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      Impact of del32–71-GH (Exon 3 Skipped GH) on Intracellular GH Distribution, Secretion and Cell Viability: A Quantitative Confocal Microscopy Analysis

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          Background: Familial isolated growth hormone deficiency (IGHD) is a disorder with about 5–30% of patients having affected relatives. Among those familial types, IGHD type II is an autosomal dominant form of short stature, associated in some families with mutations that result in missplicing to produce del32–71-GH, a GH peptide which cannot fold properly. The mechanism by which this mutant GH may alter the controlled secretory pathway and therefore suppress the secretion of the normal 22-kDa GH product of the normal allele is not known in detail. Previous studies have shown variance depending on cell type, transfection technique used, as well as on the method of analysis performed. Aim: The aim of our study was to analyse and compare the subcellular distribution/localization of del32–71-GH or wild-type (wt)-GH (22-kDa GH), each stably transfected into AtT-20, a mouse pituitary cell line endogenously producing ACTH, employed as the internal control for secretion assessment. Methods: Co-localizationof wt- and del32–71 mutant GH form was studied by quantitative confocal microscopy analysis. Using the immunofluorescent technique, cells were double stained for GH plus one of the following organelles: endoplasmic reticulum (ER anti-Grp94), Golgi (anti-βCOP) or secretory granules (anti-Rab3a). In addition, GH secretion and cell viability were analysed in detail. Results/Conclusions: Our results show that in AtT-20 neuroendocrine cells, in comparison to the wt-GH, the del32–71-GH has a major impact on the secretory pathway not only affecting GH but also other peptides such as ACTH. The del32–71-GH is still present at the secretory vesicles’ level, albeit in reduced quantity when compared to wt-GH but, importantly, was secretion-deficient. Furthermore, while focusing on cell viability an additional finding presented that the various splice site mutations, even though leading eventually to the same end product, namely del32–71-GH, have different and specific consequences on cell viability and proliferation rate.

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          Most cited references 34

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          Human growth hormone and extracellular domain of its receptor: crystal structure of the complex

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            Dimerization of the extracellular domain of the human growth hormone receptor by a single hormone molecule

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              Beta-COP localizes mainly to the cis-Golgi side in exocrine pancreas

               J. Geuze,  T. Kreis,  R. Duden (1993)
              We examined the distribution of the non-clathrin-coated vesicle- associated coat protein beta-COP in rat exocrine pancreatic cells by immunogold cytochemistry. Labeling for beta-COP was found in the Golgi region (48%) where it was associated with vesicles and buds of approximately 50 nm, showing a characteristic approximately 10-nm-thick coat. The other half of the label was present in the cytoplasm, not associated with visible coats or membranes, with a minor fraction present on small clusters of tubules and vesicles. Clathrin-coated vesicles were typically located at the trans-side of the Golgi complex, and showed a thicker coat of approximately 18 nm. Of the total beta-COP labeling over the Golgi region, 68% occurred on the cis-side, 6% on the cisternae, 17% on the rims of the cisternae, and only 9% on the trans- side. For clathrin these figures were 16, 2, 4, and 78%, respectively. At the cis-Golgi side beta-COP was present in transitional areas (TA), on so-called peripheral elements (PE), consisting of tubules and vesicles located between the cup-shaped transitional elements (TE) of the RER and the cis-most Golgi cisternae. Label for Sec23p was also present in TA but was located closer to the TE, while beta-COP labeled PE were located near the cis-Golgi cisternae. Upon energy depletion, Golgi associated beta-COP was almost exclusively (86%) in spherical aggregates of 200-500 nm in diameter, whereas the cis-side (6%), the cisternae (1%), the rims (4%) and trans-side (3%) of the Golgi complex, were barely labeled; 50% of the total label remained in the cytoplasm. The aggregates were predominantly located at the cis-side of the Golgi stack, next to, but distinct from the Sec23p positive TA, that were devoid of beta-COP and had only a few recognizable vesicles left. Incubation with aluminum fluoride resulted in fragmentation of the Golgi complex into large clusters of beta-COP positive vesicles, while 50% of the label remained in the cytoplasm, as in control cells. After 10 min of Brefeldin A treatment 91% of beta-COP was cytoplasmic and only 7% associated with membranes of the Golgi complex. The total label for beta-COP over exocrine cells remained unchanged during the incubation with either of the drugs, indicating that the drugs induce reallocation of beta-COP. Our data suggest that beta-COP plays a role in membrane transport at the cis-side of the Golgi complex.

                Author and article information

                Horm Res Paediatr
                Hormone Research in Paediatrics
                S. Karger AG
                March 2006
                29 March 2006
                : 65
                : 3
                : 132-141
                aPaediatric Endocrinology, University Children’s Hospital, Inselspital, and bInstitute of Pharmacology, Bern, Switzerland
                91607 Horm Res 2006;65:132–141
                © 2006 S. Karger AG, Basel

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                Page count
                Figures: 3, Tables: 2, References: 46, Pages: 10
                Original Paper


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