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-β1 (TGF-β1) Elicited Increase in Neurofibromin mRNA Steady-State Levels in Dermal Fibroblasts

Abstract

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.

Evidence of Increased Bone Resorption in Neurofibromatosis Type 1 Using Urinary Pyridinium Crosslink Analysis

“…It is known that neurofibromin directly impacts the Ras-signaling pathway, which interacts with multiple signaling pathways, several of which are important in bone. For example, transforming growth factor-beta increases neurofibromin mRNA (34), murine Nf1 Ϯ mast cells secrete elevated concentrations of transforming growth factor-beta (35), fibroblast growth factors activate the Ras/mitogen-activated phosphorylation kinase pathway (36), and inactivation of the SHP2-Ras-mitogen-activated phosphorylation kinase pathway in mice results in enhanced bone formation after an increase in osteoclast activity suggesting a dissociation of the intercellular communications between osteoclasts and osteoblasts (37,38). Specific investigations using the Nf1 haploinsufficient transgenic mouse model has shown abnormalities in myeloid cells.…”

Genetically Modified Mouse Models in Studies on Cutaneous Wound Healing

“…Neurofibromin is expressed in the skin (Malhotra & Ratner, 1994) and upregulated in fibroblasts after wounding (Yla-Outinen et al 1998). Excisional wounding demonstrated enlarged, deepened scar formation, as well as a pronounced increase in granulation tissue formation (even penetrating the underlying muscle), with a sustained fibroblast proliferation in vivo and in vitro (Atit et al 1999).…”

Occult Neurofibroma and Increased S100 Protein in the Skin of Patients With Neurofibromatosis Type 1

“…7,8 Interestingly, recent results demonstrate up-regulation of NF1 gene expression in response to tissue trauma and suggest that a "second hit" in a form of somatic mutations in lesional neurofibromatosis cells is not necessarily a prerequisite for the development of neurofibromas. 9 Atit et al 10 have shown that, in mice with NF1 mutations, injury promoted specific features of neurofibromas found in human patients,…”