemical and biophysical means, that recombinant, purified DeltaFosB forms homodimers as well, at concentrations less than 500 nM, and that these homodimers specifically bind to DNA oligonucleotides containing AP-1 consensus sequences in the absence of any Jun partner. Our results suggest that, as DeltaFosB accumulates to abnormally elevated protein levels in highly specific regions of the brain in response to chronic stimulation, functional homodimers of DeltaFosB are formed with the potential to uniquely regulate patterns of gene expression and thereby contribute to the complex processes of neural and behavioral adaptation.

Regulation of DeltaFosB transcriptional activity by Ser27 phosphorylation.

The transcription factor, DeltaFosB, is an important mediator of the long-term plasticity induced in brain by chronic exposure to drugs of abuse, stress, or several other psychoactive stimuli. We have previously demonstrated that the casein kinase 2 (CK2)-mediated phosphorylation of a highly conserved N-terminal serine (Ser27) plays a critical role in regulating DeltaFosB's unusual stability, while it does not affect that of the full-length FosB protein. In the present study, we analysed whether CK2 and Ser27 phosphorylation also play a role in regulating DeltaFosB's transcriptional activity. Our findings indicate that CK2 activation increases DeltaFosB's transactivation potential, while CK2 inhibition decreases it. Further, we show that preventing Ser27 phosphorylation by mutating the site to Ala results in a significant decrease in DeltaFosB transactivation, without affecting DeltaFosB's subcellular localization or DNA-binding affinity. In contrast, Ser27 does not seem to play a role in the transactivation potential of full-length FosB. These findings constitute the first evidence of a role for phosphorylation in DeltaFosB's transcriptional activity.

The transcription factor DeltaFosB is recruited by inflammatory pain.

DeltaFosB, a stable splice variant of FosB, has been proposed to mediate persistent brain adaptation in response to several chronic perturbations, but it has not yet been considered in the context of sustained pain. Inflammatory pain induces neuronal plasticity that can result in persistent alteration of nociceptive pathways. This neuronal plasticity can partly result from changes in gene expression controlled by transcription factors. In the present study, we analyse the capacity of carrageenan-mediated inflammation to induce DeltaFosB in the spinal cord. We found that hind-paw inflammation increases FosB-like immunoreactivity in the superficial layers of rat lumbar spinal cord for at least 7 days. This induction parallels mechanical hyperalgesia and is maximal in the dorsal horn of segment L4 of the spinal cord which corresponds to the primary nociceptive afferent regions from the hind paw. We identified this FosB-like signal as DeltaFosB by comparing data obtained with antibodies raised against either an epitope present in both FosB and DeltaFosB, or the FosB C-terminal region that is deleted in DeltaFosB. The week-lasting changes in DeltaFosB highlight the interest in this protein as a molecular marker of sustained pain, and suggest a role of this transcription factor in pain-related plasticity within the spinal cord.

Regulation of DeltaFosB stability by phosphorylation.

The transcription factor DeltaFosB (also referred to as FosB2 or FosB[short form]) is an important mediator of the long-term plasticity induced in brain by chronic exposure to several types of psychoactive stimuli, including drugs of abuse, stress, and electroconvulsive seizures. A distinct feature of DeltaFosB is that, once induced, it persists in brain for relatively long periods of time in the absence of further stimulation. The mechanisms underlying this apparent stability, however, have remained unknown. Here, we demonstrate that DeltaFosB is a relatively stable transcription factor, with a half-life of approximately 10 h in cell culture. Furthermore, we show that DeltaFosB is a phosphoprotein in brain and that phosphorylation of a highly conserved serine residue (Ser27) in DeltaFosB protects it from proteasomal degradation. We provide several lines of evidence suggesting that this phosphorylation is mediated by casein kinase 2. These findings constitute the first evidence that DeltaFosB is phosphorylated and demonstrate that phosphorylation contributes to its stability, which is at the core of its ability to mediate long-lasting adaptations in brain.

DeltaFosB accumulates in a GABAergic cell population in the posterior tail of the ventral tegmental area after psychostimulant treatment.

The transcription factor deltaFosB is induced in the nucleus accumbens and dorsal striatum by chronic exposure to several drugs of abuse, and increasing evidence supports the possibility that this induction is involved in the addiction process. However, to date there has been no report of deltaFosB induction by drugs of abuse in the ventral tegmental area (VTA), which is also a critical brain reward region. In the present study, we used immunohistochemistry to demonstrate that chronic forced administration of cocaine induces deltaFosB in the rat VTA. This induction occurs selectively in a gamma-aminobutyric acid (GABA) cell population within the posterior tail of the VTA. A similar effect is seen after chronic cocaine self-administration. Induction of deltaFosB in the VTA occurs after psychostimulant treatment only: it is seen with both chronic cocaine and amphetamine, but not with chronic opiates or stress. The expression of deltaFosB appears to be mediated by dopamine systems, as repeated administration of a dopamine uptake inhibitor induced deltaFosB in the VTA, while administration of serotonin or norepinephrine uptake inhibitors failed to produce this effect. Time course analysis showed that, following 14 days of cocaine administration, deltaFosB persists in the VTA for almost 2 weeks after cocaine withdrawal. This accumulation and persistence may account for some of the long-lasting changes in the brain associated with chronic drug use. These results provide the first evidence of deltaFosB induction in a discrete population of GABA cells in the VTA, which may regulate the functioning of the brain's reward mechanisms.

DeltaFosB: a molecular switch for long-term adaptation in the brain.

DeltaFosB is a unique transcription factor that plays an essential role in long-term adaptive changes in the brain associated with diverse conditions, such as drug addiction, Parkinson's disease, depression, and antidepressant treatment. It is induced in brain, in a region- and cell-type-specific manner by many types of chronic perturbations. Once induced, it persists for long periods of time due to its unusual stability. The transcriptional effects of DeltaFosB are complex, because the protein can function as both a transcriptional activator and repressor. Progress has been made in identifying specific target genes for DeltaFosB and in relating some of these genes to DeltaFosB's cellular and behavioral actions. Future studies will help us to better understand the biochemical basis of DeltaFosB's unique stability, as well as the precise molecular pathways through which this transcription factor produces its complex effects on neuronal plasticity and complex behavior.

Induction of deltaFosB in reward-related brain structures after chronic stress.

Acute and chronic stress differentially regulate immediate-early gene (IEG) expression in the brain. Although acute stress induces c-Fos and FosB, repeated exposure to stress desensitizes the c-Fos response, but FosB-like immunoreactivity remains high. Several other treatments differentially regulate IEG expression in a similar manner after acute versus chronic exposure. The form of FosB that persists after these chronic treatments has been identified as DeltaFosB, a splice variant of the fosB gene. This study was designed to determine whether the FosB form induced after chronic stress is also DeltaFosB and to map the brain regions and identify the cell populations that exhibit this effect. Western blotting, using an antibody that recognizes all Fos family members, revealed that acute restraint stress caused robust induction of c-Fos and full-length FosB, as well as a small induction of DeltaFosB, in the frontal cortex (fCTX) and nucleus accumbens (NAc). The induction of c-Fos (and to some extent full-length FosB) was desensitized after 10 d of restraint stress, at which point levels of DeltaFosB were high. A similar pattern was observed after chronic unpredictable stress. By use of immunohistochemistry, we found that chronic restraint stress induced DeltaFosB expression predominantly in the fCTX, NAc, and basolateral amygdala, with lower levels of induction seen elsewhere. These findings establish that chronic stress induces DeltaFosB in several discrete regions of the brain. Such induction could contribute to the long-term effects of stress on the brain.

Platelet-derived growth factor (PDGF)-induced tyrosine phosphorylation of the low density lipoprotein receptor-related protein (LRP). Evidence for integrated co-receptor function betwenn LRP and the PDGF.

The low density lipoprotein receptor-related protein (LRP) functions in the catabolism of numerous ligands including proteinases, proteinase inhibitor complexes, and lipoproteins. In the current study we provide evidence indicating an expanded role for LRP in modulating cellular signaling events. Our results show that platelet-derived growth factor (PDGF) BB induces a transient tyrosine phosphorylation of the LRP cytoplasmic domain in a process dependent on PDGF receptor activation and c-Src family kinase activity. Other growth factors, including basic fibroblast growth factor, epidermal growth factor, insulin-like growth factor-1, were unable to mediate tyrosine phosphorylation of LRP. The basis for this selectivity may result from the ability of LRP to bind PDGFBB, because surface plasmon resonance experiments demonstrated that only PDGF, and not basic fibroblast growth factor, epidermal growth factor, or insulin-like growth factor-1, bound to purified LRP immobilized on a sensor chip. The use of LRP mini-receptor mutants as well as in vitro phosphorylation studies demonstrated that the tyrosine located within the second NPXY motif found in the LRP cytoplasmic domain is the primary site of tyrosine phosphorylation by Src and Src family kinases. Co-immunoprecipitation experiments revealed that PDGF-mediated tyrosine phosphorylation of LRPs cytoplasmic domain results in increased association of the adaptor protein Shc with LRP and that Shc recognizes the second NPXY motif within LRPs cytoplasmic domain. In the accompanying paper, Boucher et al. (Boucher, P., Liu, P. V., Gotthardt, M., Hiesberger, T., Anderson, R. G. W., and Herz, J. (2002) J. Biol. Chem. 275, 15507-15513) reveal that LRP is found in caveolae along with the PDGF receptor. Together, these studies suggest that LRP functions as a co-receptor that modulates signal transduction pathways initiated by the PDGF receptor.