Search PubMed⌕ Search

Biomedical subjects

J Rømer

Publications and source records attributed to J Rømer.

At least 19 recordsLinked to original sources

Regulation of pancreatic beta-cell mass and proliferation by SOCS-3.

Growth hormone and prolactin are important growth factors for pancreatic beta-cells. The effects exerted by these hormones on proliferation and on insulin synthesis and secretion in beta-cells are largely mediated through the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathway. Suppressors of cytokine signaling (SOCS) proteins are specific inhibitors of the JAK/STAT pathway acting through a negative-feedback loop. To investigate in vivo effects of SOCS-3 in growth hormone (GH)/prolactin signaling in beta-cells we generated transgenic mice with beta-cell-specific overexpression of SOCS-3. The relative beta-cell proliferation and volume in the mice were measured by morphometry. Beta-cell volume of transgenic female mice was reduced by over 30% compared with beta-cell volume in wild-type female mice. Stimulation of transgenic islets in vitro with GH showed a reduced tyrosine phosphorylation of STAT-5 when compared with wild-type islets. Transduction of primary islet cultures with adenoviruses expressing various SOCS proteins followed by stimulation with GH or glucagon-like peptide-1 (GLP-1) revealed that SOCS-3 inhibited GH- but not GLP-1-mediated islet cell proliferation, indicating that the decreased beta-cell volume observed in female transgenic mice could be caused by an inhibition of GH-induced beta-cell proliferation by SOCS-3. In spite of the reduced beta-cell volume the transgenic female mice exhibited enhanced glucose tolerance compared with wild-type littermates following an oral glucose-tolerance test. Together these data suggest that SOCS-3 modulates cytokine signaling in pancreatic beta-cells and therefore potentially could be a candidate target for development of new treatment strategies for diabetes.

Animals↗

Adipogenic and orexigenic effects of the ghrelin-receptor ligand tabimorelin are diminished in leptin-signalling-deficient ZDF rats.

OBJECTIVE: The aim was to investigate the possible interactions of the two peripheral hormones, leptin and ghrelin, that regulate the energy balance in opposite directions. METHODS: Leptin-receptor mutated Zucker diabetic fatty (ZDF) and lean control rats were treated with the ghrelin-receptor ligand, tabimorelin (50 mg/kg p.o.) for 18 days, and the effects on body weight, food intake and body composition were investigated. The level of expression of anabolic and catabolic neuropeptides and their receptors in the hypothalamic area were analysed by in situ hybridization. RESULTS: Tabimorelin treatment induced hyperphagia and adiposity (increased total fat mass and gain in body weight) in lean control rats, while these parameters were not increased in ZDF rats. Treatment with tabimorelin of lean control rats increased hypothalamic mRNA expression of the anabolic neuropeptide Y (NPY) mRNA and decreased hypothalamic expression of the catabolic peptide pro-opiomelanocortin (POMC) mRNA. In ZDF rats, the expression of POMC mRNA was not affected by treatment with tabimorelin, whereas NPY mRNA expression was increased in the hypothalamic arcuate nucleus. CONCLUSION: This shows that tabimorelin-induced adiposity and hyperphagia in lean control rats are correlated with increased hypothalamic NPY mRNA and decreased POMC mRNA expression. The elimination of tabimorelin-induced adiposity and hyperphagia in ZDF rats may be due to lack of POMC mRNA downregulation. In conclusion, we suggest that ghrelin-receptor ligands exert their adipogenic and orexigenic effects via hypothalamic mechanisms that are dependent on intact leptin-receptor signalling.

Adipose Tissue↗

Comparative study of protein tyrosine phosphatase-epsilon isoforms: membrane localization confers specificity in cellular signalling.

To study the influence of subcellular localization as a determinant of signal transduction specificity, we assessed the effects of wild-type transmembrane and cytoplasmic protein tyrosine phosphatase (PTP) epsilon on tyrosine kinase signalling in baby hamster kidney (BHK) cells overexpressing the insulin receptor (BHK-IR). The efficiency by which differently localized PTPepsilon and PTPalpha variants attenuated insulin-induced cell rounding and detachment was determined in a functional clonal-selection assay and in stable cell lines. Compared with the corresponding receptor-type PTPs, the cytoplasmic PTPs (cytPTPs) were considerably less efficient in generating insulin-resistant clones, and exceptionally high compensatory expression levels were required to counteract phosphotyrosine-based signal transduction. Targeting of cytPTPepsilon to the plasma membrane via the Lck-tyrosine kinase dual acylation motif restored high rescue efficiency and abolished the need for high cytPTPepsilon levels. Consistent with these results, expression levels and subcellular localization of PTPepsilon were also found to determine the phosphorylation level of cellular proteins including focal adhesion kinase (FAK). Furthermore, PTPepsilon stabilized binding of phosphorylated FAK to Src, suggesting this complex as a possible mediator of the PTPepsilon inhibitory response to insulin-induced cell rounding and detachment in BHK-IR cells. Taken together, the present localization-function study indicates that transcriptional control of the subcellular localization of PTPepsilon may provide a molecular mechanism that determines PTPepsilon substrate selectivity and isoform-specific function.

Animals↗

Cancer cell expression of urokinase-type plasminogen activator receptor mRNA in squamous cell carcinomas of the skin.

In this study we have used in situ hybridization with radiolabeled antisense RNA probes to examine the expression of mRNA for urokinase-type plasminogen activator and its receptor in histologic samples of squamous cell (n = 7) and basal cell (n = 7) carcinomas of the skin. Messenger RNA for both urokinase-type plasminogen activator and its receptor were expressed in all of the squamous cell carcinomas, but could not be detected in the basal cell carcinomas. In all of the seven squamous cell carcinomas a signal for urokinase-type plasminogen activator receptor mRNA was detected focally in well-differentiated cancer cells surrounding keratinized pearls, and in four specimens urokinase-type plasminogen activator receptor mRNA was in addition expressed by cancer cells at the edge of invasively growing strands of tumor. Urokinase-type plasminogen activator mRNA expression was found in virtually all the cancer cells of the squamous cell carcinomas, and importantly we found, by hybridizations for urokinase-type plasminogen activator and its receptor mRNA on adjacent sections of squamous cell carcinomas, that it was exactly the invading cancer cells that simultaneously expressed both these components required for plasmin-mediated proteolysis at the cell surface. We have previously shown that both urokinase-type plasminogen activator and its receptor mRNA are expressed by the leading-edge keratinocytes in regenerating epidermis during mouse skin wound healing, and that wound healing is impaired in mice made deficient in plasminogen by targeted gene disruption. We propose that there are similarities between the mechanisms of generation and regulation of extracellular proteolysis during skin re-epithelialization and squamous cell carcinoma invasion. The ability of the squamous carcinoma cells to mimic the "invasive" phenotype of re-epithelializing keratinocytes may be one of the factors that make squamous cell carcinomas more aggressive tumors than basal cell carcinomas.

Basal Cell Carcinoma↗

Effects of growth hormone and its secretagogues on bone.

The growth hormone (GH)/insulin-like growth factor-1 axis is not only of importance for linear body growth during childhood, but it is also one of the major determinants of adult bone mass. Studies show that GH treatment increases bone mass in rodents as well as in adult GH-deficient humans, but the effect of GH treatment on bone mass in healthy humans has so far not been impressive. Recently, a new class of GH secretagogues (GHSs) has been developed. In humans, GHS treatment affects biochemical markers of bone turnover and increases growth velocity in selected short children with or without GH deficiency. In rodents, GHS treatment increase bone mineral content, but it has not yet been shown that GHS treatment can affect bone mass in adult humans.

Adult↗

The proglucagon-derived peptide, glucagon-like peptide-2, is a neurotransmitter involved in the regulation of food intake.

The dorsomedial hypothalamic nucleus harbors leptin sensitive neurons and is intrinsically connected to hypothalamic nuclei involved in feeding behavior. However, it also receives ascending input from the visceroceptive neurons of the brainstem. We have identified a unique glucagon-like-peptide-2 containing neuronal pathway connecting the nucleus of the solitary tract with the dorsomedial hypothalamic nucleus. A glucagon-like-peptide-2 fiber plexus targets neurons expressing its receptor within the dorsomedial hypothalamic nucleus. Pharmacological and behavioral studies confirmed that glucagon-like-peptide-2 signaling is a specific transmitter inhibiting rodent feeding behavior and with potential long-term effects on body weight homeostasis. The glucagon-like-peptide-1 receptor antagonist, Exendin (9-39) is also a functional antagonist of centrally applied glucagon-like-peptide-2.

Animals↗

The GH secretagogues ipamorelin and GH-releasing peptide-6 increase bone mineral content in adult female rats.

Growth hormone (GH) is of importance for normal bone remodelling. A recent clinical study demonstrated that MK-677, a member of a class of GH secretagogues (GHSs), increases serum concentrations of biochemical markers of bone formation and bone resorption. The aim of the present study was to investigate whether the GHSs, ipamorelin (IPA) and GH-releasing peptide-6 (GHRP-6), increase bone mineral content (BMC) in young adult female rats. Thirteen-week-old female Sprague-Dawley rats were given IPA (0.5 mg/kg per day; n=7), GHRP-6 (0.5 mg/kg per day; n=8), GH (3.5 mg/kg per day; n=7), or vehicle administered continuously s.c. via osmotic minipumps for 12 weeks. The animals were followed in vivo by dual X-ray absorptiometry (DXA) measurements every 4th week. After the animals were killed, femurs were analysed in vitro by mid-diaphyseal peripheral quantitative computed tomography (pQCT) scans. After this, excised femurs and vertebrae L6 were analysed by the use of Archimedes' principle and by determinations of ash weights. All treatments increased body weight and total tibial and vertebral BMC measured by DXA in vivo compared with vehicle-treated controls. However, total BMC corrected for the increase in body weight (total BMC:body weight ratio) was unaffected. Tibial area bone mineral density (BMD, BMC/area) was increased, but total and vertebral area BMDs were unchanged. The pQCT measurements in vitro revealed that the increase in the cortical BMC was due to an increased cross-sectional bone area, whereas the cortical volumetric BMD was unchanged. Femur and vertebra L6 volumes were increased but no effect was seen on the volumetric BMDs as measured by Archimedes' principle. Ash weight was increased by all treatments, but the mineral concentration was unchanged. We conclude that treatment of adult female rats with the GHSs ipamorelin and GHRP-6 increases BMC as measured by DXA in vivo. The results of in vitro measurements using pQCT and Archimedes' principle, in addition to ash weight determinations, show that the increases in cortical and total BMC were due to an increased growth of the bones with increased bone dimensions, whereas the volumetric BMD was unchanged.

Absorptiometry, Photon↗

Cancer invasion and tissue remodeling--cooperation of protease systems and cell types.

Proteolytic degradation of the extracellular matrix plays a crucial role in both cancer invasion and non-neoplastic tissue remodeling processes. In human cancers the components of matrix degrading protease systems (uPA, uPAR, PAI-1 and MMPs) can be expressed by either the non-neoplastic stromal cells, the cancer cells or both. Studies of the prognostic impact of these components in human cancer and the effect of targeted gene inactivation on cancer metastasis in mice support the assumption that proteases promote cancer progression, independent of whether they are expressed by cancer cells or stromal cells. The pattern of expression of components of protease systems is usually very similar in different cases of the same type of cancer, while it varies between different types of cancer. There are intriguing similarities between the cellular expression pattern of components of protease systems seen in cancer invasion and in certain types of non-neoplastic tissue remodeling. We propose that cancer invasion can be viewed as tissue remodeling gone out of control. The stromal cell involvement in cancer invasion represents a new paradigm with important implications for cancer pathophysiology and cancer therapy.

Animals↗

Co-localization of growth hormone secretagogue receptor and NPY mRNA in the arcuate nucleus of the rat.

Growth hormone secretagogues (GHS) are small, synthetic compounds which have the potential of releasing growth hormone (GH) from the pituitary. The mechanism of action of GHS has not been fully elucidated. A specific GHS receptor (GHS-R) is expressed in the pituitary gland and in several areas of the brain including the hypothalamus. We have characterized the GHS-R-mRNA-expressing neurons with respect to co-expression of selected neurotransmitters in the hypothalamus. This was done by dual chromogenic and autoradiographic in situ hybridization with riboprobes for GHS-R mRNA and neuropeptide Y (NPY), pro-opiomelanocortin (POMC), somatostatin (SRIH) or GH-releasing hormone (GHRH) mRNA. In the arcuate nucleus, GHS-R mRNA was expressed in 94 +/- 1% of the neurons expressing NPY, 8 +/- 2% of those expressing POMC and 30 +/- 6% expressing SRIH mRNA. 20-25% of the GHRH- mRNA-expressing neurons contained GHS-R mRNA, whereas the vast majority of the arcuate GHS-R-mRNA-containing cells did not contain GHRH mRNA. The finding of a significant co-expression of GHS-R and NPY mRNA in the arcuate nucleus is in accordance with the previous demonstration by Dickson et al. that c-Fos is induced in NPY neurons following GHS administration. These results indicate that GHS have other effects on neuroendocrine regulation than GH release via GHRH neurons. Stimulation of the arcuate NPY neurons via GHS-R may explain the increased appetite and the cortisol release seen after administration of some GHS compounds.

Animals↗

Cancer invasion and tissue remodeling: common themes in proteolytic matrix degradation.

Analysis of extracellular matrix degradation systems has led to the insight that in cancer invasion there is often crucial interplay between cancer cells and several types of surrounding non-neoplastic stromal cells. Likewise, in normal tissue remodeling processes, the synthesis of proteolytic components is often distributed between several cell types, and there are strong similarities between neoplastic and non-neoplastic processes in the same tissue. Thus, tissue remodeling events are excellent models for studies of extracellular proteolysis in cancer. This has become even clearer by recent analyses of genetically modified mice.

Breast Neoplasms↗

Proteoglycan expression in the normal rat kidney.

Proteoglycans constitute a heterogenous group of complex macromolecules, consisting of a backbone core protein and a variable number of sulfated polysaccharide side chains covalently linked to the core. A dual function for these polyanionic glycosaminoglycans in kidney physiology has been proposed: to maintain a fixed negative charge in the glomerular filtration barrier, and to bind and sequester cytokines essential for renal development and function. With the aim of identifying proteoglycan genes expressed in kidney glomeruli, we have performed in situ hybridization for selected proteoglycan core proteins in the normal rat kidney. Syndecan-4, glypican-1 and biglycan were all expressed in normal glomeruli, whereas syndecan-1, perlecan and versican mRNAs were confined to the papillary area. Decorin mRNA was detected in interstitial cells found between tubuli and surrounding larger vessels. No signal for betaglycan mRNA could be detected. By hybridizing adjacent sections with a probe for the podocyte-specific PTPase GLEPP-1, the glomerular cells containing mRNA for syndecan-4 and glypican-1 could be identified as podocytes, whereas the cells expressing biglycan were identified as mesangial cells. These results demonstrate that seven out of the eight proteoglycans investigated are expressed in the normal kidney in detectable amounts and, importantly, that each proteoglycan gene shows a unique pattern of expression. The constitutive expression of syndecan-4, glypican-1 and biglycan in glomerular cells points to a role for these polyanionic molecules in maintaining the integrity of the glomerular filtration barrier.

Amino Acid Sequence↗

Urokinase-type plasminogen activation in three human breast cancer cell lines correlates with their in vitro invasiveness.

In order to invade and spread cancer cells must degrade extracellular matrix proteins. This degradation is catalysed by the concerted action of several enzymes, including the serine protease plasmin. Several experimental studies have shown that inhibition of plasmin formation reduces cancer cell invasion and metastasis, indicating a critical role of this proteolytic pathway in these processes. In order to further study the role of plasmin in cancer progression, we have characterized urokinase-type plasminogen activator (uPA) mediated plasmin formation in three human breast cancer cell lines. Using monoclonal antibodies against uPA and its receptor uPAR, we have investigated the contribution of uPA and uPAR to invasive capacity in an in vitro invasion assay. MDA-MB-231 BAG cells were found to express high protein levels of uPA, uPAR and PAI-1. MDA-MB 435 BAG cells produced low amounts of uPA, PAI-1 and moderate amounts of uPAR, whereas MCF-7 BAG cells showed low levels of uPA, uPAR and PAI-1 protein. In a plasmin generation assay MDA-MB-231 BAG cells were highly active in mediating plasmin formation, which could be abolished by adding either an anticatalytic monoclonal antibody to uPA (clone 5) or an anti-uPAR monoclonal antibody (clone R3), which blocks binding of uPA to uPAR. The two other cell lines lacked the capacity to mediate plasmin formation. In the Matrigel invasion assay the cells showed activity in this order: MCF-7 BAG < MDA-MB-435 BAG < MDA-MB-231 BAG. Testing MDA-MB-231 BAG cells in the Matrigel invasion assay revealed that invasion could be inhibited in a dose-dependent manner either by the clone 5 uPA antibody or by the clone R3 uPAR antibody, suggesting that the cell surface uPA system is actively involved in this invasive process. It is concluded that these three cell lines constitute a valuable model system for in vitro studies of the role of cell surface uPA in cancer cell invasion and has application in the search for novel compounds which inhibit mechanisms involved in uPA-mediated plasmin generation on cancer cells.

Antibodies, Monoclonal↗

Differential expression of urokinase-type plasminogen activator, its receptor, and inhibitors in mouse skin after exposure to a tumor-promoting phorbol ester.

The cellular distribution of mRNAS for urokinase-type plasminogen activator (uPA), its specific receptor (uPAR), and its inhibitors (PAI-1 and -2) in mouse skin was analyzed by in situ hybridization after topical application of the tumor promoter phorbol 12-myristate 13-acetate. In the epidermis, strong signals for uPA and PAI-1 mRNA were detected 24 h after treatment in the basal and suprabasal epidermal keratinocytes in areas with pronounced hyperproliferation and increased terminal differentiation, and in some hair follicle keratinocytes. After 48 h, both uPAR and PAI-2 mRNAs were expressed in the epidermal layers from the suprabasal keratinocytes up to the differentiating cells beneath the cornified layer and in hair follicle keratinocytes. Induction of PAI-2 mRNA was detected in epidermis as early as 3 h after treatment and remained stable for up to 7 days. In the dermis, 5 h after application of phorbol 12-myristate 13-acetate to the skin, uPA mRNA was detected in fibroblast-like cells below and around the skin muscle, and PAI-1 mRNA was detected in stromal cells located above the skin muscle. After longer exposure to phorbol 12-myristate 13-acetate, the PAI-1 mRNA-expressing stromal cells were located more superficially, apparently moving toward the epidermal layer. After 9 h, most of the PAI-1 mRNA-positive cells were identified as endothelial cells. Up to 24 h after the application of phorbol 12-myristate 13-acetate, the intensity of the signal for both uPA and PAI-1 increased, followed by a gradual decrease for up to 7 days. These results show that in mouse skin treated with a tumor-promoting phorbol ester, the various components of the plasminogen activation system are expressed by both epithelial and stromal cell types, which in dermis and subcutis are located in different places, depending on the time of exposure to the phorbol ester. Our results suggest that urokinase-mediated extracellular proteolysis has diverse functional roles during the early steps of tumor promotion.

Animals↗

Two distinct phases of apoptosis in mammary gland involution: proteinase-independent and -dependent pathways.

Postlactational involution of the mammary gland is characterized by two distinct physiological events: apoptosis of the secretory, epithelial cells undergoing programmed cell death, and proteolytic degradation of the mammary gland basement membrane. We examined the spatial and temporal patterns of apoptotic cells in relation to those of proteinases during involution of the BALB/c mouse mammary gland. Apoptosis was almost absent during lactation but became evident at day 2 of involution, when beta-casein gene expression was still high. Apoptotic cells were then seen at least up to day 8 of involution, when beta-casein gene expression was being extinguished. Expression of sulfated glycoprotein-2 (SGP-2), interleukin-1 beta converting enzyme (ICE) and tissue inhibitor of metalloproteinases-1 was upregulated at day 2, when apoptotic cells were seen initially. Expression of the matrix metalloproteinases gelatinase A and stromelysin-1 and the serine proteinase urokinase-type plasminogen activator, which was low during lactation, was strongly upregulated in parallel starting at day 4 after weaning, coinciding with start of the collapse of the lobulo-alveolar structures and the intensive tissue remodeling in involution. The major sites of mRNA synthesis for these proteinases were fibroblast-like cells in the periductal stroma and stromal cells surrounding the collapsed alveoli, suggesting that the degradative phase of involution is due to a specialized mesenchymal-epithelial interaction. To elucidate the functional role of these proteinases during involution, at the onset of weaning we treated mice systemically with the glucocorticoid hydrocortisone, which is known to inhibit mammary gland involution. Although the initial wave of apoptotic cells appeared in the lumina of the gland, the dramatic regression and tissue remodeling usually evident by day 5 was substantially inhibited by systemic treatment with hydrocortisone. mRNA and protein for gelatinase A, stromelysin-1 and uPA were weakly induced, if at all, in hydrocortisone-treated mice. Furthermore, mRNA for membrane-type matrix metalloproteinase decreased after hydrocortisone treatment and paralleled the almost complete inhibition of activation of latent gelatinase A. Concomitantly, the gland filled with an overabundance of milk. Our data support the hypothesis that there are at least two distinct phases of involution: an initial phase, characterized by induction of the apoptosis-associated genes SGP-2 and ICE and apoptosis of fully differentiated mammary epithelial cells without visible degradation of the extracellular matrix, and a second phase, characterized by extracellular matrix remodeling and altered mesenchymal-epithelial interactions, followed by apoptosis of cells that are losing differentiated functions.

Animals↗

Laminin-5 is a marker of invading cancer cells in some human carcinomas and is coexpressed with the receptor for urokinase plasminogen activator in budding cancer cells in colon adenocarcinomas.

Recombinant human gamma 2 chain of laminin-5 was expressed in Escherichia coli, and used to generate specific polyclonal antibodies which were used to study the distribution of the protein in human cancers. A total of 72 biopsies of human cancers were stained, including 23 cases of colon adenocarcinomas, 16 ductal breast carcinomas, 9 malignant melanomas, 14 squamous cell carcinomas of the skin and cervix, and 10 sarcomas. As a control for the specificity of the antibodies, we performed in situ hybridization on adjacent sections of a number of the cases, and in all of these cases the localization of the gamma 2 chain protein and mRNA was identical. We found gamma 2 chain immunoreactivity in cancer cells in all cases of colon adenocarcinomas and squamous cell carcinomas but not in any of the sarcomas, supporting the view that the laminin-5 protein is specific for cells of epithelial origin. Notably, in all of the cases of colon adenocarcinomas, the positive staining was invariably associated with budding cancer cells located at the tip of invading malignant epithelium, whereas the cancer cells deeper in the tumors were most often negative. The staining was cytoplasmic in all cases and only in one case did we see additional extracellular immunoreactivity, indicating that this laminin isoform in cancer tissue is not laid down in the extracellular matrix but probably exerts its function at the cell surface or in its immediate vicinity. Using in situ hybridization to analyze the coexpression of laminin-5 and components of the plasminogen activation system, we found that the histological distribution of laminin-5-positive budding cancer cells at the invasion front in colon adenocarcinomas was identical to that of the receptor for urokinase-type plasminogen activator. These findings suggest that laminin-5 is a marker of invading cancer cells in at least some human malignancies, and that it therefore might represent a valuable marker for the invasive potential of these cancers. The colocalization of laminin-5 and urokinase-type plasminogen activator receptor in a subset of cancer cells in colon cancer also suggests that a controlled up-regulation of a number of gene products is a characteristic of budding colon cancer cells, and that these gene products serve functions crucial for the invasive phenotype of these cancer cells.

Adenocarcinoma↗

The receptor for urokinase-type plasminogen activator is not essential for mouse development or fertility.

The urokinase-type plasminogen activator receptor (uPAR) gene was disrupted in mice in order to explore the role of cell surface-associated plasminogen activation in development and hemostasis. Homozygous, uPAR-/- mice were born and survived to adulthood with no overt phenotypic abnormalities. There was no indication of loss of fetal animals based on the Mendelian pattern of transmission of the mutant uPAR gene. uPAR-/- mice carried no detectable uPAR in lung, spleen, and other tissues when measured both immunologically by Western blot analysis and functionally by ligand cross-linking analyses. In addition, activated peritoneal macrophages collected from uPAR-/- mice failed to promote plasminogen activation in vitro. The loss of the receptor also resulted in a redistribution of uPA in some tissues but had no impact on pro-uPA activation in the urogenital tract. Thus, in the absence of other challenging factors such as infection, injury, or other functional deficits, uPAR deficiency does not compromise fertility, development, or hemostasis. These mice provide a means to test the proposed function of uPA/uPAR in wound repair, atherogenesis, and tumor cell invasion in vivo.

Animals↗