Human H9 cells proliferation is differently controlled by vasoactive intestinal peptide or peptide histidine methionine: implication of a GTP-insensitive form of VPAC1 receptor

Mechanism of VIPR1 gene regulating human lung adenocarcinoma H1299 cells

The vasoactive intestinal peptide receptor-1(VIPR1) has prominent growth effects on a number of common neoplasms. However, there were contradictions in the effect cross different cancers. We aimed to explore the effect of VIPR1 overexpression on a human lung adenocarcinoma cell line H1299. GEO dataset was used to screen differentially expressed genes in lung adenocarcinoma tissues. The expression of VIPR1 mRNA was determined in the cancer Genome Atlas (TCGA). Immunohistochemical analysis was performed to determine VIPR1 protein expression in lung adenocarcinoma and corresponding adjacent tissues (n = 22). Fluorescence real-time quantitative PCR detected the expression of VIPR1 in human normal lung epithelial cell line BEAS-2B and lung adenocarcinoma cell line H1299. Overexpression strategies were employed to assess functions of VIPR1 expression on several malignant phenotypes in H1299. The expression of VIPR1 was lower in lung adenocarcinoma tissues than that in adjacent tissues. Compared with the normal lung epithelial cells BEAS-2B, VIPR1 was down-regulated in lung cancer cells H1299 (P < 0.05). After the overexpression of VIPR1, we found that VIPR1 significantly inhibited growth, migration, and invasion of H1299 cells (P < 0.05). Our findings point out the tumor suppressor roles of VIPR1 in human LUAD pathogenesis.

Vasoactive intestinal peptide induces proliferation of human hepatocytes

OBJECTIVES

Proliferation of hepatocytes in vitro can be stimulated by growth factors such as epidermal growth factor (EGF), but the role of vasoactive intestinal peptide (VIP) remains unclear. We have investigated the effect of VIP on maintenance and proliferation of human hepatocytes.

MATERIALS AND METHODS

Human hepatocytes were isolated from liver specimens obtained from patients undergoing liver surgery. Treatment with VIP or EGF was started 24 h after plating and continued for 3 or 5 d. DNA replication was investigated by Bromodeoxyuridine (BrdU) incorporation and cell viability detected by MTT assay. Cell lysate was analysed by western blotting and RT-PCR. Urea and albumin secretion into the culture supernatants were measured.

RESULTS

VIP increased DNA replication in hepatocytes in a dose-dependant manner, with a peak response at day 3 of treatment. VIP treatment was associated with an increase in mRNA expression of antigen identified by monoclonal antibody Ki-67 (MKI-67) and Histone Cluster 3 (H3) genes. Western blotting analysis showed that VIP can induce a PKA/B-Raf dependant phosphorylation of extracellular signal-regulated kinases (ERK). Although EGF can maintain hepatocyte functions up to day 5, no marked efffect was found with VIP.

CONCLUSIONS

VIP induces proliferation of human hepatocytes with little or no effect on hepatocyte differentiation. Further investigation of the role of VIP is required to determine if it may ultimately support therapeutic approaches of liver disease.

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.

Vasoactive intestinal peptide signaling axis in human leukemia

The vasoactive intestinal peptide (VIP) signaling axis constitutes a master “communication coordinator” between cells of the nervous and immune systems. To date, VIP and its two main receptors expressed in T lymphocytes, vasoactive intestinal peptide receptor (VPAC)1 and VPAC2, mediate critical cellular functions regulating adaptive immunity, including arresting CD4 T cells in G₁ of the cell cycle, protection from apoptosis and a potent chemotactic recruiter of T cells to the mucosa associated lymphoid compartment of the gastrointestinal tissues. Since the discovery of VIP in 1970, followed by the cloning of VPAC1 and VPAC2 in the early 1990s, this signaling axis has been associated with common human cancers, including leukemia. This review highlights the present day knowledge of the VIP ligand and its receptor expression profile in T cell leukemia and cell lines. Also, there will be a discussion describing how the anti-leukemic DNA binding transcription factor, Ikaros, regulates VIP receptor expression in primary human CD4 T lymphocytes and T cell lymphoblastic cell lines (e.g. Hut-78). Lastly, future goals will be mentioned that are expected to uncover the role of how the VIP signaling axis contributes to human leukemogenesis, and to establish whether the VIP receptor signature expressed by leukemic blasts can provide therapeutic and/or diagnostic information.

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

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.

Unconventional binding sites and receptors for VIP and related peptides PACAP and PHI/PHM: an update

The 28-amino-acid neuropeptide VIP and related peptides PACAP and PHI/PHM modulate virtually all of the vital functions in the body. These peptides are also commonly recognized as major regulators of cell growth and differentiation. Through their trophic and cytoprotective functions, they appear to play major roles in embryonic development, neurogenesis and the progression of a number of cancer types. These peptides bind to three well-characterized subtypes of G-protein coupled receptors: VPAC1 and VPAC2 share a common high affinity in the nanomolar range for VIP and PACAP; a third receptor type, PAC1, has been characterized for its high affinity for PACAP but its low affinity for VIP. Complex effects and pharmacological behaviors of these peptides suggest that multiple subtypes of binding sites may cooperate to mediate their function in target cells and tissues. In this complex response, some of these binding sites correspond to the definition of the conventional receptors cited above, while others display unexpected pharmacological and functional properties. Here we present potential clues that may lead investigators to further characterize the molecular nature and functions of these atypical binding species.

Effects of PACAP and VIP on cyclic AMP formation in rat neuronal and astrocyte cultures under normoxic and hypoxic condition

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) concentration (0.001-1000 nM)-dependently stimulated cyclic AMP production in rat primary neuronal and glial cell (astrocyte) cultures. The actions of both peptides were much more pronounced in astrocytes than in neuronal cultures. Stimulatory effects of PACAP and VIP on cyclic AMP formation were significantly smaller in cell cultures subjected to 24h lasting hypoxic conditions, induced either chemically (100 microM cobalt chloride) or by low 3% oxygen hypoxia, compared to the normoxic condition (95% air and 5% CO(2)). This picture contrasted with the effects of forskolin that were similar under normoxic and hypoxic conditions. It is suggested that hypoxia leads to changes in PACAP- and VIP-driven cyclic AMP-dependent signaling in the rat brain by influencing molecular processes likely occurring at the level of receptor protein or receptor-Gs protein coupling.