A novel neurofibromin (NF1) interaction with the leucine-rich pentatricopeptide repeat motif-containing protein links neurofibromatosis type 1 and the French Canadian variant of Leigh's syndrome in a common molecular complex.

Loss-of-function mutations and deletions in the neurofibromin tumor suppressor gene (NF1) cause neurofibromatosis type 1 (NF-1), the most common inherited syndrome of the nervous system in humans, with a birth incidence of 1:3,000. The most visible features of NF-1 are the neoplastic manifestations caused by the loss of Ras-GTPase-activating protein (Ras-GAP) activity mediated through the GAP-related domain (GRD) of neurofibromin (NF1), the protein encoded by NF1. However, the syndrome is also characterized by cognitive dysfunction and a number of developmental abnormalities. The molecular etiology of many of these nonneoplastic phenotypes remains unknown. Here we show that the tubulin-binding domain (TBD) of NF1 is a binding partner of the leucine-rich pentatricopeptide repeat motif-containing (LRPPRC) protein. These two proteins complex with Kinesin 5B, hnRNP A2, Staufen1, and Myelin Basic Protein (MBP) mRNA, likely in RNA granules. This interaction is of interest in that it links NF-1 with Leigh's syndrome, French Canadian variant (LSFC), an autosomal recessive neurodegenerative disorder that arises from mutations in the LRPPRC gene. Our findings provide clues to how loss or mutation of NF1 and LRPPRC may contribute to the manifestations of NF-1 and LSFC.

Preclinical in vivo evaluation of rapamycin in human malignant peripheral nerve sheath explant xenograft.

Neurofibromatosis type 1 (NF1) patients are prone to the development of malignant tumors, the most common being Malignant Peripheral Nerve Sheath Tumor (MPNST). NF1-MPNST patients have an overall poor survival due to systemic metastasis. Currently, the management of MPNSTs includes surgery and radiation; however, conventional chemotherapy is not very effective, underscoring the need for effective biologically-targeted therapies. Recently, the NF1 gene product, neurofibromin, was shown to negatively regulate the phosphoinositide-3-kinase (PI3K)/Protein Kinase-B (Akt)/mammalian Target Of Rapamycin (mTOR) pathway, with loss of neurofibromin expression in established human MPNST cell lines associated with high levels of mTOR activity. We developed and characterized a human NF1-MPNST explant grown subcutaneously in NOD-SCID mice, to evaluate the effect of the mTOR inhibitor rapamycin. We demonstrate that rapamycin significantly inhibited human NF1-MPNST mTOR pathway activation and explant growth in vivo at doses as low as 1.0 mg/kg/day, without systemic toxicities. While rapamycin was effective at reducing NF1-MPNST proliferation and angiogenesis, with decreased CyclinD1 and VEGF respectively, there was no increase in tumor apoptosis. Rapamycin effectively decreased activation of S6 downstream of mTOR, but there was accompanied increased Akt activation. This study demonstrates the therapeutic potential and limitations of rapamycin in NF1-associated, and likely sporadic, MPNSTs.

Neurofibromin interacts with the cytoplasmic Dynein Heavy Chain 1 in melanosomes of human melanocytes.

Neurofibromin (NF1) is encoded by the NF1 tumour suppressor gene. Mutations result in a disorder known as Neurofibromatosis Type 1 (NF-1), and patients are often diagnosed due to the presence of unusual pigmentary patterns that include Café au lait macules (CALMs). Little is known about how loss of NF1 results in pigmentary defects in melanocytes. We sought to identify novel NF1 interacting proteins and elucidate the molecular mechanisms underlying the pigmentary defects. The cytoplasmic Dynein Heavy Chain 1 (DHC) was found to interact with NF1 along microtubules in vesicular structures identified to be melanosomes. Our studies suggest that NF1 is involved in melanosomal localization, and that disruptions in NF1-DHC interactions may contribute to the abnormal pigmentary features commonly associated with this debilitating syndrome.