We first studied expression of neurofibromin by immunohistochemistry in scars obtained from operations involving areas of healing wounds. The results demonstrated increased immunoreactivity for neurofibromin in the fibroblastic cell population of the lesions when compared with fibroblasts of apparently healthy perilesional skin, or those of intact control skin. Furthermore, dermal fibroblasts of 19 and 34 wk-old fetuses displayed a clearly detectable immunosignal for neurofibromin. In vitro studies were designed to investigate the potential effects of selected growth factors--known to be operative in wound healing--on neurofibromin mRNA steady-state levels in cultured fibroblasts. Northern transfer analyses revealed that different isoforms of platelet derived growth factor (PDGF) exerted selective effects on the neurofibromin mRNA levels: PDGF isoform AB elevated neurofibromin mRNA levels in a concentration-dependent manner when concentrations of 0.1, 1, 10, and 30 ng per ml were used. The maximal upregulatory effect of PDGF BB was reached at a concentration of 1 ng per ml. In contrast, PDGF AA did not alter the steady-state levels of neurofibromin mRNA. As estimated by RNase protection assay, transforming growth factor-beta1 (TGF-beta1) upregulated neurofibromin gene expression when concentrations of 0.5 and 5 ng per ml were used. Reverse transcription followed by polymerase chain reaction did not detect apparent alterations in the ratio of type I/type II neurofibromin isoforms in PDGF- or TGF-beta1-treated cultures. Taken together, our results suggest that expression of tumor suppressor protein neurofibromin is upregulated in response to skin injury, and that this upregulation can be mediated through PDGF and TGF-beta.
Arachnoidal fibrosis following subarachnoid hemorrhage (SAH) has been suggested to play a pathogenic role in the development of late post-hemorrhagic hydrocephalus in humans. The purpose of this study was to investigate the rate of collagen synthesis in the arachnoid and the dura in the rat under normal conditions and to study the time schedule and the localization of the increased collagen synthesis following an experimental SAH. We found that the activity of prolyl 4-hydroxylase, a key enzyme in collagen synthesis, was 3-fold higher in the dura than that in the arachnoid and was similar to the activity in the skin. We then induced SAH in rats by injecting autologous arterial blood into cisterna magna. After SAH, we observed an increase in prolyl 4-hydroxylase activity of the arachnoid and the dura at 1 week. At this time point the enzyme activity in both tissues was 1.7-1.8-fold compared to that in the controls and after this time point the activities declined but remained slightly elevated at least till week 4. The rate of collagen synthesis was measured in vitro by labeling the tissues with [(3)H]proline. The rate increased to be 1.7-fold at 1 to 2 weeks after the SAH in both of the tissues. Immunohistochemically we observed a deposition of type I collagen in the meninges at 3 weeks after the SAH. SAH is followed by a transient increase in the rate of collagen synthesis in the arachnoid and, surprisingly, also the dura. Increased synthesis also resulted in an accumulation of type I collagen in the meningeal tissue, suggesting that the meninges are a potential site for fibrosis. The time schedule of these biochemical and histological events suggest that meningeal fibrosis may be involved in the pathogenesis of late post-hemorrhagic hydrocephalus.
We have previously shown that NF1 (type 1 neurofibromatosis) p21ras GTPase-activating tumor suppressor protein undergoes major relocalization during the formation of cell-cell junctions in differentiating keratinocytes in vitro. This prompted us to study the distribution of NF1 mRNA under the same conditions by in situ hybridization. In differentiating keratinocytes, the NF1 mRNA signal intensified within the cell cytoplasm within the first 0.5 to 2 hours after induction of cellular differentiation. First, the hybridization signal was evenly distributed throughout the cytoplasm. Subsequently, NF1 mRNA was gradually polarized to the cellular periphery at the side of cell-cell junctions and finally disappeared. Reappearance of NF1 mRNA was found in migrating keratinocytes forming a bilayered culture. Disruption of microfibrillar cytoskeleton, but not microtubules, caused a marked change in the subcellular distribution of NF1 mRNA. This data may suggest that intact actin microfilaments are essential for transport of NF1 mRNA to the cell periphery. This is the first study demonstrating that NF1, or any tumor suppressor mRNA, belongs to a rare group of mRNAs not targeted to free polysomes or ribosomes of the rough endoplasmic reticulum. This finding recognizes a potential way for post-transcriptional modification of NF1 expression.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.