Rasopatias : mutações germinativas na via de sinalização Ras/MAPK e associação ao desenvolvimento de patologia neoplásica

Trabalho Final do Curso de Mestrado Integrado em Medicina, Faculdade de Medicina, Universidade de Lisboa, 2014

The scaffold protein KSR1, a novel therapeutic target for the treatment of Merlin-deficient tumors

Merlin has broad tumor-suppressor functions as its mutations have been identified in multiple benign tumors and malignant cancers. In all schwannomas, the majority of meningiomas and 1/3 of ependymomas Merlin loss is causative. In neurofibromatosis type 2, a dominantly inherited tumor disease because of the loss of Merlin, patients suffer from multiple nervous system tumors and die on average around age 40. Chemotherapy is not effective and tumor localization and multiplicity make surgery and radiosurgery challenging and morbidity is often considerable. Thus, a new therapeutic approach is needed for these tumors. Using a primary human in vitro model for Merlin-deficient tumors, we report that the Ras/Raf/mitogen-activated protein, extracellular signal-regulated kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) scaffold, kinase suppressor of Ras 1 (KSR1), has a vital role in promoting schwannomas development. We show that KSR1 overexpression is involved in many pathological phenotypes caused by Merlin loss, namely multipolar morphology, enhanced cell-matrix adhesion, focal adhesion and, most importantly, increased proliferation and survival. Our data demonstrate that KSR1 has a wider role than MEK1/2 in the development of schwannomas because adhesion is more dependent on KSR1 than MEK1/2. Immunoprecipitation analysis reveals that KSR1 is a novel binding partner of Merlin, which suppresses KSR1's function by inhibiting the binding between KSR1 and c-Raf. Our proteomic analysis also demonstrates that KSR1 interacts with several Merlin downstream effectors, including E3 ubiquitin ligase CRL4DCAF1. Further functional studies suggests that KSR1 and DCAF1 may co-operate to regulate schwannomas formation. Taken together, these findings suggest that KSR1 serves as a potential therapeutic target for Merlin-deficient tumors.

The potential role of environmental exposures and genomic signaling in development of central nervous system tumors

The etiology of central nervous system tumors (CNSTs) is mainly unknown. Aside from extremely rare genetic conditions, such as neurofibromatosis and tuberous sclerosis, the only unequivocally identified risk factor is exposure to ionizing radiation, and this explains only a very small fraction of cases. Using meta-analysis, gene networking and bioinformatics methods, this dissertation explored the hypothesis that environmental exposures produce genetic and epigenetic alterations that may be involved in the etiology of CNSTs. A meta-analysis of epidemiological studies of pesticides and pediatric brain tumors revealed a significantly increased risk of brain tumors among children whose mothers had farm-related exposures during pregnancy. A dose response was recognized when this risk estimate was compared to those for risk of brain tumors from maternal exposure to non-agricultural pesticides during pregnancy, and risk of brain tumors among children exposed to agricultural activities. Through meta-analysis of several microarray studies which compared normal tissue to astrocytomas, we were able to identify a list of 554 genes which were differentially expressed in the majority of astrocytomas. Many of these genes have in fact been implicated in development of astrocytoma, including EGFR, HIF-1α, c-Myc, WNT5A, and IDH3A. Reverse engineering of these 554 genes using Bayesian network analysis produced a gene network for each grade of astrocytoma (Grade I-IV), and ‘key genes’ within each grade were identified. Genes found to be most influential to development of the highest grade of astrocytoma, Glioblastoma multiforme (GBM) were: COL4A1, EGFR, BTF3, MPP2, RAB31, CDK4, CD99, ANXA2, TOP2A, and SERBP1. Lastly, bioinformatics analysis of environmental databases and curated published results on GBM was able to identify numerous potential pathways and geneenvironment interactions that may play key roles in astrocytoma development. Findings from this research have strong potential to advance our understanding of the etiology and susceptibility to CNSTs. Validation of our ‘key genes’ and pathways could potentially lead to useful tools for early detection and novel therapeutic options for these tumors.

Retrocaval mass in patient with von Recklinghausen disease. Case report

Type I Neurofibromatosis (NF1) is an autosomal-dominant inheritable disorder, with an incidence of 1:3,000, and a prevalence of 1:4,000 to 5,000. Pathogenesis is based on mutations of the NF1 gene, a tumor suppressor gene encoding a cytoplasmic protein named neurofibromin that controls cellular proliferation. Patients affected by NF1 typically present with cutaneous neurofibromas, cafè au lait spots and eye involvement, but they can also be affected by various visceral tumors, such as neurofibromas (nodular or plexiform type), gastrointestinal stromal tumors or endocrine tumors, such as pheochromocytomas. Visceral neurofibromas are often asymptomatic but when growing in size they may present with pain, palpable abdominal mass, symptoms secondary to bowel obstruction or main vessels compression, and even gastrointestinal bleeding when mucosa or submucosa are involved. In these cases surgery becomes mandatory in order to remove all neoplastic tissue. The Authors describe a case of a young man affected by NF1 with associated retrocaval abdominal mass with compression and displacement of the inferior vena cava, thus requiring a complex surgical procedure.

Vacuum-assisted closure treatment of leg skin necrosis after angiographic embolization of a giant plexiform neurofibroma

Type 1 neurofibromatosis is a relatively common inherited disease of the nervous system, with a frequency of almost 1 in 3000. It is associated with neurofibromas of various sites. Our case report is about the surgical management of a giant neurofibroma of the right gluteal fold in a 46-year-old male with NF1. The patient presented with increasing edema and accelerated growth of the mass; he underwent percutaneous embolization of lesion vessels that induced necrosis of the neurofibroma. The patient was taken to the operating room, where surgical resection of the bulk of the lesion was undertaken. The postoperative course was complicated by delayed wound closure managed with antibiotics and vacuum-assisted wound closure. Giant neurofibromas similar to this tumor require complex preoperative, intraoperative and postoperative management strategies. Surgical debulk is best managed with preoperative percutaneous embolization that help to avoid surgical bleeding. Postoperative delayed wound closure was managed with the application of negative pressure in a closed environment that triggers granulation and tissue formation.

Tumores malignos de la vaina nerviosa periférica como origen de dolor orofacial

Los tumores malignos de la vaina nerviosa periférica (TMVNP), también llamados neurofribrosarcomas o schwannomas malignos, representan el 10% de todos los sarcomas de tejidos blandos. El tumor usualmente se encuentra en las extremidades inferiores, y solo del 10 al 20% de las lesiones ocurren en la región de cabeza y cuello, convirtiéndolas en una entidad rara. Los neurofibromas son tumores de la vaina nerviosa que aparecen comúnmente en la neurofibromatosis 1 o enfermedad de Von Recklinghausen. Se ha reportado que los individuos con antecedentes familiares de neurofibromatosis 1 tienen un riesgo incrementado de desarrollar TMVNP en el transcurso de sus vidas, sin embargo, esta asociación no se ha confirmado en TMVNP a nivel de los nervios craneales. En este artículo los autores analizaron la literatura actual con respecto a los TMVNP del nervio trigémino, así como la inclusión de un caso inusual que involucra las 3 ramas de dicho nervio.