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Pituitary adenylate cyclase-activating polypeptide (PACAP), a pleiotropic neuropeptide, performs a variety of physiological functions. The PACAP-specific receptor PAC1 has several variants that result mainly from alternative splicing in the mRNA regions encoding the first extracellular (EC1) domain and the third intracellular cytoplasmic (IC3) loop. The effects on downstream signaling produced by combinations of alternative splicing events in the EC1 domain and IC3 loop have not yet been clarified. In this study, we have used semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) to examine the tissue distributions of four PAC1 isoforms in mice. We then established cell lines constitutively expressing each of the PAC1 isoforms and characterized the binding properties of each isoform to PACAP-38, vasoactive intestinal polypeptide (VIP), and the PAC1-specific agonist maxadilan, as well as the resulting effects on two major intracellular signaling pathways: cAMP production and changes in the intracellular calcium concentration. The results demonstrate that the variants of the IC3 loop affect the binding affinity of the ligands for the receptor, whereas the variants of the EC1 domain primarily affect the intracellular signaling downstream of PAC1. Accordingly, this study indicates that the combination of alternative splicing events in the EC1 domain and the IC3 loop create a variety of PAC1 isoforms, which in turn may contribute to the functional pleiotropism of PACAP. This study not only contributes to the understanding of the multiple functions of PACAP but also helps to elucidate the relationship between the structures and functions of G-protein-coupled receptors.Pituitary adenylate cyclase-activating polypeptide (PACAP), a pleiotropic neuropeptide first isolated from ovine hypothalamus, occurs in two forms: one consists of 38 amino acid residues (PACAP-38) and the other contains 27 amino acid residues (PACAP-27) (Miyata et al., 1989. The actions of PACAP are mediated through G-protein-coupled receptors (GPCRs) that belong to group II of the secretin receptor family. Three PACAP/vasoactive intestinal polypeptide (VIP) receptor genes have been cloned: one encodes the PACAP-preferring receptor PAC1 (Hashimoto et al., 1993;Hosoya et al., 1993;Morrow et al., 1993;Pisegna and Wank, 1993;Spengler et al., 1993;Aino et al., 1995;Vaudry et al., 2000;Harmar, 2001), whereas the other two encode receptors that respond equally to PACAP and VIP (VPAC1 and VPAC2) (Ishihara et al., 1992;Lutz et al., 1993Lutz et al., , 1999. Typically, group II receptors signal through the protein kinase A (PKA) pathway, although PAC1 not only activates the PKA pathway but is also coupled to the phospholipase C (PLC) pathway, resulting in changes in the intracellular calcium concentration ([Ca 2ϩ ] i ). In mice, the PAC1 gene contains more than 18 exons, and more splice variants of PAC1 have been identified than for most of the other GPCRs (Aino et al., 1995). Most of the PAC1 isoforms are formed as a result of altern...

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Abstract. The aim of this study was to analyze the relationship between the maximum standardized uptake value (SUVmax) of 18F-fluoro-2-deoxyglucose-positron emission tomography (FDG-PET) and the effects of neoadjuvant chemoradiotherapy in oral squamous cell carcinoma (OSCC), and to identify the possible biological background of this association. Thirty-seven patients with OSCC, who underwent preoperative FDG-PET followed by cancer treatment with neoadjuvant chemoradiotherapy, were enrolled in this study. The various histological effects following neoadjuvant chemoradiotherapy were compared to the SUVmax in the primary OSCC. These effects were also compared to the immunohistochemical staining score of hypoxia-inducible factor-1· (HIF-1·), glucose membrane transporter (GLUT)-1 and vascular endothelial growth factor (VEGF) in the biopsy specimen. Furthermore, we analyzed the chemosensitivity of KB-3-1 cells to cisplatin under hypoxic conditions using the MTT assay. A negative correlation was observed between the SUVmax and the histological effects following neoadjuvant chemoradiotherapy (p<0.01). The SUVmax was also correlated with the staining score of HIF-1· (p<0.03), but not with GLUT-1 and VEGF. The mean staining score of HIF-1· in the highly effective group was 2.7±1.1, which was significantly lower than that (3.7±0.9) of the poorly effective group (p<0.05). The cell chemosensitivity assay revealed chemoresistant effects under a hypoxic condition in OSCC. In conclusion, the SUVmax is correlated with the effectiveness of neoadjuvant chemoradiotherapy in OSCC.Our clinical and experimental analyses further suggest a possible association of the upregulation of HIF-1· with chemoradiosensitivity in SCC cells.