Induction of serpinb1a by PACAP or NGF is required for PC12 cells survival after serum withdrawal.

PC12 cells are used to study the signaling mechanisms underlying the neurotrophic and neuroprotective activities of pituitary adenylate cyclase-activating polypeptide (PACAP) and nerve growth factor (NGF). Previous microarray experiments indicated that serpinb1a was the most induced gene after 6 h of treatment with PACAP or NGF. This study confirmed that serpinb1a is strongly activated by PACAP and NGF in a time-dependent manner with a maximum induction (~ 50-fold over control) observed after 6 h of treatment. Co-incubation with PACAP and NGF resulted in a synergistic up-regulation of serpinb1a expression (200-fold over control), suggesting that PACAP and NGF act through complementary mechanisms. Consistently, PACAP-induced serpinb1a expression was not blocked by TrkA receptor inhibition. Nevertheless, the stimulation of serpinb1a expression by PACAP and NGF was significantly reduced in the presence of extracellular signal-regulated kinase, calcineurin, protein kinase A, p38, and PI3K inhibitors, indicating that the two trophic factors share some common pathways in the regulation of serpinb1a. Finally, functional investigations conducted with siRNA revealed that serpinb1a is not involved in the effects of PACAP and NGF on PC12 cell neuritogenesis, proliferation or body cell volume but mediates their ability to block caspases 3/7 activity and to promote PC12 cell survival.

DeltaNp73 regulates neuronal survival in vivo.

Apoptosis occurs widely during brain development, and p73 transcription factors are thought to play essential roles in this process. The p73 transcription factors are present in two forms, the full length TAp73 and the N-terminally truncated DeltaNp73. In cultured sympathetic neurons, overexpression of DeltaNp73 inhibits apoptosis induced by nerve growth factor withdrawal or p53 overexpression. To probe the function of DeltaNp73 in vivo, we generated a null allele and inserted sequences encoding the recombinase Cre and green fluorescent protein (EGFP). We show that DeltaNp73 is heavily expressed in the thalamic eminence (TE) that contributes neurons to ventral forebrain, in vomeronasal neurons, Cajal-Retzius cells (CRc), and choroid plexuses. In DeltaNp73(-/-) mice, cells in preoptic areas, vomeronasal neurons, GnRH-positive cells, and CRc were severely reduced in number, and choroid plexuses were atrophic. This phenotype was enhanced when DeltaNp73-positive cells were ablated by diphtheria toxin expression. However, ablation of cells that express DeltaNp73 and Wnt3a did neither remove all CRc, nor did they abolish Reelin secretion or generate a reeler-like cortical phenotype. Our data emphasize the role of DeltaNp73 in neuronal survival in vivo and in choroid plexus development, the importance of the TE as a source of neurons in ventral forebrain, and the multiple origins of CRc, with redundant production of Reelin.

Atypical cadherins Celsr1-3 differentially regulate migration of facial branchiomotor neurons in mice.

During hindbrain development, facial branchiomotor neurons (FBM neurons) migrate from medial rhombomere (r) 4 to lateral r6. In zebrafish, mutations in planar cell polarity genes celsr2 and frizzled3a block caudal migration of FBM neurons. Here, we investigated the role of cadherins Celsr1-3, and Fzd3 in FBM neuron migration in mice. In Celsr1 mutants (knock-out and Crash alleles), caudal migration was compromised and neurons often migrated rostrally into r2 and r3, as well as laterally. These phenotypes were not caused by defects in hindbrain patterning or neuronal specification. Celsr1 is expressed in FBM neuron precursors and the floor plate, but not in FBM neurons. Consistent with this, conditional inactivation showed that the function of Celsr1 in FBM neuron migration was non-cell autonomous. In Celsr2 mutants, FBM neurons initiated caudal migration but moved prematurely into lateral r4 and r5. This phenotype was enhanced by inactivation of Celsr3 in FBM neurons and mimicked by inactivation of Fzd3. Furthermore, Celsr2 was epistatic to Celsr1. These data indicate that Celsr1-3 differentially regulate FBM neuron migration. Celsr1 helps to specify the direction of FBM neuron migration, whereas Celsr2 and 3 control its ability to migrate.

Pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates the expression and the release of tissue plasminogen activator (tPA) in neuronal cells: involvement of tPA in the neuroprotective effect of PACAP.

Pituitary adenylate cyclase-activating polypeptide (PACAP) and tissue plasminogen activator (tPA) play important roles in neuronal migration and survival. However, a direct link between the neurotrophic effects of PACAP and tPA has never been investigated. In this study, we show that, in PC12 cells, PACAP induced a 9.85-fold increase in tPA gene expression through activation of the protein kinase A- and protein kinase C-dependent signaling pathways. In immature cerebellar granule neurons (CGN), PACAP stimulated tPA mRNA expression and release of proteolytically active tPA. Immunocytochemical labeling revealed the presence of tPA in the cytoplasm and processes of cultured CGN. The inhibitory effect of PACAP on CGN motility was not affected by the tPA substrate plasminogen or the tPA inhibitor plasminogen activator inhibitor-1. In contrast, plasminogen activator inhibitor-1 significantly reduced the stimulatory effect of PACAP on CGN survival. Altogether, these data indicate that tPA gene expression is activated by PACAP in both tumoral and normal neuronal cells. The present study also demonstrates that PACAP stimulates the release of tPA which promotes CGN survival by a mechanism dependent of its proteolytic activity.

A cAMP-dependent, protein kinase A-independent signaling pathway mediating neuritogenesis through Egr1 in PC12 cells.

The neurotrophic peptide PACAP (pituitary adenylate cyclase-activating polypeptide) elevates cAMP in PC12 cells. Forskolin and dibutyryl cAMP mimic PACAP's neuritogenic and cell morphological effects, suggesting that they are driven by cAMP. Comparison of microarray expression profiles after exposure of PC12 cells to either forskolin, dibutyryl cAMP, or PACAP revealed a small group of cAMP-dependent target genes. Neuritogenesis induced by all three agents is protein kinase A (PKA)-independent [not blocked by N-[2-(4-bromocinnamylamino)ethyl]-5-isoquinoline (H89)] and extracellular signal-regulated kinase (ERK)-dependent [blocked by 1,4-diamino-2,3-dicyano-1,4-bis(methylthio) butadiene (U0126)], and therefore cAMP-dependent target genes potentially mediating neuritogenesis were selected for further analysis based on the pharmacological profile of their induction by PACAP (i.e., mimicking that of neuritogenesis). Small interfering RNA (siRNA) targeting one of these genes, Egr1, blocked PACAP-induced neuritogenesis, and siRNA targeting another, Vil2, blocked a component of the cell size increase elicited by PACAP. Neither siRNA blocked PACAP's PKA-dependent antiproliferative effects. PACAP signaling to neuritogenesis was also impaired by dominant-negative Rap1 expression but was not affected by inhibition of protein kinase C (PKC), indicating a G-protein-coupled receptor-mediated differentiation pathway distinct from the one activated by receptor tyrosine kinase ligands such as nerve growth factor (NGF), that involves both Rap1 and PKC. We have thus identified a cAMP-dependent, PKA-independent pathway proceeding through ERK that functions to up-regulate the transcription of two genes, Egr1 and Vil2, required for PACAP-dependent neuritogenesis and increased cell size, respectively. Dominant-negative Rap1 expression impairs both PACAP-induced neuritogenesis and Egr1 activation by PACAP, suggesting that cAMP elevation and ERK activation by PACAP are linked through Rap1.

Peroxiredoxin 2 is involved in the neuroprotective effects of PACAP in cultured cerebellar granule neurons.

The neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) is known to counteract in vitro the deleterious effects of toxic agents on cerebellar granule cell survival and differentiation. The potent antiapoptotic action of PACAP is mediated through inhibition of caspase-3 activity; however, additional proteins are likely involved and remain to be identified. Two-dimensional gel electrophoresis analysis coupled with mass spectrometry characterization led to the identification of a protein, peroxiredoxin 2, which was induced after a 6-h treatment with PACAP. Western blot analysis confirmed the regulation of peroxiredoxin 2 by PACAP and revealed that this protein is induced by both cyclic AMP and protein kinase C stimulators. Inhibition of peroxiredoxin 2 expression, using two distinct small-interfering RNAs (siRNAs), reduced the effect of PACAP on caspase-3 activity and cerebellar granule cell survival. Peroxiredoxin 2 expression was also induced in vivo and in vitro by ethanol. Although ethanol and PACAP exert opposite effects on caspase-3 activity, inhibition of peroxiredoxin 2 expression, using siRNAs, only reduced the ability of PACAP to prevent ethanol-induced caspase-3 activity. Taken together, these data indicate that peroxiredoxin 2 is probably involved in the neurotrophic effect of PACAP and suggest that this protein may have a therapeutic potential for the treatment of some neurodegenerative diseases.

DeltaNp73 transcription factors modulate cell survival and tumor development.

The p73 locus encodes two types of transcription factors: full length pro-apoptotic isoforms (TAp73), and N-terminally truncated anti-apoptotic proteins (DeltaNp73). To study the function of DeltaNp73 in vivo, we generated mutant mice in which DeltaNp73 is inactivated, but TAp73 expression is intact. In addition, we knocked in the locus the Cre recombinase, and the enhanced green fluorescent protein (EGFP). Using this allele, we refined the expression of DeltaNp73 during brain development and emphasized the importance of the thalamic eminence, a transient source that contributes neurons to the telencephalon. We showed that DeltaNp73 inactivation increases apoptosis in neurons. We also investigated the role of DeltaNp73 in carcinogenesis by inducing tumors with methylcholanthrene in mutant and control mice, and found that mutant females, but not males, have decreased propensity to tumor development. Both effects on neuronal apoptosis and tumor development were milder than predicted from in vitro studies.

Altered cerebellar development in mice lacking pituitary adenylate cyclase-activating polypeptide.

Previous studies have demonstrated that pituitary adenylate cyclase-activating polypeptide (PACAP) exerts trophic effects during neurodevelopment. In particular, the occurrence of PACAP and its receptors in the cerebellum during pre- and postnatal periods suggests that it could play a crucial role in ontogenesis of this structure. To test this hypothesis, we compared the histogenesis of cerebellar cortex in wild-type and PACAP-knockout (PACAP-/-) mice at postnatal days (P)4 and 7. Morphometric analysis of PACAP-/- mice revealed a significant reduction in the thickness of the external granule cell layer at P4 and of the internal granule cell layer at P7. Expression of nestin, a neural precursor marker, and synaptophysin, a mature neuronal marker, was quantified by real-time PCR and Western blot. No modification of nestin expression was noticed between wild-type and PACAP-/- mice, but a substantial decrease in synaptophysin expression was observed in PACAP-/- mice at P4 and P7. Immunohistochemistry revealed a reduction in synaptophysin labelling in the molecular and internal granule cell layers of PACAP-/- mice at P7. Caspase-3 activation was significantly increased in PACAP-/- mice at P4 and P7. Autoradiographic studies revealed no difference in PACAP binding site distributions and PACAP was effective at stimulating cAMP production in both wild-type and PACAP-/- cultured granule cells. This study demonstrates that disruption of the PACAP gene induces alteration of the immature cerebellum. Neuronal differentiation of granule cells was delayed whereas cell death that naturally occurs during ontogeny was increased in PACAP-/- mice. These data provide the first evidence of a physiological role for PACAP during cerebellar development.

Cycloheximide treatment to identify components of the transitional transcriptome in PACAP-induced PC12 cell differentiation.

Pituitary adenylate cyclase-activating polypeptide (PACAP) promotes neurite outgrowth, reduces proliferation and inhibits apoptosis of PC12 cells. We have partially characterized the transcriptome changes induced by PACAP after 6 h of treatment, when commitment to differentiation has occurred. Here, we have investigated the effects of a 6-h treatment with PACAP (10(-7) m) in the presence of cycloheximide (5 microm) to identify, via superinduction, components of the transitional transcriptome initially induced by PACAP and potentially participating in the regulation of late-response genes required for differentiation. Approximately 100 new transcripts were identified in this screen, i.e. as many individual genes as make up the 6-h PACAP differentiation transcriptome itself. Six known transcripts in this cohort were then measured at several time points between 0 and 6 h by real-time PCR to determine whether these transcripts are induced early following PACAP treatment in the absence of cycloheximide, and therefore may be of functional importance in differentiation. Five out of the six transcripts were indeed induced by PACAP alone soon (between 30 min and 3 h) after cell treatment. beta-Cell translocation gene 2, antiproliferative (Btg2), serum/glucocorticoid-regulated kinase (Sgk), nuclear factor for the kappa chain of B-cells (NFkappaB), seven in absentia homologue 2 (Siah2) and FBJ osteosarcoma related oncogene (Fos) showed a 2.5-200-fold induction by PACAP between 15 min and 3 h, and mRNA levels returned either to baseline or near baseline after 6 h. This work provides new information concerning genes whose transient regulation early after PACAP exposure may contribute to the expression of the differentiated transcriptome in PC12 cells, and should help to elucidate the molecular mechanisms involved in the control of nerve cell survival and differentiation.

The neurotrophic effects of PACAP in PC12 cells: control by multiple transduction pathways.

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) are closely related members of the secretin superfamily of neuropeptides expressed in both the brain and peripheral nervous system, and they exhibit neurotrophic and neurodevelopmental effects in vivo. Like the index member of the Trk receptor ligand family, nerve growth factor (NGF), PACAP promotes the differentiation of PC12 cells, a well-established cell culture model, to investigate neuronal differentiation, survival and function. Stimulation of catecholamine secretion and enhanced neuropeptide biosynthesis are effects exerted by PACAP at the adrenomedullary synapse in vivo and on PC12 cells in vitro through stimulation of the specific PAC1 receptor. Induction of neuritogenesis, growth arrest, and promotion of cell survival are effects of PACAP that occur in developing cerebellar, hippocampal and cortical neurons, as well as in the more tractable PC12 cell model. Study of the mechanisms through which PACAP exerts its various effects on cell growth, morphology, gene expression and survival, i.e. its actions as a neurotrophin, in PC12 cells is the subject of this review. The study of neurotrophic signalling by PACAP in PC12 cells reveals that multiple independent pathways are coordinated in the PACAP response, some activated by classical and some by novel or combinatorial signalling mechanisms.

Somatostatin down-regulates the expression and release of endozepines from cultured rat astrocytes via distinct receptor subtypes.

Endozepines, a family of regulatory peptides related to diazepam-binding inhibitor (DBI), are synthesized and released by astroglial cells. Because rat astrocytes express various subtypes of somatostatin receptors (sst), we have investigated the effect of somatostatin on DBI mRNA level and endozepine secretion in rat astrocytes in secondary culture. Somatostatin reduced in a concentration-dependent manner the level of DBI mRNA in cultured astrocytes. This inhibitory effect was mimicked by the selective sst4 receptor agonist L803-087 but not by the selective sst1, sst2 and sst3 receptor agonists L779-591, L779-976 and L797-778, respectively. Somatostatin was unable to further reduce DBI mRNA level in the presence of the MEK inhibitor U0126. Somatostatin and the sst1, sst2 and sst4 receptor agonists induced a concentration-dependent inhibition of endozepine release. Somatostatin and the sst1, sst2 and sst4 receptor agonists also inhibited cAMP formation dose-dependently. In addition, somatostatin reduced forskolin-induced endozepine release. H89 mimicked the inhibitory effect of somatostatin on endozepine secretion. In contrast the PLC inhibitor U73122, the PKC activator PMA and the PKC inhibitor calphostin C had no effect on somatostatin-induced inhibition of endozepine release. The present data demonstrate that somatostatin reduces DBI mRNA level mainly through activation of sst4 receptors negatively coupled to the MAPK pathway, and inhibits endozepine release through activation of sst1, sst2 and sst4 receptors negatively coupled to the adenylyl cyclase/PKA pathway.

Analysis of the PC12 cell transcriptome after differentiation with pituitary adenylate cyclase-activating polypeptide (PACAP).

Pituitary adenylate cyclase-activating polypeptide (PACAP) promotes neurite outgrowth and inhibits proliferation of rat pheochromocytoma (PC12) cells. Characterizing the PACAP-differentiated PC12 cell transcriptome should provide genetic insight into how these processes occur in these cells, and in neuronal precursors in vivo. For this purpose, RNA samples were collected from PC12 cells before or after a 6-h treatment with PACAP, from which a labeled cDNA was hybridized to a high-density cDNA array containing 15 365 genes. The genomic response to PACAP involves at least 73 genes. Among the genes differentially expressed in the presence of PACAP, 71% were up regulated, and 29% down regulated, 2-fold or more. Sixty-six percent of the messages affected by PACAP code for functionally categorized proteins, most not previously known to be regulated during PC12 cell differentiation. PACAP has been shown to induce PC12 cell neurite outgrowth through the mitogen-activated protein kinase kinase (MEK) pathway independently of protein kinase A (PKA). Therefore treatments were conducted in the absence or presence of the PKA inhibitor H89, or the MEK inhibitor U0126 in order to identify subsets of genes involved in specific aspects of PC12 cell differentiation. Co-treatment of PC12 cells with PACAP plus H89 revealed a cluster of five genes specifically regulated through the PKA pathway and co-treatment of the cells with PACAP and U0126 revealed a cluster of 13 messages specifically activated through the MEK pathway. Many of the known genes regulated by PACAP have been associated with neuritogenesis (i.e. villin 2 or annexin A2) or cell growth (i.e. growth arrest specific 1 or cyclin B2). Thus, some of the expressed sequence tags (ESTs) that exhibit the same regulation pattern (i.e. AU016391 or AW552690) may also be involved in the neuritogenic and anti-mitogenic effects of PACAP in PC12 cells. Among the 73 PACAP regulated genes, 10 are disqualified on pharmacological grounds as actors in PACAP-mediated neurite outgrowth or growth arrest, leaving 63 new PACAP-regulated genes implicated in neuronal differentiation. Thirteen of these are candidates for mediating ERK-dependent neurite outgrowth, and 47 are possibly involved in the ERK-independent growth arrest induced by PACAP.