Regulation of PC12 Cell Differentiation by cAMP Signaling to ERK Independent of PKA: Do All the Connections Add Up?

Little is known about the regulation of the innate host defense peptide cathelicidin at the mucosal surfaces. Expression is believed to be transcriptionally regulated, and several cis-acting elements have been identified in the cathelicidin putative promoter. However, the trans-acting factors have not been clearly defined. We have recently reported that bacterial exotoxins suppress cathelicidin expression in sodium butyrate-differentiated intestinal epithelial cells (ECs), and this may be mediated through inducible cAMP early repressor. Here we have shown that cAMP-signaling pathways transcriptionally regulate cathelicidin expression in various ECs. cAMP-response elementbinding protein (CREB) and AP-1 (activator protein-1) bind to the cathelicidin putative promoter in vitro. Additionally, transcriptional complexes containing CREB, AP-1, and cathelicidin upstream regulatory sequences are formed within ECs. We have also shown that these complexes may activate cathelicidin promoter and are required for its inducible expression in ECs. This is underscored by the fact that silencing of CREB and AP-1 results in failure of ECs to up-regulate cathelicidin, and hepatitis B virus X protein may use CREB to induce cathelicidin. On the other hand, inducible cAMP early repressor competes with CREB and AP-1 for binding to the cathelicidin promoter and represses transcription, thus functioning as a counter-regulatory mechanism. Finally, both CREB and AP-1 were shown to play major roles in the regulation of cathelicidin in sodium butyrate-differentiated HT-29 cells. This is the first report of a detailed mechanistic study of inducible cathelicidin expression in the mucosal ECs. At the same time, it describes a novel immunomodulatory function of cAMP.

Section: Discussionmentioning

confidence: 84%

cAMP Stringently Regulates Human Cathelicidin Antimicrobial Peptide Expression in the Mucosal Epithelial Cells by Activating cAMP-response Element-binding Protein, AP-1, and Inducible cAMP Early Repressor

Chakraborty

Maity

Sil

et al. 2009

“…Besides playing a central role in neuritogenesis, ERK1 and -2, activated in response to PKC oxidative activation, protect cells from oxidants. ERK-activated p90RSK phosphorylates and activates CREB, which in turn induces the transcriptional activation of cell survival proteins that have a cAMP-response element in their promoter region (4,5). In this context, it is interesting to note that thioredoxin, a protein-disulfide reductase, has a cAMP-response element in its promoter region, and its induction plays a key role in neuroprotection (76,77).…”

Section: Discussionmentioning

confidence: 99%

“…NGF induces neuritogenesis in PC12 cells by binding to and activating receptor-associated tyrosine kinase, TrkA (4,5,16). The associated signaling pathway leads to the activation of B-Raf (via Ras and Rap1), which is coupled to the activation of mitogen-activated protein kinase (MAPK) kinase.…”

mentioning

confidence: 99%

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A Direct Redox Regulation of Protein Kinase C Isoenzymes Mediates Oxidant-induced Neuritogenesis in PC12 Cells

Gopalakrishna

Gundimeda

Schiffman

et al. 2008

In this study, we have used the PC12 cell model to elucidate the mechanisms by which sublethal doses of oxidants induce neuritogenesis. The xanthine/xanthine oxidase (X/XO) system was used for the steady state generation of superoxide, and CoCl 2 was used as a representative transition metal redox catalyst. Upon treatment of purified protein kinase C (PKC) with these oxidants, there was an increase in its cofactor-independent activation. Redox-active cobalt competed with the redoxinert zinc present in the zinc-thiolates of the PKC regulatory domain and induced the oxidation of these cysteine-rich regions. Both CoCl 2 and X/XO induced neurite outgrowth in PC12 cells, as determined by an overexpression of neuronal marker genes. Furthermore, these oxidants induced a translocation of PKC from cytosol to membrane and subsequent conversion of PKC to a cofactor-independent form. Isoenzyme-specific PKC inhibitors demonstrated that PKC⑀ plays a crucial role in neuritogenesis. Moreover, oxidant-induced neurite outgrowth was increased with a conditional overexpression of PKC⑀ and decreased with its knock-out by small interfering RNA. Parallel with PKC activation, an increase in phosphorylation of the growth-associated neuronal protein GAP-43 at Ser 41 was observed. Additionally, there was a sustained activation of extracellular signal-regulated kinases 1 and 2, which was correlated with activating phosphorylation (Ser 133 ) of cAMP-responsive element-binding protein. All of these signaling events that are causally linked to neuritogenesis were blocked by antioxidant N-acetylcysteine (both L and D-forms) and by a variety of PKC-specific inhibitors. Taken together, these results strongly suggest that sublethal doses of oxidants induce neuritogenesis via a direct redox activation of PKC⑀.Understanding the signaling mechanisms involved in neuritogenesis resulting from a compensatory response to injury is crucial to the development of therapeutic agents for recovery after spinal cord and traumatic brain injuries (1, 2). The study of neuritogenesis requires the identification of molecular targets using a suitable experimental model. One of the best characterized cellular models for studying the neuronal pathways involved in neuritogenesis is the rat pheochromocytoma cell line PC12 (3). This cell line continues to be an important model system for the study of cell signaling mechanisms induced by a variety of stimuli, including neurotrophins, hormones, and oxidants (4, 5).In addition to damage from mechanical forces, spinal cord and traumatic brain injuries may result from secondary mechanisms involving ischemia, excitotoxicity, cytokines, and an infiltration of neutrophils at the site of injury (6, 7). The inflammatory response results in the generation of reactive oxygen species (ROS), 2 including superoxide and hydrogen peroxide, which can cause oxidative damage to tissues and lead to cell death (8). Paradoxically, sublethal doses of oxidants can also induce a variety of cellular processes, including cell growth, adhesion, inva...

“…The predominant PACAP target receptor in the adrenal medulla is the high affinity PAC 1 -R, a G s -linked receptor that activates adenylate cyclase to increase cyclic adenosine monophosphate (cAMP) (24,25). Recent studies have shown that PACAP stimulation activates the stimulatory exchange protein activated by cAMP (Epac) pathway through the elevation in cAMP (26,27), triggering phospholipase C and a protein kinase C (PKC)-dependent subthreshold depolarization that is necessary for catecholamine release from chromaffin cells (16). PACAP-mediated exocytosis is independent of sodium-based action potentials (28) or nicotinic acetylcholine receptor function (29,30), thus bypassing key sites of nicotinic secretory desensitization.…”

mentioning

confidence: 99%

Pituitary Adenylate Cyclase-activating Peptide (PACAP) Recruits Low Voltage-activated T-type Calcium Influx under Acute Sympathetic Stimulation in Mouse Adrenal Chromaffin Cells

Hill

Chan

Kuri

et al. 2011

Background:The acute stress secretagogue PACAP leads to catecholamine release, but the source of calcium necessary for secretion is unknown. Results: PACAP stimulation increases LVA Ca v 3.2 influx in a PKC-dependent process. Conclusion: PACAP-mediated acute sympathetic stress functionally recruits a pool of latent Ca v 3.2 channels to supply calcium for secretion. Significance: Native sympathoadrenal stimulation elicits catecholamine release through a non-canonical mechanism.