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Aiming to identify signalling pathways relevant for ss-cell growth we performed an explorative micro-array analysis comparing the gene expression profiles of three human insulinomas and one normal pancreatic islet preparation. This revealed an insulinoma-associated down-regulation of the transforming growth factor beta 1 (TGF-beta1) and its target genes. Comparative quantitative real-time PCR (qRT-PCR) including an expanded sample number of both insulinomas (n=9) and pancreatic islet preparations (n=4) confirmed the decreased TGF-beta1 expression and its target molecules (TGFBI, NNMT, RPN2) in insulinomas. Similarly, TGF-beta1 immunofluorescence analysis revealed reduced expression in insulinomas when compared to pancreatic islets. In contrast, TGFBR2 (transforming growth factor beta receptor II) was found up-regulated. However, the consistent down-regulation of the TGF-beta1 targets TGFBI (transforming growth factor, beta-induced), NNMT (nicotinamide N-methyltransferase), RPN2 (ribophorin II) indicates that the parallel up-regulation of TGFBR2 does not compensate for the only marginal TGF-beta1 expression levels in insulinomas. TGFBR2 expression was confirmed at the protein level in insulinomas. SMAD2/3 protein expression was found at higher levels in human pancreatic islets when compared with insulinomas by dual colour confocal microscopy. TGF-beta1 signalling is known to be involved in cell replication and is abrogated in ductal pancreatic tumours. The down-regulation of TGF-beta1 expression and its target molecules in insulinomas is a new aspect of this cytokine. Our data underline parallels in endocrine and exocrine pancreatic tumour development, which may implicate common progenitor cells.

Objective: Long-term in vitro maintenance of human insulin-secreting insulinoma cells., Methods: (1) Cell culture of ex vivo-derived insulinoma cell suspensions from 8 individual human donors, using various cell culture medium supplementations; (2) determination of insulin synthesis and secretion using immunocytochemistry and insulin and pro-insulin radioimmunoassays; (3) nestin-immunostaining of long-term in vitro grown insulinoma cell suspensions, and (4) phase-contrast light microscopy for analyzing the in vitro growth characteristics of the insulinoma cells., Results: (1) Parallel persistence of in vitro insulinoma cell proliferation as well as insulin-synthesizing and -secreting capacity depended on both the co-culture of insulinoma cells with human fibroblasts and the supplementation of the cell culture medium with tissue culture supernatant derived from the rodent pituitary adenoma cell line GH-3; (2) immunostaining for insulin and secretagogin confirmed the neuroendocrine origin of the insulinoma cells grown in vitro; (3) insulin secretion capability persisted up to an observation period of 25 weeks; (4) insulin secretion rates after 6 weeks of in vitro growth ranged from 3.5 to 83.3 muU/ml/h/60,000 cells plated, and (5) after long-term in vitro growth of insulinoma-derived cell suspensions with persistent insulin-secreting capacity, nestin staining was observed predominantly in co-cultured fibroblasts., Conclusion: Our data describe for the first time the long-term in vitro culture of insulin-secreting human insulinomas and highlight the importance of beta-cell trophic factors for insulinoma cell growth.

In order to identify neuroendocrine tumour-specific protein expression, we generated monoclonal antibodies (mAbs) with a tumour-related reaction pattern using a human insulinoma as immunogen. One of the generated mAbs (mAb 1D4) exhibited striking immunoreactivity against various neuroendocrine tumours without staining pancreatic islets of Langerhans. Furthermore, mAb 1D4 immunostained a characteristic subtype of hypothalamic neurones. Using two-dimensional (2-D) gel electrophoresis, mAb 1D4 immunoblotting and mass spectrometry, heat shock protein 70 (Hsp70) isoforms were identified as the mAb 1D4-specific antigen. In hypothalamic tissue, the presence of two different Hsp70 isoforms (Hsp70-8 and Hsp70-1) was revealed by 2-D gel immunoblots and consecutive mass spectrometric peptide analysis. In contrast, insulinoma and other neuroendocrine tumours displayed solely Hsp70-8 expression. Moreover, the tumour-specific presence of an additional mAb 1D4 immunoreactive protein of 40 kDa was observed in eight out of eight tested neuroendocrine tumours. For this variant, exclusively, peptides derived from the C terminus excluding the 299 amino-terminal residues were detected. In cultured tumour-derived fibroblasts, expression of the truncated Hsp70-8 subtype was not present. In conclusion, we have demonstrated a neuroendocrine tumour-specific expression pattern of Hsp70 isoforms and identified an as yet unknown N-terminally truncated Hsp70-8 variant., (Copyright 2004 Society for Endocrinology)