The role of neurofibromin in N-Ras mediated AP-1 regulation in malignant peripheral nerve sheath tumors.
Plexiform neurofibromas commonly found in patients with Neurofibromatosis type I (NF1) have a 5% risk of being transformed into malignant peripheral nerve sheath tumors (MPNST). Germline mutations in the NF1 gene coding for neurofibromin, which is a Ras GTPase activating protein (RasGAP) and a negative regulator of Ras, result in an upregulation of the Ras pathway. We established a direct connection between neurofibromin deficiency and downstream effectors of Ras in cell lines from MPNST patients by demonstrating that knockdown of NF1 expression using siRNA in a NF1 wild type MPNST cell line, STS-26T, activates the Ras/ERK1,2 pathway and increases AP-1 binding and activity. We believe this is the first time the transactivation of AP-1 has been linked directly to neurofibromin deficiency in a disease relevant MPNST cell line. Previously, we have shown that N-Ras is constitutively activated in cell lines derived from independent MPNSTs from NF1 patients. We therefore sought to analyze the role of the N-Ras pathway in deregulating AP-1 transcriptional activity. We show that STS-26T clones conditionally expressing oncogenic N-Ras show increased phosphorylated ERK1,2 and phosphorylated JNK expression concomitant with increased AP-1 activity. MAP kinase pathways (ERK1,2 and JNK) were further examined in ST88-14, a neurofibromin-deficient MPNST cell line. The basal activity of ERK1,2 but not JNK was found to increase AP-1 activity. These experiments further confirmed the link between the loss of neurofibromin and increased activity of Ras/MAP kinase pathways and the activation of downstream transcriptional mechanisms in MPNSTs from NF1 patients.
Kraniak
Janice M
JM
Programs in Molecular Biology and Genetics, Barbara Ann Karmanos Cancer Institute, Detroit, MI 48201, USA.
Sun
Daochun
D
Mattingly
Raymond R
RR
Reiners
John J
JJ
Tainsky
Michael A
MA
D001483:Base Sequence; D045744:Cell Line, Tumor; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D011905:Genes, ras; D006801:Humans; D018317:Nerve Sheath Neoplasms / Q000235:genetics / Q000503:physiopathology*; D025542:Neurofibromin 1 / Q000502:physiology*; D009838:Oligodeoxyribonucleotides; D010766:Phosphorylation
D025542:Neurofibromin 1; D009838:Oligodeoxyribonucleotides; D048049:Extracellular Signal-Regulated MAP Kinases