adrenomedullin and Astrocytoma

Glioblastoma multiforme is the most malignant of the primary brain tumors and is almost always fatal. The treatment strategies for this disease have not changed appreciably for many years and most are based on a limited understanding of the biology of the disease. Growth factors are potential targets for therapeutic strategies because they are essential for tumor growth and progression. Adrenomedullin (AM) is a multifunctional regulatory peptide with mitogenic and angiogenic capabilities among others. Real-time quantitative reverse transcriptase-polymerase chain reaction analysis showed that AM mRNA was correlated to the tumor type and grade, with high expression in all glioblastomas analysed, whereas a low expression was found in anaplastic astrocytomas and barely detectable levels in low-grade astrocytomas and oligodendriogliomas. The correlation of AM expression to the grade of glioma support the hypothesis that AM may participate in the progression of gliomas. We demonstrate that AM may function as an autocrine/paracrine growth factor for glioblastoma cells. The data demonstrated that the anti-AM antibody significantly suppress the growth of established glioblastoma xenografts. The action of AM is specific and is mediated by the calcitonin receptor-like receptor/receptor activity-modifying protein-2 and -3 (CRLR/RAMP2, CRLR/RAMP3). Furthermore, the proangiogenic action of AM on cultured endothelial cells via CRLR/RAMP2 and CRLR/RAMP3 receptors may translate in vivo into enhanced neovascularization and therefore identify AM and its receptors acting as potential new targets for antiangiogenic therapies.

Topics: Adrenomedullin; Angiogenic Proteins; Astrocytoma; Brain Neoplasms; Cell Hypoxia; Glioblastoma; Humans; Neoplasm Invasiveness; Neoplasm Proteins; Neovascularization, Pathologic; Neuropeptides; Oligodendroglioma; Peptides

Adrenomedullin (ADM), a secretory peptide with multiple functions in physiological to pathological conditions, is upregulated in several human cancers, including brain, breast, colon, prostate, and lung cancer. However, the molecular mechanisms underlying the regulation of ADM expression in cancerous cells are not fully understood. Here, we report that oncostatin M (OSM), a cytokine belonging to the interleukin-6 family, induces ADM expression in astroglioma cells through induction of signal transducer and activator of transcription-3 (STAT-3) phosphorylation, nuclear translocation, and subsequent DNA binding to the ADM promoter. STAT-3 knockdown decreased OSM-mediated expression of ADM, indicating that ADM expression is regulated by STAT-3 in astroglioma cells. Lastly, scratch wound healing assay showed that astroglioma cell migration was significantly enhanced by ADM peptides. These data suggest that aberrant activation of STAT-3, which is observed in malignant brain tumors, may function as one of the key regulators for ADM expression and glioma invasion.

Topics: Adrenomedullin; Apoptosis; Astrocytoma; Blotting, Western; Brain Neoplasms; Cell Movement; Cell Proliferation; Electrophoretic Mobility Shift Assay; Gene Expression Regulation, Neoplastic; Humans; Neoplasm Invasiveness; Oncostatin M; Phosphorylation; Real-Time Polymerase Chain Reaction; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; RNA, Small Interfering; STAT3 Transcription Factor; Tumor Cells, Cultured

Clinical and experimental studies suggest that angiogenesis is a prerequisite for solid tumour growth. Glioblastoma (GBM) and pilocytic astrocytoma (PA), both angiogenic tumours display strong contrast enhancement associated with peripheral oedema in GBM but not in PA indicating differences in vascular permeability in these two types of gliomas. Here we show that expression of adrenomedullin (AM) mRNA is induced in GBM whereas is barely detectable in PA. In situ analysis of tumour specimens undergoing neovascularisation shows that the production of AM is specifically induced in a subset of GBM cells distinguished by their immediate proximity to necrotic foci (presumably hypoxic regions), suggesting a hypoxic induction of AM expression in GBM. Vascular endothelial growth factor (VEGF) mRNA levels are increased in GBM and moderate in PA. Immunohistochemical study showed that cytoplasmic AM, VEGF and HIF-1α nuclear immunoreactivity were recorded in GBM located near large necrotic areas whereas they were not expressed by PA tumour cells. Interestingly, double fluorescence immunostaining demonstrated that 85% of AM immunoreactivity colocalised with VEGF. AM transduces its effects through calcitonin receptor-like receptor/receptor activity modifying protein-2 and -3 (CLR/RAMP2 and CLR/RAMP3). Real-time quantitative RT-PCR showed expression of RAMP2, RAMP3 and CLR in PA and GBM, suggesting that AM may function as an autocrine/paracrine growth factor for GBM cells. These observations strongly support the concept that tumour angiogenesis is regulated by paracrine mechanisms and identify beside VEGF, AM as a potential tumour angiogenesis factor in vivo which constitutes a potential interesting molecular target in GBM treatment.

Topics: Adrenomedullin; Angiogenesis Inhibitors; Astrocytoma; Brain Neoplasms; Cell Line, Tumor; DNA Primers; Gene Expression Regulation, Neoplastic; Glioblastoma; Humans; Hypoxia; Immunohistochemistry; In Situ Hybridization; Microscopy, Fluorescence; Neovascularization, Pathologic; Vascular Endothelial Growth Factor A