PACAP38 and PACAP6-38 Exert Cytotoxic Activity Against Human Retinoblastoma Y79 Cells

Abstract

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, [Disc6]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.

Occurrence and Functions of PACAP in the Placenta

“…The reason for this is not known at the moment, and may or may not reflect the physiological role of the peptide, since these experiments were performed in choriocarcinoma cells, in which the receptor expression and signaling induced by PACAP may be significantly altered. Similar results were described in retinoblastoma cells, where PACAP treatment induced cell death [55] in spite of the well-known protective effects of PACAP in the retina [56,57]. PACAP also inhibited the growth of the neuronal tumor medulloblastoma in spite of the well-known neuroprotective effects of the peptide [58][59][60].…”

“…This does not seem to be specific for this cell line, since agonistic effects were found for example on rat trachea neuropeptide release, retinoblastoma cell survival and cartilage and bone development [55,[62][63][64]. The reason for this might be the expression of a yet unknown splice variant of the receptor or the tumorous nature of the JAR cells.…”

Protective Effects of PACAP in the Retina

“…Interestingly, PACAP1-27 and maxadilan had negligible effects, while two membrane-penetrating analogs of PACAP also decreased cell viability. The authors also revealed that this cytotoxic effect might be via an interaction of p38, MEK1/2, and JNK signaling, because inhibitors of these pathways led to an even more expressed cytotoxicity [ 115 ]. These results suggest that high concentrations of PACAP1-38 might lead to a transmembrane penetration and lead to direct cytotoxicity at sites other than the conventional PACAP receptor-mediated signaling.…”

“…These results provide evidence that PACAP1-38 has neuroprotective effects in hypoxic/ anoxic conditions in the adult turtle retina in vitro. Nanomolar: no effect on cell viability Micromolar: ↓: Cell viability, further ↓: with PACAP6-38; no effect: PACAP1-27 and maxadilan [ 115 ] …”

“…Human retinoblastoma cells are known to express PACAP receptors [ 114 ]. In Y79 retinoblastoma cells, PACAP1-38 did not infl uence cell survival at nanomolar concentrations, but at 1-5 μM concentrations, it reduced survival [ 115 ]. Interestingly, PACAP1-27 and maxadilan had negligible effects, while two membrane-penetrating analogs of PACAP also decreased cell viability.…”