Effects of PACAP and VIP on cAMP-generating System and Proliferation of C6 Glioma Cells

Abstract

An identification of PAC1- and VPAC-type receptors in a great number of neoplastic cells gave rise to intensive studies on the biochemical and physiological role of the mentioned peptides in cancers. Our earlier studies focused on effects of pituitary adenylate cyclase-activating peptide (PACAP) and vasoactive intestinal peptide (VIP) in C6 glioma cells have shown their stimulatory receptor-mediated action on the cyclic adenosine monophosphate (cAMP)-generating system. In the present study, we demonstrated that truncated peptides, i.e., PACAP6-38 and VIP6-28, both produced a significant inhibition of the VIP-induced increase in cAMP production, whereas only PACAP6-38 did antagonize the PACAP-38 effect. In contrast to the well-expressed PACAP-38 and VIP effects on cAMP production in C6 cells, helodermin and secretin were poorly active as cAMP stimulators in this cell line, displaying some activity only at a high 5-microM dose. PACAP-38 and, to a lesser extent VIP stimulated the proliferation of C6 glioma cells, which was shown by an increased incorporation of 3H-thymidine into the cells, and the effects of these two peptides were antagonized by PACAP6-38. The truncated PACAP (10 microM) by itself significantly inhibited C6 cell proliferation. The study with the use of forskolin and dibutyryl-cAMP revealed that the growth effects of PACAP were cAMP independent. Our findings suggest that glioma C6 cells possess PAC1- and VPAC-type receptors, but the density of PAC1 seems to be much larger than VPAC receptors. Although the proliferative activity of PACAP and VIP is mediated via the PAC1-type receptor, the signaling cascade underlying this phenomenon does not seem to involve cAMP.

Atypical nuclear localization of VIP receptors in glioma cell lines and patients

“…VIP and PACAP can exert pro-or antitumoral effects depending on the cancer type [14,26,27,[32][33][34][35]. This differential response is also observed in glioma cell lines, where VIP and PACAP can either increase, decrease or have no effect on cell proliferation [16][17][18][20][21][22]. These neuropeptides also negatively regulate migration in GBM cells [19].…”

“…So far, little is known about the possible involvement of nuclear GPCRs in tumor progression. Our group and others have demonstrated that glioblastoma (GBM) cells express VIP or PACAP and their receptors, allowing an autocrine/ paracrine regulation of proliferation and migration [16][17][18][19][20][21][22]. The aim of the present study was to analyze the expression and the subcellular localization of VPAC1/2 receptors in glioma cell lines and tissue microarrays (TMA) from gliomas of different grades of malignancy.…”

“…We investigated the nuclear localization of the two VIP receptors VPAC1 and VPAC2 in glioma cell lines and patients, as these receptors are known to be involved in GBM progression [17][18][19][20]. First, we searched for the presence of a nuclear localization sequence (NLS) signal in the amino-acid sequence of the two receptors.…”

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

“…It has been demonstrated that depending on the cell line, PACAP can increase or decrease cancer cell viability. Thus, PACAP38 stimulated proliferation of rat C6 glioma cells (Sokołowska and Nowak 2008) and prevented apoptosis of androgen-independent prostate cancer PC-3 cells (Gutiérrez-Cañas et al 2003). On the other hand, PACAP27 reduced proliferation of two human colonic tumor cell lines: DLD-1 and Caco-2 (Lelièvre et al 1998), and PACAP38 inhibited proliferation of primary medulloblastoma-derived tumor spheres (Cohen et al 2010).…”

Examination of PACAP-Like Immunoreactivity in Urogenital Tumor Samples

“…PACAP inhibits growth of myeloma cells (Arimura et al 2006a, b), of serum-starved glioma cells (D'Amico et al 2013), and of cervical carcinoma (Lee et al 2014), as well as proliferation in primary medulloblastomaderived tumorsphere cultures (Cohen et al 2010). On the other hand, PACAP stimulates the growth of colon (Le et al 2002), small cell lung cancer (Moody et al 1993), astrocytoma , glioblastoma cells (Dufes et al 2003;Sokolowska and Nowak 2008) as well as pancreatic carcinoma cells (Schafer et al 1996;Germano et al 2009). PACAP(6-38), the antagonist of PAC1 receptor, inhibits the growth of prostate cancer (Leyton et al 1998), breast cancer (Leyton et al 1999), and non-small cell lung cancer cells (Zia et al 1995).…”