Effects of PACAP and VIP on cAMP-generating system and proliferation of C6 glioma cells

The Heterogeneity of Response of PC12 Cells from Different Laboratories to Nerve Growth Factor and Pituitary Adenylate Cyclase-Activating Polypeptide Questions the Reproducibility of Studies Carried Out with Tumor Cell Lines

BACKGROUND

PC12 pheochromocytoma tumor cell lines are widely used to decipher the intracellular signaling mechanisms mediating the effects of some growth factors. Nevertheless, the disparity in appearance of some PC12 cell lines used in the different publications questions our ability to compare the results obtained by the numerous laboratories which use them. This led us to analyze the phenotypic aspect and transcriptomic expression of 5 PC12 cell lines from different origins under control conditions and after treatment with nerve growth factor (NGF) or pituitary adenylate cyclase-activating polypeptide (PACAP).

METHODS

Characterization of the 5 PC12 cell lines was conducted using imaging techniques and high-throughput real-time PCR combined with bioinformatics analysis.

RESULTS

The results show that the 5 cell lines are very variable in terms of shape, proliferation rate, motility, adhesion to the substrate, and gene expression. This high heterogeneity of the cell lines is also found when looking at their response to NGF or PACAP on gene expression or differentiation, with even in some cases opposite effects, as, for example, on cell proliferation. Actually, only 2 of the cell lines tested exhibited some phenotypic similarities with each other, even though the transcriptomic analyses show that they are far from identical.

DISCUSSION/CONCLUSION

As this issue of cell heterogenicity is not restricted to PC12 cells, the present results highlight the need to facilitate the supply of cell lines at low cost, the necessity to standardize practices regarding the use of cell lines, and the requirement to define precise markers of established cell lines which should be monitored in every publication. Regarding this latter point, the present data show that transcriptomic analysis by real-time PCR using a panel of genes of interest is easy to implement and provides a reliable method to control the possible drift of the cells over time in culture. Transcriptomic phenotyping combined with bioinformatics analysis can also be a useful approach to predict the response of the cells to treatments in terms of cell signaling activation, which can help to choose among several cell lines the most appropriate one for the investigation of a particular mechanism. Taken together, the results from this study highlight the need to use well-characterized cell lines with standardized protocols to generate reproducible results from 1 laboratory to the other.

Effect of PACAP on Hypoxia-Induced Angiogenesis and Epithelial-Mesenchymal Transition in Glioblastoma

Pituitary adenylate cyclase-activating polypeptide (PACAP) exerts different effects in various human cancer. In glioblastoma (GBM), PACAP has been shown to interfere with the hypoxic micro-environment through the modulation of hypoxia-inducible factors via PI3K/AKT and MAPK/ERK pathways inhibition. Considering that hypoxic tumor micro-environment is strictly linked to angiogenesis and Epithelial–Mesenchymal transition (EMT), in the present study, we have investigated the ability of PACAP to regulate these events. Results have demonstrated that PACAP and its related receptor, PAC1R, are expressed in hypoxic area of human GBM colocalizing either in epithelial or mesenchymal cells. By using an in vitro model of GBM cells, we have observed that PACAP interferes with hypoxic/angiogenic pathway by reducing vascular-endothelial growth factor (VEGF) release and inhibiting formation of vessel-like structures in H5V endothelial cells cultured with GBM-conditioned medium. Moreover, PACAP treatment decreased the expression of mesenchymal markers such as vimentin, matrix metalloproteinase 2 (MMP-2) and matrix metalloproteinase 9 (MMP-9) as well as CD44 in GBM cells by affecting their invasiveness. In conclusion, our study provides new insights regarding the multimodal role of PACAP in GBM malignancy.

Multimodal Role of PACAP in Glioblastoma

Glioblastoma multiforme (GBM) is the deadliest form of brain tumors. To date, the GBM therapeutical approach consists of surgery, radiation-therapy and chemotherapy combined with molecules improving cancer responsiveness to treatments. In this review, we will present a brief overview of the GBM classification and pathogenesis, as well as the therapeutic approach currently used. Then, we will focus on the modulatory role exerted by pituitary adenylate cyclase-activating peptide, known as PACAP, on GBM malignancy. Specifically, we will describe PACAP ability to interfere with GBM cell proliferation, as well as the tumoral microenvironment. Considering its anti-oncogenic role in GBM, synthesis of PACAP agonist molecules may open new perspectives for combined therapy to existing gold standard treatment.

Insights About Circadian Clock and Molecular Pathogenesis in Gliomas

The circadian clock is an endogenous time-keeping system that has been discovered across kingdoms of life. It controls and coordinates metabolism, physiology, and behavior to adapt to variations within the day and the seasonal environmental cycles driven by earth rotation. In mammals, although circadian rhythm is controlled by a set of core clock genes that are present in both in suprachiasmatic nucleus (SCN) of the hypothalamus and peripheral tissues, the generation and control of the circadian rhythm at the cellular, tissue, and organism levels occurs in a hierarchal fashion. The SCN is central pacemaker comprising the principal circadian clock that synchronizes peripheral circadian clocks to their appropriate phase. Different epidemiological studies have shown that disruption of normal circadian rhythm is implicated in increasing the risk of developing cancers. In addition, deregulated expression of clock genes has been demonstrated in various types of cancer. These findings indicate a close association between circadian clock and cancer development and progression. Here, we review different evidences of this association in relation to molecular pathogenesis in gliomas.

Evidence for antimicrobial and anticancer activity of pituitary adenylate cyclase-activating polypeptide (PACAP) from North African catfish (Clarias gariepinus): Its potential use as novel therapeutic agent in fish and humans

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a regulatory neuropeptide that belongs to the secretin/glucagon superfamily, of which some members have shown antimicrobial activities. Contrasting to mammals, published studies on the action of PACAP in non-mammalian vertebrate immune system remain scarce. Some of our recent studies added this peptide to the growing list of mediators that allow cross-talk between the nervous, endocrine and immune systems in teleost fish. Regulation of PACAP and expression of its receptor genes has been demonstrated during an immune response mounted against acute bacterial infection in fish, though the direct effect of PACAP against fish pathogenic bacteria has never been addressed. Current work provides evidence of antimicrobial activity of Clarias gariepinus PACAP against a wide spectrum of Gram-negative and Gram-positive bacteria and fungi of interest for human medicine and aquaculture, in which computational prediction studies supported the putative PACAP therapeutic activity. Results also indicated that catfish PACAP not only exhibits inhibitory effects on pathogen growth, but also affects the proliferation of human non-small cell lung cancer cell line H460 in a dose-dependent manner. The observed cytotoxic activity of catfish PACAP against human tumor cells and pathogenic microorganisms, but not healthy fish and mammalian erythrocytes support a potential physiological role of this neuropeptide in selective microbial and cancer cell killing. All together, our findings extend the mechanisms by which PACAP could contribute to immune responses, and open up new avenues for future therapeutic application of this bioactive neuropeptide.

PKA at a Cross-Road of Signaling Pathways Involved in the Regulation of Glioblastoma Migration and Invasion by the Neuropeptides VIP and PACAP

Glioblastoma (GBM) remains an incurable disease, mainly due to the high migration and invasion potency of GBM cells inside the brain. PI3K/Akt, Sonic Hedgehog (SHH), and PKA pathways play major regulatory roles in the progression of GBM. The vasoactive intestinal peptide (VIP) family of neuropeptides and their receptors, referred in this article as the “VIP-receptor system”, has been reported to regulate proliferation, differentiation, and migration in a number of tumor cell types and more particularly in GBM cells. These neuropeptides are potent activators of the cAMP/PKA pathway. The present study aimed to investigate the cross-talks between the above cited signaling cascades. Regulation by VIP-related neuropeptides of GBM migration and invasion was evaluated ex vivo in rat brain slices explanted in culture. Effects of different combinations of VIP-related neuropeptides and of pharmacological and siRNA inhibitors of PKA, Akt, and of the SHH/GLI1 pathways were tested on GBM migration rat C6 and human U87 GBM cell lines using the wound-healing technique. Quantification of nuclear GLI1, phospho-Akt, and phospho-PTEN was assessed by western-immunoblotting. The VIP-receptor system agonists VIP and PACAP-38 significantly reduced C6 cells invasion in the rat brain parenchyma ex vivo, and C6 and U87 migration in vitro. A VIP-receptor system antagonist, VIP_10-28 increased C6 cell invasion in the rat brain parenchyma ex vivo, and C6 and migration in vitro. These effects on cell migration were abolished by selective inhibitors of the PI3K/Akt and of the SHH pathways. Furthermore, VIP and PACAP-38 reduced the expression of nuclear GLI1 while VIP_10-28 increased this expression. Selective inhibitors of Akt and PKA abolished VIP, PACAP-38, and VIP_10-28 effects on nuclear GLI1 expression in C6 cells. PACAP-38 induced a time-dependent inhibition of phospho-Akt expression and an increased phosphorylation of PTEN in C6 cells. All together, these data indicate that triggering the VIP-receptor system reduces migration and invasion in GBM cells through a PKA-dependent blockade of the PI3K/Akt and of the SHH/GLI1 pathways. Therefore, the VIP-receptor system displays anti-oncogenic properties in GBM cells and PKA is a central core in this process.

Vasoactive intestinal peptide/pituitary adenylate cyclase activating polypeptide, and their receptors and cancer

PURPOSE OF REVIEW

To summarize the roles of vasoactive intestinal peptide (VIP)/pituitary adenylate cyclase activating polypeptide (PACAP) and their receptors (VPAC1, VPAC2, PAC1) in human tumors as well as their role in potential novel treatments.

RECENT FINDINGS

Considerable progress has been made in understanding of the effects of VIP/PACAP on growth of various tumors as well as in the signaling cascades involved, especially in the role of transactivation of the epidermal growth factor family. The overexpression of VPAC1/2 and PAC1 on a number of common neoplasms (breast, lung, prostate, central nervous system and neuroblastoma) is receiving increased attention both as a means of tumor imaging the location and extent of these tumors, as well as for targeted directed treatment, by coupling cytotoxic agents to VIP/PACAP analogues.

SUMMARY

VIP/PACAP has prominent growth effects on a number of common neoplasms, which frequently overexpressed the three subtypes of their receptors. The increased understanding of their signaling cascades, effect on tumor growth/differentiation and the use of the overexpression of these receptors for localization/targeted cytotoxic delivery are all suggesting possible novel tumor treatments.

Comparison of expression and proliferative effect of pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptors on human astrocytoma cell lines

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a pleiotropic neuropeptide considered to be a potent regulator of astrocytes. It has been reported that PACAP also affects astrocytoma cell properties, but the proliferative effects of this peptide in previous reports were inconsistent. The purpose of this study was to search for correlations between malignant potential, PACAP/PACAP receptor expression, and the proliferative potential of four astrocytoma cell lines (KNS-81, KINGS-1, SF-126, and YH-13). Immunohistochemical observations were performed using astrocyte lineage markers with a view to establishing malignant potential, which is inversely correlated to differentiation status in astrocytoma cells. YH-13 showed the most undifferentiated astrocyte-like status, and was immunopositive to a cancer stem cell marker, CD44. These observations suggest that YH-13 is the most malignant of the astrocytoma cell lines tested. Moreover, the strongest PAC1-R immunoreactivity was observed in YH-13 cells. Using real-time PCR analysis, no significant differences among cell lines were detected with respect to PACAP mRNA, but PAC1-R and VPAC1-R mRNA levels were significantly increased in YH-13 cells compared with the other cell lines. Furthermore, when cell lines were treated with PACAP (10(-11) M) for 3 days, the YH-13 cell line, but not of the other cell lines, exhibited a significantly increased cell number. These results suggest that PACAP receptor expression is correlated with the malignant and proliferative potential of astrocytoma cell lines.

PACAP38 and PACAP6-38 exert cytotoxic activity against human retinoblastoma Y79 cells

Pituitary adenylate cyclase activating polypeptide (PACAP) is a multifunctional neuropeptide expression of which has been found in various tumors of the brain and peripheral organs. Despite numerous studies, the exact role the peptide plays in the development and progression of tumors is not fully understood. In the present study, we investigated the effect of PACAP on human retinoblastoma Y79 cell viability. We found that both PACAP38 and PACAP6-38, a selective PAC1 receptor antagonist, did not affect Y79 cell viability at nanomolar concentrations, but when used at 1-5 μM potently reduced cell survival in a dose-dependent manner. PACAP27 and maxadilan, a high affinity agonist of PAC1 receptors, had negligible effects. Two membrane-penetrating analogs of PACAP38 inactive at PAC1/VPAC receptors, [Disc(6)]PACAP38 and FITC-Ahx-PACAP11-38, also decreased viability of Y79 cells, albeit with lower potency than PACAP38. The cytotoxic effect of PACAP38 was augmented by p38, MEK1/2, and JNK inhibitors, indicating that high concentrations of the peptide might decrease the activity of these kinases, leading to cell death. It is suggested that the cytotoxic activity of PACAP38 and PACAP6-38 against human retinoblastoma Y79 cell line may result from their interaction with target sites other than PAC1 and VPAC receptors, but this is yet unknown.

Antiproliferative effects of PACAP and VIP in serum-starved glioma cells

Emerging evidence have suggested that calorie restriction (CR) is a reliable method to decrease cancer development since it produces changes in tumor microenvironment that interfere with cell proliferation, tissue invasion, and formation of metastases. Studies on the role of pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) in cancer cells indicate that their influence on cell growth is either cell type specific or dependent on culture conditions. Evidence showing the effect of PACAP and VIP in glioma cells grown under conditions mimicking CR are currently unavailable. Therefore, we explored the effects of both PACAP and VIP in C6 glioma cells either grown in a normal growth medium or exposed to serum starvation, to resemble an acute condition of CR. Cell viability, expression of proteins related to cell proliferation (cyclin D1), apoptosis (Bcl2, p53, and cleaved caspase-3), and cell malignancy (GFAP and nestin) were assessed by MTT assay, immunoblot, and immunolocalization, respectively. Results demonstrated that CR significantly decreased cell proliferation, reduced levels of cyclin D1 and Bcl2, and increased the expression of p53 and cleaved caspase-3. Surprisingly, all of these CR-driven effects were further exacerbated by PACAP or VIP treatment. We also found that PACAP or VIP prevented GFAP decrease caused by CR and further reduced the expression of nestin, a prognostic marker of malignancy. In conclusion, these data demonstrate that PACAP and VIP possess antiproliferative properties against glioma cells that depend on the specific culture settings, further supporting the idea that CR might offer new avenues to improve peptide-oriented glioma cancer treatment.

Effects of cyclopeptide C*HSDGIC* from the cyclization of PACAP (1-5) on the proliferation and UVB-induced apoptosis of the retinal ganglion cell line RGC-5

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide that confers potent neurotrophic and neuroprotective effects. Cyclopeptide C*HSDGIC* (CHC), which results from the cyclization of PACAP (1-5) with disulfide, has been demonstrated to represent a potent agonist for the PACAP-specific receptor PAC1 which mediates the majority of PACAP's effects. In this study, the expression of PAC1 in a rat retinal ganglion cell line (RGC-5) was confirmed using a western blot analysis, and it was determined that CHC promoted the proliferation of RGC-5 cells using the cell counting kit-8 (CCK8) assay and flow cytometry. Furthermore, the treatment of CHC attenuated the decrease of cell viability in cells exposed to UVB irradiation. Flow cytometry and a JC-1 assay revealed that the CHC treatment protected the RGC-5 cells against UVB-induced apoptosis. In addition, similar to PACAP, the anti-apoptotic effect of CHC was related to the down-regulation of caspase-3. In summary, these results demonstrate for the first time that PAC1 is present in RGC-5 cells and that CHC, a cyclopeptide from PACAP, promotes RGC-5 cell proliferation and attenuates UVB-induced apoptosis.

Vasoactive intestinal peptide (VIP) inhibits human renal cell carcinoma proliferation

Clear renal cell carcinoma (cRCC) is an aggressive and fatal neoplasm. The present work was undertaken to investigate the antiproliferative potential of vasoactive intestinal peptide (VIP) exposure on non-tumoral (HK2) and tumoral (A498, cRCC) human proximal tubular epithelial cell lines. Reverse transcription and semiquantitative PCR was used at the VIP mRNA level whereas enzyme immunoanalysis was performed at the protein level. Both renal cell lines expressed VIP as well as VIP/pituitary adenylate cyclase-activating peptide (VPAC) receptors whereas only HK2 cells expressed formyl peptide receptor-like 1 (FPRL-1). Receptors were functional, as shown by VIP stimulation of adenylyl cyclase activity. Treatment with 0.1μM VIP (24h) inhibited proliferation of A498 but not HK2 cells as based on a reduction in the incorporation of [(3)H]-thymidine and BrdU (5'-Br-2'-deoxyuridine), PCNA (proliferating-cell nuclear antigen) expression and STAT3 (signal transducer and activator of transcription 3) expression and activation. VPAC(1)-receptor participation was established using JV-1-53 antagonist and siRNA transfection. Growth-inhibitory response to VIP was related to the cyclic adenosine monophosphate (cAMP)/exchange protein directly activated by cAMP (EPAC)/phosphoinositide 3-kinase (PI3-K) signaling systems as shown by studies on adenylate cyclase stimulation, and using the EPAC-specific compound 8CPT-2Me-cAMP and specific kinase inhibitors such as H89, wortmannin and PD98059. The efficacy of VIP on the prevention of tumor progression was confirmed in vivo using xenografted athymic mouse. These actions support a potential role of this peptide and its agonists in new therapies for cRCC.

A novel cyclopeptide from the cyclization of PACAP(1-5) with potent activity towards PAC1 attenuates STZ-induced diabetes

The N-terminal deletion of pituitary adenylate cyclase-activating polypeptide (PACAP)(1-5) generates its own antagonist. The cyclopeptide C*HSDGIC*, which results from the cyclization of PACAP(1-5) with disulfide, was designed and synthesized. CHO cells expressing a PAC1 N/R splice variant (PAC1-CHO) were used to detect the potent activation of PAC1 by C*HSDGIC*. In vitro cell assays showed that C*HSDGIC* stimulated cAMP production and increased the viability of PAC1-CHO cells at micromolar concentrations, about 1000 fold that of PACAP. PACAP(6-38) blocked the effects of PACAP on the proliferation of PAC1-CHO cells but did not interfere with the effects of C*HSDGIC*, suggesting that the activation of PAC1 by C*HSDGIC* was independent of the binding of PAC1 to the C-terminus of PACAP. In experiments in vivo, 10mumol/kg C*HSDGIC* decreased the plasma glucose level, increased the plasma insulin level and improved glucose tolerance significantly (P<0.01) when co-injected with STZ for 5 days. The results of these in vitro and in vivo studies of the biological characteristics of C*HSDGIC* reveal that it is a potent activator of PAC1.

Glioblastoma cells express functional cell membrane receptors activated by daily used medical drugs

PURPOSE

Calcium ions are highly versatile spacial and temporal intracellular signals of non-excitable cells and have an important impact on nearly every aspect of cellular life controlling cell growth, metabolism, fluid secretion, information processing, transcription, apoptosis, and motility. Neurons and glia respond to stimuli, including neurotransmitters, neuromodulators, and hormones, which increase the intracellular calcium concentration. The function of intracellular calcium in gliomas is unknown. Lots of daily used drugs may act via receptors that can be linked to the intracellular calcium system and therefore could influence glioma biology.

METHODS

Glioma cells were loaded with the calcium ion sensitive dye Fura 2-AM. Subsequently, cells were stimulated with 25 different medical drugs for 30 s. The increase of free intracellular calcium ions was measured and calculated by a microscope-camera-computer-unit.

RESULTS

Except for the buffer solution HEPES that served as negative control and for the cortisol derivative dexamethasone, all other 24 tested drugs induced a rise of intracellular calcium ions. The cellular calcium responses were classified into seven functional groups. The tested substances activated several types of calcium channels and receptors.

CONCLUSIONS

Our study impressively demonstrates that medical drugs are potent inducers of intracellular calcium signals. Totally unexpected, the results show a high amount of functional cellular receptors and channels on glioma cells, which could be responsible for certain biological effects like migration and cell growth. This calcium imaging study proves the usability of the calcium imaging as a screening system for functional receptors on human glioma cells.