Neurofibromatosis type 1 tumour suppressor gene expression is deficient in psoriatic skin in vivo and in vitro: a potential link to increased Ras activity.

BACKGROUND: Neurofibromatosis type 1 (NF1) protein (neurofibromin) accelerates the inactivation of Ras-GTP in various cell types. Somatic mutations of the NF1 gene may lead to malignant transformation and uncontrolled proliferation. We have previously shown that NF1 protein expression is downregulated in psoriasis in vivo. OBJECTIVES: To study the functional expression and distribution of NF1 mRNA and protein in vivo and in psoriatic and normal keratinocyte cultures. METHODS: Immunohistochemistry and in situ hybridization were used to study NF1 gene and protein expression in psoriasis in vivo. Furthermore, Northern and in situ hybridizations, immunoblot and localization analyses were utilized to study NF1 mRNA and protein in vitro in keratinocyte cultures. RESULTS: NF1 tumour suppressor gene expression was reduced in lesional psoriatic skin compared with perilesional and normal skin in vivo. The in vitro results showed that the levels of NF1 mRNA and protein were reduced in cultured psoriatic keratinocytes during cellular differentiation even after multiple passaging of the cells. Moreover, cultured nonlesional psoriatic keratinocytes were almost equally defective as lesional cells with respect to NF1 expression. CONCLUSIONS: Our findings demonstrate that psoriatic keratinocytes maintain an altered phenotype and gene expression profile even when isolated from interaction with lymphocytes and fibroblasts, which are known to increase proliferation of keratinocytes. As NF1 protein is regarded as a Ras proto-oncogene regulator, the aberrant expression and distribution of NF1 protein and mRNA found in the present study may be causative to the previously described increased activation of Ras in psoriatic lesions, and relate to altered cellular behaviour.

Increase of collagen synthesis and deposition in the arachnoid and the dura following subarachnoid hemorrhage in the rat.

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.

Upregulation of tumor suppressor protein neurofibromin in normal human wound healing and in vitro evidence for platelet derived growth factor (PDGF) and transforming growth factor-beta1 (TGF-beta1) elicited increase in neurofibromin mRNA steady-state levels in dermal fibroblasts.

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.

Expression of laminin and collagen genes by cells cultured from developing human sciatic nerves.

The expression of laminin alpha1, alpha2, beta1, beta2 and gamma1 subunits and proalpha1(I), proalpha1(III), alpha1(IV), alpha1(VI), alpha2(VI) and alpha3(VI) collagen chains was studied by Northern hybridizations, RNase protection assays and indirect immunofluorescence (IIF) labellings in cell cultures initiated from sciatic nerves of 14-27-wk-old human fetuses. The cultures represented mixed populations of Schwann cells, perineurial cells and fibroblasts, as estimated by morphology and S 100 protein immunolabellings. The mRNAs for certain basement membrane (BM) components, laminin beta1 and gamma1 chains and collagen alpha1(IV) chain, were readily detectable by Northern analyses in all cultures. In contrast, laminin alpha1, alpha2 and beta2 chain mRNAs were expressed at markedly lower levels. The expression of laminin alpha1 chain was detectable only by RNase protection assay. RNase protection analysis also demonstrated that the expression of laminin alpha2 chain increased with the developmental stage of the nerve used as the source for cell cultures. The expression of laminin beta2 chain was detected only at the protein level by IIF which demonstrated a faint immunosignal in a small subpopulation of cells. The mRNAs for type I, III and VI collagens were readily detectable in the cultures by Northern hybridizations. In summary, the extracellular matrix genes expressed in fetal human peripheral nerves and corresponding cell cultures display marked similarities. Cell cultures characterized here may prove useful in analyses elucidating potential roles of selected growth factors and cytokines in the induction of e.g. laminin alpha1 and beta2 chain expression by cells of developing peripheral nerves.

Neurofibromin: expression by normal human keratinocytes in vivo and in vitro and in epidermal malignancies.

BACKGROUND: Neurofibromin is the product of the NF1 gene, the mutations of which have been linked with type 1 neurofibromatosis. The expression of neurofibromin in human skin has not been analyzed in detail. EXPERIMENTAL DESIGN: Polyclonal Ab were raised against synthetic peptides corresponding to three different sites of neurofibromin. One of the Ab selectively recognized type II neurofibromin. The localization of neurofibromin was first studied in normal human skin. Further studies concentrated on neurofibromin expression in basal cell and squamous cell carcinomas. Reverse transcription-PCR (RT-PCR) and molecular hybridizations and immunocytochemistry were used to characterize the expression of neurofibromin in cultured keratinocytes. RESULTS: All neurofibromin-specific Ab immunolabeled the epidermis. The basal keratinocytes displayed the most prominent immunosignal for type II neurofibromin. RT-PCR demonstrated the presence of both type I and II neurofibromin mRNA transcripts in cultured keratinocytes. Keratinocytes induced to differentiate and to arrest division by a high (1.4 mM) Ca2+ concentration of the culture medium displayed a down-regulation of neurofibromin expression at the mRNA and protein levels. This was most strikingly demonstrated by a reduction of immunoreactivity for type II neurofibromin. Basal cell carcinomas displayed a weak immunosignal for type II neurofibromin. In contrast, particularly the central areas of squamous cell carcinoma, islands were intensely immunolabeled. CONCLUSIONS: The results suggest that neurofibromin acts as a regulator of the basal keratinocytes in normal skin and that cultured keratinocytes offer a human model for studies aimed to elucidate the regulation of neurofibromin gene expression. Furthermore, aberrations in neurofibromin expression may play a role in the pathogenesis of epidermal cancers.