Galanin Receptor 1 Has Anti-proliferative Effects in Oral Squamous Cell Carcinoma

Abstract

In the United States, oral cancer accounts for more deaths annually than cervical cancer, leukemias, or Hodgkin's lymphoma. Studies have shown that aberrations of chromosome 18q develop with tumor progression and are associated with significantly decreased survival in head and neck cancer patients. The G-protein-coupled receptor, galanin receptor 1 (GALR1), maps to this region of chromosome 18q. Although the role of GALR1 has been well characterized in neuronal cells, little is known regarding this receptor in nonneuronal cells. In this study, the expression, mitogenic function, and signaling mechanism of GALR1 are investigated in normal and malignant oral epithelial cells. mRNA expression was determined via reverse transcriptase-PCR. Protein quantification was done via immunoblot analysis and enzyme-linked immunosorbent assay. For functional and signaling studies, an inhibitory antibody was generated to the N-terminal ligand binding domain of GALR1. GALR1 protein and mRNA expression and GAL secretion were detected at variable levels in immortalized human oral keratinocytes and human oropharyngeal squamous cell carcinoma cell lines. Upon competitive inhibition of GALR1, proliferation was up-regulated in immortalized and malignant keratinocytes. Furthermore, studies with the inhibitory antibody and U0126, the MAPK inhibitor, show that GALR1 inhibits proliferation in immortalized and malignant keratinocytes by inactivating the MAPK pathway. GALR1s inhibitory effects on proliferation in epithelial cells raises the possibility that inactivation or disregulation of this receptor can lead to uncontrolled proliferation and neoplastic transformation.

Physiology, Signaling, and Pharmacology of Galanin Peptides and Receptors: Three Decades of Emerging Diversity

“…In human epidermis, galanin immunoreactivity has been localized in sensory Merkel cells (Fantini and Johansson, 1995) and follicular and interfollicular keratinocytes (Pincelli et al, 1990;Kofler et al, 2004). Additionally, galanin secretion has been detected in cultures of human primary foreskin and oral keratinocytes Henson et al, 2005). Keratinocytes play a crucial role in the innate immune responses of skin, including the production of proinflammatory cytokines and antimicrobial peptides (Metz and Maurer, 2009).…”

“…In rat neurons, a GAL 1 -mediated effect on voltage-dependent Ca 2+ channels has been reported (Endoh et al, 2008;Anselmi et al, 2009). Galanin Family Peptides and Receptors GAL 1 -induced effects on the MAPK/extracellular signal-regulated protein kinase (ERK) 1/2 pathway have been described in human tumor cells (Henson et al, 2005;Kanazawa et al, 2007). Activation of the MAPK/ERK pathway via GAL 1 is not linked to the phosphatidylinositol 3-kinase pathway and leads to the induction of the cell-cycle control proteins p27 Kip1 and p57…”

“…However, putative GAL 2 -like immunoreactivity has been localized in the epidermis of a human breast skin specimen and in cultured primary keratinocytes derived from this specimen, where GAL 2 seems to be functional (Dallos et al, 2006b). Interestingly, human immortalized oral keratinocytes express mRNA for all three galanin receptors (Henson et al, 2005), reflecting either different galanin receptor distributions at different anatomic sites or differential galanin receptor expression due to malignant transformation. In malignant oral keratinocytes, GAL 1 likely produces antiproliferative effects, because treatment of the cells with an anti-GAL 1 antibody resulted in increased proliferation and MAPK activation (Henson et al, 2005).…”

“…Interestingly, human immortalized oral keratinocytes express mRNA for all three galanin receptors (Henson et al, 2005), reflecting either different galanin receptor distributions at different anatomic sites or differential galanin receptor expression due to malignant transformation. In malignant oral keratinocytes, GAL 1 likely produces antiproliferative effects, because treatment of the cells with an anti-GAL 1 antibody resulted in increased proliferation and MAPK activation (Henson et al, 2005). Antiproliferative effects of galanin have also been reported after GAL 2 re-expression in p53-mutant oral carcinoma, and galanin treatment caused morphologic changes and a marked reduction in cell number (Kanazawa et al, 2009).…”

Mitogen-activated protein kinase signaling pathway in oral cancer (Review)

“…They include epigallocatechin-3-gallate, aliphatic acetogenin, galanin receptor 1, and S-allylcysteine (56)(57)(58)(59). Certain inhibitors, including pterostilbene, astaxanthin and sulfasalazine (SSZ) (60)(61)(62), may also induce tumor cell apoptosis.…”