UP-REGULATION OF TUMOR-SUPPRESSOR PROTEIN NEUROFIBROMIN IN NORMAL HUMAN WOUND-HEALING AND IN-VITRO EVIDENCE FOR PLATELET-DERIVED GROWTH-FACTOR (PDGF) AND TRANSFORMING GROWTH-FACTOR-BETA-1 (TGF-BETA-1) ELICITEDINCREASE IN NEUROFIBROMIN MESSENGER-RNA STEADY-STATE LEVELS IN DERMALFIBROBLASTS

We first studied expression of neurofibromin by immunohistochemistry i n scars obtained from operations involving areas of healing wounds. Th e results demonstrated increased immunoreactivity for neurofibromin in the fibroblastic cell population of the lesions when compared with fi broblasts of apparently healthy perilesional skin, or those of intact control skin. Furthermore, dermal fibroblasts of 19 and 34 wk-old fetu ses displayed a clearly detectable immunosignal for neurofibromin. In vitro studies were designed to investigate the potential effects of se lected growth factors - known to be operative in wound healing - on ne urofibromin mRNA steady-state levels in cultured fibroblasts. Northern transfer analyses revealed that different isoforms of platelet derive d grow th 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 BE was reached at a concentration of 1 ng per ml. In contrast, PDGF AA did n ot alter the steady-state levels of neurofibromin mRNA. As estimated b y RNase protection assay, transforming growth factor-beta 1 (TGF-beta 1) upregulated neurofibromin gene expression when concentrations of 0. 5 and 5 ng per ml were used. Reverse transcription followed by polymer ase chain reaction did not detect apparent alterations in the ratio of type I/type II neurofibromin isoforms in PDGF- or TGF-beta 1-treated cultures. Taken together, our results suggest that expression of tumor suppressor protein neurofibromin is upregulated in response to skin i njury, and that this upregulation can be mediated through PDGF and TGF -beta.