Functional expression of VIP receptors in normal, immortalized and transformed mammary epithelial cells

Signaling pathways activated by PACAP in MCF-7 breast cancer cells

PACAP has opposing roles ranging from activation to inhibition of tumor growth and PACAP agonists/antagonists could be used in tumor therapy. In this study, the effect of PACAP stimulation on signaling pathways was investigated in MCF-7 human adenocarcinoma breast cancer cells. Results showed that MCF-7 cells express VPAC1 and VPAC2, but not PAC1, receptors. In addition, PACAP increased the phosphorylation levels of STAT1, Src and Raf within seconds, confirming their involvement in early stages of PACAP signaling whereas maximal phosphorylation of AKT, ERK and p38 was reached 10 to 20 min later. Moreover, selective inhibition of Src or PI3K resulted in a significant decrease in the phosphorylation of ERK and AKT, but not p38, demonstrating that PACAP signaling follows Src/Raf/ERK and PI3K/AKT pathways. On the other hand, selective inhibition of PLC or PKA resulted in a significant decrease in the phosphorylation of p38, but not AKT or ERK, indicating that PACAP signaling also follows the PLC and PKA/cAMP pathways. Furthermore, PACAP induced ROS through H₂O₂ production whereas pretreatment with NAC inhibitor decreased AKT and ERK phosphorylation, but not p38. Selective NOX2 inhibition affected Src/Raf/Erk and PI3K/Akt pathways, without affecting the p38/PLC/PKA pathway whereas other inhibitors (ML171, VAS2870) had no effect on PACAP induced ROS generation. On the other hand, PACAP induced calcium release, which was decreased by pretreatment with PLC inhibitor. Finally, PACAP stimulation promoted apoptosis by increasing Bax and decreasing Bcl2 expression. In conclusion, we demonstrated that PACAP signaling in MCF-7 cells follows the Src/Raf/ERK and PI3K/AKT pathways and is VPAC1 dependent in a ROS dependent manner, whereas it follows PLC and PKA/cAMP pathways and is VPAC2 dependent through p38 MAP kinase activation involving calcium.

Downregulation of VPAC1R expression in breast cancer cell lines

The breast carcinoma cell line T47D was tested for 17 beta-estradiol (E2) mediated regulation of vasoactive intestinal polypeptide receptor type-1 (VPAC1) expression. E2 was found to downregulate the mRNA level. The number of VIP binding sites was reduced 66% on treatment with E2 for 72 h. Experiments with cycloheximide suggested that the effect was independent (at least partly so) of protein synthesis. Experiments with the transcriptional inhibitor, actinomycin D, showed that E2 did not influence the VPAC1 mRNA halflife. Both of two antiestrogens, ICI 182,780 and 4-hydroxy-tamoxifen, mediated a concentration dependent inhibition of the effect of E2 on the mRNA level. Transient transfection with reporter-gene constructs containing various portions of the VPAC1 5'-flanking sequence revealed the most proximal 100 bp to be essential for the basal transcriptional activity. However, E2 did not influence the expression of the reporter gene using up to 3,250 bp of the VPAC1 5'-flanking region.

Estradiol down regulates expression of vasoactive intestinal polypeptide receptor type-1 in breast cancer cell lines

Three breast carcinoma cell lines were tested for 17beta-estradiol (E(2)) mediated regulation of vasoactive intestinal polypeptide receptor type-1 (VPAC(1)) expression. In all three, E(2) was found to down-regulate the mRNA level. We studied T47D cells in more details and found a 25 and 70% decrease in the VPAC(1) mRNA level upon 7 and 48 h of E(2) treatment, respectively. The number of vasoactive intestinal polypeptide (VIP) binding sites was reduced 66% upon treatment with E(2) for 72 h. After cycloheximide pretreatment, the E(2) mediated mRNA reduction was attenuated from 50% to 25% after 24 h suggesting the effect to be at least partly independent of protein synthesis. Experiments with the transcriptional inhibitor actinomycin D showed that E(2) did not influence the VPAC(1) mRNA half-life while nuclear run-on experiments indicated that E(2) decreased the VPAC(1) transcription rate. Two antiestrogens: ICI 182780 (ICI) and 4-hydroxy-tamoxifen (4-OHT) mediated a concentration dependent inhibition of E(2)'s effect on the mRNA level. Transient transfection with reporter-gene constructs containing various portions of the VPAC(1) 5'-flanking sequence revealed the most proximal 100 bp to be essential for the basal transcriptional activity. However, E(2) did not influence the expression of the reporter gene using up to 3250 bp of the VPAC(1) 5'-flariking region.

Functional type II VIP-PACAP receptors in human airway epithelial-like cells

VIP-PACAP receptors were characterized in a human airway epithelial-like cell line (Calu-3), Pituitary adenylate cyclase activating polypeptide (PACAP) 1-27, PACAP 1-38, vasoactive intestinal polypeptide (VIP) and the beta 1- and beta 2-adrenoceptor agonist isoproterenol (3 nM-1 microM) increased cAMP concentration dependently. The peptides and isoproterenol displayed similar potencies (range of means pEC50[M]: 6.5-7.1). The maximum increase in cAMP (Emax in % of basal cAMP level) was similar for the peptides (range of means Emax: 2500-5100%). Pretreatment with the peptidase inhibitors captopril (10 microM) and phosphoramidon (1 microM) significantly increased the cAMP response to PACAP 1-38 (to 480% of control) only.

Immortalization of mouse intestinal epithelial cells by the SV40-large T gene. Phenotypic and immune characterization of the MODE-K cell line

Intestinal epithelial cells from the mouse small intestine were immortalized by SV40 large T gene transfer through a murine ecotropic virus. The resulting cell lines expressed the SV40 large T mRNA and exhibited morphological and phenotypic characteristics of normal enterocytes, including intercellular junctions, and expression of cytokeratin, villin, poly-Ig receptor (i.e., secretory component) and vasoactive intestinal peptide receptors. All expressed cell surface major histocompatibility complex class I molecules, but cell surface class II antigens were undetectable. Functional studies on antigen presentation were carried out using the MODE-K cell line established from the mouse duodenum. Interferon-gamma treatment of MODE-K cells resulted in a high level of class II molecule expression, and the ability to process and present native protein antigens to specific CD4+ T-cell hybridomas, via functional class II molecules. These data suggest that the MODE-K cell line is a suitable model for the analysis of intestinal epithelial cell function in mucosal immunity.

Interaction of VIP, PACAP and related peptides in normal and leukemic human monocytes and macrophages

The activation of the cAMP signaling pathway by vasoactive intestinal peptide (VIP), pituitary adenylate cyclase-activating peptide (PACAP) and related peptides was studied (i) in normal peripheral human monocytes and THP-1 leukemic human monocytes, (ii) in their derived macrophage counterparts respectively obtained after spontaneous differentiation or retinoic acid (RA) treatment, and (iii) in human bronchoalveolar macrophages. In THP-1 monocytes, PACAP increased basal adenylate cyclase activity 5.3-fold, with an affinity 50-times greater than that of VIP or helodermin (Ka = 3.2 x 10(-11) M VIP), whereas in normal peripheral monocytes, PACAP and VIP exhibited similar affinities and only increased cAMP generation 2-fold (EC50 = 10(-9) M). Spontaneous and RA-induced differentiation into normal and leukemic macrophages induced a progressive loss of cAMP production and regulation of superoxide anion production by VIP and related peptides. The neoplastic transformation in THP-1 monocytes and the deficiencies in the cAMP cascade observed during the terminal differentiation of normal and leukemic human macrophages may relate to a differential genetic expression of the VIP/PACAP receptor subtypes, and alterations in the functional activity of the stimulatory and inhibitory Gs/Gi subunits of adenylate cyclase.