Presence Of 7B2 Research Articles

Abnormal expression and processing of the proprotein convertases PC1 and PC2 in human colorectal liver metastases

BackgroundThe family of proprotein convertases has been recently implicated in tumorigenesis and metastasis in animal models. However, these studies have not yet been completely corroborated in human tumors.MethodsUsing RT PCR, immunoblot and immunohistochemistry we assessed the presence and the processing patterns of the convertases PC1 and PC2 as well as the PC2 specific chaperone 7B2 in human liver metastases originating from colorectal cancer and compared them to unaffected and normal liver. Furthermore, we assessed the presence and processing profiles of PC1, PC2 and 7B2 in primary colon cancers.ResultsmRNA, protein expression, and protein cleavage profiles of proprotein convertases 1 and 2 are altered in liver colorectal metastasis, compared to unaffected and normal liver. Active PC1 protein is overexpressed in tumor, correlating with its mRNA profile. Moreover, the enhanced PC2 processing pattern in tumor correlates with the overexpression of its specific binding protein 7B2. These results were corroborated by immunohistochemistry. The specific and uniform convertase pattern observed in the metastases was present only in a fraction of primary colon cancers.ConclusionThe uniformly altered proprotein convertase profile in liver metastases is observed only in a fraction of primary colon cancers, suggesting possible selection processes involving PCs during metastasis as well as an active role of PCs in liver metastasis. In addition, the exclusive presence of 7B2 in metastatic tumors may represent a new target for early diagnosis, prognosis and/or treatment.

Proglucagon processing profile in canine L cells expressing endogenous prohormone convertase 1/3 and prohormone convertase 2.

The tissue-specific differential processing of proglucagon (Pg) yields glucagon in pancreatic A cells and glucagon-like peptide-1 (GLP-1), GLP-2, and glicentin in intestinal L cells. It has been suggested that the difference in Pg cleavage in A and L cells is due to the presence of distinct prohormone convertases (PC) in the two cell types, PC1/3 in the L cell and PC2 in the A cell. PC2 has been shown to cleave the N-terminal part of Pg, being essential for glucagon formation and PC1/3 to cleave the C-terminal part of Pg, leading to the formation of GLP-1. However, some of the cleavage sites in Pg have not proven to be substrates exclusively for either PC2 or PC1/3, and the cleavage profile of Pg in a primary cultured L cell has not yet been correlated with the actual presence of PC2 and PC1/3 in the L cell. We demonstrate here the presence of PC1/3, PC2, and the PC2 chaperone 7b2, in L cells using light immunohistochemistry on sections from canine ileum and on a canine intestinal cell culture enriched for L cells. Analysis of the cultured L cells, using gel chromatography and RIA, confirms the classical intestinal cleavage profile of Pg, resulting in mainly glicentin, oxyntomodulin, GLP-1-(7-37), and GLP-2. Despite the presence of 7b2 and mature PC2, as demonstrated by Western blot, absolute minimal amounts of glucagon were detected. These data show that the presence of intracellular PC2 and 7b2 in a primary cell possessing Pg does not have to lead to the formation of glucagon. This formation must then require an additional element to occur, or alternatively, the results could be explained by a canine specific organization of PC2 and Pg into separate compartments, which would prevent interaction.

Differential expression of the neuroendocrine polypeptide 7B2 in hypothalami of Prader-(Labhart)-Willi syndrome patients

Prader-(Labhart-)Willi syndrome (PWS) is characterized by infattile hypotonia, early childhood obesity, mental deficiency, short stature, small hands and feet and hypogonadism. In 70% of the cases this syndrome is associated with a defect of chromosome 15 at 15q11-q13, close to the location of the 7B2 gene (15q13-q14). The majority of the remaining PWS patients display maternal uniparental disomy on chromosome 15. Since the 7B2 gene products are expressed in neuroendocrine cells that are probably affected in PWS, e.g. by a peiotrophic influence of the neighboring deletion, the presence of 7B2 was studied in the supraoptic and paraventricular nucleus of the hypothalamus of five subjects clinically diagnosed as PWS patients using five antibodies against various parts of the 7B2 precursor polypeptide. Three of the five PWS patients studied showed no reaction to the 7B2 antibody MON-102, whereas all 30 control patients did. However, one of the three MON-102 non-reacting PWS patients reacted to other 7B2 antibodies. In conclusion, the vanishing of 7B2 gene products is not obligatory for PWS, possibly due to the variable genetic backgroudd of PWS patients. However, in most patients there is a clear modification of 7B2 expression, pointing to altered neuroendocrine functions.

Immunohistochemical distribution of 7B2 and colocalization with calcitonin gene-related peptide in rat lung.

The novel pituitary protein 7B2 has a widespread distribution in neurons and paraneurons and is known to be associated with endocrine disorders. In the mammalian lung, solitary neuroendocrine cells (NECs) and their innervated aggregates, termed neuroepithelial bodies (NEBs), are scattered along the bronchopulmonary tree; however, presence of 7B2 in these structures has not previously been reported. Bouin fixed, paraffin embedded rat lungs were cut and stained for 7B2, using a polyclonal antibody and a streptavidin biotin immunoperoxidase method. The identity of NEBs was confirmed on adjacent serial sections by the immunocytochemical reaction for calcitonin gene-related peptide (CGRP). NEBs selectively labelled for 7B2 are distributed throughout bronchi, bronchioli and alveolar ducts, whereas NECs are always negative. Likewise, 7B2 immunoreactivity is not detected in intrapulmonary ganglion cells nor in nerve fibers. Immunoreactivity for CGRP, on the other hand, occurs in NECs, NEBs, nerve fibers and neuronal somata. Colocalization of both peptides is demonstrated in almost all NEBs. This study presents the first immunohistochemical demonstration and morphological mapping of 7B2 in the rat lung. The finding that only NEBs are stained suggests biochemical and functional variations between NEBs and NECs as well as the absence of a role for 7B2 in the pulmonary nervous system.

Evidence for secretion of 7B2 by A- and B-cells of hamster pancreatic islets

7B2 is a neuroendocrine protein, and in the pancreatic islets the presence of 7B2 in A- and B-cells was immunohistochemically demonstrated. In order to examine 7B2 secretion by A- and B-cells of pancreatic islets, we prepared isolated hamster pancreatic islet cells as well as an A-cell-rich culture, and studied 7B2 secretion under certain stimulations. 7B2 was secreted by isolated hamster pancreatic islet cells. This secretion was stimulated by theophylline and arginine, but glucose had a weak effect on the 7B2 secretion. Such a response of 7B2 to the stimulations was different from that of insulin or glucagon. 7B2 secretion was also noted in the A-cell-rich culture. These results suggest that 7B2 is secreted by both A- and B-cells of the hamster pancreatic islets and its secretion is regulated under certain conditions.

Coordinated expression of 7B2 and αMSH in the melanotrope cells of Xenopus laevis

7B2 is a highly conserved protein present in many secretory cells. Using in situ hybridization techniques and immunocytochemistry, parameters concerning the biosynthesis and storage of the 7B2 protein were studied in the pituitary gland and median eminence of the clawed toad Xenopus laevis, in relation to the physiological process of background adaptation. 7B2-like immunoreactivity was present in the median eminence, in the neural and anterior pituitary lobes and, particularly, in the melanotrope cells of the intermediate pituitary lobe. In these cells, it coexisted with immunoreactivity to proopiomelanocortin (POMC)-derived alpha-melanocyte stimulating hormone (alpha MSH). The melanotropes of black-adapted animals had abundant 7B2-mRNA and POMC-mRNA; melanotropes of white-adapted toads had only low levels of these mRNAs. The presence of 7B2 in nerve terminals and endocrine cells supports the idea that the protein has a general function in the cellular secretory process. In X. laevis, 7B2 appears to be particularly associated with POMC and alpha MSH and, therefore, may play a role in the regulation of background adaptation.

A new pituitary protein 7B2 is increased in patients with high α- or β-hCG

The presence of 7B2 (a 180 amino acid peptide first extracted from the porcine pituitary) was investigated by a specific radioimmunoassay and gel filtration chromatography in the plasma of three groups of patients known to have increased levels of alpha- and beta-hCG subunits. Plasma 7B2 immunoreactive equivalents (7B2-IE) were increased in postmenopausal women (range 67-143 pmol/l, median: 94 pmol/l, N = 20, P less than 0.05), in patients with Klinefelter's syndrome (range 195-230 pmol/l), median 213 pmol/l, N = 4, P less than 0.01) and in 17 patients with malignant endocrine gastrointestinal tumours (range 66-20,000 pmol/l, N = 32) compared with healthy controls (range 23.6-98.2 pmol/l, median 41.5 pmol/l, N = 40). Tumour tissue from 4 patients with endocrine pancreatic tumours had significantly higher 7B2-IE concentrations than normal pancreatic tissue, with the highest concentration in an insulinoma (449 pmol/g, normal: 28 pmol/g). During therapy almost parallel changes in plasma 7B2 and other hormones were noted and 7B2-IE therefore might be an additional marker for cancers of the APUD system.