Sustained activation of ERK1/2 MAPK in Schwann cells causes corneal neurofibroma.

Recent studies have shown that constitutive activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) in Schwann cells (SCs) increases myelin thickness in transgenic mice. In this secondary analysis, we report that these transgenic mice develop a postnatal corneal neurofibroma with the loss of corneal transparency by age six months. We show that expansion of non-myelinating SCs, under the control of activated ERK1/2, also drive myofibroblast differentiation that derives from both SC precursors and resident corneal keratocytes. Further, these mice also harbor activated mast cells in the central cornea, which contributes to pathological corneal neovascularization and fibrosis. This breach of corneal avascularity and immune status is associated with the growth of the tumor pannus, resulting in a corneal stroma that is nearly four times its normal size. In corneas with advanced disease, some axons became ectopically myelinated, and the disruption of Remak bundles is evident. To determine whether myofibroblast differentiation was linked to vimentin, we examined the levels and phosphorylation status of this fibrotic biomarker. Concomitant with the early upregulation of vimentin, a serine 38-phosphorylated isoform of vimentin (pSer38vim) increased in SCs, which was attributed primarily to the soluble fraction of protein-not the cytoskeletal portion. However, the overexpressed pSer38vim became predominantly cytoskeletal with the growth of the corneal tumor. Our findings demonstrate an unrecognized function of ERK1/2 in the maintenance of corneal homeostasis, wherein its over-activation in SCs promotes corneal neurofibromas. This study is also the first report of a genetically engineered mouse that spontaneously develops a corneal tumor.

Impaired Pten expression in human malignant peripheral nerve sheath tumours.

Malignant peripheral nerve sheath tumours (MPNST) are aggressive sarcomas that develop in about 10% of patients with the genetic disease neurofibromatosis type 1 (NF1). Molecular alterations contributing to MPNST formation have only partially been resolved. Here we examined the role of Pten, a key regulator of the Pi3k/Akt/mTOR pathway, in human MPNST and benign neurofibromas. Immunohistochemistry showed that Pten expression was significantly lower in MPNST (n=16) than in neurofibromas (n=16) and normal nervous tissue. To elucidate potential mechanisms for Pten down-regulation or Akt/mTOR activation in MPNST we performed further experiments. Mutation analysis revealed absence of somatic mutations in PTEN (n=31) and PIK3CA (n=38). However, we found frequent PTEN promotor methylation in primary MPNST (11/26) and MPNST cell lines (7/8) but not in benign nerve sheath tumours. PTEN methylation was significantly associated with early metastasis. Moreover, we detected an inverse correlation of Pten-regulating miR-21 and Pten protein levels in MPNST cell lines. The examination of NF1-/- and NF1+/+Schwann cells and fibroblasts showed that Pten expression is not regulated by NF1. To determine the significance of Pten status for treatment with the mTOR inhibitor rapamycin we treated 5 MPNST cell lines with rapamycin. All cell lines were sensitive to rapamycin without a significant correlation to Pten levels. When rapamycin was combined with simvastatin a synergistic anti-proliferative effect was achieved. Taken together we show frequent loss/reduction of Pten expression in MPNST and provide evidence for the involvement of multiple Pten regulating mechanisms.

Expression of emmprin and matrix metalloproteinases (MMPs) in peripheral nerve sheath tumors: emmprin and membrane-type (MT)1-MMP expressions are associated with malignant potential.

BACKGROUND: Matrix metalloproteinases (MMPs), including membrane-type (MT)-MMPs, correlate with biological aggressiveness in many carcinomas. However, their roles in peripheral nerve sheath tumors (PNSTs) have rarely been investigated. MATERIALS AND METHODS: In this study, the immunohistochemical expression of 6 MMPs, their 3 inhibitors and emmprin, an MMP inducer, was examined in 14 schwannomas, 14 neurofibromas and 12 malignant peripheral nerve sheath tumors (MPNSTs) in relation to malignant potentials. RESULTS: Higher expression levels (>3+) of emmprin and MT1-MMP were noted in 83.3% and 16.7% of MPNSTs, respectively, versus none in schwannomas and neurofibromas (p<0.0001). The overall expression rate (1-4+) of MT1-MMP was 58.3% in MPNSTs versus 7.1% in both schwannomas and neurofibromas (p=0.0093). Gelatinase A (MMP-2) showed higher expression levels (>3+) in all the tumors without significant differencies. Moreover, the expression patterns of MMP-1 and gelatinase B (MMP-9) could divide PNSTs into two groups: schwannoma versus neurofibroma/MPNST. Higher expression levels (>3+) of MMP-9 were observed in 50% of schwannomas versus none in neurofibromas and MPNSTs, while those of MMP-1 were found in 35.7% of neurofibromas and 66.7% of MPNSTs versus none in schwannomas. RECK was the main inhibitor expressed in these 3 tumors, with no significant differences. CONCLUSION: These results suggest that emmprin and MT1-MMP may be malignant potential-related proteins in PNSTs, and that MMP-1 and 9 may help differentiation between schwannoma and neurofibroma, especially in their plexiform types.

Immunolocalization of a glycosylphosphatidylinositol-specific phospholipase D in mast cells found in normal tissue and neurofibromatosis lesions.

A large number of eukaryotic proteins have been shown to be anchored to the cell membrane by glycosylphosphatidylinositol (GPI). This glycolipid anchor can serve as a substrate for anchor-specific phospholipases that convert the GPI-anchored membrane proteins into soluble forms. Soluble forms of many GPI anchored proteins have been identified in vivo in connective tissue, plasma, and urine. The authors have discovered that mammalian plasma contains a GPI-specific phospholipase D (GPI-PLD). Because it recognizes a portion of the conserved glycan core structure, all GPI-anchored proteins are potential substrates. The authors report the development of a murine monoclonal antibody specific for one form of the human GPI-PLD and the immunohistochemical localization of this enzyme to mast cells.

Creatine kinase isoenzyme patterns in neoplasms of peripheral nerve.

Normal peripheral nerve and neoplastic lesions of peripheral nerve varied in their creatine kinase (CK; EC 2.7.3.2) isoenzyme pattern, as assessed both with electrophoresis and with column chromatography. All three isoenzymes were seen in normal peripheral nerve, but the peripheral nerve tumors, neurofibroma and neurilemmoma, demonstrated predominantly CK-1 isoenzyme activity, with a trace amount of CK-3. No CK-2 activity was demonstrated in these tumors. In contrast, malignant schwannoma tissue contained all three isoenzymes, but in a different proportion than in normal peripheral nerve.

Hydrolytic enzyme activities of the nervous system.

The activities of five hydrolytic enzymes (acid and alkaline phosphatase, hexosaminidase [N-acetyl-beta-D-glucosaminidase], beta-galactosidase, and beta-glucorinidase) were measured in reconstituted homogenates of lyophilized human brain tissue and primary and metastatic tumors. The linearity of reaction, with respect to incubation time, and optimal pH of each enzyme and in tumor tissues were comparable to those in normal brain tissue. Total enzyme activities of hexosaminidase, beta-glucuronidase, and beta-galactosidase were significantly higher in tumors than in normal cerebral white matter. The ratio of hexosaminidase activity to beta-glucuronidase activity was significantly lower for metastatic than for primary tumors or normal white matter. When histological observations do not clearly establish if a brain tumor is primary or metastatic, this ratio may help. Alteration of hydrolytic enzyme activities as demonstrated here may be indicative of "ket enzymes" that are essential for maintaining the metabolic advantages of tumors.

[Enzyme patterns in connective tissue proliferations (author's transl)]. / Enzymmuster von Bindegewebswucherungen

In a series of benign or semimalignant connective tissue proliferations (4 desmoids, 1 recurrence of a dermatofibrosarcoma protuberans, 4 fibromas, 1 neurofibroma, 3 keloids, 3 Dupuytren's contractures) and a normal fascia for comparison the pattern of 18 enzymes from different metabolic pathways was investigated. It should be clarified whether alterations of the enzyme pattern wouldoccur, asthey are found in malignant tumours. The activity of most of the enzymes investigated increased about twofold in the latter of two extirpations (16 months interval) of a recurring desmoid. In the recurrence of a dermatofibrosarcoma protuberans and in a recurrance of a fibroma a remarkably high activity of glucose-6-phosphate dehydrogenase and pyruvate kinase was found. High activities of these enzymes are known to be characteristic of experimental tumours of animals and human malignant neoplasms. Therefore it is assumed that these differences from the normal patternof enzyme activity are related to recidivity and may be regarded as first signs of a deviation from benignity. Based on these results further studies haveto be done with the aim to find a biochemical tool for, evaluation and prognosis of the course of these diseases.

RNA polymerase activity in homotransplanted rat brain tumors initially induced by ethylnitrosourea.

Nuclear RNA polymerase activity was studied in homotransplanted rat glial tumors where the primary tumor was produced by transplacental injection of ethylnitrosourea. Alpha amanitin, cycloheximide, and rifampicin were tested as inhibitors of this activity. Alpha amanitin significantly inhibited RNA polymerase activity in all tumors. This indicated that the major nuclear RNA polymerase activity seen in vitro in the tumor nuclei was RNA polymerase II. This is similar to the activity seen in normal glial nuclei. Cycloheximide and rifampicin which have no effect on RNA polymerase activity in normal glial nuclei inhibited about 20% of the polymerase activity in three of the tumors. The size and multiplicity of the nucleoli in these tumor cells suggests that RNA polymerase I could account for the activity which is inhibited by cycloheximide.