Expression of Somatostatin Receptor Subtypes in Cultured Astrocytes and Gliomas

Abstract

Expression of receptors for the neuropeptide somatostatin was investigated in vitro in rat and human astrocytes, glioma cell lines, and solid human glial tumors that were all immunopositive for the astrocytic marker glial fibrillary acidic protein. After affinity labelling with a peptide‐gold conjugate of known biological activity, somatostatin‐binding sites could be visualized at the light‐ and electron‐microscopic level on the surface of glial cells. Glioma cells were generally labeled more strongly than were normal astrocytes and preferentially bound the ligand at their processes and not at their somata as were normal cells. Somatostatin transmembrane receptor (SSTR) subtype expression was probed by reverse transcription‐polymerase chain reaction: In rat and human cortical astrocytes and in one glioma cell line (U 118), a pattern of three subtypes (SSTR‐1, SSTR‐2, and SSTR‐4) was detected, whereas, in all other glioma cell lines and in six solid glial tumors investigated, the SSTR‐2 subtype was relatively stronger, expressed either alone or in combination with SSTR‐1; sometimes SSTR‐3 or SSTR‐4 was demonstrated in clearly reduced amounts. In astrocytes and gliomas, somatostatin reduced the levels of cyclic AMP elicited by the adenylate cyclase activator forskolin indicating that at least one of the receptor subtypes is negatively linked to adenylate cyclase. In contrast to other cell types, somatostatin did not inhibit the basal or the fetal calf serum‐stimulated proliferation of astrocytes, glioma cell lines, or glial tumors in culture. Thus, strong SSTR‐2 subtype expression characterizes glial tumors, but somatostatin is ineffective in inhibiting their growth.

Somatostatin Receptor Subtype 2 Is Expressed by Supratentorial Primitive Neuroectodermal Tumors of Childhood and Can Be Targeted for Somatostatin Receptor Imaging

“…In contrast to Guyotat, who was able to image all ependymomas, SRI was not helpful in the diagnosis of ependymoma recurrence in our patients. Our data are supported by other investigators, who could not image ependymomas by SRI (27,40).…”

“…We thus argue that in our samples, immunostaining is in part due to membrane-bound and otherwise due to internalized receptors. We cannot conclude whether the receptors are functionally active in the expressing tumors; however, our own studies on MB cell lines and other investigators work on glioma cells demonstrate that intracellular transduction pathways are activated upon ligand binding (13,27).…”

Matrix‐degrading proteases ADAMTS4 and ADAMTS5 (disintegrins and metalloproteinases with thrombospondin motifs 4 and 5) are expressed in human glioblastomas

“…Glioblastoma cells from solid tumors were obtained by dissociation and cultivation in DMEM plus 10% FCS as described previously. 20 Subcultures from 3-10 were used. Purity of the culture was controlled routinely by immunostaining for the cell type specific markers glial fibrillary acidic protein (GFAP, astrocytes/glioblastoma cells; antibody from Boehringer, Mannheim Germany) and CD68 (contaminating microglial cells and macrophages).…”

Pleiotrophin, an angiogenic and mitogenic growth factor, is expressed in human gliomas

“…Murine BV-2 microglial cells were a kindly gift from Elisabetta Blasi, University of Perugia, Italy, and cultivated in DMEM plus 10% FCS. Reverse transcriptase-polymerase chain reaction (RT-PCR) RNA was isolated with the guanidinium thiocyanate method, digested with DNase, cDNA generated and RT-PCR performed with the primers 5¢-CCTTCTTGGCATTCATTTTCATAC-3¢ (sense) and 5¢-GAGGTTTGGGGTTGGTCAGT-3¢ (antisense) at an annealing temperature of 60°C with 40 cycles according to previous protocols (Feindt et al 1995). The RT-PCR product was identified by agarose gel electrophoresis and by direct sequencing with the ÔDyeDeoxy Terminator Cycle SequencingÕ method using an ABI PRISM 310 Genetic Analyzer (Applied Biosystems, Foster City, CA, USA) as described (Held-Feindt et al 1999).…”

“…Proliferation assays were performed in the presence of 1% or 0.5% FCS with subconfluent glioma or BV-2 murine microglial cells, respectively, for 48 h by incorporation of [ 3 H]thymidine (Feindt et al 1995). Chemotaxis assays were performed in 48-well chambers (Neuro Probe Inc., Baltimore, MD, USA) using polycarbonate filters with 5-lm pores.…”